Robert H Brown

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Journals/Publications

• Brossier, J., Rodriguez, S., Cornet, T., Maltagliati, L., Lucas, A., Le, M. S., Solomonidou, A., Coustenis, A., Hirtzig, M., Jaumann, R., Stephan, K., & Brown, R. (2017). Constraining the composition and geological history of the main types of terrains found in the equatorial belt of Titan. European Planetary Science Congress, 11, EPSC2017-88.
• {Filacchione}, G., {Capaccioni}, F., {Ciarniello}, M., {Tosi}, F., {D'Aversa}, E., {Clark}, R., {Brown}, R., {Buratti}, B., {Cruikshank}, D., {Dalle Ore}, M., {Scipioni}, F., , P. (2016). Cassini-VIMS temperature maps of Saturn's satellites. \memsai, 87, 190.
• {Filacchione}, G., {D'Aversa}, E., {Capaccioni}, F., {Clark}, R., {Cruikshank}, D., {Ciarniello}, M., {Cerroni}, P., {Bellucci}, G., {Brown}, R., {Buratti}, B., {Nicholson}, P., {Jaumann}, R., {McCord}, T., {Sotin}, C., {Stephan}, K., , C. (2016). Saturn's icy satellites investigated by Cassini-VIMS. IV. Daytime temperature maps. \icarus, 271, 292-313.
• {Rannou}, P., {Toledo}, D., {Lavvas}, P., {D'Aversa}, E., {Moriconi}, M., {Adriani}, A., {Le Mou{\'e}lic}, S., {Sotin}, C., , R. (2016). Titan's surface spectra at the Huygens landing site and Shangri-La. \icarus, 270, 291-306.
• {Solomonidou}, A., {Coustenis}, A., {Hirtzig}, M., {Rodriguez}, S., {Stephan}, K., {Lopes}, R., {Drossart}, P., {Sotin}, C., {Le Mou{\'e}lic}, S., {Lawrence}, K., {Bratsolis}, E., {Jaumann}, R., , R. (2016). Temporal variations of Titan's surface with Cassini/VIMS. \icarus, 270, 85-99.
• {Stephan}, K., {Wagner}, R., {Jaumann}, R., {Clark}, R., {Cruikshank}, D., {Brown}, R., {Giese}, B., {Roatsch}, T., {Filacchione}, G., {Matson}, D., {Ore}, C., {Capaccioni}, F., {Baines}, K., {Rodriguez}, S., {Krupp}, N., {Buratti}, B., , P. (2016). Cassini's geological and compositional view of Tethys. \icarus, 274, 1-22.
• {{\'A}d{\'a}mkovics}, M., {Mitchell}, J., {Hayes}, A., {Rojo}, P., {Corlies}, P., {Barnes}, J., {Ivanov}, V., {Brown}, R., {Baines}, K., {Buratti}, B., {Clark}, R., {Nicholson}, P., , C. (2016). Meridional variation in tropospheric methane on Titan observed with AO spectroscopy at Keck and VLT. \icarus, 270, 376-388.
• {Cornet}, T., {Altobelli}, N., {Rodriguez}, S., {Maltagliati}, L., {Le Mou{'e}lic}, S., {Sotin}, C., {Brown}, R., {Barnes}, J., {Buratti}, B., {Baines}, K., {Clark}, R., , P. (2015). "{Investigation of Titan's surface and atmosphere photometry using the VIMS instrument onboard Cassini}". European Planetary Science Congress 2015, held 27 September - 2 October, 2015 in Nantes, France, Online at http://meetingorganizer.copernicus.org/EPSC2015, id.EPSC2015-253, 10, EPSC2015-253.
• {Maltagliati}, L., {Rodriguez}, S., {Sotin}, C., {Cornet}, T., {Rannou}, P., {Le Mouelic}, S., {Solomonidou}, A., {Coustenis}, A., , R. (2015). "{Simultaneous mapping of Titan's surface albedo and aerosol opacity from Cassini/VIMS massive inversion}". European Planetary Science Congress 2015, held 27 September - 2 October, 2015 in Nantes, France, Online at http://meetingorganizer.copernicus.org/EPSC2015, id.EPSC2015-687, 10, EPSC2015-687.
• {Neish}, C., {Barnes}, J., {Sotin}, C., {MacKenzie}, S., {Soderblom}, J., {Le Mou{'e}lic}, S., {Kirk}, R., {Stiles}, B., {Malaska}, M., {Le Gall}, A., {Brown}, R., {Baines}, K., {Buratti}, B., {Clark}, R., , P. (2015). "{Spectral properties of Titan's impact craters imply chemical weathering of its surface}". grl, 42, 3746-3754.
• {Rannou}, P., {Seignovert}, B., {Lavvas}, P., {Lemou{'e}lic}, S., {Sotin}, C., , R. (2015). "{Titan's aerosol optical properties with VIMS observations at the limb of Titan.}". European Planetary Science Congress 2015, held 27 September - 2 October, 2015 in Nantes, France, Online at http://meetingorganizer.copernicus.org/EPSC2015, id.EPSC2015-452, 10, EPSC2015-452.
• {Rannou}, P., {Toledo}, D., {Adriani}, A., {Moriconi}, M., {D'Aversa}, E., {Lemou{'e}lic}, S., {Sotin}, C., , R. (2015). "{Surface of Titan : model and VIMS observations}". European Planetary Science Congress 2015, held 27 September - 2 October, 2015 in Nantes, France, Online at http://meetingorganizer.copernicus.org/EPSC2015, id.EPSC2015-457, 10, EPSC2015-457.
• {Solomonidou}, A., {Coustenis}, A., {Lopes}, R., {Hirtzig}, M., {Rodriguez}, S., {Malaska}, M., {Drossart}, P., {Sotin}, C., {Bratsolis}, E., {Matsoukas}, C., {Brown}, R., , L. (2015). "{Spectral and morphological properties of various geological types of Titan{rsquo}s surface with Cassini VIMS and RADAR}". IAU General Assembly, 22, 2238344.
• {Solomonidou}, A., {Coustenis}, A., {Lopes}, R., {Rodriguez}, S., {Malaska}, M., {Drossart}, P., {Sotin}, C., {Lawrence}, K., {Hirtzig}, M., {Le Mou{'e}lic}, S., {Stephan}, K., {Jaumann}, R., {Maltagliati}, L., , R. (2015). "{The spectral evolution of various Titan geomorphic surface types}". European Planetary Science Congress 2015, held 27 September - 2 October, 2015 in Nantes, France, Online at http://meetingorganizer.copernicus.org/EPSC2015, id.EPSC2015-19, 10, EPSC2015-19.
• {Sotin}, C., {Lawrence}, K., {Xu}, F., {Barnes}, J., {Brown}, R., {Le Mouelic}, S., {Maltagliati}, L., {Rodriguez}, S., {Soderblom}, J., {West}, R., {Baines}, K., {Buratti}, B., {Clark}, R., , P. (2015). "{Observations of Titan's haze and clouds by Cassini VIMS}". European Planetary Science Congress 2015, held 27 September - 2 October, 2015 in Nantes, France, Online at http://meetingorganizer.copernicus.org/EPSC2015, id.EPSC2015-415, 10, EPSC2015-415.
• {Stallard}, T., {Melin}, H., {Miller}, S., {Badman}, S., {Baines}, K., {Brown}, R., {Blake}, J., {O'Donoghue}, J., {Johnson}, R., {Bools}, B., {Pilkington}, N., {East}, O., , M. (2015). "{Cassini VIMS observations of H$_{3}$$^{+}$ emission on the nightside of Jupiter}". Journal of Geophysical Research (Space Physics), 120, 6948-6973.
• {{'A}d{'a}mkovics}, M., {Mitchell}, J., {Hayes}, A., {Rojo}, P., {Corlies}, P., {Barnes}, J., {Ivanov}, V., {Brown}, R., {Baines}, K., {Buratti}, B., {Clark}, R., {Nicholson}, P., , C. (2015). "{Meridional variation in tropospheric methane on Titan observed with AO spectroscopy at Keck and VLT}". ArXiv e-prints.
• 'e, T., Rodriguez, S., Vincendon, M., Dout 'e, S., Rannou, P., Le Mou 'elic, S., Coustenis, A., Barnes, J. W., Sotin, C., & Brown, R. H. (2013). Radiative Transfer on Titan: Towards a Massive Inversion of Atmospheric and Surface Properties From VIMS/Cassini Observations of Titan. AGU Fall Meeting Abstracts, D1899.
• Badman, S. V., Bunce, E. J., Melin, H., Stallard, T., Nichols, J. D., Mitchell, D. G., Kurth, W. S., Crary, F. J., Burton, M. E., Baines, K. H., Brown, R. H., & Dougherty, M. K. (2013). Saturn's auroral dynamics during the 2013 observing campaign: in situ and remote observations (Invited). AGU Fall Meeting Abstracts, A1.
• Badman, S. V., Melin, H., Stallard, T., Blake, J. S., O'Donoghue, J., Bunce, E. J., Nichols, J. D., Baines, K. H., Brown, R. H., & Dougherty, M. K. (2013). Cassini VIMS observations of Saturn's infrared H3+ aurora during the 2013 multi-instrument campaign. European Planetary Science Congress 2013, held 8-13 September in London, UK.~Online at: http://meetings.copernicus.org/epsc2013, id.EPSC2013-761, 8, 761.
• Barnes, J. W., Buratti, B. J., Turtle, E. P., Bow, J., Dalba, P. A., Perry, J., Brown, R. H., Rodriguez, S., Mou 'elic, S. L., Baines, K. H., Sotin, C., Lorenz, R. D., Malaska, M. J., McCord, T. B., Clark, R. N., Jaumann, R., Hayne, P. O., Nicholson, P. D., Soderblom, J. M., & Soderblom, L. A. (2013). Precipitation-induced surface brightenings seen on Titan by Cassini VIMS and ISS. Planetary Science, 2, 1-22.
• Clark, R. N., Pearson, N., Perlman, Z. S., Bradley, E. T., Hendrix, A., Cuzzi, J. N., Cruikshank, D. P., Filacchione, G., Nicholson, P. D., Hedman, M. M., Brown, R. H., Buratti, B. J., Baines, K. H., Sotin, C., & Nelson, R. (2013). Surface Composition of the Non-Ice Component on Icy Satellites and Ring Particles in the Saturn System. AGU Fall Meeting Abstracts, A8.
• D'Aversa, E., Bellucci, G., Nicholson, P. D., Brown, R. H., Altieri, F., & Carrozzo, F. G. (2013). Saturn ring spokes: an overview of their near-infrared spectral properties from Cassini/VIMS data. European Planetary Science Congress 2013, held 8-13 September in London, UK.~Online at: http://meetings.copernicus.org/epsc2013, id.EPSC2013-1099, 8, 1099.
• Dalba, P. A., Buratti, B. J., Brown, R. H., Barnes, J. W., Baines, K. H., Sotin, C., Clark, R. N., Lawrence, K. J., & Nicholson, P. D. (2012). Low-latitude ethane rain on Titan. AGU Fall Meeting Abstracts.
• Filacchione, G., Capaccioni, F., Clark, R. N., Ciarniello, M., Brown, R. H., Cruikshank, D. P., Buratti, B. J., Cuzzi, J. N., Spilker, L. J., Nicholson, P. D., Dalle Ore, C., Cerroni, P., Tosi, F., & Scipioni, F. (2013). Saturn's satellites temperatures inferred from Cassini-VIMS reflectance spectra. AGU Fall Meeting Abstracts, A7.
• Filacchione, G., Ciarniello, M., Capaccioni, F., Clark, R. N., Nicholson, P. D., Hedman, M. M., Cuzzi, J. N., Cruikshank, D. P., Ore, C. M., Brown, R. H., Cerroni, P., Altobelli, N., & Spilker, L. J. (2014). Cassini-VIMS observations of Saturn's main rings: I. Spectral properties and temperature radial profiles variability with phase angle and elevation. ICARUS, 241, 45-65.
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  The spectral properties and thermal behavior of Saturn's rings are determined from a dataset of ten radial mosaics acquired by Cassini-VIMS (Visual and Infrared Mapping Spectrometer) between October 29th 2004 and January 27th 2010 with phase angle ranging between 5.7 degrees and 132.4 degrees and elevation angles between -23.5 degrees and 2.6 degrees. These observations, after reduction to spectrograms, e.g. 2D arrays containing the VIS-IR (0.35-5.1 mu m) spectral information versus radial distance from Saturn (from 73.500 to 141.375 km, 400 km/bin), allow us to compare the derived spectral and thermal properties of the ring particles on a common reference. Spectral properties: rings spectra are characterized by an intense reddening at visible wavelengths while they maintain a strong similarity with water ice in the infrared domain. Significant changes in VIS reddening, water ice abundance and grain sizes are observed across different radial regions resulting in correlation with optical depth and local structures. The availability of observations taken at very different phase angles allows us to examine spectrophotometric properties of the ring's particles. When observed at high phase angles, a remarkable increase of visible reddening and water ice band depths is found, probably as a consequence of the presence of a red-colored contaminant intimately mixed within water ice grains and of multiple scattering. At low phases the analysis of the 3.2-3.6 mu m range shows faint spectral signatures at 3.42-3.52 mu m which are compatible with the CH2 aliphatic stretch. The 3.29 mu m PAH aromatic stretch absorption is not clearly detectable on this dataset. VIMS results indicate that ring particles contain about 90-95% water ice while the remaining 5-10% is consistent with different contaminants like amorphous carbon or tholins. However, we cannot exclude the presence of nanophase iron or hematite produced by iron oxidation in the rings tenuous oxygen atmosphere, intimately mixed with the ice grains. Greater pollution caused by meteoritic material is seen in the C ring and Cassini division while the low levels of aliphatic material observed by VIMS in the A and B rings particles are an evidence that they are pristine. Thermal properties: the ring-particles' temperature is retrieved by fitting the spectral position of the 3.6 mu m continuum peak observed on reflectance spectra: in case of pure water ice the position of the peak, as measured in laboratory, shifts towards shorter wavelengths when temperature decreases, moving from about 3.65 mu m at 123 K to about 3.55 mu m at 88 K. When applied to VIMS rings observations, this method allows us to infer the average temperature across ring regions sampled through 400 km-wide radial bins. Comparing VIMS temperature radial profiles with similar CIRS measurements acquired at the same time we have found a substantial agreement between the two instruments' results across the A and B rings. In general VIMS measures higher temperatures than CIRS across C ring and Cassini division as a consequence of the lower optical depth and the resulting pollution that creates a deviation from pure water ice composition of these regions. VIMS results point out that across C ring and CD the 3.6 mu m peak wavelength is always higher than across B and A rings and therefore C ring and CD are warmer than A and B rings. VIMS observations allow us to investigate also diurnal and seasonal effects: comparing antisolar and subsolar ansae observations we have measured higher temperature on the latter.
• Hayes, A. G., Sotin, C., Hofgartner, J. D., Stiles, B. W., Barnes, J. W., Brown, R. H., Encrenaz, P., Kirk, R. L., Le Gall, A. A., Lopes, R. M., Lorenz, R. D., Lunine, J. I., Malaska, M. J., Mitchell, K. L., Paillou, P., Radebaugh, J., Turtle, E. P., Wall, S., Wood, C. A., & Zebker, H. A. (2013). The case of Titan's mysterious new island: An analysis of an anomalously bright feature observed in the T92 SAR pass over Ligeia Mare. AGU Fall Meeting Abstracts, D1898.
• Hofgartner, J. D., Hayes, A. G., Lunine, J. I., Zebker, H., Stiles, B. W., Sotin, C., Barnes, J. W., Turtle, E. P., Baines, K. H., Brown, R. H., Buratti, B. J., Clark, R. N., Encrenaz, P., Kirk, R. D., Le Gall, A., Lopes, R. M., Lorenz, R. D., Malaska, M. J., Mitchell, K. L., , Nicholson, P. D., et al. (2014). Transient features in a Titan sea. NATURE GEOSCIENCE, 7(7), 493-496.
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  Titan's surface-atmosphere system bears remarkable similarities to Earth's, the most striking being an active, global methane cycle akin to Earth's water cycle(1,2). Like the hydrological cycle of Earth, Titan's seasonal methane cycle is driven by changes in the distribution of solar energy(2). The Cassini spacecraft, which arrived at Saturn in 2004 in the midst of northern winter and southern summer, has observed surface changes, including shoreline recession, at Titan's south pole3,4 and equator(5). However, active surface processes have yet to be confirmed in the lakes and seas in Titan's north polar region(6-8). As the 2017 northern summer solstice approaches, the onset of dynamic phenomena in this region is expected(6,7,9-12). Here we present the discovery of bright features in recent Cassini RADAR data that appeared in Titan's northern sea, Ligeia Mare, in July 2013 and disappeared in subsequent observations. We suggest that these bright features are best explained by the occurrence of ephemeral phenomena such as surface waves, rising bubbles, and suspended or floating solids. We suggest that our observations are an initial glimpse of dynamic processes that are commencing in the northern lakes and seas as summer nears in the northern hemisphere.
• Le Mouelic, S., Rodriguez, S., Sotin, C., West, R. A., Rannou, P., Barnes, J. W., Brown, R. H., Cornet, T., Baines, K. H., Buratti, B. J., Clark, R. N., & Nicholson, P. D. (2012). Imaging of a Newly Forming Polar Hood Over The South Pole of Titan By VIMS/Cassini. AGU Fall Meeting Abstracts.
• Maltagliati, L., Vinatier, S., B 'ezard, B., Sotin, C., Sicardy, B., Nicholson, P. D., Hedman, M., Clark, R. N., & Brown, R. H. (2013). Investigating the Vertical Composition of Titan's Atmosphere with VIMS/Cassini Solar Occultations. European Planetary Science Congress 2013, held 8-13 September in London, UK.~Online at: http://meetings.copernicus.org/epsc2013, id.EPSC2013-625, 8, 625.
• Moores, J. E., Brown, R. H., Lauretta, D. S., & Smith, P. H. (2012). Experimental and theoretical simulation of sublimating dusty water ice with implications for D/H ratios of water ice on Comets and Mars. Planetary Science, 1, 1-30.
• Nichols, J. D., Badman, S. V., Baines, K. H., Brown, R. H., Bunce, E. J., Clarke, J. T., Cowley, S. W., Crary, F. J., Dougherty, M. K., Gerard, J. -., Grocott, A., Grodent, D., Kurth, W. S., Melin, H., Mitchell, D. G., Pryor, W. R., & Stallard, T. S. (2014). Dynamic auroral storms on Saturn as observed by the Hubble Space Telescope. GEOPHYSICAL RESEARCH LETTERS, 41(10), 3323-3330.
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  We present observations of significant dynamics within two UV auroral storms observed on Saturn using the Hubble Space Telescope in April/May 2013. Specifically, we discuss bursts of auroral emission observed at the poleward boundary of a solar wind-induced auroral storm, propagating at approximate to 330% rigid corotation from near approximate to 01h LT toward approximate to 08h LT. We suggest that these are indicative of ongoing, bursty reconnection of lobe flux in the magnetotail, providing strong evidence that Saturn's auroral storms are caused by large-scale flux closure. We also discuss the later evolution of a similar storm and show that the emission maps to the trailing region of an energetic neutral atom enhancement. We thus identify the auroral form with the upward field-aligned continuity currents flowing into the associated partial ring current.
• Nichols, J. D., Badman, S. V., Baines, K. H., Brown, R. H., Bunce, E. J., Clarke, J. T., Cowley, S. W., Crary, F. J., Dougherty, M. K., Gerard, J. M., Grocott, A., Grodent, D. C., Kurth, W. S., Melin, H., Mitchell, D. G., Pryor, W. R., & Stallard, T. (2013). Saturn's northern auroras as observed using the Hubble Space Telescope. AGU Fall Meeting Abstracts, C2196.
• Rodriguez, S., Garcia, A., Lucas, A., Appéré, T., Gall, A. L., Reffet, E., Corre, L. L., Mouélic, S. L., Cornet, T., Courrech, S., Narteau, C., Bourgeois, O., Radebaugh, J., Arnold, K., Barnes, J. W., Stephan, K., Jaumann, R., Sotin, C., Brown, R. H., , Lorenz, R. D., et al. (2014). Global mapping and characterization of Titan's dune fields with Cassini: Correlation between RADAR and VIMS observations. Icarus, 230, 168-179.
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  Abstract: Vast fields of linear dunes have been observed in the equatorial regions of Titan, Saturn's largest moon. As the Cassini mission, in orbit around Saturn since July 2004 and extended until May 2017, carries on, the high-resolution coverage of Titan's surface increases, revealing new dune fields and allowing refinements in the examination of their properties. In this paper, we present the joint analysis of Cassini's microwave and infrared global scale observations of Titan. Integrating within an up-to-date global map of Titan all the Cassini RADAR and VIMS (Visual and Infrared Mapping Spectrometer) images - the latter being empirically corrected for atmospheric scattering and surface photometry, from July 2004 through July 2013 and June 2010 respectively, we found very good qualitative and quantitative spatial matching between the geographic distribution of the dune fields and a specific infrared spectral unit (namely the "dark brown" unit). The high degree of spatial correlation between dunes and the "dark brown" unit has important implications for Titan's geology and climate. We found that RADAR-mapped dunes and the "dark brown" unit are similarly confined within the equatorial belt (±30° in latitudes) with an equivalent distribution with latitude, suggesting an increasing sediment availability and mobility at Titan's tropics relative to higher latitudes, compatible with the lower ground humidity predicted in equatorial regions by General Circulation Models. Furthermore, the strong correlation between RADAR-mapped dunes and the VIMS "dark brown" unit (72%) allows us to better constrain the total surface area covered by dune material, previously estimated from the extrapolation of the RADAR observations alone. According to our calculations, dune material cover 17.5±1.5% of Titan's surface area, equivalent to a total surface area of 14.6±1.2millionkm2 (~1.5 times the surface area of Earth's Sahara desert). The VIMS "dark brown" coloration of the dune material is here confirmed at large spatial scale. If the sand particle composition is dominated by solid organics produced in and settling from the atmosphere, as supported by our spectral modeling and by previous spectral analysis, microwave radiometric data and atmospheric modeling, dune fields are one of the major surface hydrocarbon reservoirs on Titan. Assuming two possible scenarios for the sand distribution (either the sand is (1) entirely trapped in dune landforms, or (2) trapped in dunes at places where dune landforms are firmly observed and in sand sheets elsewhere), we estimate the volume of hydrocarbons trapped in the dune sediment to be comprised between 1.7 and 4.4×105km3, corresponding to an average total mass of 230,000GT, in comparison with ~4000-30,000GT of hydrocarbons in the polar lakes and seas. This indicates a maximum age for the dune sediments of ~730-Myr, consistent with estimations of the ages of the current Titan's atmospheric methane and surface. © 2013 Elsevier Inc.
• Rodriguez, S., Le Mou 'elic, S., Barnes, J. W., Hirtzig, M., 'e, T., Rannou, P., Sotin, C., Brown, R. H., Bow, J., Vixie, G., Cornet, T., Bourgeois, O., Narteau, C., Pont, S., Griffith, C. A., Jauman, R., Stephan, K., Clark, R. N., & Coustenis, A. (2013). Singular equinoctial activity over Titan's dunefields as seen by CASSINI/VIMS. European Planetary Science Congress 2013, held 8-13 September in London, UK.~Online at: http://meetings.copernicus.org/epsc2013, id.EPSC2013-39, 8, 39.
• Rodriguez, S., Le Mou 'elic, S., Barnes, J. W., Hirtzig, M., Rannou, P., Sotin, C., Brown, R. H., Bow, J., Vixie, G., Cornet, T., Bourgeois, O., Narteau, C., Pont, S., Le Gall, A., Reffet, E., Griffith, C. A., Jauman, R., Stephan, K., Buratti, B. J., , Clark, R. N., et al. (2012). Equinoctial Atmospheric Activity over Titan Dune Fields Revealed by Cassini/VIMS. LPI Contributions, 1673, 81-82.
• Rodriguez, S., Le Mouelic, S., Barnes, J. W., Hirtzig, M., Rannou, P., Sotin, C., Brown, R. H., Bow, J., Vixie, G., Cornet, T., Bourgeois, O., Narteau, C., Courrech Du Pont, S., Le Gall, A., Reffet, E., Griffith, C. A., Jaumann, R., Stephan, K., Buratti, B. J., , Clark, R. N., et al. (2012). Equinoctial Activity Over Titan Dune Fields Revealed by Cassini/vims. AGU Fall Meeting Abstracts.
• Solomonidou, A., Coustenis, A., Hirtzig, M., Bratsolis, E., Drossart, P., Bampasidis, G., Kyriakopoulos, K., Le Mou 'elic, S., Rodriguez, S., Stephan, K., Jaumann, R., Sohl, F., Wagner, F. W., Hussmann, H., Lopes, R. M., Sotin, C., Brown, R. H., Stamatelopoulou-Seymour, K., & Moussas, X. (2013). Surface albedo changes with time on Titan's possible cryovolcanic sites: Cassini/VIMS processing and geophysical implications. European Planetary Science Congress 2013, held 8-13 September in London, UK.~Online at: http://meetings.copernicus.org/epsc2013, id.EPSC2013-88, 8, 88.
• Solomonidou, A., Hirtzig, M., Coustenis, A., Bratsolis, E., Le Mouelic, S., Rodriguez, S., Stephan, K., Drossart, P., Sotin, C., Jaumann, R., Brown, R. H., Kyriakopoulos, K., Lopes, R. M., Bampasidis, G., Stamatelopoulou-Seymour, K., & Moussas, X. (2014). Surface albedo spectral properties of geologically interesting areas on Titan. JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS, 119(8), 1729-1747.
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  We investigate the nature and possible formation processes of three areas on Titan's surface which have been suggested as geologically interesting: Hotei Regio, Tui Regio, and Sotra Patera. We also reanalyze the spectral characteristics of the Huygens Landing Site. We apply a statistical Principal Component Analysis (PCA) and a radiative transfer (RT) method on the Visual and Infrared Mapping Spectrometer Datacubes in order to retrieve the surface albedo of distinct spectral units in the near infrared. We have been able to exploit only a subset of the currently available Hotei Regio data, which are, in general, not optimal in terms of geometry for an analysis with a plane-parallel RT code. Our inferred surface albedos present generally higher values from 1 to 2 mu m and lower ones at 0.94 and in the 2.6-5 mu m region. The Regions of Interest (RoIs) within Hotei Regio, Tui Regio, and Sotra Patera are always significantly brighter than the surrounding areas. The largest variations are found longward of 2 mu m and mainly at 5 mu m. This higher surface albedo with respect to the surrounding area and, in general, the fact that the spectral behavior is different for each of these areas, is probably indicative of diverse chemical compositions and origins. We compare the spectral albedos with some suggested surface candidates on Titan (such as H2O, CO2, and CH4 ices, as well as tholin) and discuss possible chemical composition variations as well as other interpretations.
• Sotin, C., Seignovert, B., Lawrence, K., Barnes, J. W., Brown, R. H., Hayes, A., Le Mouelic, S., Baines, K. H., Buratti, B. J., Clark, R. N., & Nicholson, P. D. (2013). Evolution of Titan's Lakes and Seas: Insights from Recent Infrared Observations. AGU Fall Meeting Abstracts, B8.
• {Badman}, S., {Provan}, G., {Bunce}, E., {Mitchell}, D., {Melin}, H., {Nichols}, J., {Jinks}, S., {Cowley}, S., {Stallard}, T., {Radioti}, A., {Pryor}, W., {Kurth}, W., {Brown}, R., {Baines}, K., , M. (2014). Saturn's auroral morphology and field-aligned currents during a solar wind compression. European Planetary Science Congress 2014, EPSC Abstracts, Vol.~9, id.~EPSC2014-670, 9, EPSC2014-670.
• {Badman}, S., {Provan}, G., {Melin}, H., {Nichols}, J., {Mitchell}, D., {Pryor}, W., {Bunce}, E., {Cowley}, S., {Radioti}, K., {Kurth}, W., {Jinks}, S., {Stallard}, T., {Brown}, R., {Baines}, K., , M. (2014). Planetary Period Oscillations at Saturn: Auroral Observations. AGU Fall Meeting Abstracts.
• {Barnes}, J., {Sotin}, C., {Soderblom}, J., {Brown}, R., {Hayes}, A., {Donelan}, M., {Rodriguez}, S., {Le Mouelic}, S., {Baines}, K., , T. (2014). Cassini/VIMS Observes Rough Surfaces on Titan's Punga Mare in Specular Reflection. Planetary Science, 3, 3.
• {Clark}, R., {Perlman}, Z., {Pearson}, N., {Hendrix}, A., {Cuzzi}, J., {Cruikshank}, D., {Bradley}, E., {Filacchione}, G., {Nicholson}, P., {Hedman}, M., {Brown}, R., {Buratti}, B., {Baines}, K., {Sotin}, C., , R. (2014). Surface Composition and Physical Mixture State of the Regoliths of Outer Solar System Satellites: The Role of Scattering and Absorption by the non-Ice Components and Implications for Rayleigh Absorption and Rayleigh Scattering. AGU Fall Meeting Abstracts.
• {Cornet}, T., {Altobelli}, N., {Sotin}, C., {Le Mouelic}, S., {Rodriguez}, S., {Philippe}, S., {Brown}, R., {Barnes}, J., {Buratti}, B., {Baines}, K., {Clark}, R., , P. (2014). Studying Titan's surface photometry in the 5 microns atmospheric window with the Cassini/VIMS instrument. AGU Fall Meeting Abstracts.
• {Hofgartner}, J., {Hayes}, A., {Lunine}, J., {Zebker}, H., {Stiles}, B., {Sotin}, C., {Barnes}, J., {Turtle}, E., {Baines}, K., {Brown}, R., {Buratti}, B., {Clark}, R., {Encrenaz}, P., {Kirk}, R., {Le Gall}, A., {Lopes}, R., {Lorenz}, R., {Malaska}, M., {Mitchell}, K., , {Nicholson}, P., et al. (2014). Titan's Magic Island: Transient features in a Titan sea. AGU Fall Meeting Abstracts.
• {Le Mouelic}, S., {Rousseau}, B., {Rodriguez}, S., {Cornet}, T., {Sotin}, C., {Barnes}, J., {Brown}, R., {Buratti}, B., {Baines}, K., {Clark}, R., , P. (2014). Monitoring the Seasonal Evolution of the North and South Polar Vortex on Titan during 10 Years with Cassini/Vims. AGU Fall Meeting Abstracts.
• {Maltagliati}, L., {Rodriguez}, S., {App{\'e}r{\'e}}, T., {Vincendon}, M., {Dout{\'e}}, S., {Le Mouelic}, S., {Rannou}, P., {Sotin}, C., {Barnes}, J., {Coustenis}, A., , R. (2014). Massive Inversion of Atmospheric and Surface Properties of Titan from VIMS/Cassini Observations. European Planetary Science Congress 2014, EPSC Abstracts, Vol.~9, id.~EPSC2014-542, 9, EPSC2014-542.
• {Rannou}, P., {Lemou{\'e}lic}, S., {Sotin}, C., , R. (2014). Constraints on Titan's aerosols optical properties from VIMS observations in the 2 {$\mu$}m and 2.8 {$\mu$}m window.. European Planetary Science Congress 2014, EPSC Abstracts, Vol.~9, id.~EPSC2014-384, 9, EPSC2014-384.
• {Rannou}, P., {Toledo-Carrasco}, D., {Adriani}, A., {Moriconi}, M., {D'Aversa}, E., {Lemou{\'e}lic}, S., {Sotin}, C., , R. (2014). Surface of Titan : model and VIMS observations. European Planetary Science Congress 2014, EPSC Abstracts, Vol.~9, id.~EPSC2014-377, 9, EPSC2014-377.
• {Rodriguez}, S., {Le Mouelic}, S., {Rannou}, P., {Sotin}, C., {Barnes}, J., {Griffith}, C., {Brown}, R., {Baines}, K., {Buratti}, B., {Clark}, R., , P. (2014). 10 Years of Cloud Cover Monitoring on Titan with Vims on Board Cassini. AGU Fall Meeting Abstracts.
• {Rodriguez}, S., {Le Mou{\'e}lic}, S., {Rannou}, P., {Sotin}, C., {Barnes}, J., {Griffith}, C., {Brown}, R., {Baines}, K., {Buratti}, B., {Clark}, R., , P. (2014). 10 years of cloud cover monitoring on Titan with VIMS on board Cassini. European Planetary Science Congress 2014, EPSC Abstracts, Vol.~9, id.~EPSC2014-675, 9, EPSC2014-675.
• {Rodriguez}, S., {Maltagliati}, L., {App{\'e}r{\'e}}, T., {Vincendon}, M., {Dout{\'e}}, S., {Le Mouelic}, S., {Rannou}, P., {Sotin}, C., {Barnes}, J., {Coustenis}, A., , R. (2014). Simultaneous Mapping of Titan's Atmospheric and Surface Properties Through the Massive Inversion of Cassini/VIMS Data. AGU Fall Meeting Abstracts.
• {Solomonidou}, A., {Coustenis}, A., {Lopes}, R., {Hirtzig}, M., {Rodriguez}, S., {Stephan}, K., {Sotin}, C., {Drossart}, P., {Lawrence}, K., {Le Mou{\'e}lic}, S., {Bratsolis}, E., {Jaumann}, R., {Brown}, R., , M. (2014). Surface changes in mid-latitude regions on Titan. European Planetary Science Congress 2014, EPSC Abstracts, Vol.~9, id.~EPSC2014-115, 9, EPSC2014-115.
• {Solomonidou}, A., {Coustenis}, A., {Lopes}, R., {Rodriguez}, S., {Hirtzig}, M., {Stephan}, K., {Sotin}, C., {Drossart}, P., {Le Mouelic}, S., {Lawrence}, K., {Malaska}, M., {Jaumann}, R., {Brown}, R., , E. (2014). Unveiling Titan's Mid-Latitude Surface Regions. AGU Fall Meeting Abstracts.
• {Sotin}, C., {Brown}, R., {Baines}, K., {Barnes}, J., {Buratti}, B., {Clark}, R., {Jaumann}, R., {LeMouelic}, S., {Nicholson}, P., {Rodriguez}, S., {Soderblom}, J., {Soderblom}, L., , K. (2014). 10 years of Cassini/VIMS observations at Titan. European Planetary Science Congress 2014, EPSC Abstracts, Vol.~9, id.~EPSC2014-697, 9, EPSC2014-697.
• {Sotin}, C., {Lawrence}, K., {Le Mouelic}, S., {MacKenzie}, S., {Barnes}, J., {Brown}, R., {Cornet}, T., {Rodriguez}, S., {Baines}, K., {Buratti}, B., {Clark}, R., {Nicholson}, P., , J. (2014). Evolution of Titan's Seas and Lakes during Northern Spring. AGU Fall Meeting Abstracts.
• Barnes, J. W., Clark, R. N., Sotin, C., Ádámkovics, M., Appéré, T., Rodriguez, S., Soderblom, J. M., Brown, R. H., Buratti, B. J., Baines, K. H., Mouélic, S. L., & Nicholson, P. D. (2013). A transmission spectrum of titan's north polar atmosphere from a specular reflection of the sun. Astrophysical Journal, 777(2).
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  Abstract: Cassini/VIMS T85 observations of a solar specular reflection off of Kivu Lacus (87.°4N 241.°1E) provide an empirical transmission spectrum of Titan's atmosphere. Because this observation was acquired from short range (33,000 km), its intensity makes it visible within the 2.0, 2.7, and 2.8 μm atmospheric windows in addition to the 5 μm window where all previous specular reflections have been seen. The resulting measurement of the total one-way normal atmospheric optical depth (corresponding to haze scattering plus haze and gas absorption) provides strong empirical constraints on radiative transfer models. Using those models, we find that the total haze column abundance in our observation is 20% higher than the Huygens equatorial value. Ours is the first measurement in the 2-5 μm wavelength range that probes all the way to the surface in Titan's arctic, where the vast majority of surface liquids are located. The specular technique complements other probes of atmospheric properties such as solar occultations and the direct measurements from Huygens. In breaking the degeneracy between surface and atmospheric absorptions, our measured optical depths will help to drive future calculations of deconvolved surface albedo spectra. © 2013. The American Astronomical Society. All rights reserved.
• Filacchione, G., Capaccioni, F., Clark, R. N., Nicholson, P. D., Cruikshank, D. P., Cuzzi, J. N., Lunine, J. I., Brown, R. H., Cerroni, P., Tosi, F., Ciarniello, M., Buratti, B. J., Hedman, M. M., & Flamini, E. (2013). The radial distribution of water ice and chromophores across Saturn's system. Astrophysical Journal, 766(2).
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  Abstract: Over the past eight years, the Visual and Infrared Mapping Spectrometer (VIMS) on board the Cassini orbiter has returned hyperspectral images in the 0.35-5.1 μm range of the icy satellites and rings of Saturn. These very different objects show significant variations in surface composition, roughness, and regolith grain size as a result of their evolutionary histories, endogenic processes, and interactions with exogenic particles. The distributions of surface water ice and chromophores, i.e., organic and non-icy materials, across the Saturnian system, are traced using specific spectral indicators (spectral slopes and absorption band depths) obtained from rings mosaics and disk-integrated satellites observations by VIMS. Moving from the inner C ring to Iapetus, we found a marking uniformity in the distribution of abundance of water ice. On the other hand, the distribution of chromophores is much more concentrated in the rings particles and on the outermost satellites (Rhea, Hyperion, and Iapetus). A reduction of red material is observed on the satellites' surfaces orbiting within the E ring environment likely due to fine particles from Enceladus' plumes. Once the exogenous dark material covering the Iapetus' leading hemisphere is removed, the texture of the water ice-rich surfaces, inferred through the 2 μm band depth, appears remarkably uniform across the entire system. © 2013. The American Astronomical Society. All rights reserved..
• Goguen, J. D., Buratti, B. J., Brown, R. H., Clark, R. N., Nicholson, P. D., Hedman, M. M., Howell, R. R., Sotin, C., Cruikshank, D. P., Baines, K. H., Lawrence, K. J., Spencer, J. R., & Blackburn, D. G. (2013). The temperature and width of an active fissure on Enceladus measured with Cassini VIMS during the 14 April 2012 South Pole flyover. Icarus, 226(1), 1128-1137.
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  Abstract: The width and temperature of the active fissures on Saturn's satellite Enceladus provide key observable constraints on physical models of these geyser-like eruptions. We analyze a sequence of high spatial resolution near-infrared spectra acquired with VIMS at 0.025s intervals during a 74km altitude flyover of the South Pole of Enceladus by the Cassini spacecraft on 14 April 2012 UTC. A thermal-emission spectrum covering 3- to 5-μm wavelengths was detected as the field of view crossed one of the four major fissures, Baghdad Sulcus, within 1km of 82.36S latitude and 28.24W longitude. We interpret this spectrum as thermal emission from a linear fissure with temperature 197±20K and width 9m. At the above wavelengths, the spectrum is dominated by the warmest temperature component. Looking downward into the fissure at only 13° from the vertical, we conclude that our results measure the temperature of the interior fissure walls (and the H2O vapor) at depths within 40m of the surface. © 2013 Elsevier Inc.
• Hedman, M. M., Gosmeyer, C. M., Nicholson, P. D., Sotin, C., Brown, R. H., Clark, R. N., Baines, K. H., Buratti, B. J., & Showalter, M. R. (2013). An observed correlation between plume activity and tidal stresses on Enceladus. Nature, 500(7461), 182-184.
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  PMID: 23903658;Abstract: Saturn's moon Enceladus emits a plume of water vapour and micrometre-sized ice particles from a series of warm fissures located near its south pole. This geological activity could be powered or controlled by variations in the tidal stresses experienced by Enceladus as it moves around its slightly eccentric orbit. The specific mechanisms by which these varying stresses are converted into heat, however, are still being debated. Furthermore, it has proved difficult to find a clear correlation between the predicted tidal forces and measured temporal variations in the plume's gas content or the particle flux from individual sources. Here we report that the plume's horizontally integrated brightness is several times greater when Enceladus is near the point in its eccentric orbit where it is furthest from Saturn (apocentre) than it is when near the point of closest approach to the planet (pericentre). More material therefore seems to be escaping from beneath Enceladus' surface at times when geophysical models predict its fissures should be under tension and therefore may be wider open. © 2013 Macmillan Publishers Limited. All rights reserved.
• Badman, S. V., Achilleos, N., Arridge, C. S., Baines, K. H., Brown, R. H., Bunce, E. J., Coates, A. J., Cowley, S. W., Dougherty, M. K., Fujimoto, M., Hospodarsky, G., Kasahara, S., Kimura, T., Melin, H., Mitchell, D. G., Stallard, T., & Tao, C. (2012). Cassini observations of ion and electron beams at Saturn and their relationship to infrared auroral arcs. Journal of Geophysical Research A: Space Physics, 117(1).
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  Abstract: We present Cassini Visual and Infrared Mapping Spectrometer observations of infrared auroral emissions from the noon sector of Saturn's ionosphere revealing multiple intense auroral arcs separated by dark regions poleward of the main oval. The arcs are interpreted as the ionospheric signatures of bursts of reconnection occurring at the dayside magnetopause. The auroral arcs were associated with upward field-aligned currents, the magnetic signatures of which were detected by Cassini at high planetary latitudes. Magnetic field and particle observations in the adjacent downward current regions showed upward bursts of 100-360 keV light ions in addition to energetic (hundreds of keV) electrons, which may have been scattered from upward accelerated beams carrying the downward currents. Broadband, upward propagating whistler waves were detected simultaneously with the ion beams. The acceleration of the light ions from low altitudes is attributed to wave-particle interactions in the downward current regions. Energetic (600 keV) oxygen ions were also detected, suggesting the presence of ambient oxygen at altitudes within the acceleration region. These simultaneous in situ and remote observations reveal the highly energetic magnetospheric dynamics driving some of Saturn's unusual auroral features. This is the first in situ identification of transient reconnection events at regions magnetically conjugate to Saturn's magnetopause.
• Badman, S. V., Andrews, D. J., Cowley, S. W., Lamy, L., Provan, G., Tao, C., Kasahara, S., Kimura, T., Fujimoto, M., Melin, H., Stallard, T., Brown, R. H., & Baines, K. H. (2012). Rotational modulation and local time dependence of Saturn's infrared H3 + auroral intensity. Journal of Geophysical Research A: Space Physics, 117(9).
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  Abstract: Planetary auroral emissions reveal the configuration of magnetospheric field-aligned current systems. In this study, Cassini Visual and infrared Mapping Spectrometer (VIMS) observations of Saturn's pre-equinox infrared H3 + aurorae were analysed to show (a) rotational modulation of the auroral intensity in both hemispheres and (b) a significant local time dependence of the emitted intensity. The emission intensity is modulated by the 'planetary period' rotation of auroral current systems in each hemisphere. The northern auroral intensity also displays a lesser anti-phase dependence on the southern rotating current system, indicating that part of the southern current system closes in the northern hemisphere. The southern hemisphere aurorae were most intense in the post-dawn sector, in agreement with some past measurements of auroral field-aligned currents, UV aurora and SKR emitted power. A corresponding investigation of the northern hemisphere auroral intensity reveals a broader dawn-noon enhancement, possibly due to the interaction of the southern rotating current system with that of the north. The auroral intensity was reduced around dusk and post-midnight in both hemispheres. These observations can be explained by the interaction of a rotating field-aligned current system in each hemisphere with one fixed in local time, which is related to the solar wind interaction with magnetospheric field lines.
• Badman, S., Achilleos, N., Arridge, C., Baines, K., Brown, R., Bunce, E., Coates, A., Cowley, S., Dougherty, M., Fujimoto, M., Hospodarsky, G., Kasahara, S., Kimura, T., Melin, H., Mitchell, D., Stallard, T., & Tao, C. (2012). Correction to ``Cassini observations of ion and electron beams at Saturn and their relationship to infrared auroral arcs. Journal of Geophysical Research, 117(A4).
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  CiteID: A04220
• Buratti, B. J., Sotin, C., Lawrence, K., Brown, R. H., Mouélic, S. L., Soderblom, J. M., Barnes, J., Clark, R. N., Baines, K. H., & Nicholson, P. D. (2012). A newly discovered impact crater in Titan's Senkyo: Cassini VIMS observations and comparison with other impact features. Planetary and Space Science, 60(1), 18-25.
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  Abstract: Senkyo is an equatorial plain on Titan filled with dunes and surrounded by hummocky plateaus. During the Titan targeted flyby T61 on August 25, 2009, the Cassini Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft observed a circular feature, centered at 5.4° N and 341°W, that superimposes the dune fields and a bright plateau. This circular feature, which has been named Paxsi by the International Astronomical Union, is 120±10 km in diameter (measured from the outer edge of the crater rim) and exhibits a central bright area that can be interpreted as the central peak or pit of an impact crater. Although there are only a handful of certain impact craters on Titan, there are two other craters that are of similar size to this newly discovered feature and that have been studied by VIMS: Sinlap (Le Mouélic et al, 2008) and Selk (Soderblom et al, 2010). Sinlap is associated with a large downwind, fan-like feature that may have been formed from an impact plume that rapidly expanded and deposited icy particles onto the surface. Although much of the surrounding region is covered with dunes, the plume region is devoid of dunes. The formation process of Selk also appears to have removed (or covered up) dunes from parts of the adjacent dune-filled terrain. The circular feature on Senkyo is quite different: there is no evidence of an ejecta blanket and the crater itself appears to be infilled with dune material. The rim of the crater appears to be eroded by fluvial processes; at one point the rim is breached. The rim is unusually narrow, which may be due to mass wasting on its inside and subsequent infill by dunes. Based on these observations, we interpret this newly discovered feature to be a more eroded crater than both Sinlap and Selk. Paxsi may have formed during a period when Titan was warmer and more ductile than it is currently. © 2011 Elsevier Ltd. All rights reserved.
• Clark, R. N., Cruikshank, D. P., Jaumann, R., Brown, R. H., Stephan, K., Morea, C., Livo, K. E., Pearson, N., Curchin, J. M., Hoefen, T. M., Buratti, B. J., Filacchione, G., Baines, K. H., & Nicholson, P. D. (2012). The surface composition of Iapetus: Mapping results from Cassini VIMS. Icarus, 218(2), 831-860.
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  Abstract: Cassini VIMS has obtained spatially resolved imaging spectroscopy data on numerous satellites of Saturn. A very close fly-by of Iapetus on September 10, 2007 provided the best data on the spectral signature and spatial extent of dark material on Iapetus. This Cassini Rev 49 Iapetus fly-by provided spatially resolved imaging spectroscopy data of the dark material and the leading/trailing side transition from the dark material to visually bright ice on the trailing side. Compositional mapping and radiative transfer modeling shows that the dark material is composed of metallic iron, nano-size iron oxide (hematite), CO 2, H 2O ice, and possible signatures of ammonia, bound water, H 2 or OH-bearing minerals, trace organics, and as yet unidentified materials. CO 2 indicates a pattern of increasing CO 2 strength from the leading side apex to the transition zone to the icy trailing side. A Rayleigh scattering peak in the visible part of the spectrum indicates the dark material has a large component of fine, sub-0.5-μm diameter particles consistent with nanophase hematite and nanophase iron. Spectral signatures of ice also indicate that sub-0.5-μm diameter particles are present in the icy regions. Multiple lines of evidence point to an external origin for the dark material on Iapetus, including the global spatial pattern of dark material, local patterns including crater and cliff walls shielding implantation on slopes facing away from the leading side, exposing clean ice, and slopes facing the leading direction which show higher abundances of dark material. Multiple spectral features and overall spectral shape of the dark material on Iapetus match those seen on Phoebe, Hyperion, Dione, Epimetheus, Saturn's rings Cassini Division, and the F-ring implying the material has a common composition throughout the Saturn system. The dark material appears to have significant components of nanophase metallic iron and nanophase hematite contributing to the observed UV absorption. The blue scattering peak with a strong UV-visible absorption is observed in spectra of all satellites that contain dark material, again pointing to a common origin of contamination by metallic iron that is partially oxidized. © 2012.
• Cornet, T., Bourgeois, O., Mouélic, S. L., Rodriguez, S., Gonzalez, T. L., Sotin, C., Tobie, G., Fleurant, C., Barnes, J. W., Brown, R. H., Baines, K. H., Buratti, B. J., Clark, R. N., & Nicholson, P. D. (2012). Geomorphological significance of Ontario Lacus on Titan: Integrated interpretation of Cassini VIMS, ISS and RADAR data and comparison with the Etosha Pan (Namibia). Icarus, 218(2), 788-806.
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  Abstract: Ontario Lacus is the largest lake of the whole southern hemisphere of Titan, Saturn's major moon. It has been imaged twice by each of the Cassini imaging systems (Imaging Science Subsystem (ISS) in 2004 and 2005, Visual and Infrared Mapping Spectrometer (VIMS) in 2007 and 2009 and RADAR in 2009 and 2010). We compile a geomorphological map and derive a "hydrogeological" interpretation of Ontario Lacus, based on a joint analysis of ISS, VIMS and RADAR SAR datasets, along with the T49 altimetric profile acquired in December 2008. The morphologies observed on Ontario Lacus are compared to landforms of a semi-arid terrestrial analog, which resembles Titan's lakes: the Etosha Pan, located in the Owambo Basin (Namibia). The Etosha Pan is a flat-floored depression formed by dissolution, under semi-arid conditions, of a surface evaporitic layer (calcretes) controlled by groundwater vertical motions. We infer that Ontario Lacus is an extremely flat and shallow depression lying in an alluvial plain surrounded by small mountain ranges under climatic conditions similar to those of terrestrial semi-arid regions. Channels are seen in the southern part of Ontario Lacus in VIMS and RADAR data, acquired at a 2-years time interval. Their constancy in location with time implies that the southern portion of the depression is probably not fully covered by a liquid layer at the time of the observations, and that they most probably run on the floor of the depression. A shallow layer of surface liquids, corresponding to the darkest portions of the RADAR images, would thus cover about 53% of the surface area of the depression, of which almost 70% is located in its northern part. These liquid-covered parts of the depression, where liquid ethane was previously identified, are interpreted as topographic lows where the "alkanofer" raises above the depression floor. The rest of the depression, and mostly its southern part, is interpreted as a flat and smooth exposed floor, likely composed of a thick and liquid-saturated coating of photon-absorbing materials in the infrared. This hypothesis could explain its dark appearance both in the infrared and radar data and the persistence of channels seen on the depression floor over the time. Shorelines are observed on the border of Ontario Lacus suggesting past high-stand levels of the alkanofer table. The analogy with the Etosha Pan suggests that Ontario Lacus' depression developed at the expense of a soluble layer covering the region. Dissolution of this layer would be controlled by vertical motions of the alkanofer table over the time. During flooding events, liquid hydrocarbons covering the depression floor would dissolve the surface layer, increasing progressively the diameter of the depression on geological timescales. During drought episodes, liquid hydrocarbons of the underground alkanofer would evaporate, leading to crystallization of "evaporites" in the pores and at the surface of the substratum, and to the formation of the regional soluble layer. The presence of specific landforms (lunette dunes or evaporites) is compatible with such evaporitic regional settings. Alternatively, but not exclusively, the surface soluble layer might have formed by accumulation on the ground of soluble compounds formed in the atmosphere. © 2012 Elsevier Inc.
