Caitlin A Griffith

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Books

• Griffith, C., Mtichell, J., Lavvas, P., & Tobie, G. (2013). Titan's Evolving Climate. Tucson, AZ: University of Arizona Press.
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  In:Comparative Climatology of Terrestrial Planets; Editors: Mackwell, SJ | Simon-Miller, AA | Harder, JW | Bullock, MA; 610 pp.

Journals/Publications

• Griffith, C. A., Penteado, P. F., Turner, J. D., Neish, C. D., Mitri, G., Montiel, N. J., Schoenfeld, A., & Lopes, R. M. (2019). A corridor of exposed ice-rich bedrock across Titan's tropical region. Nature Astronomy, 3, 642-648.
• Griffith, C. A., Penteado, P. F., Turner, J. D., Neish, C. D., Mitri, G., Montiel, N. J., Schoenfeld, A., & Lopes, R. M. (2019). Author Correction: A corridor of exposed ice-rich bedrock across Titan's tropical region. Nature Astronomy, 3, 673-673.
• Pearson, K. A., Griffith, C. A., Zellem, R. T., Koskinen, T. T., & Roudier, G. M. (2019). Ground-based Spectroscopy of the Exoplanet XO-2b Using a Systematic Wavelength Calibration. \aj, 157(1), 21.
• Pearson, K., Griffith, C., Zellem, R., Koskinen, T., & Roudier, G. (2019). VizieR Online Data Catalog: Ground-based spectroscopy of the exoplanet XO-2b (Pearson+, 2019). VizieR Online Data Catalog, J/AJ/157/21.
• Waldmann, I., & Griffith, C. (2019). Mapping Saturn using deep learning. Nature Astronomy, 3, 620-625.
• Zellem, R. T., Swain, M. R., Cowan, N. B., Bryden, G., Komacek, T. D., Colavita, M., Ardila, D., Roudier, G. M., Fortney, J. J., Bean, J., Line, M. R., Griffith, C. A., Shkolnik, E. L., Kreidberg, L., Moses, J. I., Showman, A. P., Stevenson, K. B., Wong, A., Chapman, J. W., , Ciardi, D. R., et al. (2019). Constraining Exoplanet Metallicities and Aerosols with the Contribution to ARIEL Spectroscopy of Exoplanets (CASE). \pasp, 131(1003), 094401.
• Pearson, K., Palafox, L., & Griffith, C. (2018). Searching for exoplanets using artificial intelligence. \mnras, 474, 478-491.
• Rodriguez, S., Le, M. S., Barnes, J., Kok, J., Rafkin, S., Lorenz, R., Charnay, B., Radebaugh, J., Narteau, C., Cornet, T., Bourgeois, O., Lucas, A., Rannou, P., Griffith, C., Coustenis, A., App{\'er\'e}, T., Hirtzig, M., Sotin, C., Soderblom, J., , Brown, R., et al. (2018). Observational evidence for active dust storms on Titan at equinox. Nature Geoscience, 11, 727-732.
• Tinetti, G., Drossart, P., Eccleston, P., Hartogh, P., Heske, A., Leconte, J., Micela, G., Ollivier, M., Pilbratt, G., Puig, L., & al., e. (2018). A chemical survey of exoplanets with ARIEL. Experimental Astronomy, 46, 135-209.
• Chapman, J., Zellem, R., Line, M., Vasisht, G., Bryden, G., Willacy, K., Iyer, A., Bean, J., Cowan, N., Fortney, J., Griffith, C., Kataria, T., Kempton, E., Kreidberg, L., Moses, J., Stevenson, K., & Swain, M. (2017). Quantifying the Impact of Spectral Coverage on the Retrieval of Molecular Abundances from Exoplanet Transmission Spectra. \pasp, 129(10), 104402.
• Griffith, C., Penteado, P., Turner, J., Neish, C., Mitri, G., Montiel, M., Schoenfeld, A., & Lopes, R. (2017). Titan's icy scar. European Planetary Science Congress, 11, EPSC2017-950.
• Teske, J., Cunha, K., Smith, V., Schuler, S., & Griffith, C. (2017). VizieR Online Data Catalog: Hot Jupiter exoplanets host stars EW and abundances (Teske+, 2014). VizieR Online Data Catalog, 178.
• Zellem, R., Griffith, C., Deroo, P., Swain, M., & Waldmann, I. (2017). VizieR Online Data Catalog: Potential exoplanet targets with Palomar/TripleSpec (Zellem+, 2014). VizieR Online Data Catalog, 179.
• Zellem, R., Lewis, N., Knutson, H., Griffith, C., Showman, A., Fortney, J., Cowan, N., Agol, E., Burrows, A., Charbonneau, D., Deming, D., Laughlin, G., & Langton, J. (2017). VizieR Online Data Catalog: Photometric data of HD 209458b (Zellem+, 2014). VizieR Online Data Catalog, 179.
• {Turner}, J., {Pearson}, K., {Biddle}, L., {Smart}, B., {Zellem}, R., {Teske}, J., {Hardegree-Ullman}, K., {Griffith}, C., {Leiter}, R., {Cates}, I., {Nieberding}, M., {Smith}, C., {Thompson}, R., {Hofmann}, R., {Berube}, M., {Nguyen}, C., {Small}, L., {Guvenen}, B., {Richardson}, L., , {McGraw}, A., et al. (2016). "{Ground-based near-UV observations of 15 transiting exoplanets: constraints on their atmospheres and no evidence for asymmetrical transits}". mnras, 459, 789-819.
• {Zellem}, R., {Griffith}, C., {Pearson}, K., {Turner}, J., {Henry}, G., {Williamson}, M., {Ryleigh Fitzpatrick}, M., {Teske}, J., , L. (2015). "{XO-2b: A Hot Jupiter with a Variable Host Star That Potentially Affects Its Measured Transit Depth}". apj, 810, 11.
• Griffith, C. A. (2014). Disentangling degenerate solutions from primary transit and secondary eclipse spectroscopy of exoplanets. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 372(2014).
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  Abstract: Infrared transmission and emission spectroscopy of exoplanets, recorded from primary transit and secondary eclipse measurements, indicate the presence of the most abundant carbon and oxygen molecular species (H2O, CH4, CO and CO2 ) in a few exoplanets. However, efforts to constrain the molecular abundances to within several orders of magnitude are thwarted by the broad range of degenerate solutions that fit the data. Here, we explore, with radiative transfer models and analytical approximations, the nature of the degenerate solution sets resulting from the sparse measurements of 'hot Jupiter' exoplanets. As demonstrated with simple analytical expressions, primary transit measurements probe roughly four atmospheric scale heights at each wavelength band. Derived mixing ratios from these data are highly sensitive to errors in the radius of the planet at a reference pressure. For example, an uncertainty of 1% in the radius of a 1000K and H2- based exoplanet with Jupiter's radius and mass causes an uncertainty of a factor of approximately 100- 10 000 in the derived gas mixing ratios. The degree of sensitivity depends on how the line strength increases with the optical depth (i.e. the curve of growth) and the atmospheric scale height. Temperature degeneracies in the solutions of the primary transit data, which manifest their effects through the scale height and absorption coefficients, are smaller. We argue that these challenges can be partially surmounted by a combination of selected wavelength sampling of optical and infrared measurements and, when possible, the joint analysis of transit and secondary eclipse data of exoplanets. However, additional work is needed to constrain other effects, such as those owing to planetary clouds and star spots. Given the current range of open questions in the field, both observations and theory, there is a need for detailed measurements with space-based large mirror platforms (e.g. James web space telescope) and smaller broad survey telescopes as well as ground-based efforts. © 2014 The Author(s) Published by the Royal Society.