• Cornet, T., Bourgeois, O., Mouélic, S. L., Rodriguez, S., Sotin, C., Barnes, J. W., Brown, R. H., Baines, K. H., Buratti, B. J., Clark, R. N., & Nicholson, P. D. (2012). Edge detection applied to Cassini images reveals no measurable displacement of Ontario Lacus' margin between 2005 and 2010. Journal of Geophysical Research E: Planets, 117(7).
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  Abstract: [1] Ontario Lacus is thus far the largest flat-floored topographic depression of Titan's southern hemisphere interpreted as a permanent or ephemeral lake. From 2005 to 2010, it was imaged several times and at various wavelengths by ISS, VIMS and RADAR instruments onboard Cassini's spacecraft. We analyze the position and uncertainty of Ontario Lacus' margin in all these images using an edge detection method based on image derivation. We find that, given the range of uncertainties in contour locations derived from images, no measurable displacement of Ontario Lacus' margin can be detected between 2005 and 2010 at the actual image spatial resolutions. The discrepancy between this result and previous ones is attributable to differences in (1) the basics behind the methods used, (2) the actual spatial resolutions and contrasts of the available images due to differential atmospheric scattering effects at different wavelengths, and (3) the geomorphological interpretation of contours derived from images acquired at different wavelengths. This lack of measurable displacement in the images suggests that the imaged contour corresponds either (1) to the border of a surface liquid body, provided that potential changes in its extent over five terrestrial years were not sufficiently large to be measured, or (2) to the stationary topographic border between Ontario Lacus' depression and the surrounding alluvial plain. Potential displacements of Ontario Lacus' margin between 2005 and 2010 are thus below the actual resolution of currently available images or have to be sought for within the extent of the topographic depression rather than along its borders. © 2012. American Geophysical Union.
• Dalba, P. A., Buratti, B. J., Brown, R. H., Barnes, J. W., Baines, K. H., Sotin, C., Clark, R. N., Lawrence, K. J., & Nicholson, P. D. (2012). Cassini VIMS observations show ethane is present in Titan's rainfall. Astrophysical Journal Letters, 761(2).
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  Abstract: Observations obtained over two years by the Cassini Imaging Science Subsystem suggest that rain showers fall on the surface. Using measurements obtained by the Visual Infrared Mapping Spectrometer, we identify the main component of the rain to be ethane, with methane as an additional component. We observe five or six probable rainfall events, at least one of which follows a brief equatorial cloud appearance, suggesting that frequent rainstorms occur on Titan. The rainfall evaporates, sublimates, or infiltrates on timescales of months, and in some cases it is associated with fluvial features but not with their creation or alteration. Thus, Titan exhibits frequent "gentle rainfall" instead of, or in addition to, more catastrophic events that cut rivers and lay down large fluvial deposits. Freezing rain may also be present, and the standing liquid may exist as puddles interspersed with patches of frost. The extensive dune deposits found in the equatorial regions of Titan imply multi-season arid conditions there, which are consistent with small, but possibly frequent, amounts of rain, in analogy to terrestrial deserts. © 2012. The American Astronomical Society. All rights reserved.
• Filacchione, G., Capaccioni, F., Ciarniello, M., Clark, R. N., Cuzzi, J. N., Nicholson, P. D., Cruikshank, D. P., Hedman, M. M., Buratti, B. J., Lunine, J. I., Soderblom, L. A., Tosi, F., Cerroni, P., Brown, R. H., McCord, T. B., Jaumann, R., Stephan, K., Baines, K. H., & Flamini, E. (2012). Saturn's icy satellites and rings investigated by Cassini-VIMS: III - Radial compositional variability. Icarus, 220(2), 1064-1096.
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  Abstract: In the last few years Cassini-VIMS, the Visible and Infrared Mapping Spectrometer, returned to us a comprehensive view of the Saturn's icy satellites and rings. After having analyzed the satellites' spectral properties (Filacchione, G., Capaccioni, F., McCord, T.B., Coradini, A., Cerroni, P., Bellucci, G., Tosi, F., D'Aversa, E., Formisano, V., Brown, R.H., Baines, K.H., Bibring, J.P., Buratti, B.J., Clark, R.N., Combes, M., Cruikshank, D.P., Drossart, P., Jaumann, R., Langevin, Y., Matson, D.L., Mennella, V., Nelson, R.M., Nicholson, P.D., Sicardy, B., Sotin, C., Hansen, G., Hibbitts, K., Showalter, M., Newman, S. [2007]. Icarus 186, 259-290, paper I) and their distribution across the satellites' hemispheres (Filacchione, G., Capaccioni, F., Clark, R.N., Cuzzi, J.N., Cruikshank, D.P., Coradini, A., Cerroni, P., Nicholson, P.D., McCord, T.B., Brown, R.H., Buratti, B.J., Tosi, F., Nelson, R.M., Jaumann, R., Stephan, K. [2010]. Icarus 206, 507-523, paper II), we proceed in this paper to investigate the radial variability of icy satellites (principal and minor) and main rings average spectral properties. This analysis is done by using 2264 disk-integrated observations of the satellites and a 12 × 700 pixels-wide rings radial mosaic acquired with a spatial resolution of about 125. km/pixel. Using different VIS and IR spectral indicators, e.g. spectral slopes and band depths, we perform a comparative analysis of these data aimed to measure the distribution of water ice and red contaminant materials across Saturn's system. The average surface regolith grain sizes are estimated with different indicators through comparison with laboratory and synthetic spectra. These measurements highlight very striking differences in the population here analyzed, which vary from the almost uncontaminated and water ice-rich surfaces of Enceladus and Calypso to the metal/organic-rich and red surfaces of Iapetus' leading hemisphere and Phoebe. Rings spectra appear more red than the icy satellites in the visible range but show more intense 1.5-2.0μm band depths. Although their orbits are close to the F-ring, Prometheus and Pandora are different in surface composition: Prometheus in fact appears very water ice-rich but at the same time very red at VIS wavelengths. These properties make it very similar to A-B ring particles while Pandora is bluer. Moving outwards, we see the effects of E ring particles, generated by Enceladus plumes, which contaminate satellites surfaces from Mimas out to Rhea. We found some differences between Tethys lagrangian moons, Calypso being much more water ice-rich and bluer than Telesto. Among outer satellites (Hyperion, Iapetus and Phoebe) we observe a linear trend in both water ice decrease and in reddening, Hyperion being the reddest object of the population. The correlations among spectral slopes, band depths, visual albedo and phase permit us to cluster the saturnian population in different spectral classes which are detected not only among the principal satellites and rings but among co-orbital minor moons as well. These bodies are effectively the " connection" elements, both in term of composition and evolution, between the principal satellites and main rings. Finally, we have applied Hapke's theory to retrieve the best spectral fits to Saturn's inner regular satellites (from Mimas to Dione) using the same methodology applied previously for Rhea data discussed in Ciarniello et al. (Ciarniello, M., Capaccioni, F., Filacchione, G., Clark, R.N., Cruikshank, D.P., Cerroni, P., Coradini, A., Brown, R.H., Buratti, B.J., Tosi, F., Stephan, K. [2011]. Icarus 214, 541-555). © 2012 Elsevier Inc.
• Griffith, C. A., Lora, J. M., Turner, J., Penteado, P. F., Brown, R. H., Tomasko, M. G., Doose, L., & See, C. (2012). Possible tropical lakes on Titan from observations of dark terrain. Nature, 486(7402), 237-239.
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  PMID: 22699614;Abstract: Titan has clouds, rain and lakes"like Earth"but composed of methane rather than water. Unlike Earth, most of the condensable methane (the equivalent of 5m depth globally averaged) lies in the atmosphere. Liquid detected on the surface (about 2m deep) has been found by radar images only poleward of 50 ° latitude, while dune fields pervade the tropics. General circulation models explain this dichotomy, predicting that methane efficiently migrates to the poles from these lower latitudes. Here we report an analysis of near-infrared spectral images of the region between 20 °N and 20 °S latitude. The data reveal that the lowest fluxes in seven wavelength bands that probe Titan's surface occur in an oval region of about 60×40km 2, which has been observed repeatedly since 2004. Radiative transfer analyses demonstrate that the resulting spectrum is consistent with a black surface, indicative of liquid methane on the surface. Enduring low-latitude lakes are best explained as supplied by subterranean sources (within the last 10,000 years), which may be responsible for Titan's methane, the continual photochemical depletion of which furnishes Titan's organic chemistry. © 2012 Macmillan Publishers Limited. All rights reserved.
• Hedman, M. M., Nicholson, P. D., Showalter, M. R., Brown, R. H., Buratti, B. J., Clark, R. N., Baines, K., & Sotin, C. (2012). Erratum to " The Christiansen Effect in Saturn's narrow dusty rings and the spectral identification of clumps in the F ring" [Icarus 215 (2011) 695-711]. Icarus, 218(1), 735-.
• Langhans, M. H., Jaumann, R., Stephan, K., Brown, R. H., Buratti, B. J., Clark, R. N., Baines, K. H., Nicholson, P. D., Lorenz, R. D., Soderblom, L. A., Soderblom, J. M., Sotin, C., Barnes, J. W., & Nelson, R. (2012). Titan's fluvial valleys: Morphology, distribution, and spectral properties. Planetary and Space Science, 60(1), 34-51.
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  Abstract: Titan's fluvial channels have been investigated based on data obtained by the Synthetic Aperture Radar (SAR) instrument and the Visible and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft. In this paper, a database of fluvial features is created based on radar-SAR data aiming to unveil the distribution and the morphologic and spectral characteristics of valleys on Titan on a global scale. It will also study the spatial relations between fluvial valleys and Titan's geologic units and spectral surface units which have become accessible thanks to Cassini-VIMS data. Several distinct morphologic types of fluvial valleys can be discerned by SAR-images. Dendritic valley networks appear to have much in common with terrestrial dendritic systems owing to a hierarchical and tree-shaped arrangement of the tributaries which is indicative of an origin from precipitation. Dry valleys constitute another class of valleys resembling terrestrial wadis, an indication of episodic and strong flow events. Other valley types, such as putative canyons, cannot be correlated with rainfall based on their morphology alone, since it cannot be ruled out that they may have originated from volcanic/tectonic action or groundwater sapping. Highly developed and complex fluvial networks with channel lengths of up to 1200 km and widths of up to 10 km are concentrated only at a few locations whereas single valleys are scattered over all latitudes. Fluvial valleys are frequently found in mountainous areas. Some terrains, such as equatorial dune fields and undifferentiated plains at mid-latitudes, are almost entirely free of valleys. Spectrally, fluvial terrains are often characterized by a high reflectance in each of Titan's atmospheric windows, as most of them are located on Titan's bright 'continents'. Nevertheless, valleys are spatially associated with a surface unit appearing blue due to its higher reflection at 1.3μm in a VIMS false color RGB composite with R: 1.59/1.27μm, G: 2.03/1.27μm, and B: 1.27/1.08μm; the channels either dissect pure bluish surface units or they are carved into terrain with a mixed spectral signature between bright and bluish surface materials. The global picture of fluvial flows clearly indicates a high diversity of parameters controlling fluvial erosion, such as climatic processes, as well as surface and bedrock types. Recent fluvial activity is very likely in the north polar region in contrast to more arid conditions at lower latitudes and at the south pole of Titan. This divergence is probably an indication of seasonal climatic asymmetries between the hemispheres. However, traces of previous fluvial activity are scattered over all latitudes of Titan, which is indicative of previous climatic conditions with at least episodic rainfall. © 2011 Elsevier Ltd. All rights reserved.
• Mouélic, S. L., Cornet, T., Rodriguez, S., Sotin, C., Barnes, J. W., Baines, K. H., Brown, R. H., Lefèvre, A., Buratti, B. J., Clark, R. N., & Nicholson, P. D. (2012). Global mapping of Titan′s surface using an empirical processing method for the atmospheric and photometric correction of Cassini/VIMS images. Planetary and Space Science, 73(1), 178-190.
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  Abstract: We have processed all images of Titan's surface acquired by the Visual and Infrared Mapping Spectrometer between 2004 and 2010, with the objective of producing seamless global mosaics of the surface in the six infrared atmospheric windows at 1.08, 1.27, 1.59, 2.03, 2.6-2.7 and 5 μm. A systematic study of the photometry at 5 μm, where haze scattering can be neglected, shows that the surface behaves to first order like a Lambert surface. The results at 5 μm are generalized to lower wavelengths, adding an empirical correction accounting for scattering from atmospheric aerosols, using methane band wings as a proxy for the calculation of the scattering additive term. Mosaics incorporating this empirical correction for the geometry and haze scattering show significantly less seams than any previous maps integrating data acquired over such a wide range of observing geometries, and may therefore be used for the study of surface properties. We provide several suggestions for further studies aimed at improving the global mapping of the surface of Titan. With the considered thresholds limits on the acquisition parameters, we found that 13% of Titan's surface has been mapped at an instrument resolution better than 10 km/pixel, 56% of the surface was seen at a resolution between 10 and 20 km/pixel, and 24% of the coverage falls in the range 20-50 km/pixel. © 2012 Elsevier Ltd. All rights reserved.
• Mouélic, S. L., Rannou, P., Rodriguez, S., Sotin, C., Griffith, C. A., Corre, L. L., Barnes, J. W., Brown, R. H., Baines, K. H., Buratti, B. J., Clark, R. N., Nicholson, P. D., & Tobie, G. (2012). Dissipation of Titans north polar cloud at northern spring equinox. Planetary and Space Science, 60(1), 86-92.
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  Abstract: Saturns Moon Titan has a thick atmosphere with a meteorological cycle. We report on the evolution of the giant cloud system covering its north pole using observations acquired by the Visual and Infrared Mapping Spectrometer onboard the Cassini spacecraft. A radiative transfer model in spherical geometry shows that the clouds are found at an altitude between 30 and 65 km. We also show that the polar cloud system vanished progressively as Titan approached equinox in August 2009, revealing at optical wavelengths the underlying sea known as Kraken Mare. This decrease of activity suggests that the north-polar downwelling has begun to shut off. Such a scenario is compared with the Titan global circulation model of Rannou et al. (2006), which predicts a decrease of cloud coverage in northern latitudes at the same period of time. © 2011 Elsevier Ltd. All rights reserved.
• Rannou, P., Mouélic, S. L., Sotin, C., & Brown, R. H. (2012). Cloud and haze in the winter polar region of titan observed with visual and infrared mapping spectrometer on board cassini. Astrophysical Journal, 748(1).
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  Abstract: A large cloud in the north polar region of Titan was first observed by the Visual and Infrared Mapping Spectrometer (VIMS) in 2005 and then in 2006. This cloud, confined beyond the latitude 62°N, is surrounded by a mixture of aerosol and mist probably lying in the low stratosphere and troposphere. Subsequent images of this region of Titan show a gradual vanishing of this cloud which was reported previously. In this paper, we characterize the physical properties of this cloud, haze, and mist as well as their time evolutions. We note several details on the images such as a secondary cloud above the main cloud and latitudes beyond 70°N. We also show that the cloud disappearance leaves the polar region poorly loaded in aerosols, yielding an annular zone of aerosols between 50°N and 65°N. Our analysis suggests that this structure observed by VIMS in the near-IR is an annular structure observed by ISS on board Voyager one Titan year ago in 1980. © 2012 The American Astronomical Society. All rights reserved.
• Soderblom, J. M., Barnes, J. W., Soderblom, L. A., Brown, R. H., Griffith, C. A., Nicholson, P. D., Stephan, K., Jaumann, R., Sotin, C., Baines, K. H., Buratti, B. J., & Clark, R. N. (2012). Modeling specular reflections from hydrocarbon lakes on Titan. Icarus, 220(2), 744-751.
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  Abstract: During the 58th close flyby of Titan (T58), the Cassini Visual and Infrared Mapping Spectrometer (VIMS) observed a specular reflection of sunlight from Titan's Jingpo Lacus through the 5-μm methane window (Stephan, K. et al. [2010]. Geophys. Res. Lett. 37, L07104). The maximum intensity of this reflection is controlled by three basic factors: (1) the shape of the reflecting surface (its overall geometry and roughness), (2) the reflectance of the surface, as controlled by the real refractive index of the material (and that of the atmosphere), and (3) attenuation due to absorption and scattering by atmospheric gases and aerosols along the pathlength. Herein we model the expected intensity of a specular reflection off of a convex mirror-like surface on Titan. We assume the specular reflection is from a body of liquid hydrocarbons on Titan's surface with optical properties consistent with CH 4 and C 2H 6 with smaller amounts of nitrogen and heavier hydrocarbons (e.g., C 3H 8) admixed. We assume the 5-μm opacity for the polar atmosphere is a factor of two higher than that of the tropical haze. For the geometry of the T58 observations, our model predicts a maximum I/F=1-to-5; for a Lambertian surface at normal illumination I/F=1. The maximum 5-μm intensity observed during T58 was I/F~2.6, from which we conclude that Jingpo Lacus is filled with a liquid that has a real index of refraction consistent with that of methane-ethane-nitrogen liquid and that the 5-μm atmospheric opacity was τ=0.5, consistent with the higher particle column expected in the winter polar atmosphere. Future VIMS observations will allow us to refine the refractive index of the liquid in the lakes and to place a quantitative constraint on the ratio of methane to ethane. © 2012 Elsevier Inc.
• Sotin, C., Lawrence, K. J., Reinhardt, B., Barnes, J. W., Brown, R. H., Hayes, A. G., Mouélic, S. L., Rodriguez, S., Soderblom, J. M., Soderblom, L. A., Baines, K. H., Buratti, B. J., Clark, R. N., Jaumann, R., Nicholson, P. D., & Stephan, K. (2012). Observations of Titan's Northern lakes at 5μm: Implications for the organic cycle and geology. Icarus, 221(2), 768-786.
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  Abstract: Since Titan entered Northern spring in August 2009, the North Pole has been illuminated allowing observations at optical wavelengths. On June 5, 2010 the Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft observed the Northern Pole area with a pixel size from 3 to 7km. Since, as we demonstrate, little of the solar flux at 5μm is scattered by the atmosphere, these observations were obtained at relatively large incidence angles and allowed us to build a mosaic covering an area of more than 500,000km 2 that overlaps and complements observations made by the Synthetic Aperture Radar (SAR) in 2007. We find that there is an excellent correlation between the shape of the radar dark area, known as Ligeia Mare and the VIMS 5-μm dark unit. Matching most of the radar shoreline, the 2010 VIMS observations suggest that the 125,000-km 2 surface area of Ligeia Mare measured by RADAR in 2007 has not significantly changed. The VIMS observations complement the radar observations to the west of Ligeia Mare and suggest that Ligeia Mare is connected to Kraken Mare by either a diffuse network similar to a swamp area, or by well-defined, sub-pixel rivers. Considering the results of recent evaporation models of methane, our preferred interpretation of the relative constancy in surface area of Ligeia is that it is principally composed of ethane although we cannot rule out the possibility that methane evaporation is balanced with replenishment by either precipitation or underground seepage. There is also strong correlation between the location of the small radar lakes and the small VIMS 5-μm dark patches. The geographic location of the small lakes are within a VIMS pixel of the SAR location, suggesting that the non-synchronous component of Titan's spin rate, if it exists, was less than 2.3×10 -4deg/day between 2007 and 2010 in agreement with the recent T64 radar observations. These observations question the existence of non-synchronous rotation. Two radar-bright features appear dark at 5-μm. The simplest interpretation is that these are very shallow lakes, less than one meter deep. Three new small lakes, named Freeman, Cardiel, and Towada by the IAU, are found outside of the area mapped with the SAR. A single-scattering model describing reflection of sunlight at 5-μm suggests that the lake surface is mirror-like and that the albedo of the solid surfaces surrounding the lakes is about 8%. These observations together with information of the haze aerosols allow us to show that Titan's lakes, atmospheric ethane and aerosol haze are smaller carbon reservoirs than Titan's sand dunes and atmospheric methane. A simple model involving an outburst of methane a few hundreds of Myr ago followed by the dissociation of methane in the atmosphere leading to the formation of the haze particles that constitute the dune fields would be consistent with both the present observations and recent measurements of isotopic ratios in atmospheric methane (Mandt, K.E. et al. [2012]. Astrophys. J. 749(160), 14). © 2012 Elsevier Inc..
• Stallard, T. S., Melin, H., Miller, S., Badman, S. V., Brown, R. H., & Baines, K. H. (2012). Peak emission altitude of Saturn's H ₃⁺ aurora. Geophysical Research Letters, 39(15).
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  Abstract: Here we present the first detailed measurement of the altitudinal profile of H 3+ emission within Saturn's ionosphere, made using images taken by the VIMS instrument on Cassini on 11-12 October 2006, during a chance alignment between the visible limb of the planet and the position of the main auroral emission. Using this, we show that the emission profile of H 3+ can be fitted to a reasonable accuracy with a Gaussian, producing a calculated peak emission altitude at 1155 (±25) km that differs significantly from previous observations of the UV emission profile, and also from the predictions of models that calculated the H 3+ emission profile, which suggested that there would be extended emission above the peak emission altitude. This lack of extended emission is most simply explained by differences in the scale height of H and H 2, suggesting that models overestimate H 2 at high altitudes, with little H 2 from 2000km above the 1bar level. © 2012. American Geophysical Union. All Rights Reserved.
• Stallard, T. S., Melin, H., Miller, S., O'Donoghue, J., Cowley, S. W., Badman, S. V., Adriani, A., Brown, R. H., & Baines, K. H. (2012). Temperature changes and energy inputs in giant planet atmospheres: What we are learning from H ₃⁺. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 370(1978), 5213-5224.
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  PMID: 23028167;Abstract: Since its discovery at Jupiter in 1988, emission from H 3+ has been used as a valuable diagnostic tool in our understanding of the upper atmospheres of the giant planets. One of the lasting questions we have about the giant planets is why the measured upper atmosphere temperatures are always consistently hotter than the temperatures expected from solar heating alone. Here, we describe how H 3+ forms across each of the planetary disks of Jupiter, Saturn and Uranus, presenting the first observations of equatorial H 3+ at Saturn and the first profile of H 3+ emission at Uranus not significantly distorted by the effects of the Earth's atmosphere. We also review past observations of variations in temperature measured at Uranus and Jupiter over a wide variety of time scales. To this, we add new observations of temperature changes at Saturn, using observations by Cassini. We conclude that the causes of the significant level of thermal variability observed over all three planets is not only an important question in itself, but that explaining these variations could be the key to answering the more general question of why giant planet upper atmospheres are so hot. © 2012 The Royal Society.
• Stephan, K., Jaumann, R., Wagner, R., Clark, R. N., Cruikshank, D. P., Giese, B., Hibbitts, C. A., Roatsch, T., Matz, K., Brown, R. H., Filacchione, G., Cappacioni, F., Scholten, F., Buratti, B. J., Hansen, G. B., Nicholson, P. D., Baines, K. H., Nelson, R. M., & Matson, D. L. (2012). The Saturnian satellite Rhea as seen by Cassini VIMS. Planetary and Space Science, 61(1), 142-160.
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  Abstract: Since the arrival of the Cassini spacecraft at Saturn in June 2004, the Visual and Infrared Mapping Spectrometer has obtained new spectral data of the icy satellites of Saturn in the spectral range from 0.35 to 5.2 μm. Numerous flybys were performed at Saturn's second largest satellite Rhea, providing a nearly complete coverage with pixel-ground resolutions sufficient to analyze variations of spectral properties across Rhea's surface in detail. We present an overview of the VIMS observations obtained so far, as well as the analysis of the spectral properties identified in the VIMS spectra and their variations across its surface compared with spatially highly resolved Cassini ISS images and digital elevation models. Spectral variations measured across Rhea's surface are similar to the variations observed in the VIMS observations of its neighbor Dione, implying similar processes causing or at least inducing their occurrence. Thus, magnetospheric particles and dust impacting onto the trailing hemisphere appear to be responsible for the concentration of dark rocky/organic material and minor amounts of CO 2 in the cratered terrain on the trailing hemisphere. Despite the prominent spectral signatures of Rhea's fresh impact crater Inktomi, radiation effects were identified that also affect the H 2O ice-rich cratered terrain of the leading hemisphere. The concentration of H 2O ice in the vicinity of steep tectonic scarps near 270°W and geologically fresh impact craters implies that Rhea exhibits an icy crust at least in the upper few kilometers. Despite the evidence for past tectonic events, no indications of recent endogenically powered processes could be identified in the Cassini data. © 2011 Elsevier Ltd. All rights reserved.
• Vahidinia, S., Cuzzi, J. N., Hedman, M., Draine, B., Clark, R. N., Roush, T., Filacchione, G., Nicholson, P. D., Brown, R. H., Buratti, B., & Sotin, C. (2012). Erratum to " Saturn's F ring grains: Aggregates made of crystalline water ice" [Icarus 215 (2011) 682-694]. Icarus, 218(1), 736-.
• Vixie, G., Barnes, J. W., Bow, J., Mouélic, S. L., Rodriguez, S., Brown, R. H., Cerroni, P., Tosi, F., Buratti, B., Sotin, C., Filacchione, G., Capaccioni, F., & Coradini, A. (2012). Mapping Titan's surface features within the visible spectrum via Cassini VIMS. Planetary and Space Science, 60(1), 52-61.
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  Abstract: Titan shows its surface through many methane windows in the 15 μm region. Windows at shorter wavelengths also exist, polluted by scattering off of atmospheric haze that reduces the surface contrast. At visible wavelengths, the surface of Titan has been observed by Voyager I, the Hubble Space Telescope, and ground-based telescopes. We present here global surface mapping of Titan using the visible wavelength channels from Cassini's Visual and Infrared Mapping Spectrometer (VIMS). We show global maps in each of the VIMS-V channels extending from 0.35 to 1.05 μm. We find methane windows at 0.637, 0.681, 0.754, 0.827, 0.937, and 1.046μm and apply an RGB color scheme to the 0.754, 0.827 and 0.937μm windows to search for surface albedo variations. Our results show that Titan appears gray at visible wavelengths; hence scattering albedo is a good approximation of the Bond albedo. Maps of this genre have already been made and published using the infrared channels of VIMS. Ours are the first global maps of Titan shortward of 0.938μm. We compare the older IR maps to the new VIMS-V maps to constrain surface composition. For instance Tui Regio and Hotei Regio, referred to as 5μm bright spots in previous papers, do not distinguish themselves at all visible wavelengths. The distinction between the dune areas and the bright albedo spots, however, such as the difference between Xanadu and Senkyo, is easily discernible. We employ an empirically derived algorithm to remove haze layers from Titan, revealing a better look at the surface contrast. © 2011 Elsevier Ltd. All rights reserved.
• Badman, S. V., Achilleos, N., Baines, K. H., Brown, R. H., Bunce, E. J., Dougherty, M. K., Melin, H., Nichols, J. D., & Stallard, . (2011). Location of Saturn's northern infrared aurora determined from Cassini VIMS images. Geophysical Research Letters, 38(3).
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  Abstract: The location of Saturn's northern infrared aurora is described in detail using 12 selected images acquired by Cassini VIMS during 2006-2008. Bright main oval arcs and prevalent polar features are displayed, which do not exhibit a preferred local time or spatial extent. The average equatorward limit of the aurora was determined using a best fit circle method. The average circle has a radius of 16.4 ± 0.2° latitude, centred 1.6° anti-sunward of Saturn's pole. The low standard deviation of the fitted circle radii (
• Badman, S. V., Tao, C., Grocott, A., Kasahara, S., Melin, H., Brown, R. H., Baines, K. H., Fujimoto, M., & Stallard, T. (2011). Cassini VIMS observations of latitudinal and hemispheric variations in Saturn's infrared auroral intensity. Icarus, 216(2), 367-375.
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  Abstract: The intensity of Saturn's infrared H3+ aurora is investigated using Cassini VIMS images acquired during October 2006-February 2009. Polar and main oval auroral regions were defined in both hemispheres, which extend between 0-10° and 10-25° co-latitude, respectively. Average intensities were computed for these regions and compared. While the northern and southern main oval regions covered a similar range of intensities, the southern main oval was on average more intense by a factor of ∼1.3. The emission from the southern polar region was usually less intense than the main oval emissions, while this was only the case for approximately half of the northern hemisphere images. The northern hemisphere polar region displayed intensities more than twice as high as those in the south and the difference between the two hemispheres was most pronounced on the dayside. In general, more intense polar emissions were accompanied by more intense main oval emissions. Possible explanations for the hemispheric and latitudinal differences are discussed in terms of particle energies and fluxes, ionospheric conductivity, temperature and magnetic field strength. © 2011 Elsevier Inc.
• Barnes, J. W., Bow, J., Schwartz, J., Brown, R. H., Soderblom, J. M., Hayes, A. G., Vixie, G., Mouélic, S. L., Rodriguez, S., Sotin, C., Jaumann, R., Stephan, K., Soderblom, L. A., Clark, R. N., Buratti, B. J., Baines, K. H., & Nicholson, P. D. (2011). Organic sedimentary deposits in Titan's dry lakebeds: Probable evaporite. Icarus, 216(1), 136-140.
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  Abstract: We report the discovery of organic sedimentary deposits at the bottom of dry lakebeds near Titan's north pole in observations from the Cassini Visual and Infrared Mapping Spectrometer (VIMS). We show evidence that the deposits are evaporitic, making Titan just the third known planetary body with evaporitic processes after Earth and Mars, and is the first that uses a solvent other than water. © 2011 Elsevier Inc.
• Barnes, J. W., Soderblom, J. M., Brown, R. H., Soderblom, L. A., Stephan, K., Jaumann, R., Mouélic, S. L., Rodriguez, S., Sotin, C., Buratti, B. J., Baines, K. H., Clark, R. N., & Nicholson, P. D. (2011). Wave constraints for Titan's Jingpo Lacus and Kraken Mare from VIMS specular reflection lightcurves. Icarus, 211(1), 722-731.
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  Abstract: Stephan et al. (Stephan, K. et al. [2010]. Geophys. Res. Lett. 37, 7104-+.) first saw the glint of sunlight specularly reflected off of Titan's lakes. We develop a quantitative model for analyzing the photometric lightcurve generated during a flyby in which the specularly reflected light flux depends on the fraction of the solar specular footprint that is covered by liquid. We allow for surface waves that spread out the geographic specular intensity distribution. Applying the model to the VIMS T58 observations shows that the waves on Jingpo Lacus must have slopes of no greater than 0.15°, two orders of magnitude flatter than waves on Earth's oceans. Combining the model with theoretical estimates of the intensity of the specular reflection allows a tighter constraint on the waves:
• Brown, R. H., Barnes, J. W., & Melosh, H. J. (2011). On Titan's Xanadu region. Icarus, 214(2), 556-560.
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  Abstract: A large, circular marking ∼1800 km across is seen in near-infrared images of Titan. The feature is centered at 10°S, 120°W on Titan, encompasses much of Titan's western Xanadu region, and has an off-center, quasi-circular, inner margin about 700 km across, with lobate outer margins extending 200-500 km from the inner margin. On the feature's southern flank is Tui Regio, an area that has very high reflectivity at 5. μm, and is hypothesized to exhibit geologically recent cryovolcanic flows (Barnes, J.W. et al. [2006]. Geophys. Res. Lett. 33), similar to flows seen in Hotei Regio, a cryovolcanic area whose morphology may be controlled by pre-existing, crustal fractures resulting from an ancient impact (Soderblom, L.A. et al. [2009]. Icarus, 204). The spectral reflectivity of the large, circular feature is quite different than that of its surroundings, making it compositionally distinct, and radar measurements of its topography, brightness temperature and volume scattering also suggest that the feature is quite distinct from its surroundings. These and several other lines of evidence, in addition to the feature's morphology, suggest that it may occupy the site of an ancient impact. © 2011 Elsevier Inc.
• Buratti, B. J., Faulk, S. P., Mosher, J., Baines, K. H., Brown, R. H., Clark, R. N., & Nicholson, P. D. (2011). Search for and limits on plume activity on Mimas, Tethys, and Dione with the Cassini Visual Infrared Mapping Spectrometer (VIMS). Icarus, 214(2), 534-540.
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  Abstract: Cassini Visual Infrared Mapping Spectrometer (VIMS) observations of Mimas, Tethys, and Dione obtained during the nominal and extended missions at large solar phase angles were analyzed to search for plume activity. No forward scattered peaks in the solar phase curves of these satellites were detected. The upper limit on water vapor production for Mimas and Tethys is one order of magnitude less than the production for Enceladus. For Dione, the upper limit is two orders of magnitude less, suggesting this world is as inert as Rhea (Pitman, K.M., Buratti, B.J., Mosher, J.A., Bauer, J.M., Momary, T., Brown, R.H., Nicholson, P.D., Hedman, M.M. [2008]. Astrophys. J. Lett. 680, L65-L68). Although the plumes are best seen at ∼2.0. μm, Imaging Science Subsystem (ISS) Narrow Angle Camera images obtained at the same time as the VIMS data were also inspected for these features. None of the Cassini ISS images shows evidence for plumes. The absence of evidence for any Enceladus-like plumes on the medium-sized saturnian satellites cannot absolutely rule out current geologic activity. The activity may below our threshold of detection, or it may be occurring but not captured on the handful of observations at large solar phase angles obtained for each moon. Many VIMS and ISS images of Enceladus at large solar phase angles, for example, do not contain plumes, as the active "tiger stripes" in the south pole region are pointed away from the spacecraft at these times. The 7-year Cassini Solstice Mission is scheduled to gather additional measurements at large solar phase angles that are capable of revealing activity on the saturnian moons. © 2011 Elsevier Inc.
• Ciarniello, M., Capaccioni, F., Filacchione, G., Clark, R. N., Cruikshank, D. P., Cerroni, P., Coradini, A., Brown, R. H., Buratti, B. J., Tosi, F., & Stephan, K. (2011). Hapke modeling of Rhea surface properties through Cassini-VIMS spectra. Icarus, 214(2), 541-555.
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  Abstract: The surface properties of the icy bodies in the saturnian system have been investigated by means of the Cassini-VIMS (Visual Infrared Mapping Spectrometer) hyperspectral imager which operates in the 0.35-5.1. μm wavelength range. In particular, we have analyzed 111 full disk hyperspectral images of Rhea ranging in solar phase between 0.08° and 109.8°. These data have been previously analyzed by Filacchione et al. (Filacchione, G. et al. [2007]. Icarus 186, 259-290; Filacchione, G. et al. [2010]. Icarus 206, 507-523) to study, adopting various "spectral indicators" (such as spectral slopes, band depth, and continuum level), the relations among various saturnian satellites. As a further step we proceed in this paper to a quantitative evaluation of the physical parameters determining the spectrophotometric properties of Rhea's surface. To do this we have applied Hapke (Hapke, B. [1993]. Theory of Reflectance and Emittance Spectroscopy, Topics in Remote Sensing: 3 Springer, Berlin) IMSA model (Isotropic Multiple Scattering Approximation) which allow us to model the phase function at VIS-IR (visible-infrared) wavelengths as well as the spectra taking into account various types of mixtures of surface materials. Thanks to this method we have been able to constrain the size of water ice particles covering the surface, the amount of organic contaminants, the large scale surface roughness and the opposition effect surge. From our analysis it appears that wavelength dependent parameters, e.g. opposition surge width (h) and single-particle phase function parameters (b,. v), are strongly correlated to the estimated single-scattering albedo of particles. For Rhea the best fit solution is obtained by assuming: (1) an intraparticle mixture of crystalline water ice and a small amount (0.4%) of Triton tholin; (2) a monodisperse grain size distribution having a particle diameter am= 38. μm; and (3) a surface roughness parameter value of 33°. The study of phase function shows that both shadow hiding and coherent backscattering contribute to the opposition surge. This study represents the first attempt, in the case of Rhea, to join the spectral and the photometric analysis. The surface model we derived gives a good quantitative description of both spectrum and phase curve of the satellite. The same approach and model, with appropriate modifications, shall be applied to VIMS data of the other icy satellites of Saturn, in order to reveal similarities and differences in the surface characteristics to understand how these bodies interact with their environment. © 2011 Elsevier Inc.
• Hedman, M. M., Nicholson, P. D., Showalter, M. R., Brown, R. H., Buratti, B. J., Clark, R. N., Baines, K., & Sotin, C. (2011). The Christiansen Effect in Saturn's narrow dusty rings and the spectral identification of clumps in the F ring. Icarus, 215(2), 695-711.
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  Abstract: Stellar occultations by Saturn's rings observed with the Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft reveal that dusty features such as the F ring and the ringlets in the Encke and the Laplace Gaps have distinctive infrared transmission spectra. These spectra show a narrow optical depth minimum at wavelengths around 2.87μm. This minimum is likely due to the Christiansen Effect, a reduction in the extinction of small particles when their (complex) refractive index is close to that of the surrounding medium. Simple Mie-scattering models demonstrate that the strength of this opacity dip is sensitive to the size distribution of particles between 1 and 100μm across. Furthermore, the spatial resolution of the occultation data is sufficient to reveal variations in the transmission spectra within and among these rings. In both the Encke Gap ringlets and F ring, the opacity dip weakens with increasing local optical depth, which is consistent with the larger particles being concentrated near the cores of these rings. The Encke Gap ringlets also show systematically weaker opacity dips than the F ring and Laplace Gap ringlet, implying that the former has a smaller fraction of grains less than ~30μm across. However, the strength of the opacity dip varies most dramatically within the F ring; certain compact regions of enhanced optical depth lack an opacity dip and therefore appear to have a greatly reduced fraction of grains in the few-micron size range. Such spectrally-identifiable structures probably represent a subset of the compact optically-thick clumps observed by other Cassini instruments. These variations in the ring's particle size distribution can provide new insights into the processes of grain aggregation, disruption and transport within dusty rings. For example, the unusual spectral properties of the F-ring clumps could perhaps be ascribed to small grains adhering onto the surface of larger particles in regions of anomalously low velocity dispersion. © 2011 Elsevier Inc.
• Melin, H., Stallard, T., Miller, S., Gustin, J., Galand, M., Badman, S. V., Pryor, W. R., O'Donoghue, J., Brown, R. H., & Baines, K. H. (2011). Simultaneous Cassini VIMS and UVIS observations of Saturn's southern aurora: Comparing emissions from H, H₂ and H₃⁺ at a high spatial resolution. Geophysical Research Letters, 38(15).
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  Abstract: Here, for the first time, temporally coincident and spatially overlapping Cassini VIMS and UVIS observations of Saturn's southern aurora are presented. Ultraviolet auroral H and H2 emissions from UVIS are compared to infrared H3+ emission from VIMS. The auroral emission is structured into three arcs-H, H2 and H3+ are morphologically identical in the bright main auroral oval (∼73°S), but there is an equatorward arc that is seen predominantly in H (∼70°S), and a poleward arc (∼74°S) that is seen mainly in H2 and H 3+. These observations indicate that, for the main auroral oval, UV emission is a good proxy for the infrared H3+ morphology (and vice versa), but for emission either poleward or equatorward this is no longer true. Hence, simultaneous UV/IR observations are crucial for completing the picture of how the atmosphere interacts with the magnetosphere. Copyright 2011 by the American Geophysical Union.
• Palmer, E. E., & Brown, R. H. (2011). Production and detection of carbon dioxide on Iapetus. Icarus, 212(2), 807-818.
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  Abstract: Cassini VIMS detected carbon dioxide on the surface of Iapetus during its insertion orbit. We evaluated the CO2 distribution on Iapetus and determined that it is concentrated almost exclusively on Iapetus' dark material. VIMS spectra show a 4.27-μm feature with an absorption depth of 24%, which, if it were in the form of free ice, requires a layer 31nm thick. Extrapolating for all dark material on Iapetus, the total observable CO2 would be 2.3×108kg.Previous studies note that free CO2 is unstable at 10 AU over geologic timescales. Carbon dioxide could, however, be stable if trapped or complexed, such as in inclusions or clathrates. While complexed CO2 has a lower thermal volatility, loss due to photodissociation by UV radiation and gravitational escape would occur at a rate of 2.6×107kgyear-1. Thus, Iapetus' entire inventory of surface CO2 could be lost within a few decades.The high loss/destruction rate of CO2 requires an active source. We conducted experiments that generated CO2 by UV radiation of simulated icy regolith under Iapetus-like conditions. The simulated regolith was created by flash-freezing degassed water, crushing it into sub-millimeter sized particles, and then mixing it with isotopically labeled amorphous carbon (13C) dust. These samples were placed in a vacuum chamber and cooled to temperatures between 50K and 160K. The samples were irradiated with UV light, and the products were measured using a mass spectrometer, from which we measured 13CO2 production at a rate of 2.0×1012mols-1. Extrapolating to Iapetus and adjusting for the solar UV intensity and Iapetus' surface area, we calculated that CO2 production for the entire surface would be 1.1×107kgyear-1, which is only a factor of two less than the loss rate. As such, UV photochemical generation of CO2 is a plausible source of the detected CO2. © 2010 Elsevier Inc.
• Rodriguez, S., Mouélic, S. L., Rannou, P., Sotin, C., Brown, R. H., Barnes, J. W., Griffith, C. A., Burgalat, J., Baines, K. H., Buratti, B. J., Clark, R. N., & Nicholson, P. D. (2011). Titan's cloud seasonal activity from winter to spring with Cassini/VIMS. Icarus, 216(1), 89-110.
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  Abstract: Since Saturn orbital insertion in July 2004, the Cassini orbiter has been observing Titan throughout most of the northern winter season (October 2002-August 2009) and the beginning of spring, allowing a detailed monitoring of Titan's cloud coverage at high spatial resolution with close flybys on a monthly basis. This study reports on the analysis of all the near-infrared images of Titan's clouds acquired by the Visual and Infrared Mapping Spectrometer (VIMS) during 67 targeted flybys of Titan between July 2004 and April 2010.The VIMS observations show numerous sporadic clouds at southern high and mid-latitudes, rare clouds in the equatorial region, and reveal a long-lived cloud cap above the north pole, ubiquitous poleward of 60°N. These observations allow us to follow the evolution of the cloud coverage during almost a 6-year period including the equinox, and greatly help to further constrain global circulation models (GCMs). After 4. years of regular outbursts observed by Cassini between 2004 and 2008, southern polar cloud activity started declining, and completely ceased 1. year before spring equinox. The extensive cloud system over the north pole, stable between 2004 and 2008, progressively fractionated and vanished as Titan entered into northern spring. At southern mid-latitudes, clouds were continuously observed throughout the VIMS observing period, even after equinox, in a latitude band between 30°S and 60°S. During the whole period of observation, only a dozen clouds were observed closer to the equator, though they were slightly more frequent as equinox approached. We also investigated the distribution of clouds with longitude. We found that southern polar clouds, before disappearing in mid-2008, were systematically concentrated in the leading hemisphere of Titan, in particular above and to the east of Ontario Lacus, the largest reservoir of hydrocarbons in the area. Clouds are also non-homogeneously distributed with longitude at southern mid-latitudes. The n= 2-mode wave pattern of the distribution, observed since 2003 by Earth-based telescopes and confirmed by our Cassini observations, may be attributed to Saturn's tides. Although the latitudinal distribution of clouds is now relatively well reproduced and understood by the GCMs, the non-homogeneous longitudinal distributions and the evolution of the cloud coverage with seasons still need investigation. If the observation of a few single clouds at the tropics and at northern mid-latitudes late in winter and at the start of spring cannot be further interpreted for the moment, the obvious shutdown of the cloud activity at Titan's poles provides clear signs of the onset of the general circulation turnover that is expected to accompany the beginning of Titan's northern spring. According to our GCM, the persistence of clouds at certain latitudes rather suggests a 'sudden' shift in near future of the meteorology into the more illuminated hemisphere. Finally, the observed seasonal change in cloud activity occurred with a significant time lag that is not predicted by our model. This may be due to an overall methane humidity at Titan's surface higher than previously expected. © 2011 Elsevier Inc.