• Teske, J. K., Cunha, K., Smith, V. V., Schuler, S. C., & Griffith, C. A. (2014). The role of oxygen abundances in exoplanet host star C/O ratios: A case study of 55 Cnc. Proceedings of the International Astronomical Union, 8(S299), 307-308.
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  Abstract: We derive the C/O ratio for the exoplanet host star 55 Cnc based on archive Keck/HIRES spectra. The C/O ratio varies widely depending on which oxygen abundance indicator - the 6300.3 Å [O I] line, the 6363.8 Å [O I] line, or the 7774 Å O I triplet - is used, and we find there is still a large uncertainty even based on individual abundance indicators. This case study demonstrates that caution and care are necessary when determining exoplanet host star C/O ratios, and when considering host star C/O ratios in inferring exoplanet compositions. Copyright © 2013, International Astronomical Union.
• {Griffith}, C. (2014). "{Solar system: Not just a storm in a teacup}". nat, 514, 40-41.
• {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.
• {Teske}, J., {Cunha}, K., {Smith}, V., {Schuler}, S., , C. (2014). "{C/O Ratios of Stars with Transiting Hot Jupiter Exoplanets}". apj, 788, 39.
• {Teske}, J., {Turner}, J., {Mueller}, M., , C. (2014). "{Erratum: Optical observations of the transiting exoplanet GJ 1214b}". mnras, 444, 1930-1930.
• {Zellem}, R., {Griffith}, C., {Deroo}, P., {Swain}, M., , I. (2014). "{The Ground-based H-, K-, and L-band Absolute Emission Spectra of HD 209458b}". apj, 796, 48.
• {Zellem}, R., {Lewis}, N., {Knutson}, H., {Griffith}, C., {Showman}, A., {Fortney}, J., {Cowan}, N., {Agol}, E., {Burrows}, A., {Charbonneau}, D., {Deming}, D., {Laughlin}, G., , J. (2014). "{The 4.5 {$mu$}m Full-orbit Phase Curve of the Hot Jupiter HD 209458b}". apj, 790, 53.
• Teske, J. K., Cunha, K., Schuler, S. C., Griffith, C. A., & Smith, V. V. (2013). Carbon and oxygen abundances in cool metal-rich exoplanet hosts: A case study of the C/O ratio of 55 cancri. Astrophysical Journal, 778(2).
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  Abstract: The super-Earth exoplanet 55 Cnc e, the smallest member of a five-planet system, has recently been observed to transit its host star. The radius estimates from transit observations, coupled with spectroscopic determinations of mass, provide constraints on its interior composition. The composition of exoplanetary interiors and atmospheres are particularly sensitive to elemental C/O ratio, which to first order can be estimated from the host stars. Results from a recent spectroscopic study analyzing the 6300 Å [O I] line and two C I lines suggest that 55 Cnc has a carbon-rich composition (C/O = 1.12 ± 0.09). However, oxygen abundances derived using the 6300 Å [O I] line are highly sensitive to a Ni I blend, particularly in metal-rich stars such as 55 Cnc ([Fe/H] =0.34 ± 0.18). Here, we further investigate 55 Cnc's composition by deriving the carbon and oxygen abundances from these and additional C and O absorption features. We find that the measured C/O ratio depends on the oxygen lines used. The C/O ratio that we derive based on the 6300 Å [O I] line alone is consistent with the previous value. Yet, our investigation of additional abundance indicators results in a mean C/O ratio of 0.78 ± 0.08. The lower C/O ratio of 55 Cnc determined here may place this system at the sensitive boundary between protoplanetary disk compositions giving rise to planets with high (>0.8) versus low (
• Teske, J. K., Schuler, S. C., Cunha, K., Smith, V. V., & Griffith, C. A. (2013). Carbon and oxygen abundances in the hot Jupiter exoplanet host star XO-2B and its binary companion. Astrophysical Journal Letters, 768(1).
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  Abstract: With the aim of connecting the compositions of stars and planets, we present the abundances of carbon and oxygen, as well as iron and nickel, for the transiting exoplanet host star XO-2N and its wide-separation binary companion XO-2S. Stellar parameters are derived from high-resolution, high signal-to-noise spectra, and the two stars are found to be similar in their T eff, log g, iron ([Fe/H]), and nickel ([Ni/H]) abundances. Their carbon ([C/H]) and oxygen ([O/H]) abundances also overlap within errors, although XO-2N may be slightly more C-rich and O-rich than XO-2S. The C/O ratios of both stars (∼0.60 ± 0.20) may also be somewhat larger than solar (C/O ∼ 0.50). The XO-2 system has a transiting hot Jupiter orbiting one binary component but not the other, allowing us to probe the potential effects planet formation might have on the host star composition. Additionally, with multiple observations of its atmosphere the transiting exoplanet XO-2b lends itself to compositional analysis, which can be compared to the natal chemical environment established by our binary star elemental abundances. This work sets the stage for determining how similar or different exoplanet and host star compositions are, and the implications for planet formation, by discussing the C/O ratio measurements in the unique environment of a visual binary system with one star hosting a transiting hot Jupiter. © 2013. The American Astronomical Society. All rights reserved.
• Teske, J. K., Turner, J. D., Mueller, M., & Griffith, C. A. (2013). Optical observations of the transiting exoplanet GJ 1214b. Monthly Notices of the Royal Astronomical Society, 431(2), 1669-1677.
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  Abstract: We observed nine primary transits of the super-Earth exoplanet GJ 1214b in several optical photometric bands from 2012 March to August, with the goal of constraining the short-wavelength slope of the spectrum of GJ 1214b. Our observations were conducted on the Kuiper 1.55 m telescope in Arizona and the STELLA-I robotic 1.2 m telescope in Tenerife, Spain. From the derived light curves we extracted transit depths in R (0.65 μm), V (0.55 μm) and g' (0.475 μm) bands. Most previous observations of this exoplanet suggest a flat spectrum varying little with wavelength from the near-infrared to the optical, corresponding to a low-scale height, high-molecular-weight atmosphere. However, a handful of observations around Ks band (∼2.15 μm) and g band (∼0.46 μm) are inconsistent with this scenario and suggest a variation on a hydrogen- or water-dominated atmosphere that also contains a haze layer of small particles. In particular, the g-band observations of de Mooij et al., consistent with Rayleigh scattering, limit the potential atmosphere compositions of GJ 1214b due to the increasing slope at optical wavelengths. We find that our results overlap within errors the short-wavelength observations of de Mooij et al., but are also consistent with a spectral slope of zero in GJ 1214b in the optical wavelength region. Our observations thus allow for a larger suite of possible atmosphere compositions, including those with a high molecular weight and/or hazes. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.