• Vahidinia, S., Cuzzi, J. N., Hedman, M., Draine, B., Clark, R. N., Roush, T., Filacchione, G., Nicholson, P. D., Brown, R. H., Buratti, B., & Sotin, C. (2011). Saturn's F ring grains: Aggregates made of crystalline water ice. Icarus, 215(2), 682-694.
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  Abstract: We present models of the near-infrared (1-5μm) spectra of Saturn's F ring obtained by Cassini's Visual and Infrared Mapping Spectrometer (VIMS) at ultra-high phase angles (177.4-178.5°). Modeling this spectrum constrains the size distribution, composition, and structure of F ring particles in the 0.1-100μm size range. These spectra are very different from those obtained at lower phase angles; they lack the familiar 1.5 and 2μm absorption bands, and the expected 3μm water ice primary absorption appears as an unusually narrow dip at 2.87μm. We have modeled these data using multiple approaches. First, we use a simple Mie scattering model to constrain the size distribution and composition of the particles. The Mie model allows us to understand the overall shapes of the spectra in terms of dominance by diffraction at these ultra-high phase angles, and also to demonstrate that the 2.87μm dip is associated with the Christiansen frequency of water ice (where the real refractive index passes unity). Second, we use a combination of Mie scattering with Effective Medium Theory to probe the effect of porous (but structureless) particles on the overall shape of the spectrum and depth of the 2.87μm band. Such simple models are not able to capture the shape of this absorption feature well. Finally, we model each particle as an aggregate of discrete monomers, using the Discrete Dipole Approximation (DDA) model, and find a better fit for the depth of the 2.87μm feature. The DDA models imply a slightly different overall size distribution. We present a simple heuristic model which explains the differences between the Mie and DDA model results. We conclude that the F ring contains aggregate particles with a size distribution that is distinctly narrower than a typical power law, and that the particles are predominantly crystalline water ice. © 2011 Elsevier Inc.
• Brown, R. H., Lebreton, J., & Waite, J. H. (2010). Overview. Titan from Cassini-Huygens, 1-7.
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  Abstract: This book is the one of two volumes meant to capture the main scientific results of the Cassini-Huygens prime mission. The first book, Saturn from Cassini-Huygens, contains the material pertinent to Saturn, its satellites and its magnetosphere, except its largest moon Titan. This book, Titan from Cassini-Huygens is meant to capture the main scien-tific results regarding Titan, including its origin and evolution, interior, surface, atmosphere and interaction with Saturn's magnetosphere. The reason we have chosen to treat the results for Titan in a separate volume is that at the time of publication of this book, the Cassini spacecraft has flown by Titan some 62 times, including delivering the Huygens probe, which successfully landed on Titan's surface and survived for over 2 hours, transmitting a wealth of data on Titan's atmosphere and surface. The scientific results obtained for Titan are so voluminous that they cannot be properly captured as part of the Saturn from Cassini-Huygens volume and require a separate volume; thus, the two books. © 2010 Springer Science+Business Media B.V.
• Brown, R. H., Lebreton, J., & Waite, J. H. (2010). Titan from Cassini-Huygens. Titan from Cassini-Huygens, 1-535.
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  Abstract: This book comprehensively reviews our current knowledge of Saturn's largest moon Titan featuring the latest results obtained by the Cassini-Huygens mission. A global author team addresses Titan's origin and evolution, internal structure, surface geology, the atmosphere and ionosphere as well as magnetospheric interactions. The book closes with an outlook beyond the Cassini-Huygens mission. Colorfully illustrated, this large size book will serve as an authoritative reference to researchers as well as an introduction for students. © 2009 Springer Science+Business Media B.V.
• Buratti, B. J., Bauer, J. M., Hicks, M. D., Mosher, J. A., Filacchione, G., Momary, T., Baines, K. H., Brown, R. H., Clark, R. N., & Nicholson, P. D. (2010). Cassini spectra and photometry 0.25-5.1 μm of the small inner satellites of Saturn. Icarus, 206(2), 524-536.
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  Abstract: The nominal tour of the Cassini mission enabled the first spectra and solar phase curves of the small inner satellites of Saturn. We present spectra from the Visual Infrared Mapping Spectrometer (VIMS) and the Imaging Science Subsystem (ISS) that span the 0.25-5.1 μm spectral range. The composition of Atlas, Pandora, Janus, Epimetheus, Calypso, and Telesto is primarily water ice, with a small amount (∼5%) of contaminant, which most likely consists of hydrocarbons. The optical properties of the "shepherd" satellites and the coorbitals are tied to the A-ring, while those of the Tethys Lagrangians are tied to the E-ring of Saturn. The color of the satellites becomes progressively bluer with distance from Saturn, presumably from the increased influence of the E-ring; Telesto is as blue as Enceladus. Janus and Epimetheus have very similar spectra, although the latter appears to have a thicker coating of ring material. For at least four of the satellites, we find evidence for the spectral line at 0.68 μm that Vilas et al. [Vilas, F., Larsen, S.M., Stockstill, K.R., Gaffley, M.J., 1996. Icarus 124, 262-267] attributed to hydrated iron minerals on Iapetus and Hyperion. However, it is difficult to produce a spectral mixing model that includes this component. We find no evidence for CO2 on any of the small satellites. There was a sufficient excursion in solar phase angle to create solar phase curves for Janus and Telesto. They bear a close similarity to the solar phase curves of the medium-sized inner icy satellites. Preliminary spectral modeling suggests that the contaminant on these bodies is not the same as the exogenously placed low-albedo material on Iapetus, but is rather a native material. The lack of CO2 on the small inner satellites also suggests that their low-albedo material is distinct from that on Iapetus, Phoebe, and Hyperion. © 2009 Elsevier Inc.
• Clark, R. N., Curchin, J. M., Barnes, J. W., Jaumann, R., Soderblom, L., Cruikshank, D. P., Brown, R. H., Rodriguez, S., Lunine, J., Stephan, K., Hoefen, T. M., Mouélic, S. L., Sotin, C., Baines, K. H., Buratti, B. J., & Nicholson, P. D. (2010). Detection and mapping of hydrocarbon deposits on Titan. Journal of Geophysical Research E: Planets, 115(10).
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  Abstract: We report the identification of compounds on Titan's surface by spatially resolved imaging spectroscopy methods through Titan's atmosphere, and set upper limits to other organic compounds. We present evidence for surface deposits of solid benzene (C6H6), solid and/or liquid ethane (C 2H6), or methane (CH4), and clouds of hydrogen cyanide (HCN) aerosols using diagnostic spectral features in data from the Cassini Visual and Infrared Mapping Spectrometer (VIMS). Cyanoacetylene (2-propynenitrile, IUPAC nomenclature, HC3N) is indicated in spectra of some bright regions, but the spectral resolution of VIMS is insufficient to make a unique identification although it is a closer match to the feature previously attributed to CO2. We identify benzene, an aromatic hydrocarbon, in larger abundances than expected by some models. Acetylene (C2H2), expected to be more abundant on Titan according to some models than benzene, is not detected. Solid acetonitrile (CH 3CN) or other nitriles might be candidates for matching other spectral features in some Titan spectra. An as yet unidentified absorption at 5.01-μm indicates that yet another compound exists on Titan's surface. We place upper limits for liquid methane and ethane in some locations on Titan and find local areas consistent with millimeter path lengths. Except for potential lakes in the southern and northern polar regions, most of Titan appears "dry." Finally, we find there is little evidence for exposed water ice on the surface. Water ice, if present, must be covered with organic compounds to the depth probed by 1-5-μm photons: a few millimeters to centimeters. Copyright 2010 by the American Geophysical Union.
• Cruikshank, D. P., Meyer, A. W., Brown, R. H., Clark, R. N., Jaumann, R., Stephan, K., Hibbitts, C. A., Sandford, S. A., Mastrapa, R. M., Filacchione, G., M., C., Nicholson, P. D., Buratti, B. J., McCord, T. B., Nelson, R. M., Dalton, J. B., Baines, K. H., & Matson, D. L. (2010). Carbon dioxide on the satellites of Saturn: Results from the Cassini VIMS investigation and revisions to the VIMS wavelength scale. Icarus, 206(2), 561-572.
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  Abstract: Several of the icy satellites of Saturn show the spectroscopic signature of the asymmetric stretching mode of C-O in carbon dioxide (CO2) at or near the nominal solid-phase laboratory wavelength of 4.2675 μm (2343.3 cm-1), discovered with the Visible-Infrared Mapping Spectrometer (VIMS) on the Cassini spacecraft. We report here on an analysis of the variation in wavelength and width of the CO2 absorption band in the spectra of Phoebe, Iapetus, Hyperion, and Dione. Comparisons are made to laboratory spectra of pure CO2, CO2 clathrates, ternary mixtures of CO2 with other volatiles, implanted and adsorbed CO2 in non-volatile materials, and ab initio theoretical calculations of CO2 * nH2O. At the wavelength resolution of VIMS, the CO2 on Phoebe is indistinguishable from pure CO2 ice (each molecule's nearby neighbors are also CO2) or type II clathrate of CO2 in H2O. In contrast, the CO2 band on Iapetus, Hyperion, and Dione is shifted to shorter wavelengths (typically ∼4.255 μm (∼2350.2 cm-1)) and broadened. These wavelengths are characteristic of complexes of CO2 with different near-neighbor molecules that are encountered in other volatile mixtures such as with H2O and CH3OH, and non-volatile host materials like silicates, some clays, and zeolites. We suggest that Phoebe's CO2 is native to the body as part of the initial inventory of condensates and now exposed on the surface, while CO2 on the other three satellites results at least in part from particle or UV irradiation of native H2O plus a source of C, implantation or accretion from external sources, or redistribution of native CO2 from the interior. The analysis presented here depends on an accurate VIMS wavelength scale. In preparation for this work, the baseline wavelength calibration for the Cassini VIMS was found to be distorted around 4.3 μm, apparently as a consequence of telluric CO2 gas absorption in the pre-launch calibration. The effect can be reproduced by convolving a sequence of model detector response profiles with a deep atmospheric CO2 absorption profile, producing distorted detector profile shapes and shifted central positions. In a laboratory blackbody spectrum used for radiance calibration, close examination of the CO2 absorption profile shows a similar deviation from that expected from a model. These modeled effects appear to be sufficient to explain the distortion in the existing wavelength calibration now in use. A modification to the wavelength calibration for 13 adjacent bands is provided. The affected channels span about 0.2 μm centered on 4.28 μm. The maximum wavelength change is about 10 nm toward longer wavelength. This adjustment has implications for interpretation of some of the spectral features observed in the affected wavelength interval, such as from CO2, as discussed in this paper.
• D'Aversa, E., Bellucci, G., Nicholson, P. D., Hedman, M. M., Brown, R. H., Showalter, M. R., Altieri, F., Carrozzo, F. G., Filacchione, G., & Tosi, F. (2010). The spectrum of a Saturn ring spoke from Cassini/VIMS. Geophysical Research Letters, 37(1).
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  Abstract: On 2008, July, the Cassini/VIMS spectrometer detected spokes on the Saturn's B ring for the first time. These are the first measurements of the complete reflectance spectrum of the spokes in a wide spectral range (0.35-0.51 m). Here we will focus on a single broad-shaped spoke, imaged by VIMS on July, 9. Radiative transfer modeling supports a pure water ice composition for the spoke's grains, but their size distribution is found to be wider than previously thought: preliminary results yields a modal value of about 1.90 m (reff = 3.5 m, veff = 0.3) and a number density of about 0.01-0.1 grains/cm3. The unexpected abundance of micron-sized grains in the spoke may have implications for the formation models since the energy requirement increases by at least one order of magnitude. These kind of observations may also constrain the size selection effects thought to be produced by the forces governing the spokes' evolution. Copyright 2010 by the American Geophysical Union.
• Filacchione, G., Capaccioni, F., Clark, R. N., Cuzzi, J. N., Cruikshank, D. P., Coradini, A., Cerroni, P., Nicholson, P. D., McCord, T. B., Brown, R. H., Buratti, B. J., Tosi, F., Nelson, R. M., Jaumann, R., & Stephan, K. (2010). Saturn's icy satellites investigated by Cassini-VIMS. II. Results at the end of nominal mission. Icarus, 206(2), 507-523.
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  Abstract: We report the detailed analysis of the spectrophotometric properties of Saturn's icy satellites as derived by full-disk observations obtained by visual and infrared mapping spectrometer (VIMS) experiment aboard Cassini. In this paper, we have extended the coverage until the end of the Cassini's nominal mission (June 1st 2008), while a previous paper (Filacchione, G., and 28 colleagues [2007]. Icarus 186, 259-290, hereby referred to as Paper I) reported the preliminary results of this study. During the four years of nominal mission, VIMS has observed the entire population of Saturn's icy satellites allowing us to make a comparative analysis of the VIS-NIR spectral properties of the major satellites (Mimas, Enceladus, Tethys, Dione, Rhea, Hyperion, Iapetus) and irregular moons (Atlas, Prometheus, Pandora, Janus, Epimetheus, Telesto, Calypso, Phoebe). The results we discuss here are derived from the entire dataset available at June 2008 which consists of 1417 full-disk observations acquired from a variety of distances and inclinations from the equatorial plane, with different phase angles and hemispheric coverage. The most important spectrophotometric indicators (as defined in Paper I: I/F continua at 0.55 μm, 1.822 μm and 3.547 μm, visible spectral slopes, water and carbon dioxide bands depths and positions) are calculated for each observation in order to investigate the disk-integrated composition of the satellites, the distribution of water ice respect to "contaminants" abundances and typical regolith grain properties. These quantities vary from the almost pure water ice surfaces of Enceladus and Calypso to the organic and carbon dioxide rich Hyperion, Iapetus and Phoebe. Janus visible colors are intermediate between these two classes having a slightly positive spectral slope. These results could help to decipher the origins and evolutionary history of the minor moons of the Saturn's system. We introduce a polar representation of the spectrophotometric parameters as function of the solar phase angle (along radial distance) and of the effective longitude interval illuminated by the Sun and covered by VIMS during the observation (in azimuth) to better investigate the spatial distribution of the spectrophotometric quantities across the regular satellites hemispheres. Finally, we report the observed spectral positions of the 4.26 μm band of the carbon dioxide present in the surface material of three outermost moons Hyperion, Iapetus and Phoebe. © 2009 Elsevier Inc.
• Hedman, M. M., Nicholson, P. D., Baines, K. H., Buratti, B. J., Sotin, C., Clark, R. N., Brown, R. H., French, R. G., & Marouf, E. A. (2010). The architecture of the Cassini division. Astronomical Journal, 139(1), 228-251.
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  Abstract: The Cassini Division in Saturn's rings contains a series of eight named gaps, three of which contain dense ringlets. Observations of stellar occultations by the Visual and Infrared Mapping Spectrometer onboard the Cassini spacecraft have yielded 40 accurate and precise measurements of the radial position of the edges of all of these gaps and ringlets. These data reveal suggestive patterns in the shapes of many of the gap edges: the outer edges of the five gaps without ringlets are circular to within 1 km, while the inner edges of six of the gaps are eccentric, with apsidal precession rates consistent with those expected for eccentric orbits near each edge. Intriguingly, the pattern speeds of these eccentric inner gap edges, together with that of the eccentric Huygens Ringlet, form a series with a characteristic spacing of 006 day-1. The two gaps with non-eccentric inner edges lie near first-order inner Lindblad resonances (ILRs) with moons. One such edge is close to the 5:4 ILR with Prometheus, and the radial excursions of this edge do appear to have an m = 5 component aligned with that moon. The other resonantly confined edge is the outer edge of the B ring, which lies near the 2:1 Mimas ILR. Detailed investigation of the B-ring-edge data confirm the presence of an m = 2 perturbation on the B-ring edge, but also show that during the course of the Cassini Mission, this pattern has drifted backward relative to Mimas. Comparisons with earlier occultation measurements going back to Voyager suggest the possibility that the m = 2 pattern is actually librating relative to Mimas with a libration frequency L 006 day-1 (or possibly 012 day -1). In addition to the m = 2 pattern, the B-ring edge also has an m = 1 component that rotates around the planet at a rate close to the expected apsidal precession rate (̄ ω ̇ B ∼ 5.°06 day -1). Thus, the pattern speeds of the eccentric edges in the Cassini Division can be generated from various combinations of the pattern speeds of structures observed on the edge of the B ring: ωp = ̄ ω ̇B -jL for j = 1, 2, 3, ⋯, 7. We therefore suggest that most of the gaps in the Cassini Division are produced by resonances involving perturbations from the massive edge of the B ring. We find that a combination of gravitational perturbations generated by the radial excursions in the B-ring edge and the gravitational perturbations from the Mimas 2:1 ILR yields terms in the equations of motion that should act to constrain the pericenter location of particle orbits in the vicinity of each of the eccentric inner gap edges in the Cassini Division. This alignment of pericenters could be responsible for forming the Cassini-Division Gaps and thus explain why these gaps are located where they are. © 2010. The American Astronomical Society. All rights reserved.
• Mouélic, S. L., Cornet, T., Rodriguez, S., Sotin, C., Barnes, J. W., Brown, R. H., Bourgeois, O., Baines, K. H., Buratti, B. J., Clark, R. N., & Nicholson, P. D. (2010). Global mapping of Titan in the infrared using a heuristic approach to reduce the atmospheric scattering component. 2nd Workshop on Hyperspectral Image and Signal Processing: Evolution in Remote Sensing, WHISPERS 2010 - Workshop Program.
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  Abstract: Titan is the largest satellite of Saturn, and the only one to have a dense atmosphere. Whereas its surface cannot be seen at visible wavelengths due to the strong absorption and scattering of the atmospheric gases (mainly N2 and CH4) and aerosols, it can be seen at specific wavelengths in the infrared. We focus in this paper on the global mapping of Titan geological units using the Visual and Infrared Mapping Spectrometer onboard Cassini, and discuss the problem of the decorrelation between atmospheric and surface components. ©2010 IEEE.
• Penteado, P. F., Griffith, C. A., Tomasko, M. G., Engel, S., See, C., Doose, L., Baines, K. H., Brown, R. H., Buratti, B. J., Clark, R., Nicholson, P., & Sotin, C. (2010). Latitudinal variations in Titan's methane and haze from Cassini VIMS observations. Icarus, 206(1), 352-365.
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  Abstract: We analyze observations taken with Cassini's Visual and Infrared Mapping Spectrometer (VIMS), to determine the current methane and haze latitudinal distribution between 60°S and 40°N. The methane variation was measured primarily from its absorption band at 0.61 μm, which is optically thin enough to be sensitive to the methane abundance at 20-50 km altitude. Haze characteristics were determined from Titan's 0.4-1.6 μm spectra, which sample Titan's atmosphere from the surface to 200 km altitude. Radiative transfer models based on the haze properties and methane absorption profiles at the Huygens site reproduced the observed VIMS spectra and allowed us to retrieve latitude variations in the methane abundance and haze. We find the haze variations can be reproduced by varying only the density and single scattering albedo above 80 km altitude. There is an ambiguity between methane abundance and haze optical depth, because higher haze optical depth causes shallower methane bands; thus a family of solutions is allowed by the data. We find that haze variations alone, with a constant methane abundance, can reproduce the spatial variation in the methane bands if the haze density increases by 60% between 20°S and 10°S (roughly the sub-solar latitude) and single scattering absorption increases by 20% between 60°S and 40°N. On the other hand, a higher abundance of methane between 20 and 50 km in the summer hemisphere, as much as two times that of the winter hemisphere, is also possible, if the haze variations are minimized. The range of possible methane variations between 27°S and 19°N is consistent with condensation as a result of temperature variations of 0-1.5 K at 20-30 km. Our analysis indicates that the latitudinal variations in Titan's visible to near-IR albedo, the north/south asymmetry (NSA), result primarily from variations in the thickness of the darker haze layer, detected by Huygens DISR, above 80 km altitude. If we assume little to no latitudinal methane variations we can reproduce the NSA wavelength signatures with the derived haze characteristics. We calculate the solar heating rate as a function of latitude and derive variations of ∼10-15% near the sub-solar latitude resulting from the NSA. Most of the latitudinal variations in the heating rate stem from changes in solar zenith angle rather than compositional variations. © 2009 Elsevier Inc. All rights reserved.
• Rannou, P., Cours, T., Mouélic, S. L., Rodriguez, S., Sotin, C., Drossart, P., & Brown, R. (2010). Titan haze distribution and optical properties retrieved from recent observations. Icarus, 208(2), 850-867.
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  Abstract: The VIMS instrument onboard Cassini observed the north polar region of Titan at 113° phase angle, 28 December 2006. On this spectral image, a vast polar cloud can be seen northward to 62°N, and elsewhere, the haze appears as the dominant source of scattering. Because the surface does not appear in the wavelength range between 0.3 and 4.9μm, this spectro-image is ideal to study airborn scatterers both in methane bands and windows. In this work, we study this image, along with another image taken at 13° phase angle. This image probe both the atmosphere and the surface from pole to pole. First, we characterise the spatial distribution of the haze layer above 100. km between 80°S and 70°N. We find a north south asymmetry with a haze opacity increasing by a factor 3 from the south pole to the equator, then a constant value up to about 30°N and a decrease of a factor 2 between 30°N and about 60°N. Beyond 60°N, we can see the influence of the north polar cloud, even in the band, but no polar haze accumulation. The fact that the north polar region is still in the polar night is a possible explanation. No haze accumulation is observed in the southern polar region. Secondly, we partly identify the origin of spectral features in the 2.8-μm methane window, which are found to be due to deuterated methane (CH3D). This allows the analyse of this window and to retrieve the opacity of scatterers layer below 80. km (presumably made of aerosols and condensate droplets) between 35°N and 60°N. Finally, we constrained the values and the spectral behaviour of the imaginary part of the aerosol refractive index in the range between 0.3 and 4μm. To do so, we studied the 2.8-μm window with the image taken at 113° phase angle. To complete the analysis, we studied the transmission through the haze layer in the 3.4-μm band observed in solar occultation mode with VIMS, and we analysed the single scattering albedo retrieved with DISR instrument between 0.4 and 1.6μm. The imaginary part of the refractive index that we find for Titan aerosols follows Khare et al. (Khare, B.N. et al. [1984]. Icarus 60, 127-137) optical constant up to 0.8μm and becomes constant beyond this wavelength at least up to 1.6μm. It also has a prominent peak at 3.4μm and a secondary peak at 3μm, which indicates material rich in C-H bonds, with much less N-H bonds than in Khare et al. (1984) tholins. © 2010 Elsevier Inc.
• Rodriguez, S., Schmidt, F., Moussaoui, S., Mouélic, S. L., Rannou, P., Barnes, J. W., Sotin, C., Brown, R. H., Baines, K. H., Buratti, B. J., Clark, R. N., & Nicholson, P. D. (2010). Systematic detection of Titan's clouds in Vims/Cassini hyperspectral images using a new automated algorithm. 2nd Workshop on Hyperspectral Image and Signal Processing: Evolution in Remote Sensing, WHISPERS 2010 - Workshop Program.
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  Abstract: Titan is the Saturn's largest moon where meteorological processes are very active, as observed most recently by the Cassini/Huygens orbiter. Cloud monitoring is a prime method to observe, describe and understand present climate on Titan. Unlike our previous detection method, which was based on manual control of threshold, we investigate here the possibility of a fully automated methodology based on blind source separation to analyzing years of Cassini near-infrared cloud images. Since the spectral signature of Titan clouds are diverse and not known a priori, the choice of a blind source separation seems to be appropriate. Preliminary results show that Titan's cloud detection is possible using the recent implementation of a Bayesian source separation method. ©2010 IEEE.
• Soderblom, J. M., Brown, R. H., Soderblom, L. A., Barnes, J. W., Jaumann, R., Mouélic, S. L., Sotin, C., Stephan, K., Baines, K. H., Buratti, B. J., Clark, R. N., & Nicholson, P. D. (2010). Geology of the Selk crater region on Titan from Cassini VIMS observations. Icarus, 208(2), 905-912.
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  Abstract: Observations of Titan obtained by the Cassini Visual and Infrared Mapping Spectrometer (VIMS) have revealed Selk crater, a geologically young, bright-rimmed, impact crater located ∼800. km north-northwest of the Huygens landing site. The crater rim-crest diameter is ∼90. km; its floor diameter is ∼60. km. A central pit/peak, 20-30. km in diameter, is seen; the ratio of the size of this feature to the crater diameter is consistent with similarly sized craters on Ganymede and Callisto, all of which are dome craters. The VIMS data, unfortunately, are not of sufficient resolution to detect such a dome. The inner rim of Selk crater is fluted, probably by eolian erosion, while the outer flank and presumed ejecta blanket appear dissected by drainages (particularly to the east), likely the result of fluvial erosion. Terracing is observed on the northern and western walls of Selk crater within a 10-15. km wide terrace zone identified in VIMS data; the terrace zone is bright in SAR data, consistent with it being a rough surface. The terrace zone is slightly wider than those observed on Ganymede and Callisto and may reflect differences in thermal structure and/or composition of the lithosphere. The polygonal appearance of the crater likely results from two preexisting planes of weakness (oriented at azimuths of 21° and 122° east of north). A unit of generally bright terrain that exhibits similar infrared-color variation and contrast to Selk crater extends east-southeast from the crater several hundred kilometers. We informally refer to this terrain as the Selk "bench." Both Selk and the bench are surrounded by the infrared-dark Belet dune field. Hypotheses for the genesis of the optically bright terrain of the bench include: wind shadowing in the lee of Selk crater preventing the encroachment of dunes, impact-induced cryovolcanism, flow of a fluidized-ejecta blanket (similar to the bright crater outflows observed on Venus), and erosion of a streamlined upland formed in the lee of Selk crater by fluid flow. Vestigial circular outlines in this feature just east of Selk's ejecta blanket suggest that this might be a remnant of an ancient, cratered crust. Evidently the southern margin of the feature has sufficient relief to prevent the encroachment of dunes from the Belet dune field. We conclude that this feature either represents a relatively high-viscosity, fluidized-ejecta flow (a class intermediate to ejecta blankets and long venusian-style ejecta flows) or a streamlined upland remnant that formed downstream from the crater by erosive fluid flow from the west-northwest. © 2010 Elsevier Inc.
• Soderblom, L. A., Barnes, J. W., Brown, R. H., Clark, R. N., Janssen, M. A., McCord, T. B., Niemann, H. B., & Tomasko, M. G. (2010). Composition of titan's surface. Titan from Cassini-Huygens, 141-175.
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  Abstract: The Huygens Probe returned the first in situ data on Titan's surface composition in January 2005. Although Huygens landed on a dry plain, the Gas Chromatograph Mass Spectrometer (GCMS) showed evidence of methane moisture in the near subsurface suggesting methane precipitation at some time in the past. Heavier organic molecules were not found to be abundant in the atmosphere or at the surface, but the GCMS surface results did show ethane to be present and tentatively identified cyanogen, benzene, and carbon dioxide. During descent, aerosol particles were processed with the Aerosol Collector and Pyroliser; results suggested that the aerosols contain both nitriles and hydrocarbons. The Descent Imager/Spectral Radiometer (DISR also carried by the probe) measured the visible and near-infrared spectral reflectance of the dark plain surface at the landing site. Those data suggest a mixture of water ice, tholin-like materials, and dark neutral material with a blue slope in the near infrared; identification of water ice is suggested but inconclusive. Most remarkably DISR did not detect spectral features, beyond those for methane, for a wide range of spectrally active hydrocarbon and nitrile compounds that had been expected to be present on the surface. The Cassini Visual and Infrared Mapping Spectrometer (VIMS) observes the spectral properties of Titan's surface through atmospheric windows between intense methane absorption bands. VIMS data show Titan's dark blue units (in RGB composites of 2.0, 1.6, and 1.3 μm) to exhibit lower relative albedos in the 1.6, 2.0, and 5 μm windows interpreted (though not unambiguously) to result from enhancement in water ice. Spectra for bright units do not exhibit depressed albedo in these windows. This gives strong evidence that the bright units are bright organic solids and not exposed water ice. The other dark equatorial unit, the dark brown unit, correlates with the vast seas of dunes discovered in the Cassini RADAR SAR (Synthetic Aperture Radar) images, suggesting that the dunes are composed of dark organic grains. If the bright materials and dark dunes are both largely organics, then they appear to consist of physically and/or chemically different hydrocarbons and/or nitriles. The VIMS and RADAR data together lead to a model where a dark blue substrate is mantled by the seas of dark organic dunes seen in SAR images and by thinner units of bright organic solids that are invisible to SAR. Carbon dioxide has been suggested as a reasonable compositional component of Titan's surface. The GCMS did tentatively identify CO2 at the surface. VIMS observations of south mid-latitude 5 m m bright spots Hotei Regio and Tui Regio have been suggested as attributable to carbon dioxide. CO2 might explain both an unusual spectral slope in the 2.7-2.8 m m spectral region and an absorption band near 4.92 m m. However the VIMS 4.92 m m band is shifted significantly in wavelength from the position observed in the laboratory rendering the CO 2 identification in VIMS Tui Regio spectra inconclusive. An alternate suggestion for the source of the 4.92 μm feature in the VIMS Tui Regio spectrum is the nitrile cyanoacetylene (HC3 N); it offers a better spectral match than does CO2. Cyanoacetylene is a known thermospheric product detected by both the Composite Infrared Spectrometer (CIRS) and the Ion and Neutral Mass Spectrometer (INMS) Cassini instruments. If Tui Regio in fact shows a high abundance of cyanoacetylene it raises questions as to by what processes such materials are concentrated. Other surface absorption features in the 4.8-5.2 μm spectral region have been attributed to various aromatic and aliphatic hydrocarbons including benzene. Because of the low signal precision of VIMS data at these wavelengths, these features are difficult to detect, particularly in Titan's dark regions. As a result there is a debate over the certainty of their existence. One such argued absorption feature near 5.05 μm most closely matches laboratory spectra of benzene, a compound detected both at the surface by the GCMS and at high altitude by INMS in greater abundance than expected. Another absorption feature at 4.97 μ m, also in debate, is best matched by spectra of the low-molecular-weight alkanes, methane and ethane, suggestive of moist surfaces wetted with such liquids consistent with GCMS observations of subsurface methane moisture. The Cassini RADAR measurements constrain electrical properties related to Titan's surface composition in its scat-terometry and radiometry modes. Analysis of the scatterom-etry observations yields an average dielectric constant of ε ∼ 2.2. The global passive microwave radiometry map shows the effective ε to be quite uniform over the globe; >95% of the surface shows a narrow range of ε ∼1.5 ± 0.3. Both data sets suggest a high degree of volume scattering indicating substantial porosity making higher- ε materials including fractured, porous water ice, possible. At the same time, these data preclude substantial exposures of solid sheets of water ice (ε ∼ 3.1) in the near surface except perhaps as local outcrops as at Sinlap crater (ε ∼ 2.5). The radiometry analysis also yields global maps of thermal emissivity and of volume scattering. These properties show Titan's surface on the global scale to be consistent with fluffy blankets and veneers of organics, perhaps with graded density increasing with depth. The higher emissivity of the radar-dark dunes is consistent with grains having hydrocarbon and/or nitrile rich materials. Cassini SAR images showed the north-polar region (>70°N) to exhibit a plethora of features resembling terrestrial lakes and seas. Further support for their being liquid is provided from analysis of high-resolution microwave radi-ometry that shows the north polar lakes to have high emis-sivity (∼0.985) and low equivalent dielectric constant (∼1.6) consistent with methane-ethane liquid. Most significant VIMS found absorption bands in south polar lake Ontario Lacus that evidence the presence of ethane, probably in liquid solution with methane, nitrogen, and other low-molecular-weight hydrocarbons. © 2010 Springer Science+Business Media B.V.
• Stephan, K., Jaumann, R., Wagner, R., Clark, R. N., Cruikshank, D. P., Hibbitts, C. A., Roatsch, T., Hoffmann, H., Brown, R. H., Filiacchione, G., Buratti, B. J., Hansen, G. B., McCord, T. B., Nicholson, P. D., & Baines, K. H. (2010). Dione's spectral and geological properties. Icarus, 206(2), 631-652.
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  Abstract: We present a detailed analysis of the variations in spectral properties across the surface of Saturn's satellite Dione using Cassini/VIMS data and their relationships to geological and/or morphological characteristics as seen in the Cassini/ISS images. This analysis focuses on a local region on Dione's anti-saturnian hemisphere that was observed by VIMS with high spatial resolution during orbit 16 in October 2005. The results are incorporated into a global context provided by VIMS data acquired within Cassini's first 50 orbits. Our results show that Dione's surface is dominated by at least one global process. Bombardment by magnetospheric particles is consistent with the concentration of dark material and enhanced CO2 absorption on the trailing hemisphere of Dione independent of the geology. Local regions within this terrain indicate a special kind of resurfacing that probably is related to large-scale impact process. In contrast, the enhanced ice signature on the leading side is associated with the extended ejecta of the fresh impact crater Creusa (∼49°N/76°W). Although no geologically active regions could be identified, Dione's tectonized regions observed with high spatial resolution partly show some clean H2O ice implying that tectonic processes could have continued into more recent times. © 2009 Elsevier Inc. All rights reserved.
• Tosi, F., Orosei, R., Seu, R., Coradini, A., Lunine, J. I., Filacchione, G., Gavrishin, A. I., Capaccioni, F., Cerroni, P., Adriani, A., Moriconi, M. L., Negrão, A., Flamini, E., Brown, R. H., Wye, L. C., Janssen, M., West, R. D., Barnes, J. W., Wall, S. D., , Clark, R. N., et al. (2010). Correlations between VIMS and RADAR data over the surface of Titan: Implications for Titan's surface properties. Icarus, 208(1), 366-384.
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  Abstract: We apply a multivariate statistical method to Titan data acquired by different instruments onboard the Cassini spacecraft. We have searched through Cassini/VIMS hyperspectral cubes, selecting those data with convenient viewing geometry and that overlap with Cassini/RADAR scatterometry footprints with a comparable spatial resolution. We look for correlations between the infrared and microwave ranges the two instruments cover. Where found, the normalized backscatter cross-section obtained from the scatterometer measurement, corrected for incidence angle, and the calibrated antenna temperature measured along with the scatterometry echoes, are combined with the infrared reflectances, with estimated errors, to produce an aggregate data set, that we process using a multivariate classification method to identify homogeneous taxonomic units in the multivariate space of the samples.In medium resolution data (from 20 to 100. km/pixel), sampling relatively large portions of the satellite's surface, we find regional geophysical units matching both the major dark and bright features seen in the optical mosaic. Given the VIMS cubes and RADAR scatterometer passes considered in this work, the largest homogeneous type is associated with the dark equatorial basins, showing similar characteristics as each other on the basis of all the considered parameters.On the other hand, the major bright features seen in these data generally do not show the same characteristics as each other. Xanadu, the largest continental feature, is as bright as the other equatorial bright features, while showing the highest backscattering coefficient of the entire satellite. Tsegihi is very bright at 5 μm but it shows a low backscattering coefficient, so it could have a low roughness on a regional scale and/or a different composition. Another well-defined region, located southwest of Xanadu beyond the Tui Regio, seems to be detached from the surrounding terrains, being bright at 2.69, 2.78 and 5 μm but having a low radar brightness. In this way, other units can be found that show correlations or anti-correlations between the scatterometric response and the spectrophotometric behavior, not evident from the optical remote sensing data. © 2010 Elsevier Inc.
• Baines, K. H., Delitsky, M. L., Momary, T. W., Brown, R. H., Buratti, B. J., Clark, R. N., & Nicholson, P. D. (2009). Storm clouds on Saturn: Lightning-induced chemistry and associated materials consistent with Cassini/VIMS spectra. Planetary and Space Science, 57(14-15), 1650-1658.
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  Abstract: Thunderstorm activity on Saturn is associated with optically detectable clouds that are atypically dark throughout the near-infrared. As observed by Cassini/VIMS, these clouds are ~20% less reflective than typical neighboring clouds throughout the spectral range from 0.8 μm to at least 4.1 μm. We propose that active thunderstorms originating in the 10-20 bar water-condensation region vertically transport dark materials at depth to the ~1 bar level where they can be observed. These materials in part may be produced by chemical processes associated with lightning, likely within the water clouds near the ~10 bar freezing level of water, as detected by the electrostatic discharge of lightning flashes observed by Cassini/RPWS (e.g., Fischer et al. 2008, Space Sci. Rev., 137, 271-285). We review lightning-induced pyrolytic chemistry involving a variety of Saturnian constituents, including hydrogen, methane, ammonia, hydrogen sulfide, phosphine, and water. We find that the lack of absorption in the 1-2 μm spectral region by lightning-generated sulfuric and phosphorous condensates renders these constituents as minor players in determining the color of the dark storm clouds. Relatively small particulates of elemental carbon, formed by lightning-induced dissociation of methane and subsequently upwelled from depth - perhaps embedded within and on the surface of spectrally bright condensates such as ammonium hydrosulfide or ammonia - may be a dominant optical material within the dark thunderstorm-related clouds of Saturn. © 2009 Elsevier Ltd. All rights reserved.
• Barnes, J. W., Brown, R. H., Soderblom, J. M., Soderblom, L. A., Jaumann, R., Jackson, B., Mouélic, S. L., Sotin, C., Buratti, B. J., Pitman, K. M., Baines, K. H., Clark, R. N., Nicholson, P. D., Turtle, E. P., & Perry, J. (2009). Shoreline features of Titan's Ontario Lacus from Cassini/VIMS observations. Icarus, 201(1), 217-225.
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  Abstract: We analyze observations of Titan's south polar lake Ontario Lacus obtained by Cassini's Visual and Infrared Mapping Spectrometer during the 38th flyby of Titan (T38; 2007 December 5). These near-closest-approach observations have the highest signal-to-noise, the finest spatial resolution, and the least atmospheric influence of any near-infrared lake observation to date. We use the large, spatially flat, and low-albedo interior of Ontario Lacus as a calibration target allowing us to derive an analytical atmospheric correction for emission angle. The dark lake interior is surrounded by two separate annuli that follow the lake interior's contours. The inner annulus is uniformly dark, but not so much as the interior lake, and is generally 5-10 kilometers wide at the lake's southeastern margin. We propose that it represents wet lakebed sediments exposed by either tidal sloshing of the lake or seasonal methane loss leading to lower lake-volume. The exterior annulus is bright and shows a spectrum consistent with a relatively low water-ice content relative to the rest of Titan. It may represent fine-grained condensate deposits from a past era of higher lake level. Together, the annuli seem to indicate that the lake level for Ontario Lacus has changed over time. This hypothesis can be tested with observations scheduled for future Titan flybys. © 2008 Elsevier Inc.
• Barnes, J. W., Simon-Miller, A. A., Turtle, E. P., Dougherty, M. K., & Brown, R. H. (2009). Special issue: Titan, Saturn, and Saturn's Magnetosphere. Planetary and Space Science, 57(14-15), 1649-.
• Barnes, J. W., Soderblom, J. M., Brown, R. H., Buratti, B. J., Sotin, C., Baines, K. H., Clark, R. N., Jaumann, R., McCord, T. B., Nelson, R., Mouélic, S. L., Rodriguez, S., Griffith, C., Penteado, P., Tosi, F., Pitman, K. M., Soderblom, L., Stephan, K., Hayne, P., , Vixie, G., et al. (2009). VIMS spectral mapping observations of Titan during the Cassini prime mission. Planetary and Space Science, 57(14-15), 1950-1962.
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  Abstract: This is a data paper designed to facilitate the use of and comparisons to Cassini/visual and infrared mapping spectrometer (VIMS) spectral mapping data of Saturn's moon Titan. We present thumbnail orthographic projections of flyby mosaics from each Titan encounter during the Cassini prime mission, 2004 July 1 through 2008 June 30. For each flyby we also describe the encounter geometry, and we discuss the studies that have previously been published using the VIMS dataset. The resulting compliation of metadata provides a complementary big-picture overview of the VIMS data in the public archive, and should be a useful reference for future Titan studies. © 2009 Elsevier Ltd.
• Brown, M. E., Schaller, E. L., Roe, H. G., Chen, C., Roberts, J., Brown, R. H., Baines, K. H., & Clark, R. N. (2009). Discovery of lake-effect clouds on Titan. Geophysical Research Letters, 36(1).
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  Abstract: Images from instruments on Cassini as well as from telescopes on the ground reveal the presence of sporadic small-scale cloud activity in the cold late-winter north polar region of Saturn's large moon Titan. These clouds lie underneath the previously discovered uniform polar cloud attributed to a quiescent ethane cloud at ∼40 km and appear confined to the same latitudes as those of the largest known hydrocarbon lakes at the north pole of Titan. The physical properties of these clouds suggest that they are due to methane convection and condensation. Such convection could be caused by a process in some ways analogous to terrestrial lake-effect clouds. The lakes on Titan could be a key connection between the surface and the meteorological cycle. © 2009 by the American Geophysical Union.
• Brown, R. (2009). How scholars credit editors in their acknowledgements. Journal of Scholarly Publishing, 40(4), 384-398.
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  Abstract: Acknowledgements are the one place on public record where scholarly editors receive credit for their contributions to books. Some have argued that the tradition of editorial invisibility is self-defeating; one editor has proposed that editors receive official recognition from the publisher in a book's front matter, irrespective of author acknowledgement. As a preliminary to entertaining such a proposal, this article surveys current practices by authors in a content analysis of acknowledgements sampled from monographs recently published by university presses. The analysis found that editors were often characterized as manuscript shepherds having a dual role: ally to the author and expeditor of production. Speaking for scholarly editors, I oppose making editor recognition a publishing standard, as this might suggest that authors need not credit editors on their own. The cost of such omission would be high, as editors would be left out of the back story to their books.