• Griffith, C. A., Doose, L., Tomasko, M. G., Penteado, P. F., & See, C. (2012). Radiative transfer analyses of Titan's tropical atmosphere. Icarus, 218(2), 975-988.
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  Abstract: Titan's optical and near-IR spectra result primarily from the scattering of sunlight by haze and its absorption by methane. With a column abundance of 92km amagat (11 times that of Earth), Titan's atmosphere is optically thick and only ∼10% of the incident solar radiation reaches the surface, compared to 57% on Earth. Such a formidable atmosphere obstructs investigations of the moon's lower troposphere and surface, which are highly sensitive to the radiative transfer treatment of methane absorption and haze scattering. The absorption and scattering characteristics of Titan's atmosphere have been constrained by the Huygens Probe Descent Imager/Spectral Radiometer (DISR) experiment for conditions at the probe landing site (Tomasko, M.G., Bézard, B., Doose, L., Engel, S., Karkoschka, E. [2008a]. Planet. Space Sci. 56, 624-247; Tomasko, M.G. et al. [2008b]. Planet. Space Sci. 56, 669-707). Cassini's Visual and Infrared Mapping Spectrometer (VIMS) data indicate that the rest of the atmosphere (except for the polar regions) can be understood with small perturbations in the high haze structure determined at the landing site (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]. Icarus 206, 352-365). However the in situ measurements were analyzed with a doubling and adding radiative transfer calculation that differs considerably from the discrete ordinates codes used to interpret remote data from Cassini and ground-based measurements. In addition, the calibration of the VIMS data with respect to the DISR data has not yet been tested. Here, VIMS data of the probe landing site are analyzed with the DISR radiative transfer method and the faster discrete ordinates radiative transfer calculation; both models are consistent (to within 0.3%) and reproduce the scattering and absorption characteristics derived from in situ measurements. Constraints on the atmospheric opacity at wavelengths outside those measured by DISR, that is from 1.6 to 5.0μm, are derived using clouds as diffuse reflectors in order to derive Titan's surface albedo to within a few percent error and cloud altitudes to within 5km error. VIMS spectra of Titan at 2.6-3.2μm indicate not only spectral features due to CH 4 and CH 3D (Rannou, P., Cours, T., Le Mouélic, S., Rodriguez, S., Sotin, C., Drossart, P., Brown, R. [2010]. Icarus 208, 850-867), but also a fairly uniform absorption of unknown source, equivalent to the effects of a darkening of the haze to a single scattering albedo of 0.63±0.05. Titan's 4.8μm spectrum point to a haze optical depth of 0.2 at that wavelength. Cloud spectra at 2μm indicate that the far wings of the Voigt profile extend 460cm -1 from methane line centers. This paper releases the doubling and adding radiative transfer code developed by the DISR team, so that future studies of Titan's atmosphere and surface are consistent with the findings by the Huygens Probe. We derive the surface albedo at eight spectral regions of the 8×12km 2 area surrounding the Huygens landing site. Within the 0.4-1.6μm spectral region our surface albedos match DISR measurements, indicating that DISR and VIMS measurements are consistently calibrated. These values together with albedos at longer 1.9-5.0μm wavelengths, not sampled by DISR, resemble a dark version of the spectrum of Ganymede's icy leading hemisphere. The eight surface albedos of the landing site are consistent with, but not deterministic of, exposed water ice with dark impurities. © 2011 Elsevier Inc.
• Tinetti, G., Tennyson, J., Griffith, C. A., & Waldmann, I. (2012). Water in exoplanets. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 370(1968), 2749-2764.
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  PMID: 22547242;Abstract: Exoplanets-planets orbiting around stars other than our own Sun-appear to be common. Significant research effort is now focused on the observation and characterization of exoplanet atmospheres. Species such as water vapour, methane, carbon monoxide and carbon dioxide have been observed in a handful of hot, giant, gaseous planets, but cooler, smaller planets such as Gliese 1214b are now analysable with current telescopes. Water is the key chemical dictating habitability. The current observations of water in exoplanets from both space and the ground are reviewed. Controversies surrounding the interpretation of these observations are discussed. Detailed consideration of available radiative transfer models and linelists are used to analyse these differences in interpretation. Models suggest that there is a clear need for data on the pressure broadening of water transitions by H2 at high temperatures. The reported detections of water appear to be robust, although final confirmation will have to await the better quality observational data provided by currently planned dedicated space missions. © 2012 The Royal Society.
• Waldmann, I. P., Tinetti, G., Drossart, P., Swain, M. R., Deroo, P., & Griffith, C. A. (2012). Ground-based near-infrared emission spectroscopy of HD 189733B. Astrophysical Journal, 744(1).
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  Abstract: We investigate the K- and L-band dayside emission of the hot-Jupiter HD 189733b with three nights of secondary eclipse data obtained with the SpeX instrument on the NASA Infrared Telescope Facility. The observations for each of these three nights use equivalent instrument settings and the data from one of the nights have previously been reported by Swain et al. We describe an improved data analysis method that, in conjunction with the multi-night data set, allows increased spectral resolution (R ∼ 175) leading to high-confidence identification of spectral features. We confirm the previously reported strong emission at ∼3.3 μm and, by assuming a 5% vibrational temperature excess for methane, we show that non-LTE emission from the methane ν3 branch is a physically plausible source of this emission. We consider two possible energy sources that could power non-LTE emission and additional modeling is needed to obtain a detailed understanding of the physics of the emission mechanism. The validity of the data analysis method and the presence of strong 3.3 μm emission are independently confirmed by simultaneous, long-slit, L-band spectroscopy of HD 189733b and a comparison star.
• Beaulieu, J. -., Tinetti, G., Kipping, D. M., Ribas, I., Barber, R. J., Cho, J. Y., Polichtchouk, I., Tennyson, J., Yurchenko, S. N., Griffith, C. A., Batista, V., Waldmann, I., Miller, S., Carey, S., Mousis, O., Fossey, S. J., & Aylward, A. (2011). Methane in the atmosphere of the transiting hot Neptune GJ436B?. Astrophysical Journal, 731(1).
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  Abstract: We present an analysis of seven primary transit observations of the hot Neptune GJ436b at 3.6, 4.5, and 8 μm obtained with the Infrared Array Camera on the Spitzer Space Telescope. After correcting for systematic effects, we fitted the light curves using the Markov Chain Monte Carlo technique. Combining these new data with the EPOXI, Hubble Space Telescope, and ground-based V, I, H, and Ks published observations, the range 0.5-10 μm can be covered. Due to the low level of activity of GJ436, the effect of starspots on the combination of transits at different epochs is negligible at the accuracy of the data set. Representative climate models were calculated by using a three-dimensional, pseudospectral general circulation model with idealized thermal forcing. Simulated transit spectra of GJ436b were generated using line-by-line radiative transfer models including the opacities of the molecular species expected to be present in such a planetary atmosphere. A new, ab-initio-calculated, line list for hot ammonia has been used for the first time. The photometric data observed at multiple wavelengths can be interpreted with methane being the dominant absorption after molecular hydrogen, possibly with minor contributions from ammonia, water, and other molecules. No clear evidence of carbon monoxide and carbon dioxide is found from transit photometry. We discuss this result in the light of a recent paper where photochemical disequilibrium is hypothesized to interpret secondary transit photometric data. We show that the emission photometric data are not incompatible with the presence of abundant methane, but further spectroscopic data are desirable to confirm this scenario. © 2011. The American Astronomical Society. All rights reserved.