• Corre, L. L., Corre, L. L., Mouélic, S. L., Mouélic, S. L., Sotin, C., Sotin, C., Combe, J. -., Combe, J. -., Rodriguez, S., Rodriguez, S., Barnes, J. W., Barnes, J. W., Brown, R. H., Brown, R. H., Buratti, B. J., Buratti, B. J., Jaumann, R., Jaumann, R., Soderblom, J., , Soderblom, J., et al. (2009). Analysis of a cryolava flow-like feature on Titan. Planetary and Space Science, 57(7), 870-879.
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  Abstract: This paper reports on the analysis of the highest spatial resolution hyperspectral images acquired by the Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft during its prime mission. A bright area matches a flow-like feature coming out of a caldera-like feature observed in Synthetic Aperture Radar (SAR) data recorded by the Cassini radar experiment [Lopes et al., 2007. Cryovolcanic features on Titan's surface as revealed by the Cassini Titan Radar Mapper. Icarus 186, 395-412, doi:10.1016/j.icarus.2006.09.006]. In this SAR image, the flow extends about 160 km east of the caldera. The contrast in brightness between the flow and the surroundings progressively vanishes, suggesting alteration or evolution of the composition of the cryolava during the lifetime of the eruptions. Dunes seem to cover part of this flow on its eastern end. We analyze the different terrains using the Spectral Mixing Analysis (SMA) approach of the Multiple-Endmember Linear Unmixing Model (MELSUM, Combe et al., 2008). The study area can be fully modeled by using only two types of terrains. Then, the VIMS spectra are compared with laboratory spectra of known materials in the relevant atmospheric windows (from 1 to 2.78 μm). We considered simple molecules that could be produced during cryovolcanic events, including H2O, CO2 (using two different grain sizes), CH4 and NH3. We find that the mean spectrum of the cryoflow-like feature is not consistent with pure water ice. It can be best fitted by linear combinations of spectra of the candidate materials, showing that its composition is compatible with a mixture of H2O, CH4 and CO2.. © 2009 Elsevier Ltd.
• Hedman, M. M., Nicholson, P. D., Showalter, M. R., Brown, R. H., Buratti, B. J., & Clark, R. N. (2009). Spectral observations of the enceladus plume with cassini-vims. Astrophysical Journal, 693(2), 1749-1762.
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  Abstract: On 2005 November 27 (day 331), the Visual and Infrared Mapping Spectrometer instrument onboard the Cassini spacecraft obtained high signal-to-noise, spatially resolved measurements of Enceladus' particle plume. These data are processed to obtain spectra of the plume at a range of altitudes between 50 and 300 km from the surface. These spectra show that the particulate component of the plume consists primarily of fine-grained water ice. The spectral data are used to derive profiles of particle densities versus height, which are in turn converted into measurements of the velocity distribution of particles launched from the surface between 80 and 160 m s-1 (that is, between one-third and two-thirds of the escape speed). These calculations indicate that particles with radii of 1 μm are approximately equally likely to have launch speeds anywhere between 80 and 160 m s-1, while particles with radii of 2 and 3 μm have progressively steeper velocity distributions. These findings should constrain models of particle production and acceleration within Enceladus. © 2009. The American Astronomical Society. All rights reserved..
• Newman, S. F., Buratti, B. J., Brown, R. H., Jaumann, R., Bauer, J., & Momary, T. (2009). Water ice crystallinity and grain sizes on Dione. Icarus, 203(2), 553-559.
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  Abstract: Saturn's satellite Dione is becoming an increasingly important object in the outer Solar System, as evidence for its current activity accumulates. Infrared observations of the surface can provide clues to the history of the body and currently active processes. Using data from the Cassini Visual and Infrared Mapping Spectrometer (VIMS), we perform three sets of analyses that are sensitive to the ice state, temperature, thermal history, grain size and composition of surface ice. These are calculation of a "crystallinity factor", spectral ratios and water ice band depths. In our analysis, we focus on the dichotomy between the wispy and dark terrain on Dione's trailing hemisphere, to better understand the source of the different materials and their current properties. Our results suggest two different scenarios: (1) the ice from the wispy region has a higher crystallinity and water ice content than the dark region or (2) the wispy region contains larger grains. Both of these models imply recent geologic activity on Dione.
• Rodriguez, S., Mouélic, S. L., Rannou, P., Combe, J., Corre, L. L., Tobie, G., Barnes, J. W., Sotin, C., Brown, R. H., Baines, K. H., Buratti, B. J., Clark, R. N., & Nicholson, P. D. (2009). Fast forward modeling of Titan's infrared spectra to invert VIMS/Cassini hyperspectral images. WHISPERS '09 - 1st Workshop on Hyperspectral Image and Signal Processing: Evolution in Remote Sensing.
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  Abstract: The surface of Titan, the largest icy moon of Saturn, is veiled by a very thick and hazy atmosphere. The Visual and Infrared Mapping Spectrometer onboard the Cassini spacecraft, in orbit around Saturn since July 2004, conduct an intensive survey of Titan with the objective to understand the complex nature of the atmosphere and surface of the mysterious moon and the way they interact. Accurate radiative transfer modeling is necessary to analyze Titan's infrared spectra, but are often very computer resources demanding. As Cassini has gathered hitherto millions of spectra of Titan and will still observe it until at least 2010, we report here on the development of a new rapid, simple and versatile radiative transfer model specially designed to invert VIMS datacubes. © 2009 IEEE.
• Rodriguez, S., Mouélic, S. L., Rannou, P., Tobie, G., Baines, K. H., Barnes, J. W., Griffith, C. A., Hirtzig, M., Pitman, K. M., Sotin, C., Brown, R. H., Buratti, B. J., Clark, R. N., & Nicholson, P. D. (2009). Global circulation as the main source of cloud activity on Titan. Nature, 459(7247), 678-682.
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  PMID: 19494910;Abstract: Clouds on Titan result from the condensation of methane and ethane and, as on other planets, are primarily structured by circulation of the atmosphere. At present, cloud activity mainly occurs in the southern (summer) hemisphere, arising near the pole and at mid-latitudes from cumulus updrafts triggered by surface heating and/or local methane sources, and at the north (winter) pole, resulting from the subsidence and condensation of ethane-rich air into the colder troposphere. General circulation models predict that this distribution should change with the seasons on a 15-year timescale, and that clouds should develop under certain circumstances at temperate latitudes (40°) in the winter hemisphere. The models, however, have hitherto been poorly constrained and their long-term predictions have not yet been observationally verified. Here we report that the global spatial cloud coverage on Titan is in general agreement with the models, confirming that cloud activity is mainly controlled by the global circulation. The non-detection of clouds at latitude 40°N and the persistence of the southern clouds while the southern summer is ending are, however, both contrary to predictions. This suggests that Titans equator-to-pole thermal contrast is overestimated in the models and that its atmosphere responds to the seasonal forcing with a greater inertia than expected. © 2009 Macmillan Publishers Limited. All rights reserved.
• Soderblom, L. A., Brown, R. H., Soderblom, J. M., Barnes, J. W., Kirk, R. L., Sotin, C., Jaumann, R., Mackinnon, D. J., Mackowski, D. W., Baines, K. H., Buratti, B. J., Clark, R. N., & Nicholson, P. D. (2009). The geology of Hotei Regio, Titan: Correlation of Cassini VIMS and RADAR. Icarus, 204(2), 610-618.
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  Abstract: Joint Cassini VIMS and RADAR SAR data of ∼700-km-wide Hotei Regio reveal a rich collection of geological features that correlate between the two sets of images. The degree of correlation is greater than anywhere else seen on Titan. Central to Hotei Regio is a basin filled with cryovolcanic flows that are anomalously bright in VIMS data (in particular at 5 μm) and quite variable in roughness in SAR. The edges of the flows are dark in SAR data and appear to overrun a VIMS-bright substrate. SAR-stereo topography shows the flows to be viscous, 100-200 m thick. On its southern edge the basin is ringed by higher (∼1 km) mountainous terrain. The mountains show mixed texture in SAR data: some regions are extremely rough, exhibit low and spectrally neutral albedo in VIMS data and may be partly coated with darker hydrocarbons. Around the southern margin of Hotei Regio, the SAR image shows several large, dendritic, radar-bright channels that flow down from the mountainous terrain and terminate in dark blue patches, seen in VIMS images, whose infrared color is consistent with enrichment in water ice. The patches are in depressions that we interpret to be filled with fluvial deposits eroded and transported by liquid methane in the channels. In the VIMS images the dark blue patches are encased in a latticework of lighter bands that we suggest to demark a set of circumferential and radial fault systems bounding structural depressions. Conceivably the circular features are tectonic structures that are remnant from an ancient impact structure. We suggest that impact-generated structures may have simply served as zones of weakness; no direct causal connection, such as impact-induced volcanism, is implied. We also speculate that two large dark features lying on the northern margin of Hotei Regio could be calderas. In summary the preservation of such a broad suite of VIMS infrared color variations and the detailed correlation with features in the SAR image and SAR topography evidence a complex set of geological processes (pluvial, fluvial, tectonic, cryovolcanic, impact) that have likely remained active up to very recent geological time (
• Barnes, J. W., Brown, R. H., Soderblom, L., Sotin, C., Mouèlic, S. L., Rodriguez, S., Jaumann, R., Beyer, R. A., Buratti, B. J., Pitman, K., Baines, K. H., Clark, R., & Nicholson, P. (2008). Spectroscopy, morphometry, and photoclinometry of Titan's dunefields from Cassini/VIMS. Icarus, 195(1), 400-414.
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  Abstract: Fine-resolution (500 m/pixel) Cassini Visual and Infrared Mapping Spectrometer (VIMS) T20 observations of Titan resolve that moon's sand dunes. The spectral variability in some dune regions shows that there are sand-free interdune areas, wherein VIMS spectra reveal the exposed dune substrate. The interdunes from T20 are, variously, materials that correspond to the equatorial bright, 5-μm-bright, and dark blue spectral units. Our observations show that an enigmatic "dark red" spectral unit seen in T5 in fact represents a macroscopic mixture with 5-μm-bright material and dunes as its spectral endmembers. Looking more broadly, similar mixtures of varying amounts of dune and interdune units of varying composition can explain the spectral and albedo variability within the dark brown dune global spectral unit that is associated with dunes. The presence of interdunes indicates that Titan's dunefields are both mature and recently active. The spectrum of the dune endmember reveals the sand to be composed of less water ice than the rest of Titan; various organics are consistent with the dunes' measured reflectivity. We measure a mean dune spacing of 2.1 km, and find that the dunes are oriented on the average in an east-west direction, but angling up to 10° from parallel to the equator in specific cases. Where no interdunes are present, we determine the height of one set of dunes photoclinometrically to be between 30 and 70 m. These results pave the way for future exploration and interpretation of Titan's sand dunes. © 2007 Elsevier Inc. All rights reserved.
• Brown, R. H., Soderblom, L. A., Soderblom, J. M., Clark, R. N., Jaumann, R., Barnes, J. W., Sotin, C., Buratti, B., Baines, K. H., & Nicholson, P. D. (2008). The identification of liquid ethane in Titan's Ontario Lacus. Nature, 454(7204), 607-610.
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  PMID: 18668101;Abstract: Titan was once thought to have global oceans of light hydrocarbons on its surface, but after 40 close flybys of Titan by the Cassini spacecraft, it has become clear that no such oceans exist. There are, however, features similar to terrestrial lakes and seas, and widespread evidence for fluvial erosion, presumably driven by precipitation of liquid methane from Titan's dense, nitrogen-dominated atmosphere. Here we report infrared spectroscopic data, obtained by the Visual and Infrared Mapping Spectrometer (VIMS) on board the Cassini spacecraft, that strongly indicate that ethane, probably in liquid solution with methane, nitrogen and other low-molecular-mass hydrocarbons, is contained within Titan's Ontario Lacus. ©2008 Macmillan Publishers Limited. All rights reserved.
• Buratti, B. J., Soderlund, K., Bauer, J., Mosher, J. A., Hicks, M. D., Simonelli, D. P., Jaumann, R., Clark, R. N., Brown, R. H., Cruikshank, D. P., & Momary, T. (2008). Infrared (0.83-5.1 μm) photometry of Phoebe from the Cassini Visual Infrared Mapping Spectrometer. Icarus, 193(2), 309-322.
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  Abstract: Three weeks prior to the commencement of Cassini's 4 year tour of the saturnian system, the spacecraft executed a close flyby of the outer satellite Phoebe. The infrared channel of the Visual Infrared Mapping Spectrometer (VIMS) obtained images of reflected light over the 0.83-5.1 μm spectral range with an average spectral resolution of 16.5 nm, spatial resolution up to 2 km, and over a range of solar phase angles not observed before. These images have been analyzed to derive fundamental photometric parameters including the phase curve and phase integral, spectral geometric albedo, bolometric Bond albedo, and the single scattering albedo. Physical properties of the surface, including macroscopic roughness and the single particle phase function, have also been characterized. Maps of normal reflectance show the existence of two major albedo regimes in the infrared, with gradations between the two regimes and much terrain with substantially higher albedos. The phase integral of Phoebe is 0.29 ± 0.03, with no significant wavelength dependence. The bolometric Bond albedo is 0.023 ± 007. We find that the surface of Phoebe is rough, with a mean slope angle of 33°. The satellite's surface has a substantial forward scattering component, suggesting that its surface is dusty, perhaps from a history of outgassing. The spectrum of Phoebe is best matched by a composition including water ice, amorphous carbon, iron-bearing minerals, carbon dioxide, and Triton tholin. The characteristics of Phoebe suggest that it originated outside the saturnian system, perhaps in the Kuiper Belt, and was captured on its journey inward, as suggested by Johnson and Lunine (2005). © 2007 Elsevier Inc. All rights reserved.
• Clark, R. N., Curchin, J. M., Jaumann, R., Cruikshank, D. P., Brown, R. H., Hoefen, T. M., Stephan, K., Moore, J. M., Buratti, B. J., Baines, K. H., Nicholson, P. D., & Nelson, R. M. (2008). Compositional mapping of Saturn's satellite Dione with Cassini VIMS and implications of dark material in the Saturn system. Icarus, 193(2), 372-386.
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  Abstract: Cassini VIMS has obtained spatially resolved imaging spectroscopy data on numerous satellites of Saturn. A very close fly-by of Dione provided key information for solving the riddle of the origin of the dark material in the Saturn system. The Dione VIMS data show a pattern of bombardment of fine, sub-0.5-μm diameter particles impacting the satellite from the trailing side direction. Multiple lines of evidence point to an external origin for the dark material on Dione, including the global spatial pattern of dark material, local patterns including crater and cliff walls shielding implantation on slopes facing away from the trailing side, exposing clean ice, and slopes facing the trailing direction which show higher abundances of dark material. Multiple spectral features of the dark material match those seen on Phoebe, Iapetus, Hyperion, Epimetheus and the F-ring, implying the material has a common composition throughout the Saturn system. However, the exact composition of the dark material remains a mystery, except that bound water and, tentatively, ammonia are detected, and there is evidence both for and against cyanide compounds. Exact identification of composition requires additional laboratory work. A blue scattering peak with a strong UV-visible absorption is observed in spectra of all satellites which contain dark material, and the cause is Rayleigh scattering, again pointing to a common origin. The Rayleigh scattering effect is confirmed with laboratory experiments using ice and 0.2-μm diameter carbon grains when the carbon abundance is less than about 2% by weight. Rayleigh scattering in solids is also confirmed in naturally occurring terrestrial rocks, and in previously published reflectance studies. The spatial pattern, Rayleigh scattering effect, and spectral properties argue that the dark material is only a thin coating on Dione's surface, and by extension is only a thin coating on Phoebe, Hyperion, and Iapetus, although the dark material abundance appears higher on Iapetus, and may be locally thick. As previously concluded for Phoebe, the dark material appears to be external to the Saturn system and may be cometary in origin. We also report a possible detection of material around Dione which may indicate Dione is active and contributes material to the E-ring, but this observation must be confirmed.
• Coradini, A., Tosi, F., Gavrishin, A. I., Capaccioni, F., Cerroni, P., Filacchione, G., Adriani, A., Brown, R. H., Bellucci, G., Formisano, V., D'Aversa, E., Lunine, J. I., Baines, K. H., Bibring, J. -., Buratti, B. J., Clark, R. N., Cruikshank, D. P., Combes, M., Drossart, P., , Jaumann, R., et al. (2008). Identification of spectral units on Phoebe. Icarus, 193(1), 233-251.
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  Abstract: We apply a multivariate statistical method to the Phoebe spectra collected by the VIMS experiment onboard the Cassini spacecraft during the flyby of June 2004. The G-mode clustering method, which permits identification of the most important features in a spectrum, is used on a small subset of data, characterized by medium and high spatial resolution, to perform a raw spectral classification of the surface of Phoebe. The combination of statistics and comparative analysis of the different areas using both the VIMS and ISS data is explored in order to highlight possible correlations with the surface geology. In general, the results by Clark et al. [Clark, R.N., Brown, R.H., Jaumann, R., Cruikshank, D.P., Nelson, R.M., Buratti, B.J., McCord, T.B., Lunine, J., Hoefen, T., Curchin, J.M., Hansen, G., Hibbitts, K., Matz, K.-D., Baines, K.H., Bellucci, G., Bibring, J.-P., Capaccioni, F., Cerroni, P., Coradini, A., Formisano, V., Langevin, Y., Matson, D.L., Mennella, V., Nicholson, P.D., Sicardy, B., Sotin, C., 2005. Nature 435, 66-69] are confirmed; but we also identify new signatures not reported before, such as the aliphatic CH stretch at 3.53 μm and the ∼4.4 μm feature possibly related to cyanide compounds. On the basis of the band strengths computed for several absorption features and for the homogeneous spectral types isolated by the G-mode, a strong correlation of CO2 and aromatic hydrocarbons with exposed water ice, where the uniform layer covering Phoebe has been removed, is established. On the other hand, an anti-correlation of cyanide compounds with CO2 is suggested at a medium resolution scale. © 2007 Elsevier Inc. All rights reserved.
• Cruikshank, D. P., Wegryn, E., Ore, C. D., Brown, R. H., Bibring, J. -., Buratti, B. J., Clark, R. N., McCord, T. B., Nicholson, P. D., Pendleton, Y. J., Owen, T. C., Filacchione, G., Coradini, A., Cerroni, P., Capaccioni, F., Jaumann, R., Nelson, R. M., Baines, K. H., Sotin, C., , Bellucci, G., et al. (2008). Hydrocarbons on Saturn's satellites Iapetus and Phoebe. Icarus, 193(2), 334-343.
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  Abstract: Material of low geometric albedo (pV ≤ 0.1) is found on many objects in the outer Solar System, but its distribution in the saturnian satellite system is of special interest because of its juxtaposition with high-albedo ice. In the absence of clear, diagnostic spectral features, the composition of this low-albedo (or "dark") material is generally inferred to be carbon-rich, but the form(s) of the carbon is unknown. Near-infrared spectra of the low-albedo hemisphere of Saturn's satellite Iapetus were obtained with the Visible-Infrared Mapping Spectrometer (VIMS) on the Cassini spacecraft at the fly-by of that satellite of 31 December 2004, yielding a maximum spatial resolution on the satellite's surface of ∼65 km. The spectral region 3-3.6 μm reveals a broad absorption band, centered at 3.29 μm, and concentrated in a region comprising about 15% of the low-albedo surface area. This is identified as the C{single bond}H stretching mode vibration in polycyclic aromatic hydrocarbon (PAH) molecules. Two weaker bands attributed to {single bond}CH2{single bond} stretching modes in aliphatic hydrocarbons are found in association with the aromatic band. The bands most likely arise from aromatic and aliphatic units in complex macromolecular carbonaceous material with a kerogen- or coal-like structure, similar to that in carbonaceous meteorites. VIMS spectra of Phoebe, encountered by Cassini on 11 June 2004, also show the aromatic hydrocarbon band, although somewhat weaker than on Iapetus. The origin of the PAH molecular material on these two satellites is unknown, but PAHs are found in carbonaceous meteorites, cometary dust particles, circumstellar dust, and interstellar dust. © 2007 Elsevier Inc. All rights reserved.
• Jaumann, R., Brown, R. H., Stephan, K., Barnes, J. W., Soderblom, L. A., Sotin, C., Mouélic, S. L., Clark, R. N., Soderblom, J., Buratti, B. J., Wagner, R., McCord, T. B., Rodriguez, S., Baines, K. H., Cruikshank, D. P., Nicholson, P. D., Griffith, C. A., Langhans, M., & Lorenz, R. D. (2008). Fluvial erosion and post-erosional processes on Titan. Icarus, 197(2), 526-538.
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  Abstract: The surface of Titan has been revealed by Cassini observations in the infrared and radar wavelength ranges as well as locally by the Huygens lander instruments. Sand seas, recently discovered lakes, distinct landscapes and dendritic erosion patterns indicate dynamic surface processes. This study focus on erosional and depositional features that can be used to constrain the amount of liquids involved in the erosional process as well as on the compositional characteristics of depositional areas. Fluvial erosion channels on Titan as identified at the Huygens landing site and in RADAR and Visible and Infrared Mapping Spectrometer (VIMS) observations have been compared to analogous channel widths on Earth yielding average discharges of up to 1600 m3/s for short recurrence intervals that are sufficient to move centimeter-sized sediment and significantly higher discharges for long intervals. With respect to the associated drainage areas, this roughly translates to 1-150 cm/day runoff production rates with 10 years recurrence intervals and by assuming precipitation this implies 0.6-60 mm/h rainfall rates. Thus the observed surface erosion fits with the methane convective storm models as well as with the rates needed to transport sediment. During Cassini's T20 fly-by, the VIMS observed an extremely eroded area at 30° W, 7° S with resolutions of up to 500 m/pixel that extends over thousands of square kilometers. The spectral characteristics of this area change systematically, reflecting continuous compositional and/or particle size variations indicative of transported sediment settling out while flow capacities cease. To account for the estimated runoff production and widespread alluvial deposits of fine-grained material, release of area-dependent large fluid volumes are required. Only frequent storms with heavy rainfall or cryovolcanic induced melting can explain these erosional features. © 2008 Elsevier Inc.
• Jaumann, R., Stephan, K., Hansen, G. B., Clark, R. N., Buratti, B. J., Brown, R. H., Baines, K. H., Newman, S. F., Bellucci, G., Filacchione, G., Coradini, A., Cruikshank, D. P., Griffith, C. A., Hibbitts, C. A., McCord, T. B., Nelson, R. M., Nicholson, P. D., Sotin, C., & Wagner, R. (2008). Distribution of icy particles across Enceladus' surface as derived from Cassini-VIMS measurements. Icarus, 193(2), 407-419.
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  Abstract: The surface of Enceladus consists almost completely of water ice. As the band depths of water ice absorptions are sensitive to the size of particles, absorptions can be used to map variations of icy particles across the surface. The Visual and Infrared Mapping Spectrometer (VIMS) observed Enceladus with a high spatial resolution during three Cassini flybys in 2005 (orbits EN 003, EN 004 and EN 011). Based on these data we measured the band depths of water ice absorptions at 1.04, 1.25, 1.5, and 2 μm. These band depths were compared to water ice models that represent theoretically calculated reflectance spectra for a range of particle diameters between 2 μm and 1 mm. The agreement between the experimental (VIMS) and model values supports the assumption that pure water ice characterizes the surface of Enceladus and therefore that variations in band depth correspond to variations in water ice particle diameters. Our measurements show that the particle diameter of water ice increases toward younger tectonically altered surface units with the largest particles exposed in relatively "fresh" surface material. The smallest particles were generally found in old densely cratered terrains. The largest particles (∼0.2 mm) are concentrated in the so called "tiger stripes" at the south pole. In general, the particle diameters are strongly correlated with geologic features and surface ages, indicating a stratigraphic evolution of the surface that is caused by cryovolcanic resurfacing and impact gardening. © 2007 Elsevier Inc. All rights reserved.
• Mouélic, S. L., Paillou, P., Janssen, M. A., Barnes, J. W., Rodriguez, S., Sotin, C., Brown, R. H., Baines, K. H., Buratti, B. J., Clark, R. N., Crapeau, M., Encrenaz, P. J., Jaumann, R., Geudtner, D., Paganelli, F., Soderblom, L., Tobie, G., & Wall, S. (2008). Mapping and interpretation of Sinlap crater on Titan using Cassini VIMS and RADAR data. Journal of Geophysical Research E: Planets, 113(4).
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  Abstract: Only a few impact craters have been unambiguously detected on Titan by the Cassini-Huygens mission. Among these, Sinlap is the only one that has been observed both by the RADAR and VIMS instruments. This paper describes observations at centimeter and infrared wavelengths which provide complementary information about the composition, topography, and surface roughness. Several units appear in VIMS false color composites of band ratios in the Sinlap area, suggesting compositional heterogeneities. A bright pixel possibly related to a central peak does not show significant spectral variations, indicating either that the impact site was vertically homogeneous, or that this area has been recovered by homogeneous deposits. Both VIMS ratio images and dielectric constant measurements suggest the presence of an area enriched in water ice around the main ejecta blanket. Since the Ku-band SAR may see subsurface structures at the meter scale, the difference between infrared and SAR observations can be explained by the presence of a thin layer transparent to the radar. An analogy with terrestrial craters in Libya supports this interpretation. Finally, a tentative model describes the geological history of this area prior, during, and after the impact. It involves mainly the creation of ballistic ejecta and an expanding plume of vapor triggered by the impact, followed by the redeposition of icy spherules recondensed from this vapor plume blown downwind. Subsequent evolution is then driven by erosional processes and aeolian deposition. Copyright 2008 by the American Geophysical Union.
• Newman, S. F., Buratti, B. J., Brown, R. H., Jaumann, R., Bauer, J., & Momary, T. (2008). Photometric and spectral analysis of the distribution of crystalline and amorphous ices on Enceladus as seen by Cassini. Icarus, 193(2), 397-406.
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  Abstract: Photometric and spectral analysis of data from the Cassini Visual and Infrared Mapping Spectrometer (VIMS) has yielded significant results regarding the properties and composition of the surface of Saturn's satellite Enceladus. We have obtained spectral cubes of this satellite, containing both spatial and spectral information, with a wavelength distribution in the infrared far more extensive than from any previous observations and at much higher spatial resolution. Using a composite mosaic of the satellite, we map the distribution of crystalline and amorphous ices on the surface of Enceladus according to a "crystallinity factor" and also the depth of the temperature- and structure-dependent 1.65 micron water-ice band. These maps show the surface of Enceladus to be mostly crystalline, with a higher degree of crystallinity at the "tiger-stripe" cracks and a larger amorphous signature between these stripes. These results suggest recent geological activity at the "tiger stripe" cracks and an intriguing atmospheric environment over the south pole where amorphous ice is produced either through intense radiative bombardment, flash-freezing of cryovolcanic liquid, or rapid condensation of water vapor particles on icy microspherules or on the surface of Enceladus. © 2007 Elsevier Inc. All rights reserved.
• Nicholson, P. D., Hedman, M. M., Clark, R. N., Showalter, M. R., Cruikshank, D. P., Cuzzi, J. N., Filacchione, G., Capaccioni, F., Cerroni, P., Hansen, G. B., Sicardy, B., Drossart, P., Brown, R. H., Buratti, B. J., Baines, K. H., & Coradini, A. (2008). A close look at Saturn's rings with Cassini VIMS. Icarus, 193(1), 182-212.
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  Abstract: Soon after the Cassini-Huygens spacecraft entered orbit about Saturn on 1 July 2004, its Visual and Infrared Mapping Spectrometer obtained two continuous spectral scans across the rings, covering the wavelength range 0.35-5.1 μm, at a spatial resolution of 15-25 km. The first scan covers the outer C and inner B rings, while the second covers the Cassini Division and the entire A ring. Comparisons of the VIMS radial reflectance profile at 1.08 μm with similar profiles at a wavelength of 0.45 μm assembled from Voyager images show very little change in ring structure over the intervening 24 years, with the exception of a few features already known to be noncircular. A model for single-scattering by a classical, many-particle-thick slab of material with normal optical depths derived from the Voyager photopolarimeter stellar occultation is found to provide an excellent fit to the observed VIMS reflectance profiles for the C ring and Cassini Division, and an acceptable fit for the inner B ring. The A ring deviates significantly from such a model, consistent with previous suggestions that this region may be closer to a monolayer. An additional complication here is the azimuthally-variable average optical depth associated with "self-gravity wakes" in this region and the fact that much of the A ring may be a mixture of almost opaque wakes and relatively transparent interwake zones. Consistently with previous studies, we find that the near-infrared spectra of all main ring regions are dominated by water ice, with a typical regolith grain radius of 5-20 μm, while the steep decrease in visual reflectance shortward of 0.6 μm is suggestive of an organic contaminant, perhaps tholin-like. Although no materials other than H2O ice have been identified with any certainty in the VIMS spectra of the rings, significant radial variations are seen in the strength of the water-ice absorption bands. Across the boundary between the C and B rings, over a radial range of ∼7000 km, the near-IR band depths strengthen considerably. A very similar pattern is seen across the outer half of the Cassini Division and into the inner A ring, accompanied by a steepening of the red slope in the visible spectrum shortward of 0.55 μm. We attribute these trends-as well as smaller-scale variations associated with strong density waves in the A ring-to differing grain sizes in the tholin-contaminated icy regolith that covers the surfaces of the decimeter-to-meter sized ring particles. On the largest scale, the spectral variations seen by VIMS suggest that the rings may be divided into two larger 'ring complexes,' with similar internal variations in structure, optical depth, particle size, regolith texture and composition. The inner complex comprises the C and B rings, while the outer comprises the Cassini Division and A ring. © 2007 Elsevier Inc. All rights reserved.
• Palmer, E. E., & Brown, R. H. (2008). The stability and transport of carbon dioxide on Iapetus. Icarus, 195(1), 434-446.
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  Abstract: Carbon dioxide has been detected associated with Iapetus' dark material by the Cassini spacecraft. This CO2 may be primordial and/or resulting from ongoing production by photolysis of water-ice in the presence of carbonaceous material [Allamandola, L.J., Sandford, S.A., Valero, G.J., 1988. Icarus 76, 225-252]. Although any primordial CO2 would likely be complexed with the dark material and thus stable against thermal transport to Iapetus' poles [Buratti, B.J., and 28 colleagues, 2005. Astrophys. J. 622, L149-L152], active production of CO2 would result in some fraction of the CO2 being mobile enough to allow the accumulation of CO2 at Iapetus' poles. We develop a computer model to simulate ballistic transport of CO2 ice on Iapetus, accounting for Iapetus' gravitational binding energy and polar cold traps. We find that the residence time of CO2 ice outside the polar regions is very short; a sheet of CO2 ice near the equator of Iapetus decreases in thickness at a rate of 50 mm year-1. The sublimated CO2 will ballistically move around Iapetus until it reaches the polar cold traps where it can be sequestered for up to 15 years. If the total surface inventory of CO2 exceeds 3 × 107 kg, the polar ice cap will be permanent. While CO2 is moving around the surface, a small percentage will eventually reach escape velocity and be lost from the system. As such, a seasonal polar cap is lost at rate of 12% every solar orbit as the CO2 moves between the two polar cold traps. © 2008 Elsevier Inc. All rights reserved.
• Pitman, K. M., Buratti, B. J., Mosher, J. A., Bauer, J. M., Momary, T. W., Brown, R. H., Nicholson, P. D., & Hedman, M. M. (2008). First high solar phase angle observations of rhea using cassini vims: Upper limits on water vapor and geologic activity. Astrophysical Journal, 680(1 PART 2), L65-L68.
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  Abstract: Using radiances acquired with Cassini's Visual and Infrared Mapping Spectrometer (VIMS), we construct high solar phase angle curves for Saturn's second largest moon, Rhea. Ground-based studies of Rhea and Saturnian icy satellites are focussing on low phase angles; to our knowledge, these are the first solar phase curve data for Rhea on phase angles >70°. We compare these data to similar phase curves for Enceladus at near-infrared wavelengths to estimate the amount of water vapor that could possibly be generated and thus set an upper limit on the amount of geologic activity that may be occurring on Rhea. We find that Enceladus's plume manifests itself in the VIMS solar phase curve at a phase angle near 160° and peaks most strongly for λ = 2.017810 μm. No such peak can be found in the Rhea VIMS phase curve. Absence of a forward scattering peak supports the recent determination that particles in Rhea's surrounding ring are not small. We calculate that the maximum water vapor column density that could be supplied from Rhea ranges from 1.52 × 1014 to 1.91 × 1015 cm-2, 2 orders of magnitude less than what is calculated by Cassini UVIS for Enceladus. This implies that for Rhea, the level of active internal (endogenic) processes is exceedingly small, if any © 2008, The American Astronomical Society, All rights reserved.
• Stallard, T., Miller, S., Lystrup, M., Achilleos, N., Bunce, E. J., Arridge, C. S., Dougherty, M. K., W., S., Badman, S. V., Talboys, D. L., Brown, R. H., Baines, K. H., Buratti, B. J., Clark, R. N., Sotin, C., Nicholson, P. D., & Drossart, P. (2008). Complex structure within Saturn's infrared aurora. Nature, 456(7219), 214-217.
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  PMID: 19005549;Abstract: The majority of planetary aurorae are produced by electrical currents flowing between the ionosphere and the magnetosphere which accelerate energetic charged particles that hit the upper atmosphere. At Saturn, these processes collisionally excite hydrogen, causing ultraviolet emission, and ionize the hydrogen, leading to H3+ infrared emission. Although the morphology of these aurorae is affected by changes in the solar wind, the source of the currents which produce them is a matter of debate. Recent models predict only weak emission away from the main auroral oval. Here we report images that show emission both poleward and equatorward of the main oval (separated by a region of low emission). The extensive polar emission is highly variable with time, and disappears when the main oval has a spiral morphology; this suggests that although the polar emission may be associated with minor increases in the dynamic pressure from the solar wind, it is not directly linked to strong magnetospheric compressions. This aurora appears to be unique to Saturn and cannot be explained using our current understanding of Saturn's magnetosphere. The equatorward arc of emission exists only on the nightside of the planet, and arises from internal magnetospheric processes that are currently unknown. ©2008 Macmillan Publishers Limited. All rights reserved.
• Barnes, J. W., Brown, R. H., Soderblom, L., Buratti, B. J., Sotin, C., Rodriguez, S., Mouèlic, S. L., Baines, K. H., Clark, R., & Nicholson, P. (2007). Global-scale surface spectral variations on Titan seen from Cassini/VIMS. Icarus, 186(1), 242-258.
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  Abstract: We present global-scale maps of Titan from the Visual and Infrared Mapping Spectrometer (VIMS) instrument on Cassini. We map at 64 near-infrared wavelengths simultaneously, covering the atmospheric windows at 0.94, 1.08, 1.28, 1.6, 2.0, 2.8, and 5 μm with a typical resolution of 50 km/pixel or a typical total integration time of 1 s. Our maps have five to ten times the resolution of ground-based maps, better spectral resolution across most windows, coverage in multiple atmospheric windows, and represent the first spatially resolved maps of Titan at 5 μm. The VIMS maps provide context and surface spectral information in support of other Cassini instruments. We note a strong latitudinal dependence in the spectral character of Titan's surface, and partition the surface into 9 spectral units that we describe in terms of spectral and spatial characteristics. © 2006 Elsevier Inc. All rights reserved.
• Barnes, J. W., Radebaugh, J., Brown, R. H., Wall, S., Soderblom, L., Lunine, J., Burr, D., Sotin, C., Mouélic, S. L., Rodriguez, S., Buratti, B. J., Clark, R., Baines, K. H., Jaumann, R., Nicholson, P. D., Kirk, R. L., Lopes, R., Lorenz, R. D., Mitchell, K., & Wood, C. A. (2007). Near-infrared spectral mapping of Titan's mountains and channels. Journal of Geophysical Research E: Planets, 112(11).
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  Abstract: We investigate the spectral reflectance properties of channels and mountain ranges on Titan using data from Cassini's Visual and Infrared Mapping Spectrometer (VIMS) obtained during the T9 encounter (26 December 2005). We identify the location of channels and mountains using synthetic aperture radar maps obtained from Cassini's RADAR instrument during the T13 (30 April 2006) flyby. Channels are evident even in VIMS imaging with spatial resolution coarser than the channel size. The channels share spectral characteristics with Titan's dark blue terrain (e.g., the Huygens landing site) that is consistent with an enhancement in water ice content relative to the rest of Titan. We use this fact to measure widths of ∼1 km for the largest channels. Comparison of the data sets shows that in our study area within the equatorial bright spectral unit east of Xanadu, mountains are darker and bluer than surrounding smooth terrain. These results are consistent with the equatorial bright terrain possessing a veneer of material that is thinner in the regions where there are mountains and streambeds that have likely undergone more recent and extensive erosion. We suggest a model for the geographic relationship of the dark blue, dark brown, and equatorial bright spectral units based on our findings. Copyright 2007 by the American Geophysical Union.
• Cruikshank, D. P., Dalton, J. B., M., C., Bauer, J., Stephan, K., Filacchione, G., Hendrix, A. R., Hansen, C. J., Coradini, A., Cerroni, P., Tosi, F., Capaccioni, F., Jaumann, R., Buratti, B. J., Clark, R. N., Brown, R. H., Nelson, R. M., McCord, T. B., Baines, K. H., , Nicholson, P. D., et al. (2007). Surface composition of Hyperion. Nature, 448(7149), 54-56.
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  PMID: 17611536;Abstract: Hyperion, Saturn's eighth largest icy satellite, is a body of irregular shape in a state of chaotic rotation. The surface is segregated into two distinct units. A spatially dominant high-albedo unit having the strong signature of H2O ice contrasts with a unit that is about a factor of four lower in albedo and is found mostly in the bottoms of cup-like craters. Here we report observations of Hyperion's surface in the ultraviolet and near-infrared spectral regions with two optical remote sensing instruments on the Cassini spacecraft at closest approach during a fly-by on 25-26 September 2005. The close fly-by afforded us the opportunity to obtain separate reflectance spectra of the high- and low-albedo surface components. The low-albedo material has spectral similarities and compositional signatures that link it with the surface of Phoebe and a hemisphere-wide superficial coating on Iapetus. ©2007 Nature Publishing Group.
• Filacchione, G., Capaccioni, F., McCord, T. B., Coradini, A., Cerroni, P., Bellucci, G., Tosi, F., D'Aversa, E., Formisano, V., Brown, R. H., Baines, K. H., Bibring, J. P., Buratti, B. J., Clark, R. N., Combes, M., Cruikshank, D. P., Drossart, P., Jaumann, R., Langevin, Y., , Matson, D. L., et al. (2007). Saturn's icy satellites investigated by Cassini-VIMS. I. Full-disk properties: 350-5100 nm reflectance spectra and phase curves. Icarus, 186(1), 259-290.
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  Abstract: Saturn's icy satellites are among the main scientific objectives of the Cassini-VIMS (Visual and Infrared Mapping Spectrometer) experiment. This paper contains a first systematic and comparative analysis of the full-disk spectral properties of Dione, Enceladus, Epimetheus, Hyperion, Iapetus, Mimas, Phoebe, Rhea and Tethys as observed by VIMS from July 2004 to June 2005. The disk integrated properties (350-5100 nm reflectance spectra and phase curves at 550-2232 nm) and images of satellites are reported and discussed in detail together with the observed geometry. In general, the spectra in the visible spectral range are almost featureless and can be classified according to the spectral slopes: from the bluish Enceladus and Phoebe to the redder Iapetus, Hyperion and Epimetheus. In the 1000-1300 nm range the spectra of Enceladus, Tethys, Mimas and Rhea are characterized by a negative slope, consistent with a surface largely dominated by water ice, while the spectra of Iapetus, Hyperion and Phoebe show a considerable reddening pointing out the relevant role played by darkening materials present on the surface. In between these two classes are Dione and Epimetheus, which have a flat spectrum in this range. The main absorption bands identified in the infrared are the 1520, 2020, 3000 nm H2O/OH bands (for all satellites), although Iapetus dark terrains show mostly a deep 3000 nm band while the 1520 and 2020 nm bands are very faint. In this spectral range, the Iapetus spectrum is characterized by a strong reddening. The CO2 band at 4260 nm and the Fresnel ice peak around 3100 nm are evident only on Hyperion, Phoebe and Iapetus. The phase curves at 550 and at 2232 nm are reported for all the available observations in the 0°-144° range; Rhea shows an opposition surge at visible wavelengths in the 0.5°-1.17° interval. The improvement on the retrieval of the full-disk reflectance spectra can be appreciated by a direct comparison with ground-based telescopic data available from literature. Finally, data processing strategies and recent upgrades introduced in the VIMS-V calibration pipeline (flat-field and destriping-despiking algorithm) are discussed in appendices. © 2006 Elsevier Inc. All rights reserved.
• Hedman, M. M., Burns, J. A., Showalter, M. R., Porco, C. C., Nicholson, P. D., Bosh, A. S., Tiscareno, M. S., Brown, R. H., Buratti, B. J., Baines, K. H., & Clark, R. (2007). Saturn's dynamic D ring. Icarus, 188(1), 89-107.
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  Abstract: The Cassini spacecraft has provided the first clear images of the D ring since the Voyager missions. These observations show that the structure of the D ring has undergone significant changes over the last 25 years. The brightest of the three ringlets seen in the Voyager images (named D72), has transformed from a narrow,
• Hedman, M. M., Nicholson, P. D., Salo, H., Wallis, B. D., Buratti, B. J., Baines, K. H., Brown, R. H., & Clark, R. N. (2007). Self-gravity wake structures in Saturn's a ring revealed by Cassini vims. Astronomical Journal, 133(6), 2624-2629.
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  Abstract: During the summer of 2005, the Visual and Infrared Mapping Spectrometer onboard the Cassini spacecraft observed a series of occultations of the star o Ceti (Mira) by Saturn's rings. These observations revealed pronounced variations in the optical depth of the A ring with longitude, which can be attributed to oriented structures in the rings known as self-gravity wakes. While the wakes themselves are only tens of meters across and below the resolution of the measurements, we are able to obtain information about the orientation and shapes of these structures by comparing the observed transmission at different longitudes with predictions from a simple model. Our findings include the following: (1) The orientation of the wakes varies systematically with radius, trailing by between 64° and 72° relative to the local radial direction. (2) The maximum transmission peaks at roughly 8% for B = 3.45° in the middle A ring (∼129,000 km). (3) Both the wake orientation and maximum transmission vary anomalously in the vicinity of two strong density waves (Janus 5:4 and Mimas 5:3). (4) The ratio of the wake vertical thickness H to the wake pattern wavelength λ (assuming infinite, straight, regularly-spaced wake structures) varies from 0.12 to 0.09 across the A ring. Gravitational instability theory predicts λ ∼ 60 m, which suggests that the wake structures in the A ring are only ∼6 m thick. © 2007. The American Astronomical Society. All rights reserved.
• Palmer, E. E., & Brown, R. H. (2007). A possible trace carbon dioxide polar cap on Iapetus. Astrophysical Journal, 666(2 PART 2), L125-L128.
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  Abstract: We model ballistic transport of CO2 on the surface of Iapetus, accounting for gravitational binding energy and polar cold traps. We find that if CO2 is in the form of ice, it has a long enough residence time to be spectroscopically detected. We determine that at midlatitudes, CO2 is volatile, will rapidly ablate, and be sequestered in a polar cold trap. In addition, we find that due to the inclination of Iapetus's orbit, the poles provide only a temporary cold trap, requiring the CO2 to move to the opposite pole at the end of the winter season. During each transit, 5% of the CO2 will reach escape velocity and be lost from the system. Finally, we make a prediction of the latitudinal extent and thickness of a possible CO2 polar cap that could be detected during Cassini's 2007 September flyby of Iapetus. © 2007. The American Astronomical Society.
• Soderblom, L. A., Kirk, R. L., Lunine, J. I., Anderson, J. A., Baines, K. H., Barnes, J. W., Barrett, J. M., Brown, R. H., Buratti, B. J., Clark, R. N., Cruikshank, D. P., Elachi, C., Janssen, M. A., Jaumann, R., Karkoschka, E., Mouélic, S. L., Lopes, R. M., Lorenz, R. D., McCord, T. B., , Nicholson, P. D., et al. (2007). Correlations between Cassini VIMS spectra and RADAR SAR images: Implications for Titan's surface composition and the character of the Huygens Probe Landing Site. Planetary and Space Science, 55(13), 2025-2036.
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  Abstract: Titan's vast equatorial fields of RADAR-dark longitudinal dunes seen in Cassini RADAR synthetic aperture images correlate with one of two dark surface units discriminated as "brown" and "blue" in Visible and Infrared Mapping Spectrometer (VIMS) color composites of short-wavelength infrared spectral cubes (RGB as 2.0, 1.6, 1.3 μm). In such composites bluer materials exhibit higher reflectance at 1.3 μm and lower at 1.6 and 2.0 μm. The dark brown unit is highly correlated with the RADAR-dark dunes. The dark brown unit shows less evidence of water ice suggesting that the saltating grains of the dunes are largely composed of hydrocarbons and/or nitriles. In general, the bright units also show less evidence of absorption due to water ice and are inferred to consist of deposits of bright fine precipitating tholin aerosol dust. Some set of chemical/mechanical processes may be converting the bright fine-grained aerosol deposits into the dark saltating hydrocarbon and/or nitrile grains. Alternatively the dark dune materials may be derived from a different type of air aerosol photochemical product than are the bright materials. In our model, both the bright aerosol and dark hydrocarbon dune deposits mantle the VIMS dark blue water ice-rich substrate. We postulate that the bright mantles are effectively invisible (transparent) in RADAR synthetic aperture radar (SAR) images leading to lack of correlation in the RADAR images with optically bright mantling units. RADAR images mostly show only dark dunes and the water ice substrate that varies in roughness, fracturing, and porosity. If the rate of deposition of bright aerosol is 0.001-0.01 μm/yr, the surface would be coated (to optical instruments) in hundreds-to-thousands of years unless cleansing processes are active. The dark dunes must be mobile on this very short timescale to prevent the accumulation of bright coatings. Huygens landed in a region of the VIMS bright and dark blue materials and about 30 km south of the nearest occurrence of dunes visible in the RADAR SAR images. Fluvial/pluvial processes, every few centuries or millennia, must be cleansing the dark floors of the incised channels and scouring the dark plains at the Huygens landing site both imaged by Descent Imager/Spectral Radiometer (DISR). © 2007 Elsevier Ltd. All rights reserved.
• Baines, K. H., Drossart, P., Lopez-Valverde, M. A., Atreya, S. K., Sotin, C., Momary, T. W., Brown, R. H., Buratti, B. J., Clark, R. N., & Nicholson, P. D. (2006). On the discovery of CO nighttime emissions on Titan by Cassini/VIMS: Derived stratospheric abundances and geological implications. Planetary and Space Science, 54(15), 1552-1562.
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  Abstract: We present a quantitative analysis of CO thermal emissions discovered on the nightside of Titan by Baines et al. [2005. The atmospheres of Saturn and Titan in the near-infrared: First results of Cassini/VIMS. Earth, Moon, and Planets, 96, 119-147]. in Cassini/VIMS spectral imagery. We identify these emission features as the P and R branches of the 1-0 vibrational band of carbon monoxide (CO) near 4.65 μm. For CH3D, the prominent Q branch of the ν2 fundamental band of CH3D near 4.55 μm is apparent. CO2 emissions from the strong v3 vibrational band are virtually absent, indicating a CO2 abundance several orders of magnitude less than CO, in agreement with previous investigations. Analysis of CO emission spectra obtained over a variety of altitudes on Titan's nightside limb indicates that the stratospheric abundance of CO is 32±15 ppm, and together with other recent determinations, suggests a vertical distribution of CO nearly constant at this value from the surface throughout the troposphere to at least the stratopause near 300 km altitude. The corresponding total atmospheric content of CO in Titan is ∼2.9±1.5×1014 kg. Given the long lifetime of CO in the oxygen-poor Titan atmosphere (∼0.5-1.0 Gyr), we find a mean CO atmospheric production rate of 6±3×105 kg yr-1. Given the lack of primordial heavy noble gases observed by Huygens [Niemann et al., 2005. The abundances of constituents of Titan's atmosphere from the GCMS on the Huygens probe. Nature, 438, 779-784], the primary source of atmospheric CO is likely surface emissions. The implied CO/CH4 mixing ratio of near-surface material is 1.8±0.9×10-4, based on an average methane surface emission rate over the past 0.5 Gyr of 1.3×10-13 gm cm-2 s-1 as required to balance hydrocarbon haze production via methane photolysis [Wilson and Atreya, 2004. Current state of modeling the photochemistry of Titan's mutually dependent atmosphere and ionosphere. J. Geophys. Res. 109, E06002 Doi:10.1029/2003JE002181]. This low CO/CH4 ratio is much lower than expected for the sub-nebular formation region of Titan and supports the hypothesis [e.g., Atreya et al., 2005. Methane on Titan: photochemical-meteorological-hydrogeochemical cycle. Bull. Am. Astron. Soc. 37, 735] that the conversion of primordial CO and other carbon-bearing materials into CH4-enriched clathrate-hydrates occurs within the deep interior of Titan via the release of hydrogen through the serpentinization process followed by Fischer-Tropsch catalysis. The time-averaged predicted emission rate of methane-rich surface materials is ∼0.02 km3 yr-1, a value significantly lower than the rate of silicate lava production for the Earth and Venus, but nonetheless indicative of significant active geological processes reshaping the surface of Titan. © 2006 Elsevier Ltd. All rights reserved.
• Baines, K. H., Momary, T. W., Buratti, B. J., Matson, D. L., Nelson, R. M., Drossart, P., Sicardy, B., Formisano, V., Bellucci, G., Coradini, A., Griffith, C., Brown, R. H., Bibring, J. P., Langevin, Y., Capaccioni, F., Cerroni, P., Clark, R. N., Combes, M., Cruikshank, D. P., , Jaumann, R., et al. (2006). The atmospheres of Saturn and Titan in the near-infrared: First results of Cassini/Vims. Earth, Moon and Planets, 96(3-4), 119-147.
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  Abstract: The wide spectral coverage and extensive spatial, temporal, and phase-angle mapping capabilities of the Visual Infrared Mapping Spectrometer (VIMS) onboard the Cassini-Huygens Orbiter are producing fundamental new insights into the nature of the atmospheres of Saturn and Titan. For both bodies, VIMS maps over time and solar phase angles provide information for a multitude of atmospheric constituents and aerosol layers, providing new insights into atmospheric structure and dynamical and chemical processes. For Saturn, salient early results include evidence for phosphine depletion in relatively dark and less cloudy belts at temperate and mid-latitudes compared to the relatively bright and cloudier Equatorial Region, consistent with traditional theories of belts being regions of relative downwelling. Additional Saturn results include (1) the mapping of enhanced trace gas absorptions at the south pole, and (2) the first high phase-angle, high-spatial-resolution imagery of CH4 fluorescence. An additional fundamental new result is the first nighttime near-infrared mapping of Saturn, clearly showing discrete meteorological features relatively deep in the atmosphere beneath the planet's sunlit haze and cloud layers, thus revealing a new dynamical regime at depth where vertical dynamics is relatively more important than zonal dynamics in determining cloud morphology. Zonal wind measurements at deeper levels than previously available are achieved by tracking these features over multiple days, thereby providing measurements of zonal wind shears within Saturn's troposphere when compared to cloudtop movements measured in reflected sunlight. For Titan, initial results include (1) the first detection and mapping of thermal emission spectra of CO, CO2, and CH3D on Titan's nightside limb, (2) the mapping of CH4 fluorescence over the dayside bright limb, extending to ∼ 750 km altitude, (3) wind measurements of ∼0.5 ms-1, favoring prograde, from the movement of a persistent (multiple months) south polar cloud near 88°S latitude, and (4) the imaging of two transient mid-southern-latitude cloud features. © Springer Science+Business Media, Inc. 2006.
• Barnes, J. W., Brown, R. H., Radebaugh, J., Buratti, B. J., Sotin, C., Mouelic, S. L., Rodriguez, S., Turtle, E. P., Perry, J., Clark, R., Baines, K. H., & Nicholson, P. D. (2006). Cassini observations of flow-like features in western Tui Regio, Titan. Geophysical Research Letters, 33(16).
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  Abstract: A large (>3 × 104 km2), lobate, 5-μm-bright region seen by Cassini on Titan's leading equatorial region is best explained as a flow field. We discuss observations from the Visual and Infrared Mapping Spectrometer and Imaging Science Subsystem of the feature and present a map of the field. We establish relative ages of flow features and discuss possible formation mechanisms and the implications of this finding for the evolution of Titan's surface. Copyright 2006 by the American Geophysical Union.
• Brown, R. H., Baines, K. H., Bellucci, G., Buratti, B. J., Capaccioni, F., Cerroni, P., Clark, R. N., Coradini, A., Cruikshank, D. P., Drossart, P., Formisano, V., Jaumann, R., Langevin, Y., Matson, D. L., McCord, T. B., Mennella, V., Nelson, R. M., Nicholson, P. D., Sicardy, B., , Sotin, C., et al. (2006). Observations in the Saturn system during approach and orbital insertion, with Cassini's visual and infrared mapping spectrometer (VIMS). Astronomy and Astrophysics, 446(2), 707-716.
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  Abstract: The Visual and Infrared Mapping Spectrometer observed Phoebe, Iapetus, Titan and Saturn's rings during Cassini's approach and orbital insertion. Phoebe's surface contains water ice, CO2, and ferrous iron. lapetus contains CO2 and organic materials. Titan's atmosphere shows methane fluorescence, and night-side atmospheric emission that may be CO2 and CH3D. As determined from cloud motions, the winds at altitude 25-30 km in the south polar region of Titan appear to be moving in a prograde direction at velocity ∼1 m s-1. Circular albedo features on Titan's surface, seen at 2.02 μm, may be palimpsests remaining from the rheological adjustment of ancient impact craters. As such, their long-term persistence is of special interest in view of the expected precipitation of liquids and solids from the atmosphere. Saturn's rings have changed little in their radial structure since the Voyager flybys in the early 1980s. Spectral absorption bands tentatively attributed to Fe2+ suggest that iron-bearing silicates are a source of contamination of the C ring and the Cassini Division. © ESO 2006.
• Brown, R. H., Clark, R. N., Buratti, B. J., Cruikshank, D. P., Barnes, J. W., M., R., Bauer, J., Newman, S., Momary, T., Baines, K. H., Bellucci, G., Capaccioni, F., Cerroni, P., Combes, M., Coradini, A., Drossart, P., Formisano, V., Jaumann, R., Langavin, Y., , Matson, D. L., et al. (2006). Composition and physical properties of Enceladus' surface. Science, 311(5766), 1425-1428.
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  PMID: 16527972;Abstract: Observations of Saturn's satellite Enceladus using Cassini's Visual and Infrared Mapping Spectrometer instrument were obtained during three flybys of Enceladus in 2005. Enceladus' surface is composed mostly of nearly pure water ice except near its south pole, where there are light organics, CO2, and amorphous and crystalline water ice, particularly in the region dubbed the "tiger stripes." An upper limit of 5 precipitable nanometers is derived for CO in the atmospheric column above Enceladus, and 2% for NH 3 in global surface deposits. Upper limits of 140 kelvin (for a filled pixel) are derived for the temperatures in the tiger stripes.
• Buratti, B. J., Sotin, C., Brown, R. H., Hicks, M. D., Clark, R. N., Mosher, J. A., McCord, T. B., Jaumann, R., Baines, K. H., Nicholson, P. D., Momary, T., Simonelli, D. P., & Sicardy, B. (2006). Titan: Preliminary results on surface properties and photometry from VIMS observations of the early flybys. Planetary and Space Science, 54(15), 1498-1509.
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  Abstract: Cassini observations of the surface of Titan offer unprecedented views of its surface through atmospheric windows in the 1-5 μm region. Images obtained in windows for which the haze opacity is low can be used to derive quantitative photometric parameters such as albedo and albedo distribution, and physical properties such as roughness and particle characteristics. Images from the early Titan flybys, particularly T0, Ta, and T5 have been analyzed to create albedo maps in the 2.01 and 2.73 μm windows. We find the average normal reflectance at these two wavelengths to be 0.15±0.02 and 0.035±0.003, respectively. Titan's surface is bifurcated into two albedo regimes, particularly at 2.01 μm. Analysis of these two regimes to understand the physical character of the surface was accomplished with a macroscopic roughness model. We find that the two types of surface have substantially different roughness, with the low-albedo surface exhibiting mean slope angles of ∼18°, and the high-albedo terrain having a much more substantial roughness with a mean slope angle of ∼34°. A single-scattering phase function approximated by a one-term Henyey-Greenstein equation was also fit to each unit. Titan's surface is back-scattering (g∼0.3-0.4), and does not exhibit substantially different backscattering behavior between the two terrains. Our results suggest that two distinct geophysical domains exist on Titan: a bright region cut by deep drainage channels and a relatively smooth surface. The two terrains are covered by a film or a coating of particles perhaps precipitated from the satellite's haze layer and transported by eolian processes. Our results are preliminary: more accurate values for the surface albedo and physical parameters will be derived as more data is gathered by the Cassini spacecraft and as a more complete radiative transfer model is developed from both Cassini orbiter and Huygens Lander measurements. © 2006 Elsevier Ltd. All rights reserved.
• Griffith, C. A., Penteado, P., Rannou, P., Brown, R., Boudon, V., Baines, K. H., Clark, R., Drossart, P., Buratti, B., Nicholson, P., McKay, C. P., Coustenis, A., Negrao, A., & Jaumann, R. (2006). Evidence for a polar ethane cloud on Titan. Science, 313(5793), 1620-1622.
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  PMID: 16973876;Abstract: Spectra from Cassini's Visual and Infrared Mapping Spectrometer reveal the presence of a vast tropospheric cloud on Titan at latitudes 51° to 68° north and all longitudes observed (10° to 190° west). The derived characteristics indicate that this cloud is composed of ethane and forms as a result of stratospheric subsidence and the particularly cool conditions near the moon's north pole. Preferential condensation of ethane, perhaps as ice, at Titan's poles during the winters may partially explain the lack of liquid ethane oceans on Titan's surface at middle and lower latitudes.
• Jaumann, R., Stephan, K., Brown, R. H., Buratti, B. J., Clark, R. N., McCord, T. B., Coradini, A., Capaccioni, F., Filacchione, G., Cerroni, P., Baines, K. H., Bellucci, G., Bibring, J. -., Combes, M., Cruikshank, D. P., Drossart, P., Formisano, V., Langevin, Y., Matson, D. L., , Nelson, R. M., et al. (2006). High-resolution CASSINI-VIMS mosaics of Titan and the icy Saturnian satellites. Planetary and Space Science, 54(12), 1146-1155.
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  Abstract: The Visual Infrared Mapping Spectrometer (VIMS) onboard the CASSINI spacecraft obtained new spectral data of the icy satellites of Saturn after its arrival at Saturn in June 2004. VIMS operates in a spectral range from 0.35 to 5.2 μm, generating image cubes in which each pixel represents a spectrum consisting of 352 contiguous wavebands. As an imaging spectrometer VIMS combines the characteristics of both a spectrometer and an imaging instrument. This makes it possible to analyze the spectrum of each pixel separately and to map the spectral characteristics spatially, which is important to study the relationships between spectral information and geological and geomorphologic surface features. The spatial analysis of the spectral data requires the determination of the exact geographic position of each pixel on the specific surface and that all 352 spectral elements of each pixel show the same region of the target. We developed a method to reproject each pixel geometrically and to convert the spectral data into map projected image cubes. This method can also be applied to mosaic different VIMS observations. Based on these mosaics, maps of the spectral properties for each Saturnian satellite can be derived and attributed to geographic positions as well as to geological and geomorphologic surface features. These map-projected mosaics are the basis for all further investigations. © 2006 Elsevier Ltd. All rights reserved.
• Mastrapa, R. M., & Brown, R. H. (2006). Ion irradiation of crystalline H₂O-ice: Effect on the 1.65-μm band. Icarus, 183(1), 207-214.
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  Abstract: We have found that 0.8 MeV proton irradiation of crystalline H2O-ice results in temperature dependent amorphization. The H2O-ice's phase was determined using the near infrared spectrum from 1.0 μm (10,000 cm-1) to 2.5 μm (4000 cm-1). In crystalline H2O-ice, the 1.65-μm (6061 cm-1) band is strong while it is nearly absent in the amorphous spectrum [Schmitt, B., Quirico, E., Trotta, F., Grundy, W.M., 1998. In: Schmitt, B., de Bergh, C., Festou, M. (Eds.), Solar System Ices. Kluwer Academic, Norwell, MA, 1998, pp. 199-240]. In this experiment, at low temperatures (9, 25, and 40 K), irradiation of crystalline H2O-ice produced the amorphous H2O-ice's spectrum. However, at 50 K, some crystalline absorptions persisted after irradiation and at 70 and 100 K the crystalline spectrum showed only slight changes after irradiation. Our results agree with previous H2O-ice irradiation studies examining the crystalline peaks near 44 and 62 μm by Moore and Hudson [Moore, M.H., Hudson, R.L., 1992. Astrophys. J. 401, 353-360] and near 3.07 μm by Strazzulla et al. [Strazzulla, G., Baratta, G.A., Leto, G., Foti, G., 1992. Europhys. Lett. 18, 517-522] and by Leto and Baratta [Leto, G., Baratta, G.A., 2003. Astron. Astrophys. 397, 7-13]. We present a method of measuring band areas to quantify the phase and radiation dose of icy Solar System surfaces. © 2006 Elsevier Inc. All rights reserved.
• McCord, T. B., Hansen, G. B., Buratti, B. J., Clark, R. N., Cruikshank, D. P., D'Aversa, E., Griffith, C. A., Baines, E. K., Brown, R. H., Ore, C. D., Filacchione, G., Formisano, V., Hibbitts, C. A., Jaumann, R., Lunine, J. I., Nelson, R. M., & Sotin, C. (2006). Composition of Titan's surface from Cassini VIMS. Planetary and Space Science, 54(15), 1524-1539.
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  Abstract: Titan's bulk density along with Solar System formation models indicates considerable water as well as silicates as its major constituents. This satellite's dense atmosphere of nitrogen with methane is unique. Deposits or even oceans of organic compounds have been suggested to exist on Titan's solid surface due to UV-induced photochemistry in the atmosphere. Thus, the composition of the surface is a major piece of evidence needed to determine Titan's history. However, studies of the surface are hindered by the thick, absorbing, hazy and in some places cloudy atmosphere. Ground-based telescope investigations of the integral disk of Titan attempted to observe the surface albedo in spectral windows between methane absorptions by calculating and removing the haze effects. Their results were reported to be consistent with water ice on the surface that is contaminated with a small amount of dark material, perhaps organic material like tholin. We analyze here the recent Cassini Mission's visual and infrared mapping spectrometer (VIMS) observations that resolve regions on Titan. VIMS is able to see surface features and shows that there are spectral and therefore likely compositional units. By several methods, spectral albedo estimates within methane absorption windows between 0.75 and 5 μm were obtained for different surface units using VIMS image cubes from the Cassini-Huygens Titan Ta encounter. Of the spots studied, there appears to be two compositional classes present that are associated with the lower albedo and the higher albedo materials, with some variety among the brighter regions. These were compared with spectra of several different candidate materials. Our results show that the spectrum of water ice contaminated with a darker material matches the reflectance of the lower albedo Titan regions if the spectral slope from 2.71 to 2.79 μm in the poorly understood 2.8-μm methane window is ignored. The spectra for brighter regions are not matched by the spectrum of water ice or unoxidized tholin, in pure form or in mixtures with sufficient ice or tholin present to allow the water ice or tholin spectral features to be discerned. We find that the 2.8-μm methane absorption window is complex and seems to consist of two weak subwindows at 2.7 and 2.8 μm that have unknown opacities. A ratio image at these two wavelengths reveals an anomalous region on Titan that has a reflectance unlike any material so far identified, but it is unclear how much the reflectances in these two subwindows pertain to the surface. © 2006 Elsevier Ltd. All rights reserved.
• Nelson, R. M., Brown, R. H., Hapke, B. W., Smythe, W. D., Kamp, L., Boryta, M. D., Leader, F., Baines, K. H., Bellucci, G., Bibring, J. -., Buratti, B. J., Capaccioni, F., Cerroni, P., Clark, R. N., Combes, M., Coradini, A., Cruikshank, D. P., Drossart, P., Formisano, V., , Jaumann, R., et al. (2006). Photometric properties of Titan's surface from Cassini VIMS: Relevance to titan's hemispherical albedo dichotomy and surface stability. Planetary and Space Science, 54(15), 1540-1551.
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  Abstract: The Visual and Infrared Mapping Spectrometer (VIMS) instrument on the Cassini Saturn Orbiter returned spectral imaging data as the spacecraft undertook six close encounters with Titan beginning 7 July, 2004. Three of these flybys each produced overlapping coverage of two distinct regions of Titan's surface. Twenty-four points were selected on approximately opposite hemispheres to serve as photometric controls. Six points were selected in each of four reflectance classes. On one hemisphere each control point was observed at three distinct phase angles. From the derived phase coefficients, preliminary normal reflectances were derived for each reflectance class. The normal reflectance of Titan's surface units at 2.0178 μm ranged from 0.079 to 0.185 for the most absorbing to the most reflective units assuming no contribution from absorbing haze. When a modest haze contribution of τ=0.1 is considered these numbers increase to 0.089-0.215. We find that the lowest three reflectance classes have comparable normal reflectance on either hemisphere. However, for the highest brightness class the normal reflectance is higher on the hemisphere encompassing longitude 14-65° compared to the same high brightness class for the hemisphere encompassing 122-156° longitude. We conclude that an albedo dichotomy observed in continental sized units on Titan is due not only to one unit having more areal coverage of reflective material than the other but the material on the brighter unit is intrinsically more reflective than the most reflective material on the other unit. This suggests that surface renewal processes are more widespread on Titan's more reflective units than on its less reflective units. We note that one of our photometric control points has increased in reflectance by 12% relative to the surrounding terrain from July of 2004 to April and May of 2005. Possible causes of this effect include atmospheric processes such as ground fog or orographic clouds; the suggestion of active volcanism cannot be ruled out. Several interesting circular features which resembled impact craters were identified on Titan's surface at the time of the initial Titan flyby in July of 2004. We traced photometric profiles through two of these candidate craters and attempted to fit these profiles to the photometric properties expected from model depressions. We find that the best-fit attempt to model these features as craters requires that they be unrealistically deep, approximately 70 km deep. We conclude that despite their appearance, these circular features are not craters, however, the possibility that they are palimpsests cannot be ruled out. We used two methods to test for the presence of vast expanses of liquids on Titan's surface that had been suggested to resemble oceans. Specular reflection of sunlight would be indicative of widespread liquids on the surface; we found no evidence of this. A large liquid body should also show uniformity in photometric profile; we found the profiles to be highly variable. The lack of specular reflection and the high photometric variability in the profiles across candidate oceans is inconsistent with the presence of vast expanses of flat-lying liquids on Titan's surface. While liquid accumulation may be present as small, sub-pixel-sized bodies, or in areas of the surface which still remain to be observed by VIMS, the presence of large ocean-sized accumulations of liquids can be ruled out. The Cassini orbital tour offers the opportunity for VIMS to image the same parts of Titan's surface repeatedly at many different illumination and observation geometries. This creates the possibility of understanding the properties of Titan's atmosphere and haze by iteratively adapting models to create a best fit to the surface reflectance properties. © 2006 Elsevier Ltd. All rights reserved.
• Rodriguez, S., Mouélic, S. L., Sotin, C., Clénet, H., Clark, R. N., Buratti, B., Brown, R. H., McCord, T. B., Nicholson, P. D., & Baines, K. H. (2006). Cassini/VIMS hyperspectral observations of the HUYGENS landing site on Titan. Planetary and Space Science, 54(15), 1510-1523.
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  Abstract: Titan is one of the primary scientific objectives of the NASA-ESA-ASI Cassini-Huygens mission. Scattering by haze particles in Titan's atmosphere and numerous methane absorptions dramatically veil Titan's surface in the visible range, though it can be studied more easily in some narrow infrared windows. The Visual and Infrared Mapping Spectrometer (VIMS) instrument onboard the Cassini spacecraft successfully imaged its surface in the atmospheric windows, taking hyperspectral images in the range 0.4-5.2 μm. On 26 October (TA flyby) and 13 December 2004 (TB flyby), the Cassini-Huygens mission flew over Titan at an altitude lower than 1200 km at closest approach. We report here on the analysis of VIMS images of the Huygens landing site acquired at TA and TB, with a spatial resolution ranging from 16 to14.4 km/pixel. The pure atmospheric backscattering component is corrected by using both an empirical method and a first-order theoretical model. Both approaches provide consistent results. After the removal of scattering, ratio images reveal subtle surface heterogeneities. A particularly contrasted structure appears in ratio images involving the 1.59 and 2.03 μm images north of the Huygens landing site. Although pure water ice cannot be the only component exposed at Titan's surface, this area is consistent with a local enrichment in exposed water ice and seems to be consistent with DISR/Huygens images and spectra interpretations. The images show also a morphological structure that can be interpreted as a 150 km diameter impact crater with a central peak. © 2006 Elsevier Ltd. All rights reserved.
• Tosi, F., Coradini, A., Adriani, A., Capaccioni, F., Cerroni, P., Filacchione, G., Gavrishin, A. I., & Brown, R. H. (2006). G-mode classification of spectroscopic data. Earth, Moon and Planets, 96(3-4), 165-197.
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  Abstract: We present the results of the application of the G-mode method to the spectral classification of the icy satellites of the giant planets. G-mode is a multivariate statistical technique for the classification of samples depending on many variables. Here this method is tested on the infrared spectra acquired by the Cassini/VIMS instrument onboard the Cassini spacecraft. This work demonstrates the suitability of automatic spectral classification methods for the study of fair resolution spectra, such as those from VIMS. Our data set is composed by two different kinds of data: Observations of point targets (Galilean satellites data) and observations with medium spatial resolution (Phoebe data). In both situations, the G-mode classification performed well. In the first case, of a large number of subpixel observations of the Galilean satellites, through the G-mode it was possible to find statistically meaningful spectral groups of observations. In the case of Phoebe, of some spatially resolved observations, the G-mode classification of the infrared spectra of the surface led to several types, dominated by the different illumination geometry of the pixels, because, due to the irregular shape of the satellite, a proper illumination correction was not trivial to apply. Nevertheless, the decrease of the confidence level of the test as well as the re-application of the G-mode on the main type found, led to further types, whose statistical distance can be related to different chemical abundances. We plan to use the G-mode also on the data coming from ongoing and future observations of the icy Saturnian satellites. © Springer Science+Business Media, Inc. 2006.
• Blanc, M., Moura, D., Alibert, Y., André, N., Atreya, S. K., Baraffe, I., Barthelemy, M., Barucci, A., Beebe, R., Benz, W., Bézard, B., Bockelée-Morvan, D., Bolton, S. J., Brown, R. H., Chanteur, G., Colangeli, L., Coradini, A., Doressoundiram, A., Dougherty, M., , Drossart, P., et al. (2005). Tracing the origins of the solar system. European Space Agency, (Special Publication) ESA SP, 213-224.
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  Abstract: All contemporary objects of our Solar System emerged from a solar nebula which existed 4.5 billion years ago, and whose dynamical and thermo-chemical evolution led to the condensation of solids, then to the emergence of different types of planetesimals, and finally to the accretion of solid cores and to the formation of our planets. Space exploration makes it possible today to visit the different classes of solar system objects and retrieve key information which can help us to trace back the evolutionary path of the solar system, from its origins in the Solar Nebula to its present configuration and the likely development of habitats in planetary objects. We propose three un-ordered priorities for the space programme in this perspective: 1 - access to remaining pristine material in the solar system (interplanetary dust and small bodies); 2 - in-depth exploration of the systems of giant planets; 3 - in-situ analysis of some of the physical mechanisms relevant to planetary formation in the contemporary rings and plasma environments of giant planets. This research subject, which strongly connects our solar system and its objects to exoplanets and other planetary systems, is a very promising contribution to the progressive build-up of a synthetic view of their formation and evolution scenarios. It is a central element in the build-up of a "Cosmic Vision" of our own solar system. We show how the major scientific questions related to this broad theme can be translated into specific mission targets and measurement objectives, and grouped into a "short list" of key space missions. This short list forms an ideal basis to elaborate a multi-decadal endeavour to explore the outer solar system. Most of these missions, while addressing the specific question of solar system origin, also are of major interest for comparative planetology and exo-astrobiology. While a few can be implemented in a purely European context, most of these missions can be accomplished only in the framework of a strong international collaboration. In the spirit of the successful Cassini-Huygens mission, we trust that ESA will take advantage of the Cosmic Vision programme to develop with its international partners a long-term vision of the search for solar system origins, from the Solar Nebula to the emergence of potential habitats.
• Brown, R. H., Baines, K. H., Bellucci, G., Bibring, J. -., Buratti, B. J., Capaccioni, F., Cerroni, P., Clark, R. N., Coradini, A., Cruikshank, D. P., Drossart, P., Formisano, V., Jaumann, R., Langevin, Y., Matson, D. L., Mccord, T. B., Mennella, V., Miller, E., Nelson, R. M., , Nicholson, P. D., et al. (2005). The Cassini visual and infrared mapping spectrometer (VIMS) investigation. Space Science Reviews, 115(1-4), 111-168.
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  Abstract: The Cassini visual and infrared mapping spectrometer (VIMS) investigation is a multidisciplinary study of the Saturnian system. Visual and near-infrared imaging spectroscopy and high-speed spectrophotometry are the observational techniques. The scope of the investigation includes the rings, the surfaces of the icy satellites and Titan, and the atmospheres of Saturn and Titan. In this paper, we will elucidate the major scientific and measurement goals of the investigation, the major characteristics of the Cassini VIMS instrument, the instrument calibration, and operation, and the results of the recent Cassini flybys of Venus and the Earth-Moon system. © 2004 Kluwer Academic Publishers.
• Buratti, B. J., Cruikshank, D. P., Brown, R. H., Clark, R. N., Bauer, J. M., Jaumann, R., Mccord, T. B., Simonelli, D. P., Hibbitts, C. A., Hansen, G. B., Owen, T. C., Baines, K. H., Bellucci, G., Bibring, J. -., Capaccioni, F., Cerroni, P., Coradini, A., Drossart, P., Formisano, V., , Langevin, Y., et al. (2005). Cassini Visual and Infrared Mapping Spectrometer observations of Iapetus: Detection of CO₂. Astrophysical Journal Letters, 622(2 II), L149-L152.
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  Abstract: The Visual and Infrared Mapping Spectrometer (VIMS) instrument aboard the Cassini spacecraft obtained its first spectral map of the satellite lapetus in which new absorption bands are seen in the spectra of both the low-albedo hemisphere and the H2O ice-rich hemisphere. Carbon dioxide is identified in the low-albedo material, probably as a photochemically produced molecule that is trapped in H2O ice or in some mineral or complex organic solid. Other absorption bands are unidentified. The spectrum of the low-albedo hemisphere is satisfactorily modeled with a combination of organic tholin, poly-HCN, and small amounts of H2O ice and Fe 2O3. The high-albedo hemisphere is modeled with H 2O ice slightly darkened with tholin. The detection of CO2 in the low-albedo material on the leading hemisphere supports the contention that it is carbon-bearing material from an external source that has been swept up by the satellite's orbital motion. © 2005. The American Astronomical Society. All rights reserved.
• Clark, R. N., Brown, R. H., Jaumann, R., Cruikshank, D. P., Nelson, R. M., Buratti, B. J., McCord, T. B., Lunine, J., Baines, K. H., Bellucci, G., Bibring, J. -., Capaccioni, F., Cerroni, P., Coradini, A., Formisano, V., Langevin, Y., Matson, D. L., Mennella, V., Nicholson, P. D., , Sicardy, B., et al. (2005). Compositional maps of Saturn's moon Phoebe from imaging spectroscopy. Nature, 435(7038), 66-69.
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  PMID: 15875014;Abstract: The origin of Phoebe, which is the outermost large satellite of Saturn, is of particular interest because its inclined, retrograde orbit suggests that it was gravitationally captured by Saturn, having accreted outside the region of the solar nebula in which Saturn formed. By contrast, Saturn's regular satellites (with prograde, low-inclination, circular orbits) probably accreted within the sub-nebula in which Saturn itself formed. Here we report imaging spectroscopy of Phoebe resulting from the Cassini-Huygens spacecraft encounter on 11 June 2004. We mapped ferrous-iron-bearing minerals, bound water, trapped CO2, probable phyllosilicates, organics, nitriles and cyanide compounds. Detection of these compounds on Phoebe makes it one of the most compositionally diverse objects yet observed in our Solar System. It is likely that Phoebe's surface contains primitive materials from the outer Solar System, indicating a surface of cometary origin.
• Emery, J. P., Burr, D. M., Cruikshank, D. P., Brown, R. H., & Dalton, J. B. (2005). Near-infrared (0.8-4.0 μm) spectroscopy of mimas, enceladus, tethys, and rhea. Astronomy and Astrophysics, 435(1), 353-362.
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  Abstract: Spectral measurements from the ground in the time leading up to the Cassini mission at Saturn provide important context for the interpretation of the forthcoming spacecraft data. Whereas ground-based observations cannot begin to approach the spatial scales Cassini will achieve, they do possess the benefits of better spectral resolution, a broader possible time baseline, and unique veiewing geometries not obtained by spacecraft (i.e., opposition). In this spirit, we present recent NIR reflectance spectra of four icy satellites of Saturn measured with the SpeX instrument at the IRTF. These measurements cover the range 0.8-4.0 μm of both the leading and trailing sides of Tethys and the leading side of Rhea. The L-band region (2.8-4.0 μm) offers new opportunities for searches of minor components on these objects. Additionally, these data include 0.8-2.5 μm spectra of both the leading and trailing sides of Mimas and of the (mostly) trailing side of Enceladus. The spectrum of Enceladus shows activity near 2.25 μm that we interpret as a possible signature of NH 3 ice. The presence of ammonia in the Saturn system is not unexpected, and may help explain the apparent recent geologic activity of Enceladus. Analysis of leading/trailing differences in H 2O band depths, spectral slopes, and albedo imply a separate regime of surface modification for Mimas and Enceladus than for the more distant icy satellites (Tethys, Dione, Rhea). Aside from the potential NH 3 on Enceladus, no other minor constituents are detected in these icy surfaces. © ESO 2005.
• Griffith, C. A., Penteado, P., Baines, K., Drossart, P., Barnes, J., Bellucci, G., Bibring, J., Brown, R., Buratti, B., Capaccioni, F., Cerroni, P., Clark, R., Combes, M., Coradini, A., Cruikshank, D., Formisano, V., Jaumann, R., Langevin, Y., Matson, D., , McCord, T., et al. (2005). The evolution of Titan's mid-latitude clouds. Science, 310(5747), 474-477.
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  PMID: 16239472;Abstract: Spectra from Cassini's Visual and Infrared Mapping Spectrometer reveal that the horizontal structure, height, and optical depth of Titan's clouds are highly, dynamic. Vigorous cloud centers are seen to rise from the middle to the upper troposphere within 30 minutes and dissipate within the next hour. Their development indicates that Titan's clouds evolve convectively; dissipate through rain; and, over the next several hours, waft downwind to achieve their great longitude extents. These and other characteristics suggest that temperate clouds originate from circulation-induced convergence, in addition to a forcing at the surface associated with Saturn's tides, geology, and/or surface composition.
• Sotin, C., Jaumann, R., Buratti, B. J., Brown, R. H., Clark, R. N., Soderblom, L. A., Baines, K. H., Bellucci, G., Bibring, J. -., Capaccioni, F., Cerroni, P., Combes, M., Coradini, A., Cruikshank, D. P., Drossart, P., Formisano, V., Langevin, Y., Matson, D. L., McCord, T. B., , Nelson, R. M., et al. (2005). Release of volatiles from a possible cryovolcano from near-infrared imaging of Titan. Nature, 435(7043), 786-789.
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  PMID: 15944697;Abstract: Titan is the only satellite in our Solar System with a dense atmosphere. The surface pressure is 1.5 bar (ref. 1) and, similar to the Earth, N 2 is the main component of the atmosphere. Methane is the second most important component, but it is photodissociated on a timescale of 10 years (ref. 3). This short timescale has led to the suggestion that Titan may possess a surface or subsurface reservoir of hydrocarbons to replenish the atmosphere. Here we report near-infrared images of Titan obtained on 26 October 2004 by the Cassini spacecraft. The images show that a widespread methane ocean does not exist; subtle albedo variations instead suggest topographical variations, as would be expected for a more solid (perhaps icy) surface. We also find a circular structure ∼30 km in diameter that does not resemble any features seen on other icy satellites. We propose that the structure is a dome formed by upwelling icy plumes that release methane into Titan's atmosphere.
• Bellucci, G., D'Aversa, E., Formisano, V., Cruikshank, D., Nelson, R. M., Clark, R. N., Baines, K. H., Matson, D., Brown, R. H., McCord, T. B., Buratti, B. J., & Nicholson, P. D. (2004). Cassini/VIMS observation of an Io post-eclipse brightening event. Icarus, 172(1 SPEC.ISS.), 141-148.
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  Abstract: During the Cassini-Jupiter flyby, VIMS observed Io at different phase angles, both in full sunlight and in eclipse. By using the sunlight measurements, we were able to produce phase curves in the visual through all the near infrared wavelengths covered by the VIMS instrument (0.85-5.1 μm). The phase angle spanned from ∼2° to ∼120°. The measurements, done just after Io emerged from Jupiter's shadow, show an increase of about 15% in Io's reflectance with respect to what would be predicted by the phase curve. This behavior is observed at wavelengths >1.2 μm. Moreover, just after emergence from eclipse an increase of about 25% is observed in the depth of SO2 frost bands at 4.07 and 4.35 μm. At 0.879
• Bellucci, G., Formisano, V., D'Aversa, E., Brown, R. H., Baines, K. H., Bibring, J. P., Buratti, B. J., Capaccioni, F., Cerroni, P., Clark, R. N., Coradini, A., Cruikshank, D. P., Drossart, P., Jaumann, R., Langevin, Y., Matson, D. L., McCord, T. B., Mennella, V., Nelson, R. M., , Nicholson, P. D., et al. (2004). Principal components analysis of Jupiter VIMS spectra. Advances in Space Research, 34(8), 1640-1646.
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  Abstract: During Cassini - Jupiter flyby occurred in December 2000, Visual-Infrared mapping spectrometer (VIMS) instrument took several image cubes of Jupiter at different phase angles and distances. We have analysed the spectral images acquired by the VIMS visual channel by means of a principal component analysis technique (PCA). The original data set consists of 96 spectral images in the 0.35-1.05 μm wavelength range. The product of the analysis are new PC bands, which contain all the spectral variance of the original data. These new components have been used to produce a map of Jupiter made of seven coherent spectral classes. The map confirms previously published work done on the Great Red Spot by using NIMS data. Some other new findings, presently under investigation, are presented. © 2004 Published by Elsevier Ltd on behalf of COSPAR.
• Chamberlain, M. A., & Brown, R. H. (2004). Near-infrared spectroscopy of Himalia. Icarus, 172(1 SPEC.ISS.), 163-169.
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  Abstract: We present the first spectrum through the L band of an irregular satellite from the outer Solar System. Spectra of Himalia (JVI) were obtained with the Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft. The Himalia spectrum is essentially featureless, showing a slight red slope and the suggestion of an absorption at 3 μm that might indicate the presence of water in some form. Better measurements of the spectrum of Himalia, particularly in the region of the apparent 3-μm band, could help determine whether water is present, and if so, in what form. © 2004 Elsevier Inc. All rights reserved.
• Coradini, A., Filacchione, G., Capaccioni, F., Cerroni, P., Adriani, A., Brown, R. H., Langevin, Y., & Gondet, B. (2004). CASSINI/VIMS-V at Jupiter: Radiometric calibration test and data results. Planetary and Space Science, 52(7), 661-670.
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  Abstract: During the Cassini-Huygens flyby of Jupiter in December 2000, VIMS-V acquired multispectral data cubes of Jupiter's atmosphere. The visual and infrared imaging spectrometer-visual channel (VIMS-V) is one of the principal contributions of Italian Space Agency (ASI) to the Cassini-Huygens mission to Saturn. VIMS-V is an imaging spectrometer operating in the wavelength range 300-1050 nm, with a (nominal) spectral resolution of 7.3 nm, and a (nominal) spatial resolution of 500 μrad. VIMS-V is boresighted with the VIMS-IR channel operating in the wavelength range 0.8-5.1 μm. During the early phases of the Cassini mission, the spacecraft encountered Venus (June 23, 1999), followed shortly thereafter by a flyby of the Earth. During the Earth flyby the Moon (August 17, 1999) was observed. Following the Earth-Moon flyby, the spacecraft encountered Jupiter (closest approach on December 31, 2000), and during the roughly 6 months prior to Jupiter closest approach a series of observations were made of most of the objects in the Jovian system. We have determined the instrumental transfer function of VIMS-V using the Moon and Venus day side data. This transfer function was then used to remove instrumental effects from the Jupiter data and to convert raw instrumental response numbers to spectral radiance from the target. It was thus possible to study the spectral variability of Jupiter's atmosphere across its disk using data from both the visual (V) and infrared (IR) channels of VIMS. In this paper we discuss the main results obtained by the V channel. We have analyzed the principal spectral features of Jupiter atmosphere, and in particular, the spatial variation of methane and ammonia absorption bands over the Jovian disk. Using the instrument's spatial mapping capabilities we have investigated the nature of the absorption band in the spectrum of Jupiter's atmosphere at 929 nm that is consistent with the presence of ammonia or water vapor. After comet Shoemaker-Levy 9 impacted Jupiter, water vapor was considered the most likely cause of the 929 nm absorption feature, but our data indicate that ammonia is the source of this band. Other analyses were performed using standard techniques such as forming band ratios and removal of the continuum. Our analyses confirm previous ground or satellite based observations. We were also able to verify the instrument radiometric calibration, using observations conducted during the close encounters with Venus and the Moon. © 2003 Published by Elsevier Ltd.
• Emery, J. P., & Brown, R. H. (2004). The surface composition of Trojan asteroids: Constraints set by scattering theory. Icarus, 170(1), 131-152.
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  Abstract: We present the results of spectral modeling of 17 Trojan asteroids. The surface composition of this group of objects (located just beyond the main belt, trapped in Jupiter's stable Lagrange points) remains uncertain due to an absence of diagnostic absorption features in their spectra. We quantitatively analyze spectra of these objects covering the range 0.3-4.0 μm using the formulation for scattering in a particulate medium developed by Hapke. Since the widest spectral range possible is desired to provide the most robust results, recently measured near-IR spectra are combined with previously published visible and near-IR data. These composite spectra are converted to and modeled in terms of geometric albedo to provide the additional constraint of the absolute brightness of the asteroids. It is important that this modeling is performed for a large number of objects, and results are derived based on trends among best-fit models. Under this rigorous examination, we find that it is unlikely that the red spectral slope is a result of organics on the surfaces, due mainly to the lack of absorptions in the L-band. Instead, anhydrous silicates adequately describe the spectral characteristics of this group of objects. A significant fraction of carbonaceous material is also likely present, but is not responsible for the red spectral slope in these models. Also, using these models, we estimate that these surfaces contain at most a few wt% of H2O ice and no more than 10-30 wt% of hydrated silicates. © 2004 Elsevier Inc. All rights reserved.