• Mousis, O., Lunine, J. I., Petit, J. -., Zahnle, K., Biennier, L., Picaud, S., Johnson, T. V., Mitchell, J. B., Boudon, V., Cordier, D., Devel, M., Georges, R., Griffith, C., Iro, N., Marley, M. S., & Marboeuf, U. (2011). On the volatile enrichments and heavy element content in HD189733b. Astrophysical Journal, 727(2).
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  Abstract: Favored theories of giant planet formation center around two main paradigms, namely the core accretion model and the gravitational instability model. These two formation scenarios support the hypothesis that the giant planet metallicities should be higher or equal to that of the parent star. Meanwhile, spectra of the transiting hot Jupiter HD189733b suggest that carbon and oxygen abundances range from depleted to enriched with respect to the star. Here, using a model describing the formation sequence and composition of planetesimals in the protoplanetary disk, we determine the range of volatile abundances in the envelope of HD189733b that is consistent with the 20-80 M * of heavy elements estimated to be present in the planet's envelope. We then compare the inferred carbon and oxygen abundances to those retrieved from spectroscopy, and we find a range of supersolar values that directly fit both spectra and internal structure models. In some cases, we find that the apparent contradiction between the subsolar elemental abundances and the mass of heavy elements predicted in HD189733b by internal structure models can be explained by the presence of large amounts of carbon molecules in the form of polycyclic aromatic hydrocarbons and soots in the upper layers of the envelope, as suggested by recent photochemical models. A diagnostic test that would confirm the presence of these compounds in the envelope is the detection of acetylene. Several alternative hypotheses that could also explain the subsolar metallicity of HD189733b are formulated: the possibility of differential settling in its envelope, the presence of a larger core that did not erode with time, a mass of heavy elements lower than the one predicted by interior models, a heavy element budget resulting from the accretion of volatile-poor planetesimals in specific circumstances, or the combination of all these mechanisms. © 2011. The American Astronomical Society.
• Beaulieu, J. P., Kipping, D. M., Batista, V., Tinetti, G., Ribas, I., Carey, S., Noriega-Crespo, J., Griffith, C. A., Campanella, G., Dong, S., Tennyson, J., Barber, R. J., Deroo, P., Fossey, S. J., Liang, D., Swain, M. R., Yung, Y., & Allard, N. (2010). Water in the atmosphere of HD 209458b from 3.6-8 μm IRAC photometric observations in primary transit. Monthly Notices of the Royal Astronomical Society, 409(3), 963-974.
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  Abstract: The hot Jupiter HD 209458b was observed during primary transit at 3.6, 4.5, 5.8 and 8.0 μm using the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. We describe the procedures we adopted to correct for the systematic effects present in the IRAC data and the subsequent analysis. The light curves were fitted including limb-darkening effects and fitted using Markov Chain Monte Carlo and prayer-bead Monte Carlo techniques, obtaining almost identical results. The final depth measurements obtained by a combined Markov Chain Monte Carlo fit are at 3.6 μm, 1.469 ± 0.013 and 1.448 ± 0.013 per cent; at 4.5 μm, 1.478 ± 0.017 per cent; at 5.8 μm, 1.549 ± 0.015 per cent; and at 8.0 μm, 1.535 ± 0.011 per cent. Our results clearly indicate the presence of water in the planetary atmosphere. Our broad-band photometric measurements with IRAC prevent us from determining the additional presence of other molecules such as CO, CO2 and methane for which spectroscopy is needed. While water vapour with a mixing ratio of combined with thermal profiles retrieved from the day side may provide a very good fit to our observations, this data set alone is unable to resolve completely the degeneracy between water abundance and atmospheric thermal profile. © 2010 The Authors. Journal compilation © 2010 RAS.
• Penteado, P. F., & Griffith, C. A. (2010). Ground-based measurements of the methane distribution on Titan. Icarus, 206(1), 345-351.
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  Abstract: Using spectra taken with NIRSPEC (Near Infrared Spectrometer) and adaptive optics on the Keck II telescope, we resolved the latitudinal variation of the 3 ν2 band of CH3 D at 1.56 μm. As CH3 D is less abundant than CH4 by a factor of 50 ± 10 × 10- 5, these CH3 D lines do not saturate in Titan's atmosphere, and are well characterized by laboratory measurements. Thus they do not suffer from the large uncertainties of the CH4 lines that are weak enough to be unsaturated in Titan. Our measurements of the methane abundance are confined to the latitude range of 32°S-18°N and longitudes sampled by a 0.04″ slit centered at ∼195°W. The methane abundance below 10 km is constant to within 20% in the tropical atmosphere sampled by our observations, consistent with the low surface insolation and lack of surface methane [Griffith, C.A., McKay, C.P., Ferri, F., 2008. Astrophys. J. 687, L41-L44]. © 2009 Elsevier Inc. All rights reserved.
• Swain, M. R., Deroo, P., Griffith, C. A., Tinetti, G., Thatte, A., Vasisht, G., Chen, P., Bouwman, J., Crossfield, I. J., Angerhausen, D., Afonso, C., & Henning, T. (2010). A ground-based near-infrared emission spectrum of the exoplanet HD 189733b. Nature, 463(7281), 637-639.
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  PMID: 20130645;Abstract: Detection of molecules using infrared spectroscopy probes the conditions and compositions of exoplanet atmospheres. Water (H2 O), methane (CH4), carbon dioxide (CO2), and carbon monoxide (CO) have been detected in two hot Jupiters. These previous results relied on space-based telescopes that do not provide spectroscopic capability in the 2.4-5.2 μm spectral region. Here we report ground-based observations of the dayside emission spectrum for HD 189733b between 2.0-2.4 μm and 3.1-4.1 μm, where we find a bright emission feature. Where overlap with space-based instruments exists, our results are in excellent agreement with previous measurements. A feature at ∼ 3.25 μm is unexpected and difficult to explain with models that assume local thermodynamic equilibrium (LTE) conditions at the 1 bar to 1 ×-10-6 bar pressures typically sampled by infrared measurements. The most likely explanation for this feature is that it arises from non-LTE emission from CH4, similar to what is seen in the atmospheres of planets in our own Solar System. These results suggest that non-LTE effects may need to be considered when interpreting measurements of strongly irradiated exoplanets. © 2010 Macmillan Publishers Limited. All rights reserved.
• Tinetti, G., Deroo, P., Swain, M. R., Griffith, C. A., Vasisht, G., Brown, L. R., Burke, C., & McCullough, P. (2010). Probing the terminator region atmosphere of the hot-jupiter xo-1b with transmission spectroscopy. Astrophysical Journal Letters, 712(2 PART 2), L139-L142.