• McCord, T. B., Coradini, A., Hibbitts, C. A., Capaccioni, F., Hansen, G. B., Filacchione, G., Clark, R. N., Cerroni, P., Brown, R. H., Baines, K. H., Bellucci, G., Bibring, J. -., Buratti, B. J., Bussoletti, E., Combes, M., Cruikshank, D. P., Drossart, P., Formisano, V., Jaumann, R., , Langevin, Y., et al. (2004). Cassini VIMS observations of the Galilean satellites including the VIMS calibration procedure. Icarus, 172(1 SPEC.ISS.), 104-126.
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  Abstract: The Visual and Infrared Mapping Spectrometer (VIMS) observed the Galilean satellites during the Cassini spacecraft's 2000/2001 flyby of Jupiter, providing compositional and thermal information about their surfaces. The Cassini spacecraft approached the jovian system no closer than about 126 Jupiter radii, about 9 million kilometers, at a phase angle of < 90 °, resulting in only sub-pixel observations by VIMS of the Galilean satellites. Nevertheless, most of the spectral features discovered by the Near Infrared Mapping Spectrometer (NIMS) aboard the Galileo spacecraft during more than four years of observations have been identified in the VIMS data analyzed so far, including a possible 13C absorption. In addition, VIMS made observations in the visible part of the spectrum and at several new phase angles for all the Galilean satellites and the calculated phase functions are presented. In the process of analyzing these data, the VIMS radiometric and spectral calibrations were better determined in preparation for entry into the Saturn system. Treatment of these data is presented as an example of the VIMS data reduction, calibration and analysis process and a detailed explanation is given of the calibration process applied to the Jupiter data. © 2004 Elsevier Inc. All rights reserved.
• Brown, R. H., Baines, K. H., Bellucci, G., Bibring, J. -., Buratti, B. J., Capaccioni, F., Cerroni, P., Clark, R. N., Coradini, A., Cruikshank, D. P., Drossart, P., Formisano, V., Jaumann, R., Langevin, Y., Matson, D. L., McCord, T. B., Mennella, V., Nelson, R. M., Nicholson, P. D., , Sicardy, B., et al. (2003). Observations with the Visual and Infrared Mapping Spectrometer (VIMS) during Cassini's flyby of Jupiter. Icarus, 164(2), 461-470.
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  Abstract: The Cassini Visual and Infrared Mapping Spectrometer (VIMS) is an imaging spectrometer covering the wavelength range 0.3-5.2 μm in 352 spectral channels, with a nominal instantaneous field of view of 0.5 mrad. The Cassini flyby of Jupiter represented a unique opportunity to accomplish two important goals: scientific observations of the jovian system and functional tests of the VIMS instrument under conditions similar to those expected to obtain during Cassini's 4-year tour of the saturnian system. Results acquired over a complete range of visual to near-infrared wavelengths from 0.3 to 5.2 μm are presented. First detections include methane fluorescence on Jupiter, a surprisingly high opposition surge on Europa, the first visual-near-IR spectra of Himalia and Jupiter's optically-thin ring system, and the first near-infrared observations of the rings over an extensive range of phase angles (0-120°). Similarities in the center-to-limb profiles of H3+ and CH4 emissions indicate that the H3+ ionospheric density is solar-controlled outside of the auroral regions. The existence of jovian NH3 absorption at 0.93 μm is confirmed. Himalia has a slightly reddish spectrum, an apparent absorption near 3 μm, and a geometric albedo of 0.06 ± 0.01 at 2.2 μm (assuming an 85-km radius). If the 3-μm feature in Himalia's spectrum is eventually confirmed, it would be suggestive of the presence of water in some form, either free, bound, or incorporated in layer-lattice silicates. Finally, a mean ring-particle radius of 10 μm is found to be consistent with Mie-scattering models fit to VIMS near-infrared observations acquired over 0-120° phase angle. © 2003 Elsevier Inc. All rights reserved.
• Emery, J. P., & Brown, R. H. (2003). Constraints on the surface composition of Trojan asteroids from near-infrared (0.8-4.0μm) spectroscopy. Icarus, 164(1), 104-121.
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  Abstract: We present new near-infrared spectra of 20 Trojan asteroids. The spectra were recorded at the NASA Infrared Telescope Facility (IRTF) using the recently commissioned medium-resolution spectrograph SpeX and at the Multiple Mirror Telescope (MMT) using the instrument FSPEC. Spectra of all of these objects were measured in K-band (1.95-2.5 μm), 8 of these in L-band (2.8-4.0 μm), and 14 in the range 0.8-2.5 μm. These observations nearly double the number of published 0.8-2.5 μm spectra of Trojan asteroids and provide the first systematic study of the L-band region for these distant asteroids. The data show that the red spectral slope measured in the near-IR extends through the L-band, though it is not as steep here as at shorter wavelengths. A significant diversity is apparent in the near-IR spectral slopes of this sampling of objects. Most of the spectra do not contain any definitive absorption features characteristic of surface composition (e.g., H2O, organics, silicates) as seen on main-belt asteroids and several Centaur and Kuiper Belt objects. A few objects may display spectral activity, and the reliability of these possible features is discussed. While these spectra are generally compatible with silicate surfaces to explain the spectral slope mixed with some fraction of low albedo material, there is no absolute indication of silicates. The spectral slope could also be explained by the presence of hydrocarbons, but the lack of absorption features, especially in L-band where very strong fundamental absorptions from these molecules appear, constrains the character and abundance of these materials at the surface. © 2003 Elsevier Inc. All rights reserved.
• Formisano, V., D'Aversa, E., Bellucci, G., Baines, K. H., Bibring, J. P., Brown, R. H., Buratti, B. J., Capaccioni, F., Cerroni, P., Clark, R. N., Coradini, A., Cruikshank, D. P., Drossart, P., Jaumann, R., Langevin, Y., Matson, D. L., McCord, T. B., Mennella, V., Nelson, R. M., , Nicholson, P. D., et al. (2003). Cassini-VIMS at Jupiter: Solar occultation measurements using Io. Icarus, 166(1), 75-84.
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  Abstract: We report unusual and somewhat unexpected observations of the jovian satellite Io, showing strong methane absorption bands. These observations were made by the Cassini VIMS experiment during the Jupiter flyby of December/January 2000/2001. The explanation is straightforward: Entering or exiting from Jupiter's shadow during an eclipse, Io is illuminated by solar light which has transited the atmosphere of Jupiter. This light, therefore becomes imprinted with the spectral signature of Jupiter's upper atmosphere, which includes strong atmospheric methane absorption bands. Intercepting solar light refracted by the jovian atmosphere, Io essentially becomes a "miffor" for solar occultation events of Jupiter. The thickness of the layer where refracted solar light is observed is so large (more than 3000 km at Io's orbit), that we can foresee a nearly continuous multi-year period of similar events at Saturn, utilizing the large and bright ring system. During Cassini's 4-year nominal mission, this probing tecnique should reveal information of Saturn's atmosphere over a large range of southern latitudes and times. © 2003 Elsevier Inc. All rights reserved.
• Rivkin, A. S., Davies, J. K., Johnson, J. R., Ellison, S. L., Trilling, D. E., Brown, R. H., & Lebofsky, L. A. (2003). Hydrogen concentrations on C-class asteroids derived from remote sensing. Meteoritics and Planetary Science, 38(9), 1383-1398.
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  Abstract: We present spectroscopic observations of 16 asteroids from 1.9-3.6 μm collected from the United Kingdom Infrared Telescope (UKIRT) from 1996-2000. Of these 16 asteroids, 11 show some evidence of a 3 μm hydrated mineral absorption feature greater than 2σ at 2.9 μm. Using relations first recognized for carbonaceous chondrite powders by Miyamoto and Zolensky (1994) and Sato et al. (1997), we have determined the hydrogen to silicon ratio for these asteroids and calculated their equivalent water contents, assuming all the hydrogen was in water. The asteroids split into 2 groups, roughly defined as equivalent water contents greater than ∼7% (8 asteroids, all with 3 μm band depths greater than ∼20%) and less than ∼3% for the remaining 8 asteroids. This latter group includes some asteroids for which a weak but statistically significant 3 μm band of non-zero depth exists. The G-class asteroids in the survey have higher water contents, consistent with CM chondrites. This strengthens the connection between CM chondrites and G asteroids that was proposed by Burbine (1998 . We find that the 0.7 μm and 3 μm band depths are correlated for the population of target objects.
• Belluci, G., Brown, R. H., Formisano, V., Baines, K. H., Bibring, J. -., Buratti, B. J., Capaccioni, F., Cerroni, P., Clark, R. N., Coradini, A., Cruikshank, D. P., Drossart, P., Jaumann, R., Langevin, Y., Matson, D. L., McCord, T. B., Mennella, V., Miller, E., Nelson, R. M., , Nicholson, P. D., et al. (2002). Cassini/VIMS observations of the moon. Advances in Space Research, 30(8), 1889-1894.
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  Abstract: In this paper, we present preliminary scientific results obtained from the analysis of VIMS (Visible and Infrared Mapping Spectrometer) lunar images and spectra. These data were obtained during the Cassini Earth flyby in August 1999. Spectral ratios have been produced in order to derive lunar mineralogical maps. Some spectra observed at the north-east lunar limb, show few unusual absorption features located at 0.357, 0.430 and 0.452 μm, the origin of which is presently unknown. © 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.
• Cruikshank, D. P., Geballe, T. R., Owen, T. C., M., C., Roush, T. L., Brown, R. H., & Lewis, J. H. (2002). Search for the 3.4-μm C-H spectral bands on low-albedo asteroids. Icarus, 156(2), 434-441.
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  Abstract: A report of the detection of the C-H hydrocarbon band complex at 3.4 μm in an asteroid spectrum, by D.P. Cruikshank and R. H. Brown (1987, Science 238, 183-184) is not confirmed by recent data of higher quality. Spectra of the same asteroid and six other low-albedo asteroids do not show this feature, which if present would indicate the presence of hydrocarbons and might link these asteroids with certain classes of carbonaceous meteorites. © 2002 Elsevier Science (USA).
• Rivkin, A. S., Brown, R. H., Trilling, D. E., III, J. B., & Plassmann, J. H. (2002). Near-infrared spectrophotometry of phobos and deimos. Icarus, 156(1), 64-75.
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  Abstract: We have observed the leading and trailing hemispheres of Phobos from 1.65 to 3.5 μm and Deimos from 1.65 to 3.12 μm near opposition. We find the trailing hemisphere of Phobos to be brighter than its leading hemisphere by 0.24 ± 0.06 magnitude at 1.65 μm and brighter than Deimos by 0.98 ± 0.07 magnitude at 1.65 μm. We see no difference larger than observational uncertainties in spectral slope between the leading and trailing hemispheres when the spectra are normalized to 1.65 μm. We find no 3-μm absorption feature due to hydrated minerals on either hemisphere to a level of ∼5-10% on Phobos and ∼20% on Deimos. When the infrared data are joined to visible and near-IR data obtained by previous workers, our data suggest the leading (Stickney-dominated) side of Phobos is best matched by T-class asteroids. The spectral slope of the trailing side of Phobos and leading side of Deimos are bracketed by the D-class asteroids. The best laboratory spectral matches to these parts of Phobos are mature lunar soils and heated carbonaceous chondrites. The lack of 3-μm absorption features on either side of Phobos argues against the presence of a large interior reservoir of water ice according to current models of Phobos' interior (F. P. Fanale and J. R. Salvail 1989, Geophys. Res. Lett. 16, 287-290; Icarus 88, 380-395). © 2002 Elsevier Science (USA).
• Dumas, C., Terrile, R. J., Brown, R. H., Schneider, G., & Smith, B. A. (2001). Hubble Space Telescope NICMOS spectroscopy of Charon's leading and trailing hemispheres. Astronomical Journal, 121(2), 1163-1170.
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  Abstract: We used the near-infrared camera and multiobject spectrometer NICMOS on the Hubble Space Telescope to obtain 1.1-2.4 μm, low-resolution (R ∼ 200) slitless grism spectrophotometry of the individual members of the Pluto-Charon system. Water ice is present in its crystalline state on both the leading and trailing hemispheres of Charon. A 2.21 μm absorption band, possibly due to the presence of ammonia hydrate in surface, is detected in the reflectance spectrum of its leading side only. Geological activity on Charon or implantation of ions escaped from Pluto's atmosphere could account for the formation of species such as NH3 · H2O locally on the satellite. We also measured a slightly higher geometric albedo for Charon than reported from the mid-1980s observations of the mutual events.
• Trilling, D. E., Koerner, D. W., Barnes, J. W., Ftaclas, C., & Brown, R. H. (2001). Near-infrared coronagraphic imaging of the circumstellar disk around TW hydrae. Astrophysical Journal Letters, 552(2 PART 2), L147-L154.
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  Abstract: We present ground-based near-infrared (H-band) imaging of the circumstellar disk around the nearby classical T Tauri star TW Hydrae. The scattered-light image shows a face-on disk with a radius of 4″ (corresponding to 225 AU) and a morphology that agrees with recent images from the Hubble Space Telescope and the Very Large Array. The best-fit power-law for the disk's radial surface brightness profile obeys the law r-3.3±03. We use our image and published continuum flux densities to derive properties of the disk with a simple model of emission from a flat disk. The best-fit values for disk mass and inner radius are 0.03 M⊙ and 0.3 AU, respectively; the best-fit values for the temperature, density, and grain opacity power-law exponents (q, p, and β) are 0.7, 1.3, and 0.9, respectively. These properties are similar to those of disks around classical T Tauri stars located in more distant molecular clouds. Because of TW Hydrae's nearby location and pole-on orientation, it is a uniquely favorable object for future studies of radial disk structure at the classical T Tauri stage.
• Baines, K. H., Bellucci, G., Bibring, J., Brown, R. H., Buratti, B. J., Bussoletti, E., Capaccioni, F., Cerroni, P., Clark, R. N., Coradini, A., Cruikshank, D. P., Drossart, P., Formisano, V., Jaumann, R., Langevin, Y., Matson, D. L., McCord, T. B., Mennella, V., Nelson, R. M., , Nicholson, P. D., et al. (2000). Detection of Sub-Micron Radiation from the Surface of Venus by Cassini/VIMS. Icarus, 148(1), 307-311.
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  Abstract: We report the first detection and profile characterization of thermal emission from the surface of Venus at 0.85 and 0.90 μm, observed in the first planetary spectrum acquired by the Visual-Infrared Mapping Spectrometer onboard the Cassini spacecraft en route to the Saturn system. The strength and shape of these two newly observed nightside emissions agree with theoretical predictions based on the strength of the strong emission observed at 1.01 μm. These emissions, together with previously-reported surface emission features at 1.01, 1.10, and 1.18 μm, potentially provide a new technique for remotely mapping the mineralogical composition of the venusian surface. © 2000 Academic Press.
• Girard, T. M., Wu, H., Lee, J. T., Dyson, S. E., Altena, W. V., Horch, E. P., Gilliland, R. L., Schaefer, K. G., Bond, H. E., Ftaclas, C., Brown, R. H., Toomey, D. W., Shipman, H. L., Provencal, J. L., & Pourbaix, D. (2000). A redetermination of the mass of procyon. Astronomical Journal, 119(5), 2428-2436.
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  Abstract: The parallax and astrometric orbit of Procyon have been redetermined from PDS measurements of over 250 photographic plates spanning 83 years, with roughly 600 exposures used in the solution. These data are combined with two modern measurements of the primary-white dwarf separation, one utilizing a ground-based coronagraph, the other, the Planetary Camera (PC) of the Hubble Space Telescope. Together with the redetermined astrometric orbit and parallax, these yield new estimates of the component masses. The derived masses are 1.497 ± 0.037 M⊙ for the primary and 0.602 ± 0.015M⊙ for the white dwarf secondary. These mass values are heavily weighted by the PC separation measurement, which, while being somewhat discordant with the ground-based measures, we argue is more precise and more accurate and thus deserving of its greater weight. This stated, the long-standing discrepancy between previous determinations of the observed mass of Procyon A (1.75 M⊙) and the value supported by stellar evolution models (1.50 M⊙) appears to be reconciled.
• Trilling, D. E., & Brown, R. H. (2000). Red, Gray, and Blue: Near Infrared Spectrophotometry of Faint Moons of Uranus and Neptune. Icarus, 148(1), 301-306.
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  Abstract: Using the CoCo Cold Coronagraph at NASA's Infrared Telescope Facility on Mauna Kea, we observed the uranian satellites Miranda, Puck, Portia, and Rosalind and the neptunian satellite Proteus in the near infrared (JHK) to determine the albedos of those faint satellites. In V-J, all of Puck, Portia, Rosalind, and Proteus are very blue, similar to the colors of many icy satellites and of water ice. The satellites we observed have a wide range of J-H colors, with Miranda being blue, Proteus being gray, and Puck, Portia, and Rosalind being red. For the satellites for which we could determine H-K (Miranda, Puck, and Proteus), the colors are gray to red. As a whole, spectrally, these five satellites lie between icy Solar System satellites (e.g., saturnian satellites or the major uranian satellites) and Kuiper belt objects. The redness of Proteus and Puck and perhaps other satellites suggests the presence of organic material, although the redness is also similar to that of C- and D-class asteroids and some outer jovian moons. In all cases, diagnostic spectral features could be masked by broadband photometry. © 2000 Academic Press.
• Trilling, D. E., Brown, R. H., & Rivkin, A. S. (2000). Circumstellar dust disks around stars with known planetary companions. Astrophysical Journal Letters, 529(1 PART 1), 499-505.
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  Abstract: We have searched six stars with known radial velocity planetary companions for circumstellar disks. Disks are expected around stars with planetary systems that accreted from regular protoplanetary disks, and remnant disks are expected to be similar to our solar system's Kuiper Belt. To date, we have detected circumstellar disks around three such stars: 55 Cnc, ρ CrB, and HD 210277. All these systems now resemble mature planetary systems with Jupiter-mass companions and Kuiper Belt-like disks. Our previous detection of the 55 Cnc disk (Trilling & Brown) is included here to place that disk in the context of the other two newly detected disks. Measuring the inclinations of the disks and assuming the disks are coplanar with the planets' orbits determines the masses of the planets around these three stars to be 1.9+1.1-0.4 MJ, 1.5+0.2-0.1 MJ, and 2.2+0.6-0.2 MJ, respectively (1 MJ is one Jupiter mass). We also report nondetections for three stars - 51 Peg, υ And, and G1876 - that are known to have radial velocity companions. A number of possibilities exist to explain nondetections of disks, from the absence of a disk to limits on disk mass, radial extent, or inclination. We may also be looking through a disk's central hole, especially for the nearby star G1876. The radial brightness profiles of each of the observed disks follow a power law with index ∼-5, including a power of -2 from the stellar flux drop off, similar to the suggested value for our solar system's Kuiper Belt. This likely suggests that uniform physical processes govern the Kuiper Belt's population out to at least 100 AU, and may be ubiquitous among disks. Last, we discuss how disk characterizations can lead us toward refining theories of planetary system formation.
• Brown, R. H., Cruikshank, D. P., & Pendleton, Y. (1999). Water ice on Kuiper Belt object 1996 TO₆₆. Astrophysical Journal Letters, 519(1 PART 2), L101-L104.
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  Abstract: The 1.40-2.45 μm spectrum of Kuiper Belt object 1996 TO66 was measured at the Keck Observatory in 1998 September. Its spectrum shows the strong absorptions near 1.5 and 2.0 μm that are characteristic of water ice - the first such detection on a Kuiper Belt object. The depth of the absorption bands and the continuum reflectance of 1996 TO66 suggest the presence of a black- to slightly blue-colored, spectrally featureless particulate material as a minority component mixed with the water ice. In addition, there is evidence that the intensity of the water bands in the spectrum of 1996 TO66 varies with rotational phase, suggesting a "patchy" surface.
• Brown, R. H., Cruikshank, D. P., Pendleton, Y., & Veeder, G. J. (1999). Water Ice on Nereid. Icarus, 139(2), 374-378.
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  Abstract: A near-infrared spectrum of Neptune's satellite Nereid was obtained at the Keck Observatory on 1997 May 1. The spectrum shows two absorptions near 1.54 and 2.03 μm and is well matched by a synthetic spectrum of an intimate mix of low-temperature, particulate water ice and dark, blue-colored material. Comparisons of Nereid's spectrum with those of other objects such as the Centaurs 1997 CU26 and 5145 Pholus, and Neptune's largest regular satellite Proteus, admit the possibility that Nereid is a primordial satellite of Neptune (and perhaps its only remaining one) rather than a captured object, but more data are needed to rule out one scenario or the other. © 1999 Academic Press.
• Leggett, S. K., Toomey, D. W., Geballe, T. R., & Brown, R. H. (1999). Revised fluxes for Gliese 229B. Astrophysical Journal Letters, 517(2 PART 2), L139-L142.
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  Abstract: We have used the coronagraphic instrument CoCo with the Infrared Telescope Facility's camera, NSFCAM, to obtain improved photometry at JHKL' of the giant planet/brown dwarf Gliese 229B. We have recalibrated the published spectra for this object and recalculated its luminosity. Our L' value and our flux calibration of the spectra at JHK are significantly different from those previously published. Our results show good agreement at all bands except H with evolutionary models by Burrows et al. which include grain condensation. The model comparison implies that Gliese 229B is likely to be a 0.5 Gyr old 25M, object with Teff ∼ 900 K.
• Brown, R. H., Cruikshank, D. P., Pendleton, Y., & Veeder, G. J. (1998). Identification of water ice on the Centaur 1997 CU26. Science, 280(5368), 1430-1432.
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  PMID: 9603731;Abstract: Spectra of the Centaur 1997 CU26 were obtained at the Keck Observatory on 27 October 1997 (universal time). The data show strong absorptions at 1.52 and 2.03 micrometers attributable to water ice on the surface of 1997 CU26. The reflectance Spectrum of 1997 CU26 is matched by the spectrum of a mixture of low-temperature, particulate water ice and spectrally featureless but otherwise red-colored material. Water ice dominates the spectrum of 1997 CU26, whereas methane or methane-like hydrocarbons apparently dominate the spectrum of the Kuiper belt object 1993 SC, perhaps indicating different origins, thermal histories, or both for these two objects.
• Cruikshank, D. P., Roush, T. L., Bartholomew, M. J., Geballe, T. R., Pendleton, Y. J., White, S. M., III, J. B., Davies, J. K., Owen, T. C., Bergh, C. D., Tholen, D. J., Bernstein, M. P., Brown, R. H., Tryka, K. A., & Ore, C. D. (1998). The Composition of Centaur 5145 Pholus. Icarus, 135(2), 389-407.
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  Abstract: We present a new spectrum of the Centaur object 5145 Pholus between 1.15 and 2.4 μm. We model this, and the previously published (0.4- to 1.0-μm) spectrum, using Hapke scattering theory. Seen in absorption are the 2.04-μm band of H2O ice and a strong band at 2.27 μm, interpreted as frozen methanol and/or a photolytic product of methanol having small molecular weight. The presence of small molecules is indicative of a chemically primitive surface, since heating and other processes remove the light hydrocarbons in favor of macromolecular carbon of the kind found in carbonaceous meteorites. The unusually red slope of Pholus' spectrum is matched by fine grains of a refractory organic solid (tholin), as found previously by M. Hoffmannet al. (1993,J. Geophys. Res.98, 7403-7407) and P. D. Wilsonet al.(1994,Icarus107, 288-303). Olivine (which we model with Fo 82) also appears to be present on Pholus. We present a five-component model for the composite spectrum of all spectroscopic and photometric data available for 5145 Pholus and conclude that this is a primitive object which has not yet been substantially processed by solar heat. The properties of Pholus are those of the nucleus of a large comet that has never been active. © 1998 Academic Press.
• Toomey, D. W., Ftaclas, C., Brown, R. H., & Trilling, D. (1998). CoCo: An experiment in infrared coronagraphy at the IRTF. Proceedings of SPIE - The International Society for Optical Engineering, 3354, 782-790.
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  Abstract: Imaging planets, brown dwarfs and disks around nearby stars is a challenging endeavor due to the required scene contrast. Success requires imaging down to m = 20-25 within arcseconds of stars that are 4th-6th magnitude. Light scattered and diffracted from a variety of sources increases the background flux in the area of interest by orders of magnitude masking the target objects. As first shown by M. B. Lyot in 1939 masks can be placed in the focal pane and pupil planes of a camera to occult the bright central source making it possible to image the faint extensions around it. CoCo is an experiment in using a coronagraphic camera, for IR observations, on a large telescope in an effort to understand how a coronagraph can help and how to properly design one of the new generation of large telescopes. Recent result with CoCo show a factor of 5-10 reduction in background levels in the area from 2-7 arcseconds from the central object. This paper will describe those result and summarize what has been learned towards building coronagraphic cameras for today's large telescopes. ©2003 Copyright SPIE - The International Society for Optical Engineering.
• Trilling, D. E., & Brown, R. H. (1998). A circumstellar dust disk around a star with a known planetary companion. Nature, 395(6704), 775-777.
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  Abstract: A planet with a minimum mass of 0.84 Jupiter masses (M(j)) has been indirectly detected in a close orbit (radius 0.11 astronomical units, period 14.65 days) around the star 55 Cancri, which is of spectral type G8 and about 3 billion years old. The detection of excess infrared emission from this system also suggests the presence of circumstellar dust. Our Solar System has a disk of dust (and larger bodies) that is roughly coplanar with the planets- the so-called Kuiper Belt. Here we report infrared coronagraphic observations of 55 Cancri in which the light from the primary star is blocked, allowing us to image a circumstellar dust disk. We find that the dust lies in a disk that extends to at least 40 AU, comparable to the expected extent for our Kuiper Belt, whereas the inferred mass of the disk is approximately ten times that estimated for our Kuiper Belt. The disk around 55 Cancri is relatively dark at a wavelength of 2.3 μm, which is consistent with absorption of light by methane ice on the dust particles. Assuming that the disk is coplanar with the planet, we determine the planet's mass to be 1.9-0.4/+1.1 Jupiter masses. All the available evidence is suggestive of a mature planetary system around 55 Cancri.
• Brown, R. H., & Cruikshank, D. P. (1997). Determination of the composition and state of icy surfaces in the outer solar system. Annual Review of Earth and Planetary Sciences, 25, 243-277.
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  Abstract: Telescopic data combined with data gathered by spacecraft has brought worlds as distant as Pluto and the Kuiper belt objects under increasingly close scrutiny. Of particular interest here is the progress that has been made in our understanding of the properties of the satellites of the giant planets. As such, the purpose of this chapter is to review the present understanding of the nature of icy surfaces in the outer solar system, the ongoing processes that affect the composition, distribution, and physical state of volatiles on icy surfaces, and new techniques for probing the mysteries of the origin and evolution of icy bodies in the Solar System.
• Brown, R. H., Cruikshank, D. P., Pendleton, Y., & Veeder, G. J. (1997). Surface composition of Kuiper belt object 1993SC. Science, 276(5314), 937-939.
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  PMID: 9163038;Abstract: The 1.42- to 2.40-micrometer spectrum of Kuiper belt object 1993SC was measured at the Keck Observatory in October 1996. It shows a strongly red continuum reflectance and several prominent infrared absorption features. The strongest absorptions in 1993SC's spectrum occur near 1.62, 1.79, 1.95, 2.20, and 2.32 micrometers in wavelength. Features near the same wavelengths in the spectra of Pluto and Neptune's satellite Triton are due to CH4 on their surfaces, suggesting the presence of a simple hydrocarbon ice such as CH4, C2H6, C2H4, or C2H2 on 1993SC. In addition, the red continuum reflectance of 1993SC suggests the presence of more complex hydrocarbons.
• Duxbury, N. S., & Brown, R. H. (1997). The role of an internal heat source for the eruptive plumes on Triton. Icarus, 125(1), 83-93.
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  Abstract: For the first time the role of the internal heat source, due to radioactive decay in Triton's core, is investigated with respect to geyser-like plumes. Triton is one of only three known objects in the Solar System (the other two are Earth and the jovian satellite Io) where eruptive activity has been definitely observed. A new mechanism of energy supply to the Tritonian eruptive plumes is proposed. This mechanism is based on heat transport in the solid-nitrogen polar caps due to thermal convection, in addition to conduction. The conductive-convective model shows that a 1 K increase in the N2ice subsurface temperature over the surface value is reached much closer to the surface in the region of an upwelling subsurface plume compared with a pure conductive case. This temperature rise is sufficient to double the nitrogen vapor pressure. Therefore, it is enough to drive the atmospheric plumes to the observed height of ≈8 km, provided 1 K warmer nitrogen ice encounters a vent and hence is exposed to the ≈15-μbar Tritonian atmosphere. Solid-state convection onsets if a nitrogen layer is sufficiently thick and the average solid N2grain size is small enough. Critical values of these parameters are presented for Triton. A possible origin of the subsurface vents on Triton is also suggested. © 1997 Academic Press.
• Duxbury, N. S., Brown, R. H., & Anicich, V. (1997). Condensation of nitrogen: Implications for Pluto and Triton. Icarus, 129(1), 202-206.
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  Abstract: We have observed in the laboratory that nitrogen condenses initially as a transparent layer if the deposition rate is less than about 3 μm/hr. To correlate our laboratory results with the Voyager observations of Triton and ground-based observations of Pluto, we have calculated the nitrogen deposition rates on these bodies. The maximum deposition rate for Pluto (with 40K icy surface temperature) is calculated to be about 1.65 μm/hr and for Triton is ≈1.38 μm/hr at 38 K. This implies that nitrogen on these bodies may preferentially condense as a transparent layer. Voyager 2 observations in August 1989 revealed that Triton's northern hemisphere had an overall lower albedo than the southern hemisphere. This was surprising since at that time deposition of fresh N2frost should have taken place over most of Triton's northern hemisphere (subsolar point was 45°S). In contrast, the subliming southern cap was seen as a bright feature. Our new approach to this problem is based on the combination of the energy balance calculations and the laboratory results. We explain the darker northern hemisphere by the condensation of an initially transparent layer on a dark substrate, which might be dark organics produced by UV photolysis of CH4ice. The bright southern cap can be a result of N2shattering due to the earlier passage of the cubic-hexagonal phase transition fronts. If there is a similar puzzling north/south albedo asymmetry on Pluto, as indicated by two independent sets of observations (M. W. Buie, D. J. Tholen, and K. Horne, 1992,Icarus97, 211-227; E. F. Young and R. P. Binzel, 1993,Icarus102, 134-149), our results offer an explanation for it. We also infer an original grain size of N2ice on Triton and, possibly, on Pluto. The role of impurities is discussed. © 1997 Academic Press.
• Tryka, K. A., Brown, R. H., & Anicich, V. (1995). Near-Infrared Absorption Coefficients of Solid Nitrogen as a Function of Temperature. Icarus, 116(2), 409-414.
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  Abstract: We present the results of laboratory measurements characterizing the near infrared spectrum of solid nitrogen at temperatures between 35 K and 60 K. The measurements show that the appearance of the spectrum in the regions of both the fundamental vibrational transition and its first overtone is temperature dependent. The temperature dependence of the spectrum in the overtone region provides a means of determining the temperature of N2 ice on Solar System objects using groundbased spectroscopy. © 1995 Academic Press. All rights reserved.
• Brown, R. H., & Kirk, R. L. (1994). Coupling of volatile transport and internal heat flow on Triton. Journal of Geophysical Research, 99(E1), 1965-1981.
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  Abstract: Recently Brown et al. (1991) showed that Triton's internal heat source could amount to 5-20% of the absorbed insolation on Triton, thus significantly affecting volatile transport and atmospheric pressure. Subsequently, Kirk and Brown (1991a) used simple analytical models of the effect of internal heat on the distribution of volatiles on Triton's surface, confirming the speculation of Brown et al. that Triton's internal heat flow could strongly couple to the surface volatile distribution. To further explore this idea numerical models are presented of the permanent distribution of nitrogen ice on Triton that include the effects of sunlight, the two-dimensional distribution of internal heat flow, the coupling of internal heat flow to the surface distribution of nitrogen ice, and the finite viscosity of nitrogen ice. -from Authors
• Tryka, K. A., Brown, R. H., Cruikshank, D. P., Owen, T. C., Geballe, T. R., & Debergh, C. (1994). Temperature of Nitrogen Ice on Pluto and Its Implications for Flux Measurements. Icarus, 112(2), 513-527.
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  PMID: 11538596;Abstract: Previous work by K. A. Tryka et al. (Science261, 751-754, 1993) has shown that the profile of the 2.148-μm band of solid nitrogen can be used as a "thermometer" and determined the temperature of nitrogen ice on Triton to be 38+2-1. Here we reevaluate that data and refine the temperature value to 38 ± 1 K. Applying the same technique to Plato we determine that the temperature of the N2 ice on that body is 40 ± 2 K. Using this result we have created a nonisothermal flux model of the Pluto-Charon system. The model treats Pluto as a body with symmetric N2 polar caps and an equatorial region devoid of N2. Comparison with the infrared and millimeter flux measurements shows that the published fluxes are consistent with models incorporating extensive N2 polar caps (down to ±15° or ±20° latitude) and an equatorial region with a bolometric albedo ≤0.2. © 1994 Academic Press. All rights reserved.
• Cruikshank, D. P., Roush, T. L., Owen, T. C., Geballe, T. R., Bergh, C. D., Schmitt, B., Brown, R. H., & Bartholomew, M. J. (1993). Ices on the surface of Triton. Science, 261(5122), 742-745.
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  PMID: 17757211;Abstract: The near-infrared spectrum of Triton reveals ices of nitrogen, methane, carbon monoxide, and carbon dioxide, of which nitrogen is the dominant component. Carbon dioxide ice may be spatially segregated from the other more volatile ices, covering about 10 percent of Triton's surface. The absence of ices of other hydrocarbons and nitriles challenges existing models of methane and nitrogen photochemistry on Triton.
• Duxbury, N. S., & Brown, R. H. (1993). The phase composition of Triton's polar caps. Science, 261(5122), 748-751.
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  PMID: 17757213;Abstract: Triton's polar caps are modeled as permanent nitrogen deposits hundreds of meters thick. Complex temperature variations on Triton's surface induce reversible transitions between the cubic and hexagonal phases of solid nitrogen, often with two coexisting propagating transition fronts. Subsurface temperature distributions are calculated using a two-dimensional thermal model with phase changes. The phase changes fracture the upper nitrogen layer, increasing its reflectivity and thus offering an explanation for the surprisingly high southern polar cap albedo (approximately 0.8) seen during the Voyager 2 flyby. The model has other implications for the phase transition phenomena on Triton, such as a plausible mechanism for the origin of geyser-like plume vent areas and a mechanism of energy transport toward them.
• Gaffey, M. J., Bell, J. F., Brown, R., Burbine, T. H., Piatek, J. L., Reed, K. L., & Chaky, D. A. (1993). Mineralogical Variations within the S-Type Asteroid Class. Icarus, 106(2), 573-602.
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  Abstract: A systematic spectral analysis has been Carried out on a large subset (39 of 144) of the S-type asteroid population. The S-asteroid class includes a number of distinct compositional subtypes [designated S(I)-S(VII)] which exhibit surface silicate assemblages ranging from pure olivine (dunites) through olivine-pyroxene mixtures to pure pyroxene or pyroxene-feldspar mixtures (basalts). S-asteroid absorption bands are weaker than expected for pure mafic silicate assemblages, indicating the presence of an additional phase, most probably FeNi metal, although the abundance of metallic or feldspar components is not well constrained, The diversity within the S-class probably arises from several sources, including the coexistence of undifferentiated, partially differentiated, and fully differentiated bodies within the general S-asteroid population and the exposure of compositionally distinct units from within metamorphosed and partially and fully differentiated parent bodies. Partial differentiation within planetesimals appears to be an important source of this diversity. The surface assemblages of these subtypes include both analogues to known meteorite classes (e.g., pallasites, mesosiderites, ureilites, lodranites, brachinites, winonaites) and materials not sampled in our present meteorite collections. No specific ordinary chondrite parent bodies have been identified within the S-class, but silicate mineralogy provides a strong test for possible ordinary chondritic affinities. This test is failed by 75% of the S-asteroids. Only the S(IV)-subtype objects have silicates consistent with ordinary chondrites (OC). This subtype provides the only viable OC parent body candidates among the large main-belt S-asteroid population, although the individual objects remain to be evaluated. The S(IV) objects are concentrated near the 3:1 Kirkwood gap at 2.5 AU, and their ejecta can be readily injected into the associated chaotic region and rapidly converted into Earth-crossing orbits which may contribute to the high abundance of OC meteorites. S-asteroid absorption band depth correlates with asteroid diameter. It is relatively constant for objects larger than 100 km and increases steeply toward smaller sizes. This suggests that some equilibrium has been attained in the optical surfaces of S-asteroids larger than 100 km but not on smaller bodies. © 1993 Academic Press. All rights reserved.
• Owen, T. C., Roush, T. L., Cruikshank, D. P., Elliot, J. L., Young, L. A., Bergh, C. D., Schmitt, B., Geballe, T. R., Brown, R. H., & Bartholomew, M. J. (1993). Surface ices and the atmospheric composition of pluto. Science, 261(5122), 745-748.
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  PMID: 17757212;Abstract: Observations of the 1.4- to 2.4-micrometer spectrum of Pluto reveal absorptions of carbon monoxide and nitrogen ices and confirm the presence of solid methane. Frozen nitrogen is more abundant than the other two ices by a factor of about 50; gaseous nitrogen must therefore be the major atmospheric constituent. The absence of carbon dioxide absorptions is one of several differences between the spectra of Pluto and Triton in this region. Both worlds carry information about the composition of the solar nebula and the processes by which icy planetesimals formed.
• Tryka, K. A., Brown, R. H., Anicich, V., Cruikshank, D. P., & Owen, T. C. (1993). Spectroscopic determination of the phase composition and temperature of nitrogen ice on Triton. Science, 261(5122), 751-754.
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  PMID: 17757214;Abstract: Laboratory spectra of the first overtone band (2.1480 micrometers, 4655.4 reciprocal centimeters) of solid nitrogen show additional structure at 2.1618 micrometers (4625.8 reciprocal centimeters) over a limited temperature range. The spectrum of Neptune's satellite Triton shows the nitrogen overtone band as well as the temperature-sensitive component. The temperature dependence of this band may be used in conjunction with ground-based observations of Triton as an independent means of determining the temperature of surface deposits of nitrogen ice. The surface temperature of Triton is found to be 38.0-1.0+2.0 K, in agreement with previous temperature estimates and measurements. There is no spectral evidence for the presence of α-nitrogen on Triton's surface, indicating that there is less than 10 percent carbon monoxide in solid solution with the nitrogen on the surface.
• V., T., Clark, R. N., Calvin, W. M., Sherman, D. M., & Brown, R. H. (1992). Evidence for ammonium-bearing minerals on ceres. Science, 255(5051), 1551-1553.
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  PMID: 17820166;Abstract: Spectra obtained from recent telescopic observation of 1-Ceres and laboratory measurements and theoretical calculations of three component mixtures of Ceres analog material suggest that an ammoniated phyllosilicate is present on the surface of the asteroid, rather than H2O frost as had been previously reported. The presence of an ammoniated phyllosilicate, most likely ammoniated saponite, on the surface of Ceres implies that secondary temperatures could not have exceeded 400 kelvin.
• Brown, R. H. (1991). Physical properties of the Uranian satellites. Uranus, 513-527.
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  Abstract: Reviews the latest results concerning the physical properties of the satellites of Uranus. Topics covered are the sizes, shapes, topography, masses, densities and models of internal structures of the five major satellites. For the 10 small satellites discovered by Voyager 2, their sizes and shapes are discussed. The physical properties of the large satellites of Uranus are then compared to those other satellites in the outer solar system, particularly those of Jupiter and Saturn, and the implications that these comparisons have for understanding the origin and evolution of the satellites of Uranus are discussed. -from Authors
• Brown, R. H., Johnson, T. V., Goguen, J. D., Schubert, G., & Ross, M. N. (1991). Triton's global heat budget. Science, 251(5000), 1465-1467.
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  PMID: 17779439;Abstract: Internal heat flow from radioactive decay in Triton's interior along with absorbed thermal energy from Neptune total 5 to 20 percent of the insolation absorbed by Triton, thus comprising a significant fraction of Triton's surface energy balance. These additional energy inputs can raise Triton's surface temperature between ∼0.5 and 1.5 K above that possible with absorbed sunlight alone, resulting in an increase of about a factor of ∼1.5 to 2.5 in Triton's basal atmospheric pressure. If Triton's internal heat flow is concentrated in some areas, as is likely, local effects such as enhanced sublimation with subsequent modification of albedo could be quite large. Furthermore, indications of recent global albedo change on Triton suggest that Triton's surface temperature and pressure may not now be in steady state, further suggesting that atmospheric pressure on Triton was as much as ten times higher in the recent past.
• Cruikshank, D. P., Allamandola, L. J., Hartmann, W. K., Tholen, D. J., Brown, R. H., Matthews, C. N., & Bell, J. F. (1991). Solid CN bearing material on outer solar system bodies. Icarus, 94(2), 345-353.
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  PMID: 11538090;Abstract: Using telescopic observations by ourselves and other observers, we have identified cyano-group containing molecules in the very dark solids on the surfaces of a few D-class asteroids, the dust of some comets, and low-albedo hemisphere of Iapetus, and the rings of Uranus, through spectroscopic detection of the 2.2-μm overtone of the CN stretching fundamental mode. The occurrence of this band on all four classes of small Solar System bodies may be diagnostic of the duration of exposure and degree of modification of surface materials, and may also establish a link between outer Solar System and interstellar materials. © 1991.
• Cruikshank, D. P., Tholen, D. J., Hartmann, W. K., Bell, J. F., & Brown, R. H. (1991). Three basaltic earth-approaching asteroids and the source of the basaltic meteorites. Icarus, 89(1), 1-13.
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  Abstract: We report five-color photometry, near-infrared spectra (0.8-2.5 μm), and thermal observations of the Earth-approaching asteroids (3551) 1983 RD, (3908) 1980 PA, and (4055) 1985 DO2. We derive their diameters as 1.2, 1.0, and 3.4 km, respectively. Apart from greater absorption band depths, the spectra of these three small asteroids are nearly identical to that of Vesta, which is known to have a differentiated basaltic surface. The deeper pyroxene bands (0.9 and 1.9 μm) relative to Vesta are consistent with more pyroxene-rich surfaces, larger mineral grain sizes in their optically immature regoliths, more bare rock surfaces, or all of these factors. These small Earth-approaching asteroids have similar orbits, with perihelia near Earth's orbit in July August. They are probably not fragments of Vesta, but may be fragments of one or more Vesta-like parent bodies. The spectra of Vesta and the three Earth-approachers resemble those of the basaltic meteorites, i.e., eucrites, howardites, and diogenites (HED meteorites). We find that HED fall times show a weak peak in July/August, suggesting that 3551, 3908, and 4055 may be fragments of the source bodies of the HED meteorites, or perhaps of a single common HED parent body. The kilometer-size asteroids have regoliths with significant insulating properties, but these regoliths differ from that of the Moon in that the particle sizes are larger than on the Moon, and lunar-like glasses and agglutinates are largely absent. The causes of these differences are related to impact velocities, impact shaking, and debris retention on small bodies. Differentiated basalt or mantle-like asteroids may have impacted Earth and left discontinuities in the geologic/climatic record without leaving the chemical signatures associated with the KT boundary event. © 1991.
• Veverka, J., Brown, R. H., & Bell, J. F. (1991). Uranus satellites: surface properties. Uranus, 528-560.
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  Abstract: Reviews the post-Voyager knowledge of the photometric, colorimetric, spectral and thermal properties of the satellites of Uranus. The Voyager observations have made it possible to determine most of the basic photometric characteristics of the satellites and to investigate albedo/color variations on their surfaces. While albedo variations of at least a factor of 2 exist, color differences (within the limited spectral range of the Voyager cameras) are almost absent (Miranda) or subdued (Oberon). There is strong evidence that albedo patterns on the satellites are related to geology, and little if any that they are correlated with charged particle dose. On some satellites (e.g., Oberon) geologically produced albedo/color patterns have been preserved for periods in excess of several Gyr. -from Authors
• Brown, R. H., Kirk, R. L., Johnson, T. V., Soderblom, L. A., Brown, R. H., Johnson, T. V., Kirk, R. L., & Soderblom, L. A. (1990). Energy sources for triton's geyser-like plumes. Science, 250(4977), 431-435.
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  Abstract: Four geyser-like plumes were discovered near Triton's south pole in areas now in permanent sunlight. Because Triton's southern hemisphere is nearing a maximum summer solstice, insolation as a driver or a trigger for Triton's geyser-like plumes is an attractive hypothesis. Trapping of solar radiation in a translucent, low-conductivity surface layer (in a solid-state greenhouse), which is subsequently released in the form of latent heat of sublimation, could provide the required energy. Both the classical solid-state greenhouse consisting of exponentially absorbed insolation in a gray, translucent layer of solid nitrogen, and the "super" greenhouse consisting of a relatively transparent solid-nitrogen layer over an opaque, absorbing layer are plausible candidates. Geothermal heat may also play a part if assisted by the added energy input of seasonal cycles of insolation.
• Fanale, F. P., Salvail, J. R., Matson, D. L., & Brown, R. H. (1990). The effect of volume phase changes, mass transport, sunlight penetration, and densification on the thermal regime of icy regoliths. Icarus, 88(1), 193-204.
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  Abstract: A thermal model is presented which quantitatively accounts for the effects of sublimation condensation, and convection throughout a volume of a porous ice crust subjected to solar insolation. The effect of penetration of insolation into ice that is translucent to visible radiation but opaque to infrared radiation is also included. The governing energy differential equation, which also satisfies conservation of mass and accounts for the possibility of free molecular or continuum flow, is solved for various conditions defined by a reasonable range of thermal conductivities, sunlight absorption coefficients, and pore sizes. Quasi-steady-state temperatures, H2O mass fluxes, and rates of change of mass density for the ice are computed as functions of depth and time of day. We find that, when the effects of latent heat and mass transport are included in the model, the increase in the near surface temperature (the boundary condition for crustal heat flow) brought about by the "solid-state greenhouse" is greatly diminished. If the lowest thermal conductivities reported for the surface of Europa (∼100 erg/cm sec K) are assumed to apply to the upper crust as well, the melting point could be approached at very shallow depth. However, this is precluded except as a transient and shallow phenomenon which could not affect deep crustal temperatures because densification would raise the thermal conductivity to ≥1000 erg cm-1 sec-1 K in the underlying material in a geologically negligible period of time. If thermal conductivities ≥1000 erg/cm sec K are assumed, then the greenhouse effect raises near-surface temperatures ≤35 K, but the densification is slow enough that deep crustal temperatures would be augmented, allowing for melting at a depth of 7-19 km, depending on assumptions concerning tidal dissipation. Thus, when the effects of latent heat, mass transport, and densification are all taken into account, the existence of a significant solid-state greenhouse effect can be shown to be compatible both with morphological evidence for significant crustal strength and with evidence for decoupling of the icy shell from the lithosphere. © 1990.
• Hillier, J., Helfenstein, P., Verbiscer, A., Veverka, J., Brown, R. H., Goguen, J., & Johnson, T. V. (1990). Voyager disk-integrated photometry of triton. Science, 250(4977), 419-421.
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  Abstract: Hapke's photometric model has been combined with a plane-parallel thin atmospheric haze model to describe Voyager whole-disk observations of Triton, in the violet (0.41 μm), blue (0.48 μm), and green (0.56 μm) wavelength bands, in order to obtain estimates of Triton's geometric albedo, phase integral, and Bond albedo. Phase angle coverage in these filters ranging from ∼12° to 159° was obtained by combining narrow- and wide-angle camera images. An upturn in the data at the highest phase angles observed can be explained by including scattering in a thin atmospheric haze layer with optical depths systematically decreasing with wavelength from ∼0.06 in the violet to 0.03 for the green filter data. The geometric albedo, phase integral, and spherical albedo of Triton in each filter corresponding to our best fit Hapke parameters yield an estimated Bond albedo of 0.82 ± 0.05. If the 14-μbar N2 atmosphere detected by Voyager is in vapor equilibrium with the surface (therefore implying a surface temperature of 37.5 K), our Bond albedo implies a surface emissivity of 0.59 ± 0.16.
• Kirk, R. L., Brown, R. H., & Soderblom, L. A. (1990). Subsurface energy storage and transport for solar-powered geysers on triton. Science, 250(4977), 424-429.
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  Abstract: The location of active geyser-like eruptions and related features close to the current subsolar latitude on Triton suggests a solar energy source for these phenomena. Solid-state greenhouse calculations have shown that sunlight can generate substantially elevated subsurface temperatures. A variety of models for the storage of solar energy in a sub-greenhouse layer and for the supply of gas and energy to a geyser are examined. "Leaky greenhouse" models with only vertical gas transport are inconsistent with the observed upper Limit on geyser radius of ∼1.5 kilometers. However, lateral transport of energy by gas flow in a porous N2 layer with a block size on the order of a meter can supply the required amount of gas to a source region ∼1 kilometer in radius. The decline of gas output to steady state may occur over a period comparable with the inferred active geyser lifetime of five Earth years. The required subsurface permeability may be maintained by thermal fracturing of the residual N2 polar cap. A lower limit on geyser source radius of ∼50 to 100 meters predicted by a theory of negatively buoyant jets is not readily attained.
• Soderblom, L. A., Kieffer, S. W., Becker, T. L., Brown, R. H., II, A. C., Hansen, C. J., Johnson, T. V., Kirk, R. L., & Shoemaker, E. M. (1990). Triton's geyser-like plumes: Discovery and basic characterization. Science, 250(4977), 410-415.
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  Abstract: At least four active geyser-like eruptions were discovered in Voyager 2 images of Triton, Neptune's large satellite. The two best documented eruptions occur as columns of dark material rising to an altitude of about 8 kilometers where dark clouds of material are left suspended to drift downwind over 100 kilometers. The radii of the rising columns appear to be in the range of several tens of meters to a kilometer. One model for the mechanism to drive the plumes involves heating of nitrogen ice in a sub-surface greenhouse environment; nitrogen gas pressurized by the solar heating explosively vents to the surface carrying clouds of ice and dark particles into the atmosphere. A temperature increase of less than 4 kelvins above the ambient surface value of 38 ± 3 kelvins is more than adequate to drive the plumes to an 8-kilometer altitude. The mass flux in the trailing clouds is estimated to consist of up to 10 kilograms of fine dark particles per second or twice as much nitrogen ice and perhaps several hundred or more kilograms of nitrogen gas per second. Each eruption may last a year or more, during which on the order of a tenth of a cubic kilometer of ice is sublimed.
• Cruikshank, D. P., Brown, R. H., Giver, L. P., & Tokunaga, A. T. (1989). Triton: Do we see to the surface?. Science, 245(4915), 283-286.
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  Abstract: The quantity and physical state of methane and nitrogen in the atmosphere of Neptune's satellite Triton and on the surface are evaluated by means of new telescopic data and laboratory measurements of these volatiles. Methane ice is seen in some spectral regions, indicating that the atmosphere is sufficiently transparent to permit sunlight penetration to the surface. Some of the molecular nitrogen absorption occurs in the atmosphere, though some must occur in condensed nitrogen (liquid or solid) on Triton's surface, or in a thin cloud of condensed nitrogen. The Voyager spacecraft cameras should see the surface of Triton.
• Goguen, J. D., Hammel, H. B., & Brown, R. H. (1989). V photometry of Titania, Oberon, and Triton. Icarus, 77(2), 239-247.
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  Abstract: V filter photometry with the 2.2-m University of Hawaii telescope on Mauna Kea obtained during 1982-1983 is analyzed to determine the phase angle and orbital brightness variations of Titania, Oberon, and Triton. The unit distance opposition magnitudes and phase coefficients (α < 3°) are Titania, V(1,0) = 1.016 ± 0.042, β = 0.102 ± 0.021 mag/deg; Oberon, V(1,0) = 1.231 ± 0.035, β = 0.103 ± 0.018 mag/deg; Triton V(1,0) = -1.236 ± 0.041; β = 0.027 ± 0.035 mag/deg. The phase coefficients for Titania and Oberon are comparable to those observed for asteroids at similar small phase angles. Measurements made at α = 0.°06 show an ≈0.2-mag additional increase in brightness similar to that reported in the near-infrared by R. H. Brown and D. P. Cruikshank ((1983), Icarus 55, 83-92). The small phase coefficient for Triton indicates the light may not be scattered from a low-albedo, porous regolith, but suggests a high-albedo surface, a significant atmosphere, or a smooth surface, e.g., an ocean. Orbital lightcurves are less than 0.1 mag in amplitude for Titania, Oberon, and Triton. The Titania data agree well with photometry at phase angles ≥0.°8 from the Voyager 2 imaging experiment (J. Veverka, P. Thomas, P. Helfenstein, R. H. Brown, and T. V. Johnson, 1987, J. Geophys. Res. 92, 14,895-14,904). © 1989.
• Matson, D. L., & Brown, R. H. (1989). Solid-state greenhouse and their implications for icy satellites. Icarus, 77(1), 67-81.
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  Abstract: Subsurface heating by sunlight can considerably raise the temperatures of relatively translucent, high-albedo materials. We call this the solid-state greenhouse effect and apply it to the study of planetary surfaces. Of special interest to us in this paper are the frost and ice surfaces found on satellites in the outer Solar System. We compute temperatures as a function of depth for an illustrative range of thermal variables. We find that the surface regions and interiors of these bodies can be much warmer than previously expected. For example, in the case of Europa, thermal metamorphosis of the surface layer is indicated. We identify the solid-state greenhouse temperatures as the relevant temperature to use for the upper-boundary condition for the calculations of the thermal state of the interior. Several mechanisms are identified whereby modest alteration of surface properties can substantially change the greenhouse and force an adjustment of inferior temperatures. © 1989.
• Bell, J. F., Brown, R. H., & Hawke, B. (1988). Composition and size of Apollo asteroid 1984 KB. Icarus, 73(3), 482-486.
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  Abstract: Reflection spectra and thermal-emission radiometry were obtained for the Earth-crossing asteroid 1984 KB. The spectrum exhibits the spectral signatures of olivine, pyroxene, and NiFe metal; it is typical of Class S objects and suggests a surface material similar to the rare lodranite meteorites. A standard asteroid thermal model implies a radius of ∼0.7 km and an albedo of ∼0.16 (similar to Class S objects). An analysis of the same thermal data with a bare-rock thermal model gives an albedo inconsistent with the IR spectrum, suggesting that this object has a significant regolith despite its small size. © 1988.
• Brown, R. H., Cruikshank, D. P., Tokunaga, A. T., Smith, R. G., & Clark, R. N. (1988). Search for volatiles on icy satellites. I. Europa. Icarus, 74(2), 262-271.
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  Abstract: New reflectance spectra have been obtained for both the leading and trailing sides of Europa, using the Cooled Grating Array Spectrometer (CGAS) of the NASA Infrared Telescope Facility (IRTF). The spectra are of higher precision than any yet obtained. Spectra of Europa's trailing side (central meridian longitude ≈300°) obtained in 1985 show two weak absorptions near 2.2 and 2.3 μm. Both of these features as well as others are seen in spectra obtained by R. N. Clark, R. B. Singer, P. D. Owensby, and F.P. Fanale (1980a, Bull. Amer. Astron. Soc. 12, 713-714) at similar central meridian longitude. Data obtained with an improved detector array in 1986, however, do not show the absorptions seen in the 1980 and 1985 spectra. It is not clear why the newest data do not show the apparent absorptions seen in previous years, but the suggestion is that either the 1980 and 1985 data are spurious or that the material responsible for the weak absorptions is no longer detectable. Analysis of the 1980 and 1985 data did not reveal any obvious source of systematic error capable of introducing spurious features, but we are skeptical of any explanation that cites transient deposition, movement, and/or destruction of material on Europa's trailing side to account for the nondetection of the features in the 1986 data. If the weak absorptions seen in the 1980 and 1985 data are real, they can be interpreted as indicating the transient spectroscopic presence of a molecular component on Europa's trailing side different from the water ice that is known to be the dominant surface constituent. Further monitoring is required to determine if the apparent absorptions are real. © 1988.
• Cruikshank, D. P., Brown, R. H., Tokunaga, A. T., Smith, R. G., & Piscitelli, J. R. (1988). Volatiles on triton: The infrared spectral evidence, 2.0-2.5 μm. Icarus, 74(3), 413-423.
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  Abstract: We report new infraredspectra of Triton in which the methane band at 2.3 μm is shown in greater detail than in previous data. The spectral band at 2.15 μm reported by D. P. Cruikshank, R. H. Brown, and R. N. Clark (1984, Icarus 58, 293-305) is also present. Comparisons are made with methane ice spectra and with laboratory spectra of methane dissolved in liquid nitrogen. Based on these comparisons, we conclude that the 2.3-μm band in Triton's spectrum cannot be attributed entirely to methane gas; the methane also exists either in the solid state or possibly as a weak solute nitrogen. If the band is caused by methane frost, the grain size must be exceedingly small. The strength of the 2.3-μm band does not show an obvious correlation with the satellite's orbital position in the new data set, but it is notably weaker than it was in data obtained at lower spectral resolution in 1980. The new spectral data support the earlier evidence for both methane and molecular nitrogen on Triton, but the physical state of these constituents remains uncertain. © 1988.
• Goguen, J. D., Sinton, W. M., Matson, D. L., Howell, R. R., Dyck, H. M., Johnson, T. V., Brown, R. H., Veeder, G. J., Lane, A. L., Nelson, R. M., & Laren, R. M. (1988). Io hot spots: Infrared photometry of satellite occultations. Icarus, 76(3), 465-484.
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  Abstract: Infrared photometry of occultations of Io by the other Galilean satellites is used to map Io's active hot spots. Excluding a 15° wide longitude strip centered near 215°W, each point on Io's surface was occulted during at least one of seven occultations observed during the latter half of 1985. The greatest spatial resolution and sensitivity to hot spots occurs near the sub-Earth point, which always lies near the equator, and both spatial resolution and sensitivity decrease away from the sub-Earth point due to foreshortening. Most of the measurements were made with some combination of the UH 2.2 m, UKIRT, IRTF, and CFHT telescopes on Mauna Kea, Hawaii, or with the AAT in Australia, usually with one broad-bandpass infrared filter d centered at 3.8 μm (L′), 4.8 μm (M), or 8.7 μm used at each telescope. For several of the oscillations, data in more than one bandpass were acquired. A model for the occultation lightcurves is developed and fit to the data to determine the apparent path of the occulting satellite relative to Io. The astrometric results are compared to existing Galilean satellite ephemerides and are used to improve on them. The mean error in the apparent relative position of the occulting satellite is estimated to be 178 km. An occultation of Loki, Io's largest hot spot, measured at 3.8 μm wavelength, shows the region of thermal emission spatially resolved and approximately 200 km in diameter. The location of the emitting area is 308 ± 1°W longitude and 20 ± 3°N latitude, near Loki Patera and the fissure that was the source of two eruptive plumes during the Voyager encounters. A new hot spot is discovered on Io's leading hemisphere at 79 ± 5°W longitude and 22 ± 5°S latitude in the 3.8- and 4.8-μm data from 10 July UT. The region of emission is smaller than ∼20 km in diameter. © 1988.
• Johnson, T. V., Veeder, G. J., Matson, D. L., Brown, R. H., Nelson, R. M., & Morrison, D. (1988). Io: Evidence for silicate volcanism in 1986. Science, 242(4883), 1280-1283.
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  Abstract: Infrared observations of Io during the 1986 apparition of Jupiter indicate that a large eruptive event occurred on the leading side of Io on 7 August 1986, Universal Time. Measurements made at 4.8, 8.7, and 20 micrometers suggest that the source of the event was about 15 kilometers in radius with a model temperature of ∼900 Kelvin. Together with previously reported events, these measurements indicate that high-temperature volcanic activity on the leading side of Io may be more frequent than previously thought. The inferred temperature is significantly above the boiling point of sulfur in a vacuum (715 Kelvin) and thus constitutes strong evidence for active silicate volcanism on the surface of Io.
• Brown, R. H., & Matson, D. L. (1987). Thermal effects of insolation propagation into the regoliths of airless bodies. Icarus, 72(1), 84-94.
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  Abstract: We have investigated thermal models for planetary surfaces composed of particles that are bright and optically thin in the visual, and dark and opaque in the thermal infrared. The models incorporate the assumption that insolation is absorbed over a finite distance in the regolith, predicting lower daytime and higher nighttime temperatures than those predicted if the insolation were a absorbed only at the surface. The magnitude of the effect depends on the scale length for absorption of insolation relative to the diurnal skin depth for thermal diffusion, and can be significant when insolation penetrates to a depth comparable to the diurnal skin depth. In particular, for bodies like Enceladus and Europa, the maximum daytime temperature depression and nighttime temperature elevation can be 10°K or more for penetration-depth scales ∼ 1.5 cm. If insolation penetrates deeply enough into a surface, and the thermal-infrared opacity of its constituent particles is very high (e.g., in a regolith composed of particles of water ice), a solid-state greenhouse can result! This has important implications for geophysical models of high-albedo, icy bodies because actual boundary-layer temperatures may in fact be significantly higher than those assumed in previous studies, making it easier to melt the interiors of such bodies. Another important implication of the models is that where insolation- penetration is significant, thermal inertias inferred from models that do not allow for this effect will be upper limits to the real thermal inertia. © 1987.
• Cruikshank, D. P., & Brown, R. H. (1987). Organic matter on asteroid 130 Elektra. Science, 238(4824), 183-184.
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  Abstract: Infrared absorption spectra of a low-albedo water-rich asteroid appear to show a weak 3.4-micrometer carbon-hydrogen stretching mode band, which suggests the presence of hydrocarbons on asteroid 130 Elektra. The organic extract from the primitive carbonaceous chondritic Murchison meteorite shows similar spectral bands.
• Orton, G. S., Baines, K. H., Bergstralh, J. T., Brown, R. H., Caldwell, J., & Tokunaga, A. T. (1987). Infrared radiometry of Uranus and Neptune at 21 and 32 μm. Icarus, 69(2), 230-238.
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  Abstract: Radiometric measurement of Uranus and Neptune near 21 and 32 μm have been made with filters with widths of 8 and 5 μm, respectively. The observations at 21 μm, made on 1985 June 19 at the NASA Infrared telescope facility at Mauna Kea, Hawaii, were calibrated against α Boo and corresponded to brightness temperatures of 54.1 ± 0.3 K for Uranus and 58.1 ± 0.3 K for Neptune. The observations at 32 μm were made on three nights: 1983 May 1 and 1984 May 30 and 31, also at the NASA IRTF. Calibrated against the Jovian satellites Callisto (J4) and Ganymede (J3), these measurements corresponded to brightness temperatures of 51.8 ± 1.5 K for Uranus and 55.6 ± 1.2 K for Neptune. The observations are consistent with higher-resolution studies and confirm the general decrease of brightness temperatures going from about 20 to 30 μm. © 1987.
• Thomas, P., Veverka, J., Johnson, T. V., & Brown, R. H. (1987). Voyager observations of 1985U1. Icarus, 72(1), 79-83.
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  Abstract: 1985U1 is an irregularly shapedsatellite about 75 km in average radius that orbits Uranus between the ε{lunate} ring and Miranda. It is the only one of the 10 satellites of Uranus discovered by Voyager that was resolved in sufficient detail to permit determinations of the size, shape, and photometric properties. The albedo (0.07-0.09) is considerably lower than those of the large Uranian satellites and slightly higher than that of Saturn's Phoebe. The satellite's opposition magnitude should be about +20.5 in the V filter. © 1987.
• Lebofsky, L. A., Sykes, M. V., Tedesco, E. F., Veeder, G. J., Matson, D. L., Brown, R. H., Gradie, J. C., Feierberg, M. A., & Rudy, R. J. (1986). A refined "standard" thermal model for asteroids based on observations of 1 Ceres and 2 Pallas. Icarus, 68(2), 239-251.
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  Abstract: We present ground-based thermal infrared observations of asteroids 1 Ceres and 2 Pallas made over a period of 2 years. By analysing these data in light of the recently determined occultation diameter of Ceres (933-945 km) and Pallas (538 km) and their known small-amplitude lightcurves, we have determined a new value for the infrared beaming parameter used in the "standard" thermal emission model for asteroids. The new value is significantly lower than that previously used, and when applied in the reduction of thermal infrared observations of other asteroids, should yield model diameters that are closer to actual diameters. In our formulation, we also incorporate the recently adopted IAU magnitude convention for asteroids, which uses the zero-phase magnitudes (including the opposition effect) the same as is used for satellites. © 1986.
• Smith, B. A., Soderblom, L. A., Beebe, R., Bliss, D., Boyce, J. M., Brahic, A., Briggs, G. A., Brown, R. H., Collins, S. A., II, A. C., Croft, S. K., Cuzzi, J. N., Danielson, G. E., Davies, M. E., & Dowling, T. E. (1986). VOYAGER 2 IN THE URANIAN SYSTEM: IMAGING SCIENCE RESULTS.. Science, 233(4759), 43-64.
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  Abstract: Voyager 2 images of the southern hemisphere of Uranus indicate that submicrometer-size haze particles and particles of a methane condensation cloud produce faint patterns in the atmosphere. The alignment of the cloud bands is similar to that of bands on Jupiter and Saturn, but the zonal winds are nearly opposite. Nine of the newly discovered small satellites (40 to 165 kilometers in diameter) orbit between the rings and Miranda; the tenth is within the ring system. Two of these small objects may gravitationally confine the epsilon ring. Oberon and Umbriel have heavily created surfaces resembling the ancient cratered highlands of Earth's moon, although Umbriel is almost completely covered with uniform dark material, which perhaps indicates some ongoing process. Titania and Ariel show crater populations different from those on Oberon and Umbriel; these were probably generated by collisions with debris confined to their orbits.
• Brown, R. H. (1985). Ellipsoidal geometry in asteroid thermal models: The standard radiometric model. Icarus, 64(1), 53-63.
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  Abstract: This paper reports results of the incorporation of ellipsoidal geometry into the standard radiometric model for asteroids. For small departures from spherical shape the standard model using spherical geometry predicts fluxes in good agreement with ellipsoidal models. Large departures from spherical shape, however, can produce substantial differences in the calculated flux depending on the subsolar temperature and the wavelength of interest. The results derived here suggest that radiometric measurements of highly nonspherical, low-obliquity asteroids interpreted with spherical models result in systematically smaller diameter and higher albedos. In addition, non-spherical shape can also result in a systematic difference in the diameter of a particular asteroid derived from separate 10- and 20-μm flux measurements interpreted with spherical models. Thermal-infrared diurnal lightcurves calculated for ellipsoids have amplitudes that depend on wavelength as well as projected area, and phase curves calculated for ellipsoids are indistinguishable from those calculated for spheres. © 1985.
• Brown, R. H., Cruikshank, D. P., & Griep, D. (1985). Temperature of Comet IRAS-Araki-Alcock (1983d). Icarus, 62(2), 273-281.
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  Abstract: Infrared (1.5-20 μm) observations of the nuclear condensation of Comet IRAS-Araki-Alcock (1983d) during the interval 5-8 May 1983 (UT) show that the distribution of 3.5- to 20-μm radiation was blackbody in character with no evidence of 10-μm emission from silicate grains in the coma of the comet. The observed color temperature of the nuclear condensation of the comet was 319 ± 5°K on 7 May and 307 ± 5°K on 8 May. Low-resolution spectrophotometry on 5 May in the 1.5- to 2.6-μm region shows no obvious emission or absorption features, but thermal radiation of approximately the same color temperature as the 3.5- to 20-μm radiation was present along with reflected sunlight. Scans of the nuclear region of the comet indicate that most of the thermal radiation observed at 11.6 and 20.0 μm came from an ≤120-km-diameter, unresolved area centered on the nuclear region. Absolute flux measurements suggest that projected areas (unit emissivity) of 70 and 40 km2 were responsible for the thermal radiation from the nuclear condensation on 7 and 8 May, respectively. This large change in total surface area suggests that the amount of dust in the nuclear region of Comet 1983d was highly variable and is consistent with the observation by M.A. Feierberg, F.C. Witteborn, J.R. Johnson, and H. Campins (1984, Icarus, 60, 449-454) of an outburst on 11 May 1983. © 1985.
• Brown, R. H. (1984). PHYSICAL PROPERTIES OF THE URANIAN SATELLITES.. NASA Conference Publication, 437-461.
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  Abstract: Radiometric measurements have shown that Ariel, Umbriel, Titania and Oberon have diameters which range from 1630 to 1110 km and albedos which range from 0. 30 to 0. 18. Spectrophotometric observations of Miranda suggest that it may have the highest albedo of the known Uranian satellites and a diameter of about 500 km. Near-infrared measurements show that Ariel, Titania and Oberon have the largest known opposition surges. All five known satellites of Uranus have surfaces which are composed of water ice contaminated with small amounts of a dark material. Recent density determinations suggest that there may be large density differences among Ariel, Umbriel, Titania and Oberon, with density increasing with distance from Uranus.
• Brown, R. H., & Clark, R. N. (1984). Surface of Miranda: Identification of water ice. Icarus, 58(2), 288-292.
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  Abstract: Near-infrared spectrophotometry at 5% resolution shows Miranda to have a water-ice surface. Estimates of Miranda's albedo made from the depth of its 2.0-μm absorption band suggest that its visual geometric albedo is likely to be between 10 and 70%, which when combined with the satellite's visual magnitude, yields a diameter of 500 ± 225 km. There is some evidence that suggests the visual geometric albedo of Miranda may be ≥0.3, which implies that its diameter may lie near the lower end of the estimated range. With these results all the Uranian satellites are now known to have water-ice surfaces. © 1984.
• Brown, R. H., & Morrison, D. (1984). Diameters and albedos of thirty-six asteroids. Icarus, 59(1), 20-24.
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  Abstract: Radiometric diameters and albedos of 36 asteroids, most previously unmeasured by this technique, are reported. These objects were selected primarily to resolve taxonomic ambiguities resulting from the lack of albedo information. Of the sample of 36, most are of the common types C, S, and M, but also represented are types A, D, F, and P. One object, 214 Aschera, is of the rare E type (only the fourth of its kind known); 87 Sylvia is the largest known member of the P class; and albedo combined with Arizona eight-color data from Tholen (1983, Asteroid Taxonomy from Cluster Analysis of Photometry: Implications for Origin and Evolution of the Asteroid Belt. PhD dissertation, University of Arizona, Tucson) indicate that 336 Lacadiera is of type D, one of the few members of this class found in the main asteroid belt, and a prime candidate for future space missions. © 1984.
• Clark, R. N., Brown, R. H., Owensby, P. D., & Steele, A. (1984). Saturn's satellites: Nuar-infrared spectrophotometry (0.6-2.5 μm) of the leading and trailing sides and compositional implications. Icarus, 58(2), 265-281.
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  Abstract: Near-infrared spectra, 0.65-2.5 μm, are presented for Tethys, Dione, Rhea, Iapetus, and Hyperion. Water ice absorptions at 2.0, 1.5, and 1.25 μm are seen in the spectra of all five objects (except the 1.25-μm band was not detected in spectra of Hyperion) and the weak 1.04-μm ice absorption is detected on the leading and trailing sides of Rhea, and the trailing side of Dione. Upper limits to the 1.04-μm ice band depth are
• Cruikshank, D. P., Brown, R. H., & Clark, R. N. (1984). Nitrogen on Triton. Icarus, 58(2), 293-305.
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  Abstract: The near-infrared spectrum of Triton is characterized by strong absorption bands of methane, probably in the solid state. An additional absorption band at 2.16 μm is tentatively identified as the density-induced (2-0) band of molecular nitrogen in the liquid state. The fundamental overtones of this band system cannot presently be observed because of limitations of the terrestrial atmosphere or spectral signal precision. Using the absorption coefficient for this band derived from laboratory observations and from the literature, it is calculated that Triton must have a layer of nitrogen at least tens of centimeters deep over much of its surface; this quantity is plausible in terms of the cosmic abundance of nitrogen and by comparison with Titan where a massive atmosphere of nitrogen exists. The Triton spectrum has been modeled with liquid nitrogen and solid methane, and it is found that the shape of the continuum in two spectral regions can be properly accounted for by adding a spectral component corresponding to fine-grained water frost. It is speculated that yet another component, a dark, solid, photochemical derivative of methane, may occur as a trace contaminant of the surface materials. If much of the surface of Triton is liquid, the radiometric observations of the satellite must be reinterpreted to derive the radius and surface albedo. If there is liquid nitrogen exposed on the surface, the atmosphere of Triton is probably dominated by nitrogen rather than methane because of the much higher vapor pressure of the former. At the calculated subsolar temperature of Triton, the vapor pressure of nitrogen implies a surface atmospheric pressure in the range 0.13 to 0.30 atm. © 1984.
• Johnson, T. V., Morrison, D., Matson, D. L., Veeder, G. J., Brown, R. H., & Nelson, R. M. (1984). Volcanic hotspots on Io: Stability and longitudinal distribution. Science, 226(4671), 137-143.
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  Abstract: We report the first results of a program to determine the longitudinal distribution of volcanic activity on Jupiter's satellite Io. Infrared measurements at 8.7,10, and 20 micrometers have been taken at a variety of orbital longitudes: strong variation in the 8.7- and 10-micrometer flux with longitude demonstrates that infrared emission arising from volcanic hotspots on Io is strongly concentrated in a few locations. Analysis of these data suggests that the active volcanic regions observed by the Voyager experimenters are still active, particularly the region around the feature known as Loki. Another source of flux, although of somewhat smaller magnitude, is indicated on the opposite hemisphere. If these sources are the only major volcanic centers on Io, then current global heat flow estimates must be revised downward. However, heat flow from as yet unobserved longitudes, hotspots at high latitudes, and conducted heat flow must still be measured.
• Brown, R. H. (1983). The Uranian satellites and hyperion: New spectrophotometry and compositional implications. Icarus, 56(3), 414-425.
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  Abstract: New reflectance spectra at 3.5% resolution have been obtained for Ariel, Titania, Oberon, and Hyperion in the 0.8- to 1.6-μm spectral region. The new spectra show no absoptions other than the 1.5-μm water-ice feature (within the precision of the data), and demonstrate extension into the 0.8- to 1.6-μm region of the 1.5- to 2.5-μm spectral similarity of Ariel to Hyperion (R. H. Brown and D. P. Cruikshank (1983). Icarus 55,93-92). The new data confirm the presence of dark, spectrally bland component on/in the water-ice surfaces of the Uranian satellites, which, with some reservations, has spectral similarities to the dark substance on the leading side of Iapetus and the dark material on/in the surface of Hyperion, as well as other dark, spectrally neutral substances such as charcoal. Attempts were made to match the spectra of Ariel, Titania, and Oberon with additive reflectance mixes (areal coverage) of fine-grained water frost and various dark components such as charcoal, lampblack, and charcoal-water-ice mixtures. The results were broad limits on the amounts of possible areal coverage of a charcoal-like spectral component on the surfaces of the Uranian satellites, but the data are not of sufficient precision to conclusively determine whether the dominant mode of contaminant dispersal is areal or voluminal. The effect of highly variegated albedos on the diameters derived by R. H. Brown, D. P. Cruikshank, and D. Morrison (1982a) (Nature 300, 423-425) is found to be small. © 1983.
• Brown, R. H., & Cruikshank, D. P. (1983). The Uranian satellites: Surface compositions and opposition brightness surges. Icarus, 55(1), 83-92.
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  Abstract: High-precision spectrophotometry at 5% resolution has been obtained for the Uranian satellites Ariel, Umbriel, Titania, and Oberon. These spectra cover the wavelength region 1.43-2.57 μm and represent a substantial improvement in precision or wavelength coverage over previous studies. The presence of a spectrally dominant water-ice component in the surface of Ariel, Umbriel, Titania, and Oberon is confirmed. The 1.5- and 2.0-μm water absorption band depths and the continuum reflectance (as defined by the reflectance at 1.78 and 2.25 μm) indicate significant differences among the surface compositional properties of the four satellites. Comparisons of the new spectra to those of other solar system bodies, and to laboratory spectra of water ice of various degrees of purity, indicate that these satellites have a significant non-water-ice component on/in their surfaces. The lack of spectral absorptions at 5% resolution attributable to anything other than water ice suggests that the non-water-ice component is a roughly neutral reflector in the 1.5- to 2.5- μm region. The nature of the non-water-ice component cannot be uniquely determined from these data, but it is relatively dark and has spectral similarities to substances such as carbon black, the dark substance covering one face of Iapetus, or other neutral-color, low-reflectance materials. Finally, preliminary measurements of the near-infrared opposition brightness surges of Ariel, Titania, and Oberon show them to be among the largest in the solar system. © 1983.
• Cruikshank, D. P., & Brown, R. H. (1983). The nucleus of comet P/Schwassmann-Wachmann 1. Icarus, 56(3), 377-380.
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  Abstract: The thermal flux in the 20-μm Q filter band of comet P/Schwassmann-Wachmann 1 was measured some 77 days after the most recent previous eruption, and when the visual magnitude was about 17.6. Considerations of the eruptive history of the comet, and in particular its tendency to fade to a minimum threshold brightness level between eruptions, suggest that the measurement refers to an essentially bare nucleus. Using the standard photometric/radiometric technique for calculating the diameters and geometric albedos of asteroids and planetary satellites, and the assumption that the bare nucleus is measured, we find that the diameter of the nucleus is 40±5 km, and the geometric albedo is 0.13±0.04. © 1983.
• Cruikshank, D. P., Bell, J. F., Gaffey, M. J., Brown, R., Howell, R., Beerman, C., & Rognstad, M. (1983). The dark side of Iapetus. Icarus, 53(1), 90-104.
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  Abstract: This paper presents new photometric and spectrophotometric observations of the dark (leading) hemisphere of Saturn's satellite Iapetus. Spectrophotometry from 0.3-1.0 um (May 1979) shows the dark hemisphere to be very red, similar to a few asteroids and the Moon, but with no spectral features attributable to olivine or pyroxene. Near-infrared spectrophometry in the regions 1.4-2.5 um (May 1981) and 3.0-3.8 um (February 1981) reveals water ice absorption bands, probably resulting from the polar caps intruding onto the dark hemisphere. The reflectance of Iapetus is unlike that of carbonaceous chondrites or C-type asteroids and most closely resembles the reflectance (and low albedo) of carbonaceous (organic) residue from the Murchison C2 carbonaceous chondrite. The Murchison material has the same red slope and a probable spectral feature near 0.6 um seen in Iapetus data. Three hypotheses for the formation of the dark hemisphere are discussed in light of the observational data. The favored hypothesis is that debris from Phoebe or other unknown outer satellites of Saturn impacts the dark hemisphere of Iapetus as Poynting-Robertson drag causes the debris to spiral toward Saturn. The high-velocity impacts preferentially remove ice from the satellite's surface, causing enrichment of included carbonaceous material intrinsic to Iapetus. The reflectance of Phoebe itself is significantly different from that of Iapetus, suggesting that relatively little Phoebe debris lies on the dark hemisphere. There remains the possibility that the impacting debris originates from another body of composition similar to the Murchison residue and that this material is exposed on the surface of Iapetus. © 1983.
• Brown, R. H., Cruikshank, D. P., & Morrison, D. (1982). Diameters and albedos of satellites of Uranus. Nature, 300(5891), 423-425.
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  Abstract: The five known satellites of Uranus are too small and distant to permit direct measurement of their diameters. Consequently, products of the masses of the satellites, and estimates of their bulk densities and surface albedos have been used in discussions of their probable dimensions in the absence of measurements. The presence of water ice on the surfaces of Ariel, Umbriel, Titania and Oberon has been established spectrophotometrically1-4 and the brightnesses of the satellites have been measured photoelectrically 5. Determination of the masses of the uranian satellites depends on observations of perturbations of the satellite orbits and results chiefly in upper limits to the products of the masses of various pairs of satellites 6,7. The new diameter measurements reported here were made using the photometric/radiometric technique of diameter determination. This widely used technique has enabled the measurement of the diameters and albedos of approximately 250 asteroids and many planetary satellites. A recent recalibration of the technique using independent measurements of the diameters of three Solar System objects results in absolute accuracies of better than 5%. Our new albedo measurements show that Umbriel, Titania and Oberon are similar in albedo to J4 Callisto while Ariel is very similar in albedo to S7 Hyperion; the diameters of all four satellites are similar to those of the large, icy saturnian satellites S5 Rhea and S8 Iapetus. © 1982 Nature Publishing Group.
• Brown, R., Morrison, D., Telesco, C. M., & Brunk, W. E. (1982). Calibration of the radiometric asteroid scale using occultation diameters. Icarus, 52(1), 188-195.
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  Abstract: We report a new approach to the calibration of the radiometric asteroid scale using the recent accurate occultation measurements of the diameters of 2 Pallas and 3 Juno, and the Voyager diameter of J4 Callisto, and new infrared photometry of these objects obtained with the NASA 3-m Infrared Telescope Facility. This calibration is internally consistent to better than 5% and probably has an absolute accuracy of ±5%. A revision of the TRIAD radiometric diameters downward is required to bring them into agreement with the new calibration. © 1982.
• Chuikshank, D. P., & Brown, R. H. (1982). Surface composition and radius of hyperion. Icarus, 50(1), 82-87.
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  Abstract: New spectrophotometric data for Hyperion in the region 1.5-2.6 um obtained in 1981 confirm the presence of water ice bands reported by D.P. Cruikshank (1980, Icarus 41, 246-258). The bands are now shown with sufficient clarity to permit improved comparisons with other ice-bearing satellites of Jupiter and Saturn and with laboratory samples. Comparisons with Ganymede and Rhea are shown, and Hyperion is found to differ from both satellites in terms of depth and width of the water ice bands. The sense of the difference is the same as noted earlier from broadband infrared photometry, but the physical cause is not fully understood. The effective radius of Hyperion (considered circular in cross section) derived from a 20-um flux measurement and a revised value of V(1,0) = 4.62 is r = 140 ± 19 km. This result is in better accord with both preliminary and refined values of the radius derived from Voyager images; the Voyager result supercedes that deduced from infrared observations. © 1982.
• Morrison, D., Cruikshank, D. P., & Brown, R. H. (1982). Diameters of Triton and Pluto. Nature, 300(5891), 425-427.
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  Abstract: Triton, the major satellite of Neptune, and Pluto, the outermost planet, are too small and distant to permit direct measurement of their size, and indirect arguments must be used to estimate diameter and albedo. These two objects invite a comparative study because they have essentially the same brightness (absolute visual magnitude V(1, 0)≃ -1) and current distance from the Sun (30 AU). In addition, the presence of methane frost on the surface, and of a possible methane atmosphere, have been detected for both objects from IR spectroscopy1-4. On the basis of these similarities, Triton and Pluto were selected as targets for possible detection of thermal IR emission. We report here new upper limits to the thermal IR emission from these objects that permit us to set significant upper limits on their diameters and to demonstrate that both are high albedo objects. These results clearly exclude the possibility that Triton is the largest planetary satellite, and they are consistent with the small size of Pluto deduced from other data. © 1982 Nature Publishing Group.
• Brown, R., Cruikshank, D. P., & Tokunaga, A. T. (1981). The rotation period of Neptune's upper atmosphere. Icarus, 47(2), 159-165.
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  Abstract: Significant variations in the near-infrared brightness of Neptune during July and August 1980 were observed. These observations show a well-defined, large-amplitude variation in Neptune's J-K color, with a period of 17.73 ± 0.1 hr and are interpreted as diurnal variations resulting from the 17.73-hr rotation period of the upper atmosphere of Neptune in the presence of inhomogeneous weather. These results qualitatively corroborate those of D. P. Cruikshank (1978, Astrophys. J. 220, L57-L59) in an earlier study using similar techniques. In addition, variations were observed in the 5-μm spectral region which are in phase with the variations seen at shorter wavelengths. A new 5-μm measurement of Uranus is also reported. © 1981.
• Cruikshank, D. P., & Brown, R. H. (1981). The Uranian satellites: Water ice on Ariel and Umbriel. Icarus, 45(3), 607-611.
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  Abstract: New near-infrared reflectance spectra are presented for Ariel and Umbriel. Water ice on the surface of Ariel and Umbriel is verified from spectral signatures in the 2-μm region. However, the weaker bands in Umbriel's spectrum indicate that its surface is significantly different from Ariel either in degree of contamination with dark material or in microstate. Umbriel may have a lower albedo than Ariel, Titania, and Oberon and, therefore, may have a diameter comparable to that of Titania. © 1981.
• Fanale, F. P., Brown, R. H., Cruikshank, D. P., & Clake, R. N. (1979). Significance of absorption features in Io's IR reflectance spectrum. Nature, 280(5725), 761-763.
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  Abstract: Absorption features in Io's reflectance spectrum suggest that frozen SO2 molecules are present on the surface of Io as free frost; this may have important implications for Io's atmosphere. © 1979 Nature Publishing Group.
• Terrile, R. J., Capps, R. W., Backman, D. E., Becklin, E. E., Cruikshank, D. P., Beichman, C. A., Brown, R. H., & Westphal, J. A. (1979). Infrared images of Jupiter at 5-micrometer wavelength during the Voyager 1 encounter. Science, 204(4396), 1007-1008.
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  Abstract: A coordinated program to observe Jupiter at high spatial resolution in the 5-micrometer wavelength region was undertaken to support Voyager 1 imaging and infrared radiation experiment targeting. Jupiter was observed over a 5-month period from Palomar and Mauna Kea observatories. The frequency of observations allowed the selection of interesting areas for closer Voyager examination and also provided good short-term monitoring of variations in cloud morphology. Significant global changes in the 5-micrometer distribution are seen over this time period. Copyright © 1979 AAAS.