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  Abstract: We report here the first infrared spectrum of the hot-Jupiter XO-1b. The observations were obtained with the NICMOS instrument on board the Hubble Space Telescope during a primary eclipse of the XO-1 system. Near photon-noise-limited spectroscopy between 1.2 and 1.8 μm allows us to determine the main composition of this hot-Jupiter's planetary atmosphere with good precision. This is the third hot-Jupiter's atmosphere for which spectroscopic data are available in the near-IR. The spectrum shows the presence of water vapor (H 2O), methane (CH4), and carbon dioxide (CO2), and suggests the possible presence of carbon monoxide (CO). We show that the published IRAC secondary transit emission photometric data are compatible with the atmospheric composition at the terminator determined from the NICMOS spectrum, with a range of possible mixing ratios and thermal profiles; additional emission spectroscopy data are needed to reduce the degeneracy of the possible solutions. Finally, we note the similarity between the 1.2-1.8 μm transmission spectra of XO-1b and HD 209458b, suggesting that in addition to having similar stellar/orbital and planetary parameters the two systems may also have a similar exoplanetary atmospheric composition. © 2010. The American Astronomical Society. All rights reserved.
• Tinetti, G., Griffith, C. A., Swain, M. R., Deroo, P., Beaulieu, J. P., Vasisht, G., Kipping, D., Waldmann, I., Tennyson, J., Barber, R. J., Bouwman, J., Allard, N., & Brown, L. R. (2010). Exploring extrasolar worlds: From gas giants to terrestrial habitable planets. Faraday Discussions, 147, 369-377.
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  Abstract: Almost 500 extrasolar planets have been found since the discovery of 51 Peg b by Mayor and Queloz in 1995. The traditional field of planetology has thus expanded its frontiers to include planetary environments not represented in our Solar System. We expect that in the next five years space missions (Corot, Kepler and GAIA) or ground-based detection techniques will both increase exponentially the number of new planets discovered and lower the present limit of a ∼1.9 Earth-mass object [e.g. Mayor et al., Astron. Astrophys., 2009, 507, 487]. While the search for an Earth-twin orbiting a Sun-twin has been one of the major goals pursued by the exoplanet community in the past years, the possibility of sounding the atmospheric composition and structure of an increasing sample of exoplanets with current telescopes has opened new opportunities, unthinkable just a few years ago. As a result, it is possible now not only to determine the orbital characteristics of the new bodies, but moreover to study the exotic environments that lie tens of parsecs away from us. The analysis of the starlight not intercepted by the thin atmospheric limb of its planetary companion (transit spectroscopy), or of the light emitted/reflected by the exoplanet itself, will guide our understanding of the atmospheres and the surfaces of these extrasolar worlds in the next few years. Preliminary results obtained by interpreting current atmospheric observations of transiting gas giants and Neptunes are presented. While the full characterisation of an Earth-twin might requires a technological leap, our understanding of large terrestrial planets (so called super-Earths) orbiting bright, later-type stars is within reach by current space and ground telescopes. © 2010 The Royal Society of Chemistry.
• Boudon, V., Champion, J., Gabard, T., Loëte, M., Coustenis, A., Bergh, C. D., Bézard, B., Lellouch, E., Drossart, P., Hirtzig, M., Negrão, A., & Griffith, C. A. (2009). Methane in Titan's atmosphere: From fundamental spectroscopy to planetology. Europhysics News, 40(4), 17-20.
• Griffith, C. A., Penteado, P., Rodriguez, S., Mouélic, S. L., Baines, K. H., Buratti, B., Clark, R., Nicholson, P., Jaumann, R., & Sotin, C. (2009). Characterization of clouds in Titan's tropical atmosphere. Astrophysical Journal Letters, 702(2 PART 2), L105-L109.
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  Abstract: Images of Titan's clouds, possible over the past 10 years, indicate primarily discrete convective methane clouds near the south and north poles and an immense stratiform cloud, likely composed of ethane, around the north pole. Here we present spectral images from Cassini's Visual Mapping Infrared Spectrometer that reveal the increasing presence of clouds in Titan's tropical atmosphere. Radiative transfer analyses indicate similarities between summer polar and tropical methane clouds. Like their southern counterparts, tropical clouds consist of particles exceeding 5 μm. They display discrete structures suggestive of convective cumuli. They prevail at a specific latitude band between 8°-20° S, indicative of a circulation origin and the beginning of a circulation turnover. Yet, unlike the high latitude clouds that often reach 45 km altitude, these discrete tropical clouds, so far, remain capped to altitudes below 26 km. Such low convective clouds are consistent with the highly stable atmospheric conditions measured at the Huygens landing site. Their characteristics suggest that Titan's tropical atmosphere has a dry climate unlike the south polar atmosphere, and despite the numerous washes that carve the tropical landscape. © 2009. The American Astronomical Society.
• Griffith, C., & Griffith, C. A. (2009). Storms, polar deposits and the methane cycle in Titan's atmosphere. Philosophical transactions. Series A, Mathematical, physical, and engineering sciences, 367(1889).
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  In Titan's atmosphere, the second most abundant constituent, methane, exists as a gas, liquid and solid, and cycles between the atmosphere and the surface. Similar to the Earth's hydrological cycle, Titan sports clouds, rain and lakes. Yet, Titan's cycle differs dramatically from its terrestrial counterpart, and reveals the workings of weather in an atmosphere that is 10 times thicker than the Earth's atmosphere, that is two orders of magnitude less illuminated, and that involves a different condensable. While ongoing measurements by the Cassini-Huygens mission are revealing the intricacies of the moon's weather, circulation, lake coverage and geology, knowledge is still limited by the paucity of observations. This review of Titan's methane cycle therefore focuses on measured characteristics of the lower atmosphere and surface that appear particularly perplexing or alien.
• McKay, C. P., Griffith, C. A., Ferri, F., & Fulchignoni, M. (2009). Comparing methane and temperature profiles on Titan in 1980 and 2005. Planetary and Space Science, 57(14-15), 1996-2000.
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  Abstract: The Huygens Probe data provided a direct measurement of CH4, temperature, and pressure in Titan's atmosphere. This data can be used to compare to the Voyager data in which the effects of CH4, temperature, and pressure were mixed together. Comparison with Huygens data indicates that values of the surface relative humidity of CH4 at the Voyager ingress and egress were between 20% and 45%, and values above 60% are inconsistent with this comparison. The most parsimonious explanation for the Voyager data is that the temperature and CH4 surface humidity at the Voyager ingress and egress profiles were identical to the Huygens values; a surface temperature of 93.65±0.25 K, and a surface relative humidity of 43%. Thus, it is likely that these values have characterized the equatorial region of Titan from 1980 until 2005. The small reduction of 1 K, between the tropopause temperatures of the Voyager profiles and the tropopause temperature of the Huygens profile is explainable by a change in the antigreenhouse flux from the stratosphere from 0.13 to 0.1 of the total average solar flux. This could result from a small seasonal change in the optical properties of the stratospheric haze.
• Swain, M. R., Tinetti, G., Vasisht, G., Deroo, P., Griffith, C., Bouwman, J., Chen, P., Yung, Y., Burrows, A., Brown, L. R., Matthews, J., Rowe, J. F., Kuschnig, R., & Angerhausen, D. (2009). Water, methane, and carbon dioxide present in the dayside spectrum of the exoplanet HD 209458b. Astrophysical Journal Letters, 704(2), 1616-1621.