Proceedings Publications

• Baines, K., Sromovsky, L., Fry, P., Momary, T., Brown, R., Buratti, B., Clark, R., Nicholson, P., & Sotin, C. (2017, oct). Clouds and Hazes in Saturn's North Polar Vortex: New Results from Cassini/VIMS High-Spatial Resolution Spectral Imagery on the First Grand Finale Pass. In AAS/Division for Planetary Sciences Meeting Abstracts \#49, 49.
• Brossier, J., Rodriguez, S., Maltagliati, L., Cornet, T., Lucas, A., Le, M. S., Solomonidou, A., Coustenis, A., Hirtzig, M., Jaumann, R., Stephan, K., & Brown, R. (2017, mar). Equatorial Belt of Titan Revisited Using a Comprehensive Radiative Transfer Model. In Lunar and Planetary Science Conference, 48.
• Ciarniello, M., Filacchione, G., D'Aversa, E., Cuzzi, J., Capaccioni, F., Hedman, M., Dalle, O. C., Nicholson, P., Clark, R., Brown, R., Cerroni, P., & Spilker, L. (2017, oct). Spectrophotometric study of Saturn's main rings by means of Monte Carlo ray-tracing and Hapke's theory. In AAS/Division for Planetary Sciences Meeting Abstracts \#49, 49.
• Clark, R., Brown, R., Swayze, G., & Cruikshank, D. (2017, oct). Detection of Deuterium in Icy Surfaces and the D/H Ratio of Icy Objects. In AAS/Division for Planetary Sciences Meeting Abstracts \#49, 49.
• Cornet, T., Rodriguez, S., Maltagliati, L., App{\'er\'e}, T., Sotin, C., Le, M. S., Rannou, P., Solomonidou, A., Hirtzig, M., B{\'ezard}, B., Coustenis, A., Brown, R., Barnes, J., Baines, K., Buratti, B., Clark, R., & Nicholson, P. (2017, apr). A Look Toward the Surface: Radiative Transfer Modelling in Titan's Atmosphere Using Cassini/VIMS data. In EGU General Assembly Conference Abstracts, 19.
• Cornet, T., Rodriguez, S., Maltagliati, L., App{\'er\'e}, T., Sotin, C., Le, M. S., Rannou, P., Solomonidou, A., Hirtzig, M., B{\'ezard}, B., Coustenis, A., Brown, R., Barnes, J., Baines, K., Buratti, B., Clark, R., & Nicholson, P. (2017, mar). Radiative Transfer Modelling in Titan's Atmosphere: Application to Cassini/VIMS Data. In Lunar and Planetary Science Conference, 48.
• Dhingra, R., Barnes, J., Brown, R., Buratti, B., Sotin, C., Nicholson, P., Baines, K., Clark, R., Soderblom, J., Jaumann, R., Rodriguez, S., & Le Mouelic, S. (2017, mar). Transient Broad Specular Reflections from Titan's North Pole. In Lunar and Planetary Science Conference, 48.
• Filacchione, G., Capaccioni, F., Ciarniello, M., Nicholson, P., Clark, R., Cuzzi, J., Buratti, B., Cruikshank, D., & Brown, R. (2017, jan). From the Icy Satellites to Small Moons and Rings: Spectral Indicators by Cassini-VIMS Unveil Compositional Trends in the Saturnian System. In ICES IN THE SOLAR SYSTEM, ESA/ESAC Madrid, Spain, 23-27 JANUARY 2017.
• Geldzahler, B., Bershad, C., Brown, R., Cox, R., Hoblitzell, R., Kiriazes, J., Ledford, B., Miller, M., Woods, G., Cornish, T., D'Addario, L., Davarian, F., Lee, D., Morabito, D., Tsao, P., Soloff, J., Church, K., Deffenbaugh, P., Abernethy, K., , Anderson, W., et al. (2017). A Phased Array of Widely Separated Antennas for Space Communication and Planetary Radar. In Advanced Maui Optical and Space Surveillance (AMOS) Technologies Conference.
• Le, M. S., Buti, C., Tobie, G., Rodriguez, S., Sotin, C., Barnes, J., Brown, R., Baines, K., Buratti, B., Clark, R., Cornet, T., Mass{\'e}, M., Mitri, G., & Nicholson, P. (2017, mar). Mapping the Spectral Diversity of Enceladus South Pole with Cassini/VIMS Hyperspectral Images. In Lunar and Planetary Science Conference, 48.
• MacKenzie, S., Barnes, J., Rodriguez, S., Cornet, T., Brossier, J., Soderblom, J., Le, M. S., Sotin, C., Brown, R., Buratti, B., Clark, R., Nicholson, P., & Baines, K. (2017, oct). A bright intra-dune feature on Titan and its implications for sand formation and transport. In AAS/Division for Planetary Sciences Meeting Abstracts \#49, 49.
• Momary, T., Baines, K., Badman, S., Brown, R., Buratti, B., Clark, R., Nicholson, P., & Sotin, C. (2017, oct). Last Looks at the Eye of Saturn by Cassini/VIMS During the Grand Finale. In AAS/Division for Planetary Sciences Meeting Abstracts \#49, 49.
• Solomonidou, A., Coustenis, A., Lopes, R., Malaska, M., Rodriguez, S., Drossart, P., Schmitt, B., Philippe, S., Janssen, M., Le Gall, A., Lawrence, K., Hirtzig, M., Sohl, F., Stephan, K., Jaumann, R., Brown, R., Villanueva, E., Bratsolis, E., Matsoukas, C., & Schoenfeld, A. (2017, apr). The spectral nature of Titan's mid-latitude region. In EGU General Assembly Conference Abstracts, 19.
• Solomonidou, A., Coustenis, A., M.~C, L. R., Malaska, M., Rodriguez, S., Drossart, P., Elachi, C., Schmitt, B., Philippe, S., Janssen, M., Hirtzig, M., Wall, S., Lawrence, K., Altobelli, N., Bratsolis, E., Radebaugh, J., Stephan, K., Brown, R., Le, M. S., , Le Gall, A., et al. (2017, oct). Titan\rsquos mid-latitude surface region from Cassini/VIMS data: Implications on the composition. In AAS/Division for Planetary Sciences Meeting Abstracts \#49, 49.
• {Brossier}, J., {Jaumann}, R., {Stephan}, K., {Le Mou{\'e}lic}, S., , R. (2016, apr). Characterization of the Titan's VIMS - units: Using Spectral Slopes. In EGU General Assembly Conference Abstracts, 18.
• {Clark}, R., {Brown}, R., {Lytle}, D., , D. (2016, oct). Composition of Phoebe and Iapetus: Bound Water and Possible Deuterated Water. In AAS/Division for Planetary Sciences Meeting Abstracts, 48.
• {Florian Brossier}, J., {Rodriguez}, S., {Maltagliati}, L., {Le Mou{\'e}lic}, S., {Solomonidou}, A., {Coustenis}, A., {Hirtzig}, M., {Jaumann}, R., , R. (2016, oct). Equatorial belt of Titan: Aaru Region as seen by VIMS/Cassini. In AAS/Division for Planetary Sciences Meeting Abstracts, 48.
• {Hofgartner}, J., {Buratti}, B., {Brown}, R., {Barnes}, J., {Sotin}, C., , K. (2016, mar). Erosion of Titan's Craters from Cassini RADAR and VIMS Imagery. In Lunar and Planetary Science Conference, 47.
• {Le Mou{\'e}lic}, S., {Cornet}, T., {Rodriguez}, S., {Sotin}, C., {Barnes}, J., {Brown}, R., {Baines}, K., {Buratti}, B., {Clark}, R., , P. (2016, mar). Producing Seamless Global Mosaics of Titan with the VIMS Imaging Spectrometer. In Lunar and Planetary Science Conference, 47.
• {Le Mou{\'e}lic}, S., {Cornet}, T., {Rodriguez}, S., {Sotin}, C., {Barnes}, J., {Brown}, R., {Lasue}, J., {Baines}, K., {Buratti}, B., {Clark}, R., , P. (2016, oct). Global mapping of the surface of Titan through the haze with VIMS onboard Cassini. In AAS/Division for Planetary Sciences Meeting Abstracts, 48.
• {Marmuse}, F., {Sotin}, C., {Lawrence}, K., {Brown}, R., {Baines}, K., {Buratti}, B., {Clark}, R., , P. (2016, oct). Optical properties of Titan's aerosols: comparison between DISR/Huygens observations and VIMS/Cassini solar occultation observations. In AAS/Division for Planetary Sciences Meeting Abstracts, 48.
• {Momary}, T., {Baines}, K., {Badman}, S., {Brown}, R., {Buratti}, B., {Clark}, R., {Nicholson}, P., , C. (2016, oct). The Sleepy Anticyclonic Eye of the Great Storm on Saturn as seen by Cassini/VIMS. In AAS/Division for Planetary Sciences Meeting Abstracts, 48.
• {Rodriguez}, S., {Le Mou{\'e}lic}, S., {Barnes}, J., {Charnay}, B., {Kok}, J., {Lorenz}, R., {Radebaugh}, J., {Cornet}, T., {Bourgeois}, O., {Lucas}, A., {Rannou}, P., {Griffith}, C., {Coustenis}, A., {App{\'e}r{\'e}}, T., {Hirtzig}, M., {Sotin}, C., {Soderblom}, J., {Brown}, R., {Bow}, J., , G. (2016, apr). Singular climatic activity at Equinox over Titan's dunefields as seen by CASSINI. In EGU General Assembly Conference Abstracts, 18.
• {Rodriguez}, S., {Turtle}, E., {Le Mou{\'e}lic}, S., {Rannou}, P., {Sotin}, C., {Barnes}, J., {Griffith}, C., {Brown}, R., {Baines}, K., {Buratti}, B., {Clark}, R., , P. (2016, apr). Last updates on Titan's cloud cover monitoring with CASSINI. In EGU General Assembly Conference Abstracts, 18.
• {Soderblom}, J., {Barnes}, J., {Brown}, R., {Chevrier}, V., {Farnsworth}, K., , L. (2016, oct). Evidence for frozen hydrocarbons on Titan. In AAS/Division for Planetary Sciences Meeting Abstracts, 48.
• {Solomonidou}, A., {Coustenis}, A., {Drossart}, P., {Brown}, R., {Sohl}, F., {Stephan}, K., {Jaumann}, R., {Rodriguez}, S., {Bratsolis}, E., {Schmitt}, B., {Le Gall}, A., {Lopes}, R., {Malaska}, M., {Janssen}, M., {Maltagliati}, L., {Villanueva}, E., , C. (2016, jul). Titan's mid-latitude surface regions with Cassini VIMS and SAR. In 41st COSPAR Scientific Assembly, 41.
• {Solomonidou}, A., {Coustenis}, A., {Lopes}, R., {Rodriguez}, S., {Drossart}, P., {Schmitt}, B., {Philippe}, S., {Malaska}, M., {Janssen}, M., {Maltagliati}, L., {Lawrence}, K., {Jaumann}, R., {Sohl}, F., {Stephan}, K., {Brown}, R., {Bratsolis}, E., , C. (2016, apr). Constrains on the nature of Titan's surface from Cassini/VIMS and RADAR. In EGU General Assembly Conference Abstracts, 18.
• {Solomonidou}, A., {Coustenis}, A., {Lopes}, R., {Rodriguez}, S., {Schmitt}, B., {Philippe}, S., {Malaska}, M., {Lawrence}, K., {Janssen}, M., {Le Gall}, A., {Jaumann}, R., {Sohl}, F., {Stephan}, K., {Drossart}, P., {Brown}, R., {Maltagliati}, L., {Bratsolis}, E., , C. (2016, oct). Constraints on the nature of various Titan Geomorphological Units with Cassini/VIMS and SAR. In AAS/Division for Planetary Sciences Meeting Abstracts, 48.
• {Sotin}, C., {Lawrence}, K., {Marmuse}, F., {Xu}, F., {West}, R., {Brown}, R., {Baines}, K., {Buratti}, B., {Clark}, R., , P. (2016, oct). Characteristics of Titan's haze derived from solar occultation observations in the infrared. In AAS/Division for Planetary Sciences Meeting Abstracts, 48.
• {Sotin}, C., {Lawrence}, K., {Xu}, F., {West}, R., {Brown}, R., {Baines}, K., {Buratti}, B., {Clark}, R., , P. (2016, jun). Titan's haze as seen by VIMS during solar occultation observations. In Titan Aeronomy and Climate.
• {Baines}, K., {Sromovsky}, L., {Fry}, P., {Moimary}, T., {Badman}, S., {Brown}, R., {Buratti}, B., {Clark}, R., {Nicholson}, P., , C. (2015, nov). "{The Evolution of Saturn{rsquo}s Storm-Perturbed Latitudinal Band Determined from Cassini/VIMS Daytime and Nighttime Spectra}". In AAS/Division for Planetary Sciences Meeting Abstracts, 47.
• {Clark}, R., {Hedman}, M., {Brown}, R., {Filacchione}, G., {Nicholson}, P., , J. (2015, nov). "{Cassini VIMS Spectra of the Earth from Saturn Orbit: an Extrasolar Planet Analog}". In AAS/Division for Planetary Sciences Meeting Abstracts, 47.
• {Cornet}, T., {Altobelli}, N., {Rodriguez}, S., {Maltagliati}, L., {Le Mou{'e}lic}, S., {Sotin}, C., {Brown}, R., {Barnes}, J., {Buratti}, B., {Baines}, K., {Clark}, R., , P. (2015, apr). "{Investigation of Titan's surface and atmosphere photometric functions using the Cassini/VIMS instrument}". In EGU General Assembly Conference Abstracts, 17.
• {Filacchione}, G., {Capaccioni}, F., {D'Aversa}, E., {Tosi}, F., {Ciarniello}, M., {Clark}, R., {Brown}, R., {Buratti}, B., {Cruikshank}, D., {Dalle Ore}, C., {Scipioni}, F., , P. (2015, apr). "{Seasonal temperature variations observed by Cassini-VIMS on Saturn's satellites}". In EGU General Assembly Conference Abstracts, 17.
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• {Soderblom}, J., {Barnes}, J., {Brown}, R., {Soderblom}, L., {Sotin}, C., {Clark}, R., {Le Mou{'e}lic}, S., {Rodriguez}, S., {Baines}, K., {Buratti}, B., , P. (2015, apr). "{Constraining the activity of waves on Titan's polar lakes and seas}". In EGU General Assembly Conference Abstracts, 17.
• {Solomonidou}, A., {Coustenis}, A., {Lopes}, R., {Rodriguez}, S., {Hirtzig}, M., {Malaska}, M., {Stephan}, K., {Sotin}, C., {Drossart}, P., {Jaumann}, R., {Bratsolis}, E., {Le Mou{'e}lic}, S., , R. (2015, apr). "{Cassini VIMS and RADAR investigation of Titan's equatorial regions: a case for changes in surface properties}". In EGU General Assembly Conference Abstracts, 17.
• {Solomonidou}, A., {Lopes}, R., {Coustenis}, A., {Malaska}, M., {Rodriguez}, S., {Maltagliati}, L., {Drossart}, P., {Janssen}, M., {Lawrence}, K., {Jaumann}, R., {Sohl}, F., {Stephan}, K., {Brown}, R., {Bratsolis}, E., , C. (2015, nov). "{Titan{rsquo}s mid-latitude surface regions with Cassini VIMS and RADAR}". In AAS/Division for Planetary Sciences Meeting Abstracts, 47.
• {Sotin}, C., {Karkoschka}, E., {Lawrence}, K., {LeMouelic}, S., {Rodriguez}, S., {Solomonidou}, A., {Barnes}, J., {Brown}, R., {Buratti}, B., {Kirk}, R., {Soderblom}, J., {Soderblom}, L., {Baines}, K., {Clark}, R., , P. (2015, apr). "{Comparison of Cassini/VIMS and Huygens/DISR observations: Implications for Titan's geology and atmospheric haze}". In EGU General Assembly Conference Abstracts, 17.
• {Stephan}, K., {Jaumann}, R., {Wagner}, R., {Clark}, R., {Cruikshank}, D., {Dalle Ore}, C., {Brown}, R., {Giese}, B., {Roatsch}, T., {Matson}, D., {Baines}, K., {Filacchione}, G., {Capaccione}, F., {Burratti}, B., {Nicholson}, P., , S. (2015, apr). "{Tethys - Geological and Spectral Properties}". In EGU General Assembly Conference Abstracts, 17.
• Badman, S. V., Baines, K. H., Brown, R. H., Melin, H., & Stallard, T. (2012, sep). A new season of Saturn auroral observations by Cassini/VIMS. In European Planetary Science Congress 2012, 341.
• Baines, K. H., Momary, T. W., Janssen, M. A., Ingersoll, A. P., Fletcher, L. N., Brown, R. H., Buratti, B. J., Clark, R. N., Nicholson, P. D., & Sotin, C. (2012, oct). Saturn rsquos Equatorial Plumes At Depth Observed By Cassini/VIMS and Radar: Some Ammonia-wet, Some Dry. In AAS/Division for Planetary Sciences Meeting Abstracts, 44, #500.04.
• Brown, R. H. (2014, Fall). Six years of continuous observation of Titan cloud activity with Cassini/VIMS - SF2A-2013. In Proceedings of the Annual meeting of the French Society of Astronomy and Astrophysics, 71-74.
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  Editors: Cambresy, L | Martins, F | Nuss, E | Palacios, A
• Brown, R. H., Soderblom, L. A., Sotin, C., Barnes, J. W., Hayes, A. G., Lawrence, K. J., Le Mouelic, S., Rodriguez, S., Soderblom, J. M., Baines, K. H., Buratti, B. J., Clark, R. N., Jaumann, R., Nicholson, P. D., & Stephan, K. (2012, apr). Titan's lakes and Mare observed by the Visual and Infrared Mapping Spectrometer. In EGU General Assembly Conference Abstracts, 14, 13004.
• Buratti, B. J., Dalba, P. A., Barnes, J., Baines, K. H., Brown, R. H., Clark, R. N., Nicholson, P. D., & Sotin, C. (2012, apr). Spectral changes associated with rain on Titan: observations by VIMS. In Titan Through Time; Unlocking Titan's Past, Present and Future, 52.
• Buratti, B. J., Dalba, P. A., Clark, R. N., Brown, R. H., Mosher, J. A., Baines, K. H., & Nicholson, P. D. (2013, oct). The Opposition Surge of Icy Moons at 3.6 Microns: New Data from Cassini VIMS. In AAS/Division for Planetary Sciences Meeting Abstracts, 45, #406.04.
• Buratti, B., Dalba, P., Brown, R., Clark, R., Hillier, J., Mosher, J., Baines, K., & Nicholson, P. (2013, apr). Opposition Surges on Icy Moons: Observations by Cassini VIMS and ISS between 0.2 and five microns. In EGU General Assembly Conference Abstracts, 15, 6233.
• Clark, R. N., Pearson, N., Brown, R. H., Cruikshank, D. P., Barnes, J., Jaumann, R., Soderblom, L., Griffith, C., Rannou, P., Rodriguez, S., Le Mouelic, S., Lunine, J., Sotin, C., Baines, K. H., Buratti, B. J., Nicholson, P. D., Nelson, R. M., & Stephan, K. (2012, oct). The Surface Composition of Titan. In AAS/Division for Planetary Sciences Meeting Abstracts, 44, #201.02.
• Clark, R. N., Pearson, N., Brown, R. H., Cruikshank, D. P., Barnes, J., Jaumann, R., Soderblom, L., Griffith, C., Rannou, P., Rodriguez, S., Le Mouelic, S., Lunine, J., Sotin, C., Baines, K. H., Buratti, B. J., Nicholson, P. D., Nelson, R. M., & Stephan, K. (2013, oct). The Atmospheric Transmission and Surface Composition of Titan. In AAS/Division for Planetary Sciences Meeting Abstracts, 45, #309.05.
• Dalba, P., Buratti, B. J., Brown, R. H., Barnes, J. W., Baines, K. H., Sotin, C., Clark, R. N., Lawrence, K. J., & Nicholson, P. D. (2012, oct). Low-Latitude Ethane Rain on Titan. In AAS/Division for Planetary Sciences Meeting Abstracts, 44, #400.06.
• Filacchione, G., Capaccioni, F., Ciarniello, M., Clark, R. N., Nicholson, P. D., Cruikshank, D. P., Brown, R. H., Cuzzi, J. N., Altobelli, N., Spilker, L. J., Hedman, M. M., Dalle Ore, C. M., & Cerroni, P. (2013, oct). Spectral properties and temperature radial profiles of Saturn's main rings by Cassini-VIMS: variability with solar phase and elevation. In AAS/Division for Planetary Sciences Meeting Abstracts, 45, #206.04.
• Goguen, J. D., Buratti, B. J., Brown, R. H., Clark, R. N., Nicholson, P. D., Hedman, M. M., Sotin, C., Cruikshank, D. P., & Baines, K. H. (2013, oct). Baghdad Suchus on Enceladus: Constraints on the Temperature and Width at the Fissure Mouth. In AAS/Division for Planetary Sciences Meeting Abstracts, 45, #403.04.
• Goguen, J. D., Buratti, B. J., Brown, R. H., Clark, R. N., Nicholson, P. D., Hedman, M. M., Sotin, C., Cruikshank, D. P., Baines, K. H., Lawrence, K. J., Spencer, J. R., & Blackburn, D. (2012, oct). Cassini Vims Observations Of Thermal Emission From The Warmest 'Tiger Stripes' Near The South Pole On Enceladus. In AAS/Division for Planetary Sciences Meeting Abstracts, 44, #104.08.
• Griffith, C. A., Lora, J. M., Turner, J. D., Penteado, P. F., Brown, R. H., Tomasko, M. G., Doose, L., & See, C. (2012, oct). Oases on Titan?. In AAS/Division for Planetary Sciences Meeting Abstracts, 44, #400.02.
• Hennen, C. J., Barnes, J. W., Lorenz, R. D., Brown, R. H., Sotin, C., Buratti, B. J., Baines, K. H., Clark, R. N., & Nicholson, P. D. (2013, oct). The North South Asymmetry in Titan's Haze Through Time at Equinox. In AAS/Division for Planetary Sciences Meeting Abstracts, 45, #309.08.
• Jaumann, R., Stephan, K., Brown, R. H., Clark, R. N., Filacchione, G., Buratti, B. J., Nelson, R. M., Nicholson, P. D., Le Mou 'elic, S., Rodriguez, S., Hansen, G. B., Roatsch, T., Capaccionii, F., & Sotin, C. (2012, apr). Enceladus: Correlation of Surface Particle Distribution and Geology. In EGU General Assembly Conference Abstracts, 14, 7814.
• MacKenzie, S., Barnes, J. W., Brown, R., Sotin, C., Buratti, B. J., Clark, R., Baines, K. H., Nicholson, P. D., Le Mouelic, S., & Rodriguez, S. (2013, oct). Evidence of Titan's Climate History from Evaporite Distribution. In AAS/Division for Planetary Sciences Meeting Abstracts, 45, #302.04.
• Maltagliati, L., Vinatier, S., Bezard, B., Sotin, C., Sicardy, B., Nicholson, P. D., Hedman, M., Clark, R. N., & Brown, R. H. (2013, oct). The Vertical Composition of Titan rsquos Atmosphere observed by VIMS/Cassini Solar Occultations. In AAS/Division for Planetary Sciences Meeting Abstracts, 45, #305.04.
• Maltagliati, L., Vinatier, S., Sicardy, B., B 'ezard, B., Sotin, C., Nicholson, P. D., Brown, R. H., Baines, K., Buratti, B., & Clark, R. (2012, oct). Vertical Distribution of Gases and Aerosols in Titan rsquos Atmosphere Observed by VIMS/Cassini Solar Occultations. In AAS/Division for Planetary Sciences Meeting Abstracts, 44, #312.18.
• Maltagliati, L., Vinatier, S., Sicardy, B., B 'ezard, B., Sotin, C., Nicholson, P. D., Brown, R. H., Baines, K., Buratti, B., & Clark, R. (2012, sep). Vertical distribution of gases and aerosols in Titan's atmosphere observed by VIMS/Cassini solar occultations. In European Planetary Science Congress 2012, 600.
• Maltagliati, L., Vinatier, S., Sicardy, B., B 'ezard, B., Sotin, C., Nicholson, P. D., Hedman, M., Brown, R. H., Baines, K., Buratti, B., & Clark, R. (2013, apr). Vertical Distribution of Gases and Aerosols in Titan's Atmosphere Observed by VIMS/Cassini Solar Occultations. In EGU General Assembly Conference Abstracts, 15, 10014.
• Momary, T. W., Baines, K. H., Brown, R. H., Buratti, B. J., Clark, R. N., Nicholson, P. D., & Sotin, C. (2012, oct). Evolution of a Dark Anti-Cyclone on Saturn Associated with the Great Lightning Storm of 2010/2011 Through the Eyes of Cassini/VIMS. In AAS/Division for Planetary Sciences Meeting Abstracts, 44, #412.13.
• Momary, T. W., Baines, K. H., Brown, R. H., Buratti, B. J., Clark, R. N., Nicholson, P. D., Sotin, C., & Team, C. S. (2013, oct). The Polar Winds of Saturn as Determined by Cassini/VIMS: Seasonally Variable or Not?. In AAS/Division for Planetary Sciences Meeting Abstracts, 45, #312.09.
• Rannou, P., Lemou 'elic, S., Sotin, C., & Brown, R. H. (2012, sep). Transparency of the 2 $ mu$m window on Titan studied with observations made by VIMS. In European Planetary Science Congress 2012, 118.
• Soderblom, J. M., Sotin, C., Barnes, J. W., Brown, R. H., Lawrence, K. J., Le Mouelic, S., Soderblom, L. A., Baines, K. H., Buratti, B. J., Clark, R. N., Nicholson, P. D., & Team, V. (2012, oct). Specular Reflections From Titan: Implications For Titan rsquos Lakes And Atmosphere. In AAS/Division for Planetary Sciences Meeting Abstracts, 44, #400.01.
• Solomonidou, A., Coustenis, A., Hirtzig, M., Rodriguez, S., Stephan, K., Le Mou 'elic, S., Drossart, P., Bratsolis, E., Jaumann, R., Lopes, R. M., Kyriakopoulos, K., Sotin, C., & Brown, R. H. (2013, oct). Temporal Variations of Titan rsquos Surface Regions with Cassini/VIMS. In AAS/Division for Planetary Sciences Meeting Abstracts, 45, #302.09.
• Solomonidou, A., Hirtzig, M., Bratsolis, E., Bampasidis, G., Coustenis, A., Kyriakopoulos, K., Le Mou 'elic, S., Rodriguez, S., Jaumann, R., Stephan, K., Drossart, P., Sotin, C., Brown, R. H., Seymour, K., & Moussas, X. (2012, sep). New processing of Cassini/VIMS data on potentially geologically varying regions. In European Planetary Science Congress 2012, 425.
• Solomonidou, A., Hirtzig, M., Bratsolis, E., Bampasidis, G., Coustenis, A., Kyriakopoulos, K., Le Mou 'elic, S., Rodriguez, S., Jaumann, R., Stephan, K., Lopes, R. M., Drossart, P., Sotin, C., Brown, R. H., Seymour, K. S., & Moussas, X. (2012, oct). Cassini/VIMS Data Analysis of Potentially Geologically Varying Regions on Titan. In AAS/Division for Planetary Sciences Meeting Abstracts, 44, #201.03.
• Sotin, C., Lawrence, K., Brown, R., Hayne, P., Maltagliati, L., Sicardy, B., West, R., Xu, F., Clark, R., & Nicholson, P. (2013, apr). Analysis of solar occultation observations in the near infrared: implications for Titan's atmospheric properties and its surface composition. In EGU General Assembly Conference Abstracts, 15, 6570.
• {Barnes}, J., {Sotin}, C., {Soderblom}, J., {Hayes}, A., {Donelan}, M., {Brown}, R., {Rodriguez}, S., {Le Mouelic}, S., {Baines}, K., , T. (2014, mar). Specular Reflections from Titan's Punga Mare Seen by Cassini/VIMS Indicate Surface Roughness: Waves?. In Lunar and Planetary Science Conference, 45.
• {Brown}, R. (2014, may). Ten Years of VIMS at Saturn. In EGU General Assembly Conference Abstracts, 16.
• {Filacchione}, G., {Capaccioni}, F., {Clark}, R., {Nicholson}, P., {Hedman}, M., {Ciarniello}, M., {D'Aversa}, E., {Brown}, R., {Cruikshank}, D., {Cuzzi}, J., {Buratti}, B., {Spilker}, L., {Altobelli}, N., {Dalle Ore}, C., , P. (2014, may). Retrieval of temperatures from near-IR reflectance spectra of water-ice-rich bodies: application to Saturn's satellites and rings. In EGU General Assembly Conference Abstracts, 16.
• {Maltagliati}, L., {Rodriguez}, S., {App{\'e}r{\'e}}, T., {Vincendon}, M., {Dout{\'e}}, S., {LeMouelic}, S., {Rannou}, P., {Sotin}, C., {Barnes}, J., {Coustenis}, A., , R. (2014, nov). Mapping the Atmospheric and Surface Properties of Titan by the Massive Inversion of Cassini/VIMS Spectra. In AAS/Division for Planetary Sciences Meeting Abstracts, 46.
• {Rannou}, P., {Toledo}, D., {Adriani}, A., {Moriconi}, M., {D'Aversa}, E., {Le Mou{\'e}lic}, S., {Sotin}, C., , R. (2014, nov). Surface of Titan : model and VIMS observations. In AAS/Division for Planetary Sciences Meeting Abstracts, 46.
• {Soderblom}, J., {Barnes}, J., {Brown}, R., {Hayes}, A., {Perry}, J., {Soderblom}, L., , E. (2014, nov). Frozen Hydrocarbon Ponds on Titan: Implications for Titan{\rsquo}s Lakes and Seas. In AAS/Division for Planetary Sciences Meeting Abstracts, 46.
• {Solomonidou}, A., {Coustenis}, A., {Lopes}, R., {Hirtzig}, M., {Bratsolis}, E., {Drossart}, P., {Le Mou{\'e}lic}, S., {Rodriguez}, S., {Jaumann}, R., {Stephan}, K., {Bampasidis}, G., {Sotin}, C., , R. (2014, may). Looking at some equatorial regions on Titan using Cassini/VIMS and RADAR data: a case for changes in surface properties. In EGU General Assembly Conference Abstracts, 16.
• {Solomonidou}, A., {Coustenis}, A., {Lopes}, R., {Rodriguez}, S., {Hirtzig}, M., {Stephan}, K., {Sotin}, C., {Drossart}, P., {Le Mou{\'e}lic}, S., {Lawrence}, K., {Jaumann}, R., {Brown}, R., , E. (2014, nov). Temporal changes of mid-latitude surface regions on Titan. In AAS/Division for Planetary Sciences Meeting Abstracts, 46.
• {Sotin}, C., {Seignovert}, B., {Lawrence}, K., {MacKenzie}, S., {Barnes}, J., , R. (2014, may). Titan's geoid and hydrology: implications for Titan's geological evolution. In EGU General Assembly Conference Abstracts, 16.
• {Stephan}, K., {Jaumann}, R., {Wagner}, R., {Clark}, R., {Cruikshank}, D., {Dalle Ore}, C., {Brown}, R., {Giese}, B., {Roatsch}, T., {Matson}, D., {Baines}, K., {Filacchione}, G., {Capaccioni}, F., {Rodriguez}, S., {Buratti}, B., {Nicholson}, P., , N. (2014, nov). Spectral Properties of Tethys and Mimas. In AAS/Division for Planetary Sciences Meeting Abstracts, 46.

Poster Presentations

• Barnes, J., Sotin, C., Soderblom, J., Hayes, A., Donelan, M., Brown, R., Rodriguez, S., Le, M. S., Baines, K., & McCord, T. (2014, March). Specular Reflections from Titan's Punga Mare Seen by Cassini/VIMS Indicate Surface Roughness: Waves?. 45th Lunar and Planetary Science Conference. The Woodlands, TX.
  More info

  Dates: 03/17-21/14; Page: 1947; LPI Contribution No. 1777
• Brown, R. H. (2014, February). Formation and Evolution of Titan's Organic Seas. Workshop on the Habitability of Icy Worlds. Pasadena, CA.
  More info

  Pages: 4057; LPI Contribution No. 1774
• Appéré, T., Rodriguez, S., Vincendon, M., Douté, S., Rannou, P., Le, M. S., Coustenis, A., Barnes, J., Sotin, C., & Brown, R. (2013, Fall). Radiative Transfer on Titan: Towards a Massive Inversion of Atmospheric and Surface Properties From VIMS/Cassini Observations of Titan. American Geophysical Union, Fall Meeting 2013.
  More info

  Abstract #P53D-1899
• Badman, S., Bunce, E., Melin, H., Stallard, T., Nichols, J., Mitchell, D., Kurth, W., Crary, F., Burton, M., Baines, K., Brown, R., & Dougherty, M. (2013, Fall). Saturn's auroral dynamics during the 2013 observing campaign: in situ and remote observations (Invited). American Geophysical Union, Fall Meeting 2013.
  More info

  Abstract #SM14A-01
• Badman, S., Melin, H., Stallard, T., Blake, J., O'Donoghue, J., Bunce, E., Nichols, J., Baines, K., Brown, R., & Dougherty, M. (2013, September). Cassini VIMS observations of Saturn's infrared H3+ aurora during the 2013 multi-instrument campaign. European Planetary Science Congress 2013. London, UK.
  More info

  Dates: 09/08-13/13; id.EPSC2013-761
• Brown, R. H. (2013, July). Evaporative Isotopic Fractionation on Icy Bodies. International Cometary Workshop. Toulouse, France.
  More info

  Dates: 07/09-07/11; Other Information: ISAE
• Buratti, B., Dalba, P., Brown, R., Clark, R., Hillier, J., Mosher, J., Baines, K., & Nicholson, P. (2013, April). Opposition Surges on Icy Moons: Observations by Cassini VIMS and ISS between 0.2 and five microns. EGU General Assembly 2013. Vienna, Austria.
  More info

  Dates: 04/07-12/13; id. EGU2013-6233
• Buratti, B., Dalba, P., Clark, R., Brown, R., Mosher, J., Baines, K., & Nicholson, P. (2013, Fall). The Opposition Surge of Icy Moons at 3.6 Microns: New Data from Cassini VIMS. DPS meeting #45American Astronomical Society.
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  # 406.04
• Clark, R., Pearson, N., Brown, R., Cruikshank, D., Barnes, J., Jaumann, R., Soderblom, L., Griffith, C., Rannou, P., Rodriguez, S., Le, M. S., Lunine, J., Sotin, C., Baines, K., Buratti, B., Nicholson, P., Nelson, R., & Stephan, K. (2013, Fall). The Atmospheric Transmission and Surface Composition of Titan. DPS meeting #45American Astronomical Society.
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  # 309.05
• Clark, R., Pearson, N., Perlman, Z., Bradley, E., Hendrix, A., Cuzzi, J., Cruikshank, D., Filacchione, G., Nicholson, P., Hedman, M., Brown, R., Buratti, B., Baines, K., Sotin, C., & Nelson, R. (2013, December). Surface Composition of the Non-Ice Component on Icy Satellites and Ring Particles in the Saturn System. 2013 Fall Meeting, AGU. San Francisco, CA.
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  Dates: 12/09-13/13; Abstract P42A-08
• Cornet, T., Le, M. S., Rodriguez, S., Sotin, C., Bourgeois, O., Lefčvre, A., Barnes, J., Brown, R., Baines, K., Buratti, B., Clark, R., & Nicholson, P. (2013, March). Estimates of Titan's Surface Photometry in the 5 Microns Atmospheric Window Using the Cassini Visual and Infrared Mapping Spectrometer (VIMS). 44th Lunar and Planetary Science Conference. The Woodlands, TX.
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  Dates: 03/18-22/13; Page: 2048; LPI Contribution No. 1719
• Cornet, T., Philippe, S., Le, M. S., Rodriguez, S., Sotin, C., Brown, R., Barnes, J., Baines, K., Buratti, B., Clark, R., & Nicholson, P. (2013, Fall). Empirical correction of Titan surface photometry and atmospheric scattering from Cassini/VIMS data. American Geophysical Union, Fall Meeting 2013.
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  Abstract #P53D-1890
• D'Aversa, E., Bellucci, G., Nicholson, P., Brown, R., Altieri, F., & Carrozzo, F. (2013, September). Saturn ring spokes: an overview of their near-infrared spectral properties from Cassini/VIMS data. European Planetary Science Congress 2013. London, UK.
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  Dates: 09/08-13/13; id.EPSC2013-1099
• Filacchione, G., Capaccioni, F., Ciarniello, M., Clark, R., Nicholson, P., Cruikshank, D., Brown, R., Cuzzi, J., Altobelli, N., Spilker, L., Hedman, M., Dalle, O. C., & Cerroni, P. (2013, Fall). Spectral properties and temperature radial profiles of Saturn's main rings by Cassini-VIMS: variability with solar phase and elevation. DPS meeting #45American Astronomical Society.
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  # 206.04
• Filacchione, G., Capaccioni, F., Ciarniello, M., Clark, R., Nicholson, P., Cruikshank, D., Cuzzi, J., Hedman, M., Tosi, F., Buratti, B., Cerroni, P., & Brown, R. (2013, April). Constraining the radial distribution of water ice and chromophores across Saturn's rings, regular and minor satellites. EGU General Assembly 2012. Vienna, Austria.
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  Dates: 04/22-27/12; Page: 7061
• Filacchione, G., Capaccioni, F., Clark, R., Ciarniello, M., Brown, R., Cruikshank, D., Buratti, B., Cuzzi, J., Spilker, L., Nicholson, P., Dalle, O. C., Cerroni, P., Tosi, F., & Scipioni, F. (2013, December). Saturn's satellites temperatures inferred from Cassini-VIMS reflectance spectra. 2013 Fall Meeting, AGU. San Francisco, CA.
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  Dates: 12/09-13/13; Abstract P42A-07
• Garcia, A., Rodriguez, S., Le, G. A., Courrech, d., Narteau, C., Le, M. S., Lucas, A., Radebaugh, J., Arnold, K., Barnes, J., Sotin, C., Brown, R., Lorenz, R., & Turtle, E. (2013, March). Global Mapping and Characterization of Titan's Dune Fields with Cassini: Correlation Between RADAR and VIMS Observations. 44th Lunar and Planetary Science Conference. The Woodlands, TX.
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  Dates: 03/18-22/13; Page: 1978; LPI Contribution No. 1719
• Garcia, A., Rodriguez, S., Lucas, A., Appéré, T., Le, G. A., Reffet, E., Le, C. L., Le, M. S., Cornet, T., Courrech, D., Narteau, C., Bourgeois, O., Radebaugh, J., Arnold, K., Barnes, J., Sotin, C., Brown, R., Lorenz, R., & Turtle, E. (2013, Fall). Global characterization of Titan's dune fields by RADAR and VIMS observations. American Geophysical Union, Fall Meeting 2013.
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  Abstract #P53D-1895
• Goguen, J., Buratti, B., Brown, R., Clark, R., Nicholson, P., Hedman, M., Sotin, C., Cruikshank, D., & Baines, K. (2013, Fall). Baghdad Suchus on Enceladus: Constraints on the Temperature and Width at the Fissure Mouth. DPS meeting #45American Astronomical Society.
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  #403.04
• Hayes, A., Sotin, C., Hofgartner, J., Stiles, B., Barnes, J., Brown, R., Encrenaz, P., Kirk, R., Le, G. A., Lopes, R., Lorenz, R., Lunine, J., Malaska, M., Mitchell, K., Paillou, P., Radebaugh, J., Turtle, E., Wall, S., Wood, C., & Zebker, H. (2013, Fall). The case of Titan's mysterious new island: An analysis of an anomalously bright feature observed in the T92 SAR pass over Ligeia Mare. American Geophysical Union, Fall Meeting 2013.
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  Abstract #P53D-1898
• Hennen, C., Barnes, J., Lorenz, R., Brown, R., Sotin, C., Buratti, B., Baines, K., Clark, R., & Nicholson, P. (2013, Fall). The North South Asymmetry in Titan's Haze Through Time at Equinox. DPS meeting #45American Astronomical Society.
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  # 309.08
• MacKenzie, S., Barnes, J., Brown, R., Sotin, C., Buratti, B., Clark, R., Baines, K., Nicholson, P., Le, M. S., & Rodriguez, S. (2013, Fall). Evidence of Titan's Climate History from Evaporite Distribution. DPS meeting #45American Astronomical Society.
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  #302.04
• Maltagliati, L., Vinatier, S., Bezard, B., Sotin, C., Sicardy, B., Nicholson, P., Hedman, M., Clark, R., & Brown, R. (2013, Fall). The Vertical Composition of Titan's Atmosphere observed by VIMS/Cassini Solar Occultations. DPS meeting #45American Astronomical Society.
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  # 305.04
• Maltagliati, L., Vinatier, S., Bézard, B., Sotin, C., Sicardy, B., Nicholson, P., Hedman, M., Clark, R., & Brown, R. (2013, September). Investigating the Vertical Composition of Titan's Atmosphere with VIMS/Cassini Solar Occultations. European Planetary Science Congress 2013. London, UK.
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  Dates: 09/08-13/13; id.EPSC2013-625
• Maltagliati, L., Vinatier, S., Sicardy, B., Bézard, B., Sotin, C., Nicholson, P., Hedman, M., Brown, R., Baines, K., Buratti, B., & Clark, R. (2013, April). Vertical Distribution of Gases and Aerosols in Titan's Atmosphere Observed by VIMS/Cassini Solar Occultations. EGU General Assembly 2013. Vienna, Austria.
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  Dates: 04/07-12/13; id. EGU2013-10014
• Momary, T., Baines, K., Brown, R., Buratti, B., Clark, R., Nicholson, P., Sotin, C., & Team, C. S. (2013, Fall). The Polar Winds of Saturn as Determined by Cassini/VIMS: Seasonally Variable or Not?. DPS meeting #45American Astronomical Society.
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  # 312.09
• Nichols, J., Badman, S., Baines, K., Brown, R., Bunce, E., Clarke, J., Cowley, S., Crary, F., Dougherty, M., Gerard, J., Grocott, A., Grodent, D., Kurth, W., Melin, H., Mitchell, D., Pryor, W., & Stallard, T. (2013, Fall). Saturn's northern auroras as observed using the Hubble Space Telescope. American Geophysical Union, Fall Meeting 2013.
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  Abstract #SM21C-2196
• Rodriguez, S., Le, M. S., Barnes, J., Hirtzig, M., Appéré, T., Rannou, P., Sotin, C., Brown, R., Bow, J., Vixie, G., Cornet, T., Bourgeois, O., Narteau, C., Courrech, d., Griffith, C., Jauman, R., Stephan, K., Clark, R., & Coustenis, A. (2013, September). Singular equinoctial activity over Titan's dunefields as seen by CASSINI/VIMS. European Planetary Science Congress 2013. London, UK.
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  Dates: 09/08-13/13; id.EPSC2013-39
• Soderblom, J., Sotin, C., Barnes, J., Brown, R., Lawrence, K., Le, M. S., Soderblom, L., Baines, K., Buratti, B., Clark, R., Nicholson, P., & Team, V. (2013, Fall). Specular Reflections From Titan: Implications For Titan's Lakes And Atmosphere. DPS meeting #44American Astronomical Society.
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  # 400.01
• Solomonidou, A., Coustenis, A., Bratsolis, E., Drossart, P., Bampasidis, G., Kyriakopoulos, K., Le, M. S., Rodriguez, S., Hirtzig, M., Jaumann, R., Stephan, K., Lopes, R., Sotin, C., Brown, R., Sohl, F., Hussmann, H., Wagner, F., Schulze-Makuch, D., Stamatelopoulou-Seymour, K., & Moussas, X. (2013, April). Cryovolcanic candiDates areas and morphotectonic features on Saturn's satellite Titan. EGU General Assembly 2013. Vienna, Austria.
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  Dates: 04/07-12/13; id. EGU2013-9108
• Solomonidou, A., Coustenis, A., Hirtzig, M., Bratsolis, E., Drossart, P., Bampasidis, G., Kyriakopoulos, K., Le, M. S., Rodriguez, S., Jaumann, R., Stephan, K., Lopes, R., Sotin, C., Brown, R., Stamatelopoulou-Seymour, K., & Moussas, X. (2013, April). Evolution of possibly active regions on Titan using Cassini/VIMS data analysis. EGU General Assembly 2013. Vienna, Austria.
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  Dates: 04/07-12/13;id. EGU2013-224
• Solomonidou, A., Coustenis, A., Hirtzig, M., Bratsolis, E., Drossart, P., Bampasidis, G., Kyriakopoulos, K., Le, M. S., Rodriguez, S., Jaumann, R., Stephan, K., Lopes, R., Sotin, C., Brown, R., Stamatelopoulou-Seymour, K., & Moussas, X. (2013, April). Surface Albedo retrieval from Cassini/VIMS data of Titan's geologically interesting areas. EGU General Assembly 2013. Vienna, Austria.
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  Dates: 04/07-12/13; id. EGU2013-5511
• Solomonidou, A., Coustenis, A., Hirtzig, M., Bratsolis, E., Drossart, P., Bampasidis, G., Kyriakopoulos, K., Le, M. S., Rodriguez, S., Stephan, K., Jaumann, R., Sohl, F., Wagner, F., Hussmann, H., Lopes, R., Sotin, C., Brown, R., Stamatelopoulou-Seymour, K., & Moussas, X. (2013, September). Surface albedo changes with time on Titan's possible cryovolcanic sites: Cassini/VIMS processing and geophysical implications. European Planetary Science Congress 2013. London, UK.
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  Dates: 09/08-13/13; id.EPSC2013-88
• Solomonidou, A., Coustenis, A., Hirtzig, M., Rodriguez, S., Stephan, K., Le, M. S., Drossart, P., Bratsolis, E., Jaumann, R., Lopes, R., Kyriakopoulos, K., Sotin, C., & Brown, R. (2013, Fall). Temporal Variations of Titan's Surface Regions with Cassini/VIMS. DPS meeting #45American Astronomical Society.
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  # 302.09
• Sotin, C., Lawrence, K., Brown, R., Hayne, P., Maltagliati, L., Sicardy, B., West, R., Xu, F., Clark, R., & Nicholson, P. (2013, April). Analysis of solar occultation observations in the near infrared: implications for Titan's atmospheric properties and its surface composition. EGU General Assembly 2013. Vienna, Austria.
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  Dates: 04/07-12/13; id. EGU2013-6570
• Sotin, C., Seignovert, B., Lawrence, K., Barnes, J., Brown, R., Hayes, A., Le, M. S., Baines, K., Buratti, B., Clark, R., & Nicholson, P. (2013, Fall). Evolution of Titan's Lakes and Seas: Insights from Recent Infrared Observations. American Geophysical Union, Fall Meeting 2013.
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  Abstract #P52B-08
• Stephan, K., Jaumann, R., Wagner, R., Clark, R., Cruikshank, D., Dalle, O. C., Hansen, G., Brown, R., Giese, B., Roatsch, T., Matson, D., Baines, K., Filiacchione, G., Rodriguez, S., Buratti, B., Nicholson, P., & Sotin, C. (2013, April). The Saturnian satellite Tethys observed by the Cassini-VIMS instrument. EGU General Assembly 2013. Vienna, Austria.
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  Dates: 04/07-12/13; Page: 13734
• Badman, S., Andrews, D., Cowley, S., Lamy, L., Provan, G., Tao, C., Kasahara, S., Kimura, T., Fujimoto, M., Melin, H., Stallard, T., Brown, R., & Baines, K. (2012, September). Rotational modulation and local time dependence of Saturn's infrared H3+ auroral intensity. European Planetary Science Congress 2012. Madrid, Spain.
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  Dates: 09/23-28/12; id. EPSC2012-338
• Badman, S., Baines, K., Brown, R., Melin, H., & Stallard, T. (2012, September). A new season of Saturn auroral observations by Cassini/VIMS. European Planetary Science Congress 2012. Madrid, Spain.
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  Dates: 09/23-28/12; id. EPSC2012-341
• Badman, S., Cowley, S., Baines, K., Brown, R., Lamy, L., Kimura, T., Tao, C., Andrews, D., Melin, H., Stallard, T., & Fujimoto, M. (2012, July). Rotational modulation and local time dependence of Saturn's infrared H3+ auroral intensity. 39th COSPAR Scientific Assembly. Mysore, India.
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  Dates: 07/14-22/12; Page: 81; Abstract A1.1-115-12
• Baines, K., Momary, T., Janssen, M., Ingersoll, A., Fletcher, L., Brown, R., Buratti, B., Clark, R., Nicholson, P., & Sotin, C. (2012, Fall). Saturn's Equatorial Plumes At Depth Observed By Cassini/VIMS and Radar: Some Ammonia-wet, Some Dry. DPS meeting #44American Astronomical Society.
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  #500.04
• Barnes, J., Buratti, B., Turtle, E., Bow, J., Dalba, P., Perry, J., Rodriguez, S., Lemouelic, S., Baines, K., Sotin, C., Lorenz, R., Malaska, M., McCord, T., Brown, R., Clark, R., Jaumann, R., Hayne, P., Nicholson, P., Soderblom, J., & Soderblom, L. (2012, March). Cassini/VIMS Spectra and Time-Evolution of Precipitation-Associated Surface Brightenings on Titan. 43rd Lunar and Planetary Science Conference. The Woodlands, TX.
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  Dates: 03/19-23/12; LPI Contribution No. 1659; id.2762
• Barnes, J., Clark, R., Sotin, C., Adamkovics, M., Appere, T., Rodriguez, S., Soderblom, J., Brown, R., Buratti, B., Baines, K., Le, M. S., & Nicholson, P. (2012, Fall). Probing Titan's North Polar Atmosphere using a Specular Refection of the Sun. DPS meeting #45American Astronomical Society.
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  #207.01
• Brown, R. H. (2012, Fall). Geologically Active Icy Satellites. COSPAR.
• Brown, R. H. (2012, June). Equinoctial Atmospheric Activity over Titan Dune Fields Revealed by Cassini/VIMS. Third International Planetary Dunes Workshop: Remote Sensing and Data Analysis of Planetary Dunes. Flagstaff, AZ.
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  Dates: 06/12-06/15; Pages: 81-82; LPI Contribution No. 1673
• Brown, R., Soderblom, L., Sotin, C., Barnes, J., Hayes, A., Lawrence, K., Le, M. S., Rodriguez, S., Soderblom, J., Baines, K., Buratti, B., Clark, R., Jaumann, R., Nicholson, P., & Stephan, K. (2012, April). Titan's lakes and Mare observed by the Visual and Infrared Mapping Spectrometer. EGU General Assembly 2012. Vienna, Austria.
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  Dates: 04/22-27/12; Page: 13004
• Clark, R., Pearson, N., Brown, R., Cruikshank, D., Barnes, J., Jaumann, R., Soderblom, L., Griffith, C., Rannou, P., Rodriguez, S., Le, M. S., Lunine, J., Sotin, C., Baines, K., Buratti, B., Nicholson, P., Nelson, R., & Stephan, K. (2012, Fall). The Surface Composition of Titan. DPS meeting #44American Astronomical Society.
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  # 201.02
• Cornet, T., Bourgeois, O., Le, M. S., Rodriguez, S., Sotin, C., Lefčvre, A., Barnes, J., Brown, R., Baines, K., Buratti, B., Clark, R., & Nicholson, P. (2012, March). Shaping Titan's Landscapes by Dissolution and Evaporation: The Case of Ontario Lacus, a High-Latitude Semi-Arid Karst-Playa Landsystem. 43rd Lunar and Planetary Science Conference. The Woodlands, TX.
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  Dates: 03/19-23/12; LPI Contribution No. 1659; id.1914
• Dalba, P., Buratti, B., Baines, K., Barnes, J., Brown, R., Clark, R., Nicholson, P., & Sotin, C. (2012, March). The Rain in the Plain on Titan. 43rd Lunar and Planetary Science Conference. The Woodlands, TX.
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  Dates: 03/19-23/12; LPI Contribution No. 1659; id.1717
• Dalba, P., Buratti, B., Brown, R., Barnes, J., Baines, K., Sotin, C., Clark, R., Lawrence, K., & Nicholson, P. (2012, Fall). Low-Latitude Ethane Rain on Titan. DPS meeting #44American Astronomical Society.
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  #400.06
• Dalba, P., Buratti, B., Brown, R., Barnes, J., Baines, K., Sotin, C., Clark, R., Lawrence, K., & Nicholson, P. (2012, Fall). Low-latitude ethane rain on Titan. American Geophysical Union, Fall Meeting 2012.
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  Abstract #P21E-1881
• Filacchione, G., Capaccioni, F., Ciarniello, M., Nicholson, P., Clark, R., Cruikshank, D., Cuzzi, J., Hedman, M., Buratti, B., Cerroni, P., Tosi, F., & Brown, R. (2012, Fall). Water Ice, Chromophores And Organics Distribution Across Saturn'S Rings. DPS meeting #44American Astronomical Society.
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  # 511.02
• Filacchione, G., Capaccioni, F., Ciarniello, M., Nicholson, P., Clark, R., Cruikshank, D., Cuzzi, J., Hedman, M., Buratti, B., Cerroni, P., Tosi, F., Jaumann, R., Stephan, K., & Brown, R. (2012, Fall). Tracing water ice and chromophores across Saturn's moons and rings. American Geophysical Union, Fall Meeting 2012.
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  Abstract #P53B-03
• Goguen, J., Buratti, B., Brown, R., Clark, R., Nicholson, P., Hedman, M., Sotin, C., Cruikshank, D., Baines, K., Lawrence, K., Spencer JR, ., & Blackburn, D. (2012, Fall). Cassini Vims Observations Of Thermal Emission From The Warmest 'Tiger Stripes' Near The South Pole On Enceladus. DPS meeting #44American Astronomical Society.
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  #104.08
• Griffith, C., Lora, J., Turner, J., Penteado, P., Brown, R., Tomasko, M., Doose, L., & See, C. (2012, Fall). Oases on Titan?. DPS meeting #44American Astronomical Society.
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  #400.02
• Jaumann, R., Stephan, K., Brown, R., Clark, R., Filacchione, G., Buratti, B., Nelson, R., Nicholson, P., Le, M. S., Rodriguez, S., Hansen, G., Roatsch, T., Capaccionii, F., & Sotin, C. (2012, April). Enceladus: Correlation of Surface Particle Distribution and Geology. EGU General Assembly 2012. Vienna, Austria.
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  Dates: 04/22-27/12; Page: 7814
• Le, M. S., Cornet, T., Rodriguez, S., Sotin, C., Barnes, J., Brown, R., Baines, K., Buratti, B., Clark, R., Lefčvre, A., & Nicholson, P. (2012, March). Investigating the Surface of Titan in the 1-2.8 µm Range with CassiniI/VIMS Hyperspectral Images. 43rd Lunar and Planetary Science Conference. The Woodlands, TX.
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  Dates: 03/19-23/12; LPI Contribution No. 1659; id.1745
• Le, M. S., Rodriguez, S., Sotin, C., West, R., Rannou, P., Barnes, J., Brown, R., Cornet, T., Baines, K., Buratti, B., Clark, R., & Nicholson, P. (2012, Fall). Imaging of a Newly Forming Polar Hood Over The South Pole of Titan By VIMS/Cassini. American Geophysical Union, Fall Meeting 2012.
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  Abstract #P21E-1888
• Maltagliati, L., Vinatier, S., Sicardy, B., Bézard, B., Sotin, C., Nicholson, P., Brown, R., Baines, K., Buratti, B., & Clark, R. (2012, Fall). Vertical Distribution of Gases and Aerosols in Titan's Atmosphere Observed by VIMS/Cassini Solar Occultations. DPS meeting #44American Astronomical Society.
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  # 312.18
• Maltagliati, L., Vinatier, S., Sicardy, B., Bézard, B., Sotin, C., Nicholson, P., Brown, R., Baines, K., Buratti, B., & Clark, R. (2012, September). Vertical distribution of gases and aerosols in Titan's atmosphere observed by VIMS/Cassini solar occultations. European Planetary Science Congress 2012. Madrid, Spain.
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  Dates: 09/23-28/12; id. EPSC2012-600
• Momary, T., Baines, K., Brown, R., Buratti, B., Clark, R., Nicholson, P., & Sotin, C. (2012, Fall). Evolution of a Dark Anti-Cyclone on Saturn Associated with the Great Lightning Storm of 2010/2011 Through the Eyes of Cassini/VIMS. DPS meeting #44American Astronomical Society.
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  #412.13
• Rannou, P., Lemouélic, S., Sotin, C., & Brown, R. (2012, September). Transparency of the 2 mum window on Titan studied with observations made by VIMS. European Planetary Science Congress 2012. Madrid, Spain.
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  Dates: 09/23-28/12; id. EPSC2012-118
• Rodriguez, S., Le, M. S., Barnes, J., Hirtzig, M., Rannou, P., Sotin, C., Brown, R., Bow, J., Vixie, G., Cornet, T., Bourgeois, O., Narteau, C., Courrech, D., Griffith, C., Jauman, R., Stephan, K., Buratti, B., Clark, R., Baines, K., , Nicholson, P., et al. (2012, March). Singular Regional Brightening Events on Titan as Seen by Cassini/VIMS. 43rd Lunar and Planetary Science Conference. The Woodlands, TX.
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  Dates: 03/19-23/12; LPI Contribution No. 1659; id.1158
• Rodriguez, S., Le, M. S., Barnes, J., Hirtzig, M., Rannou, P., Sotin, C., Brown, R., Bow, J., Vixie, G., Cornet, T., Bourgeois, O., Narteau, C., Courrech, D., Le, G. A., Reffet, E., Griffith, C., Jaumann, R., Stephan, K., Buratti, B., , Clark, R., et al. (2012, Fall). Equinoctial Activity Over Titan Dune Fields Revealed by Cassini/vims. American Geophysical Union, Fall Meeting 2012.
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  Abstract #P21E-1886
• Solomonidou, A., Hirtzig, M., Bratsolis, E., Bampasidis, G., Coustenis, A., Kyriakopoulos, K., Le, M. S., Rodriguez, S., Jaumann, R., Stephan, K., Drossart, P., Sotin, C., Brown, R., Seymour, K., & Moussas, X. (2012, September). New processing of Cassini/VIMS data on potentially geologically varying regions. European Planetary Science Congress 2012. Madrid, Spain.
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  Dates: 09/23-28/12; id. EPSC2012-425
• Solomonidou, A., Hirtzig, M., Bratsolis, E., Bampasidis, G., Coustenis, A., Kyriakopoulos, K., Le, M. S., Rodriguez, S., Jaumann, R., Stephan, K., Lopes, R., Drossart, P., Sotin, C., Brown, R., Seymour, K., & Moussas, X. (2012, Fall). Cassini/VIMS Data Analysis of Potentially Geologically Varying Regions on Titan. DPS meeting #44American Astronomical Society.
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  #201.03
• Stephan, K., Jaumann, R., Wagner, R., Clark, R., Cruikshank, D., Dalle, O. C., Brown, R., Giese, B., Roatsch, T., Matson, D., Baines, K., Filacchione, G., Capaccione, F., Buratti, B., & Nicholson, P. (2012, March). Spectral Properties of the Saturnian Satellites Tethys as Derived from Cassini-VIMS Data. 43rd Lunar and Planetary Science Conference. The Woodlands, TX.
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  Dates: 03/19-23/12; LPI Contribution No. 1659; id.2119
• Stephan, K., Jaumann, R., Wagner, R., Clark, R., Cruikshank, D., Dalle, O. C., Hansen, G., Brown, R., Giese, B., Roatsch, T., Matson, D., Baines, K., Filiacchione, G., Cappacione, F., Rodriguez, S., Buratti, B., Nicholson, P., & Sotin, C. (2012, Fall). The Saturnian Satellite Tethys Observed By Cassini-VIMS. DPS meeting #44American Astronomical Society.
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  # 112.01

Others

• Barnes, J., Buratti, B., Turtle, E., Bow, J., Dalba, P., Perry, J., Brown, R., Rodriguez, S., LeMouelic, S., Baines, K., Sotin, C., Lorenz, R., Malaska, M., McCord, T., Clark, R., Jaumann, R., Hayne, P., Nicholson, P., Soderblom, J., & Soderblom, L. (2012, April). VIMS Near-Infrared Imaging and Spectra of Precipitation-Associated Surface Changes. Titan Through Time; Unlocking Titan's Past, Present and Future, NASA Goddard Space Flight Center. http://spacescience.arc.nasa.gov/events/titan-through-time-ii-workshop
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  Dates: 04/03-05/12; Pages: 51; Editors: Cottini, V | Nixon, C | Lorenz, R
• Buratti, B., Dalba, P., Barnes, J., Baines, K., Brown, R., Clark, R., Nicholson, P., & Sotin, C. (2012, April). Spectral changes associated with rain on Titan: observations by VIMS. Titan Through Time; Unlocking Titan's Past, Present and Future, NASA Goddard Space Flight Center. http://spacescience.arc.nasa.gov/events/titan-through-time-ii-workshop
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  Exact Date: 04/03-05/12; Pages: 52; Editors: Cottini, V | Nixon, C | Lorenz, R