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  Abstract: Using the NICMOS instrument on the Hubble Space Telescope, we have measured the dayside spectrum of HD 209458b between 1.5 and 2.5 μm. The emergent spectrum is dominated by features due to the presence of methane (CH 4) and water vapor (H2O), with smaller contributions from carbon dioxide (CO2). Combining this near-infrared spectrum with existing mid-infrared measurements shows the existence of a temperature inversion and confirms the interpretation of previous photometry measurements. We find a family of plausible solutions for the molecular abundance and detailed temperature profile. Observationally resolving the ambiguity between abundance and temperature requires either (1) improved wavelength coverage or spectral resolution of the dayside emission spectrum or (2) a transmission spectrum where abundance determinations are less sensitive to the temperature structure. © 2009. The American Astronomical Society. All rights reserved.
• Graves, S. D., McKay, C. P., Griffith, C. A., Ferri, F., & Fulchignoni, M. (2008). Rain and hail can reach the surface of Titan. Planetary and Space Science, 56(3-4), 346-357.
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  Abstract: We have calculated the condensation and evaporation of ternary CH4-N2-C2H6 liquid drops and solid CH4 hail as they fall through Titan's lower atmosphere to determine the likelihood that precipitation reaches the ground. Assuming the humidity profile determined by the Huygens probe, binary liquid CH4/N2 condensate grows in the region from ∼8 to 15 km in Titan's atmosphere because the combined humidity of CH4 and N2 exceeds saturation. These drops evaporate below ∼8 km. We determine the fate of 10 μm seeds composed of ethane, which is expected to provide condensation sites. In addition, we study the fate of already formed raindrops with radii of 1-4.75 mm falling out of the growth region. High (50%) and low (0%) ethane relative humidities (RH) are considered in the calculation. We find that drops with radii ∼3 mm and smaller dropping from 8 km reach the ground in compositional equilibrium with the atmosphere in the high ethane RH case as a result of the stabilizing influence of the ethane, and evaporate in the atmosphere in the low ethane RH case. Large drops (>∼3 mm) reach the surface large and cold because the latent heat loss due to the evaporation of methane cools the drop and slows the evaporation rate. Pure methane hail hits the ground if its radius is initially more than 4 mm at 16 km above the surface and sublimates in the atmosphere if its radius is smaller. © 2007 Elsevier Ltd. All rights reserved.
• Griffith, C. A., McKay, C. P., & Ferri, F. (2008). Titan's tropical storms in an evolving atmosphere. Astrophysical Journal, 687(1), L41-L44.
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  Abstract: The Huygens probe landed in a damp lake bed fed by fluvial channels, indicative of past rainfall. Such washes, interspersed with vast dunes, are typical of Titan's tropical landscape. Yet, Cassini-Huygens measurements reveal a highly stable tropical atmosphere devoid of deep convective storms, and the formation of washes in dune fields is not understood. Here we examine the effects of seasonal variations in humidity, surface heating, and dynamical forcing on the stability of Titan's troposphere. We find that during the probe landing, the middle troposphere was weakly unstable to convection, consistent with the tenuous cloud detected at 21 km. Yet the tropical atmosphere, at any season, is too stable to produce deep convective storms. Convection in the tropics remains weak and confined to altitudes below ∼30 km, unless the humidity is increased below 9 km altitude. Solar heating is insufficient to significantly humidify the tropical atmosphere. The large polar lakes are seasonably stable, and the methane column abundance measured by Huygens typical of the tropical atmosphere. Our study indicates the presence of distinct polar and equatorial climates. It also suggests that fluvial features in the tropics do not result from recent seasonal rainstorms, and thereby supports other origins such as geological seepage, cryovolcanism, or a wetter climate in the past. © 2008. The American Astronomical Society. All rights reserved.
• Ádámkovics, M., Pater, I. d., Hartung, M., Eisenhauer, F., Genzel, R., & Griffith, C. A. (2008). Erratum: "Titan's bright spots: Multiband spectroscopic measurement of surface diversity and hazes" (Journal of Geophysical Research (2006) vol. 111 10.1029/2005JE002610). Journal of Geophysical Research E: Planets, 113(2).
• Griffith, C. A. (2007). Titan's lower atmosphere. AIP Conference Proceedings, 930, 3-36.
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  Abstract: Saturn's largest moon, Titan, sports an atmosphere 10 times thicker than Earth's. Like Earth, the moon's atmosphere is N2 based and possesses a rich organic chemistry. In addition, similar to the terrestrial hydrological cycle, Titan has a methane cycle, with methane clouds, rain and seas. Presently, there is a revolution in our understanding of the moon, as data flows in and is analyzed from the NASA and ESA Cassini-Huygens mission. For example, seas were detected only this year. Here I will discuss the evolution of our understanding of Titan's atmosphere, its composition, chemistry, dynamics and origin. Current open questions will also be presented. Studies of Titan's atmosphere began and evolved to the present state in less time than that of a single scientist's career. This short interlude of activity demonstrates the rigors of the scientific method, and raises enticing questions about the workings and evolution of an atmosphere. © 2007 American Institute of Physics.
• Griffith, C. A. (2006). Planetary science: Titan's exotic weather. Nature, 442(7101), 362-363.
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  PMID: 16871198;Abstract: Titan is viewed as a sibling of Earth, as both bodies have rainy weather systems and landscapes formed by rivers. But as we study these similarities, Titan emerges as an intriguingly foreign world. ©2006 Nature Publishing Group.
• Ádámkovics, M., Pater, I. d., Hartung, M., Eisenhauer, F., Genzel, R., & Griffith, C. A. (2006). Titan's bright spots: Multiband spectroscopic measurement of surface diversity and hazes. Journal of Geophysical Research E: Planets, 111(7).
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  Abstract: Spatially resolved near-infrared spectra of Titan, which simultaneously cover two CH4 absorption bands (from 1.45 to 2.45 μm), have been obtained using the SINFONI integral-field spectrometer with adaptive optics at the Very Large Telescope (VLT) of the European Southern Observatory. We observe the enhancement in 2 μm surface albedo of the "5 μm bright spot" at 80°W and 24°S, and find an analogously bright region at 2 μm near 88°W and 6°S. Surface albedos are recovered at ∼60 mas (375 km) resolution in both 1.5 and 2.0 μm windows using a two-stream, plane-parallel, radiative transfer model to fit the observed spectra. The surface albedos near the center of the disk range from 8 to 15% at 1.5 μm and are generally ∼2% lower at 2.0 μm. Vertical (altitude) profiles of aerosol extinction that are consistent with the Huygens/DISR measurements are used to model these observations, and we retrieve latitudinal trends in both stratospheric and tropospheric aerosol extinction. On 28 February 2005 UT, the stratospheric aerosol extinction is measured to increase linearly at a rate of 0.65 ± 0.05% per degree latitude from 40°S to 60°N. Meanwhile, the tropospheric haze near the south pole is confined to southern latitudes above 40°S and is enhanced in extinction by a factor of ∼1.7 relative to the extinction measured at 10°S, the latitude where the Huygens probe landed. Copyright 2006 by the American Geophysical Union.
• Greathouse, T. K., Lacy, J. H., Bézard, B., Moses, J. I., Griffith, C. A., & Richter, M. J. (2005). Meridional variations of temperature, C₂H₂ and C₂H₆ abundances in Saturn's stratosphere at southern summer solstice. Icarus, 177(1), 18-31.
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  Abstract: Measurements of the vertical and latitudinal variations of temperature and C2H2 and C2H6 abundances in the stratosphere of Saturn can be used as stringent constraints on seasonal climate models, photochemical models, and dynamics. The summertime photochemical loss timescale for C2H6 in Saturn's middle and lower stratosphere (∼40 - 10,000 years, depending on altitude and latitude) is much greater than the atmospheric transport timescale; ethane observations may therefore be used to trace stratospheric dynamics. The shorter chemical lifetime for C2 H2 (∼1 - 7 years depending on altitude and latitude) makes the acetylene abundance less sensitive to transport effects and more sensitive to insolation and seasonal effects. To obtain information on the temperature and hydrocarbon abundance distributions in Saturn's stratosphere, high-resolution spectral observations were obtained on September 13-14, 2002 UT at NASA's IRTF using the mid-infrared TEXES grating spectrograph. At the time of the observations, Saturn was at a LS ≈270°, corresponding to Saturn's southern summer solstice. The observed spectra exhibit a strong increase in the strength of methane emission at 1230 cm-1 with increasing southern latitude. Line-by-line radiative transfer calculations indicate that a temperature increase in the stratosphere of ≈ 10 K from the equator to the south pole between 10 and 0.01 mbar is implied. Similar observations of acetylene and ethane were also recorded. We find the 1.16 mbar mixing ratio of C2H2 at -1° and -83° planetocentric latitude to be 9.2-3.8+6.4 × 10-7 and 2.5-1.0+1.8 × 10-7, respectively. The C2H2 mixing ratio at 0.12 mbar is found to be 1.0-0.3+0.5 × 10-5 at 1° planetocentric latitude and 2.6-0.9+1.3 × 10-6 at -83° planetocentric latitude. The 2.3 mbar mixing ratio of C2 H6 inferred from the data is 7.5-1.7+2.3 × 10 -6 and 1.0-0.2+0.3 × 10-5 at -1° and -83° planetocentric latitude, respectively. Further observations, creating a time baseline, will be required to completely resolve the question of how much the latitudinal variations of C2H2 and C2H6 are affected by seasonal forcing and/or stratospheric circulation. © 2005 Elsevier Inc. All rights reserved.
• Lorenz, R. D., Griffith, C. A., Lunine, J. I., McKay, C. P., & Rennò, N. O. (2005). Convective plumes and the scarcity of Titan's clouds. Geophysical Research Letters, 32(1), 1-4.
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  Abstract: We show that simple thermodynamic models of convective plumes predict the area fraction of convective plumes (i.e., updrafts) in Titan's atmosphere to be ∼12 smaller than on Earth. This result is in agreement with predictions by sophisticated dynamical models and with the relative tropospheric cloud cover, which is only ∼1% on Titan. Rainstorms on Titan, being so rare, may be violent. Copyright 2005 by the American Geophysical Union.
• Penteado, P. F., Griffith, C. A., Greathouse, T. K., & Bergh, C. D. (2005). Measurements of CH₃D and CH₄ in Titan from infrared spectroscopy. Astrophysical Journal Letters, 629(1 II), L53-L56.
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  Abstract: We measured the CH4 column abundance in Titan's atmosphere through an analysis of Titan's monodeuterated methane (CH3D) spectral features. CH3D is several orders of magnitude less abundant in Titan's atmosphere than CH4. Thus, unlike CH4, the strong and well-studied CH3D 3ν2 lines are not saturated and provide a sensitive measure of its column abundance. We recorded the CH3D 3ν2 lines at 1.55 μm at NASA's Infrared Telescope Facility (IRTF) equipped with the Cryogenic Echelle Spectrograph. We derive a total integrated column abundance of 2.1 ±0.1 m amagat for CH3D. We also measured stratospheric emission lines of both CH 3D and CH4 at 8.6 μm at higher resolution than previously possible to better constrain the CH3D/CH4 ratio. These observations, recorded at the IRTF using the Texas Echelon Cross Echelle Spectrograph, were analyzed with radiative transfer calculations. We determine a CH3D/CH4 ratio of (50 ±10) × 10-5 . Taken together, our measurements of the CH3D column abundance and the CH3D/CH4 ratio indicate a total CH4 column abundance of 4.2-0.9+1.3, km amagat, close to the column abundance of an atmosphere with 100% saturation in the entire troposphere. © 2005. The American Astronomical Society. All rights reserved.
• Griffith, C. A., Bézard, B., Greathouse, T., Lellouch, E., Lacy, J., Kelly, D., & Richter, M. J. (2004). Meridional transport of HCN from SL9 impacts on Jupiter. Icarus, 170(1), 58-69.
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  Abstract: In July 1994, the Shoemaker-Levy 9 (SL9) impacts introduced hydrogen cyanide (HCN) to Jupiter at a well confined latitude band around -44°, over a range of specific longitudes corresponding to each of the 21 fragments (Bézard et al. 1997, Icarus 125, 94-120). This newcomer to Jupiter's stratosphere traces jovian dynamics. HCN rapidly mixed with longitude, so that observations recorded later than several months after impact witnessed primarily the meridional transport of HCN north and south of the impact latitude band. We report spatially resolved spectroscopy of HCN emission 10 months and 6 years following the impacts. We detect a total mass of HCN in Jupiter's stratosphere of 1.5±0.7×1013 g in 1995 and 1.7±0.4×1013 g in 2000, comparable to that observed several days following the impacts (Bézard et al. 1997, Icarus 125, 94-120). In 1995, 10 months after impact, HCN spread to -30° and -65° latitude (half column masses), consistent with a horizontal eddy diffusion coefficient of Kyy=2-3×1010 cm2 s-1. Six years following impact HCN is observed in the northern hemisphere, while still being concentrated at 44° south latitude. Our meridional distribution of HCN suggests that mixing occurred rapidly north of the equator, with Kyy=2-5×1011 cm2 s-1, consistent with the findings of Moreno et al. (2003, Planet. Space Sci. 51, 591-611) and Lellouch et al. (2002, Icarus 159, 112-131). These inferred eddy diffusion coefficients for Jupiter's stratosphere at 0.1-0.5 mbar generally exceed those that characterize transport on Earth. The low abundance of HCN detected at high latitudes suggests that, like on Earth, polar regions are dynamically isolated from lower latitudes. © 2004 Elsevier Inc. All rights reserved.
• Pater, I. D., Ádámkovics, M., Gibbard, S., Roe, H. G., & Griffith, C. A. (2004). Flight through Titan's atmosphere. European Space Agency, (Special Publication) ESA SP, 313-321.
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  Abstract: We assembled spectral image data cubes of Titan in H-band (1.413-1.808 μm), using adaptive optics on the 10-m W.M. Keck telescope, by stepping a spectrometer slit across Titan's disk. We constructed images of Titan at each wavelength by 'glueing' the spectra together, producing 1400ultra-narrowband (∼0.1 nm) views of the satellite. With this method one can characterise Titan's atmosphere over the entire disk, in more specific vertical detail than possible with either narrowband imaging or slit spectroscopy at one position. Data were obtained of Titan's leading hemisphere on UT 20 February 2001. At the shorter wavelengths we probe all the way down to the surface, revealing the familiar bright and dark terrain, while at longer wavelengths we probe various altitudes in the atmosphere. The data have been assembled into a movie, showing the surface and different haze layers while stepping up in altitude. The transitions from the surface to the tropospheric haze, and through the tropopause into the upper atmospheric haze, are clearly recognised.
• Ádámkovics, M., Pater, I. d., Roe, H. G., Gibbard, S. G., & Griffith, C. A. (2004). Spatially-resolved spectroscopy at 1.6 μm of titan's atmosphere and surface. Geophysical Research Letters, 31(17), L17S05 1-4.
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  Abstract: We present spatially-resolved, low-resolution (λ/Δλ ∼ 1,500) spectroscopy of the leading hemisphere of Titan in the H-band (1.5-1.7 μm) using adaptive optics. Spatial variations of Surface albedo are observed in images at 1.55-1.57 μm, which are clearly distinct from stratospheric haze. There is a significant increase in albedo around the southern (summer) pole at 1.62 μm. Using a plane-parallel radiative transfer model to fit the observed spectra, we find a 61% increase in tropopause haze opacity (τ = 0.100 from 30-40 km) around the southern pole relative to the rest of the disk (where τ - 0.062 from 30 40-_km). Copyright 2004 by the American Geophysical Union.
• Geballe, T. R., Kim, S. J., Noll, K. S., & Griffith, C. A. (2003). High-resolution 3 micron spectroscopy of molecules in the mesosphere and troposphere of titan. Astrophysical Journal Letters, 583(1 II), L39-L42.
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  Abstract: A high-resolution 2.9-3.5 μm spectrum of Titan has revealed a surprisingly strong emission band of hydrogen cyanide (HCN) and strong absorption bands of acetylene (C2H2) and monodeuterated methane (CH3D), in addition to methane (CH4) emission and absorption known from previous observations. Whereas the C2H 2 and CH3D absorptions are largely in the troposphere, the HCN emission must occur at higher altitudes. However, the intensity of the HCN band is inconsistent with our current understanding of the upper atmosphere of Titan.
• Griffith, C. A., Owen, T., Geballe, T. R., Rayner, J., & Rannou, P. (2003). Evidence for the exposure of water ice on Titan's surface. Science, 300(5619), 628-630.
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  PMID: 12714742;Abstract: The smoggy stratosphere of Saturn's largest moon, Titan, veils its surface from view, except at narrow wavelengths centered at 0.83, 0.94, 1.07, 1.28, 1.58, 2.0, 2.9, and 5.0 micrometers. We derived a spectrum of Titan's surface within these "windows" and detected features characteristic of water ice. Therefore, despite the hundreds of meters of organic liquids and solids hypothesized to exist on Titan's surface, its icy bedrock lies extensively exposed.
• Brown, M. E., Bouchez, A. H., & Griffith, C. A. (2002). Direct detection of variable tropospheric clouds near Titan's south pole. Nature, 420(6917), 795-797.
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  PMID: 12490943;Abstract: Atmospheric conditions on Saturn's largest satellite, Titan, allow the possibility that it could possess a methane condensation and precipitation cycle with many similarities to Earth's hydrological cycle. Detailed imaging studies of Titan have hitherto shown no direct evidence for tropospheric condensation clouds, although there has been indirect spectroscopic evidence for transient clouds. Here we report images and spectra of Titan that show clearly transient clouds, concentrated near the south pole, which is currently near the point of maximum solar heating. The discovery of these clouds demonstrates the existence of condensation and localized moist convection in Titan's atmosphere. Their location suggests that methane cloud formation is controlled seasonally by small variations in surface temperature, and that the clouds will move from the south to the north pole on a 15-year timescale.
• Young, E. F., Rannou, P., Mckay, C. P., Griffith, C. A., & Noll, K. (2002). A three-dimensional map of Titan's tropospheric haze distribution based on Hubble space telescope imaging. Astronomical Journal, 123(6 1758), 3473-3486.
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  Abstract: We use Hubble Space Telescope (HST) images of Titan obtained in late 1996 to determine a three-dimensional map of haze optical depth in Titan's atmosphere. These images, taken at six wavelengths from 888 to 953 nm, probe Titan's atmosphere at various altitudes ranging from the surface to roughly 100 km. We solve for the total haze optical depths that best match each HST image and then combine the results from each wavelength into a composite three-dimensional map. The total optical depths due to haze in these maps range from 1.7 in the northernmost latitudes to 2.9 in the southernmost ones. The vertical haze profiles are roughly exponential except for a gap between 20 and 40 km, which may be a result of ethane or methane condensation onto tholins. There is a concentration of haze in the northernmost latitudes between 0 and 15 km above the surface.
• Griffith, C. A., Hall, J. L., & Gebelle, T. R. (2000). Detection of daily clouds on Titan. Science, 290(5491), 509-513.
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  PMID: 11039930;Abstract: We have discovered frequent variations in the near-infrared spectrum of Titan, Saturn's largest moon, which are indicative of the daily presence of sparse clouds covering less than 1% of the area of the satellite. The thermodynamics of Titan's atmosphere and the clouds' altitudes suggest that convection governs their evolutions. Their short lives point to the presence of rain. We propose that Titan's atmosphere resembles Earth's, with clouds, rain, and an active weather cycle, driven by latent heat release from the primary condensible species.
• Griffith, C. A., Owen, T., Miller, G. A., & Geballe, T. (1998). Transient clouds in Titan's lower atmosphere. Nature, 395(6702), 575-578.
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  PMID: 9783583;Abstract: The 1980 encounter by the Voyager 1 spacecraft with Titan, Saturn's largest moon, revealed the presence of a thick atmosphere containing nitrogen and methane (1.4 and ~0.05 bar, respectively). Methane was found to be nearly saturated at Titan's tropopause, which, with other considerations, led to the hypothesis that Titan might experience a methane analogue of Earth's vigorous hydrological cycle, with clouds, rain and seas. Yet recent analyses of Voyager data indicate large areas of supersaturated methane, more indicative of dry and stagnant conditions. A resolution to this apparent contradiction requires observations of Titan's lower atmosphere, which was hidden from the Voyager cameras by the photochemical haze (or smog) in Titan's stratosphere. Here we report near-infrared spectroscopic observations of Titan within four narrow spectral windows where the moon's atmosphere is ostensibly transparent. We detect pronounced flux enhancements that indicate the presence of reflective methane condensation clouds in the troposphere. These clouds occur at a relatively low altitude (15 ± 10 km), at low latitudes, and appear to cover ~9 per cent of Titan's disk.
• Lara, L., Bézard, B., Griffith, C. A., Lacy, J. H., & Owen, T. (1998). High-Resolution 10-micronmeter Spectroscopy of Ammonia and Phosphine Lines on Jupiter. Icarus, 131(2), 317-333.
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  Abstract: High spectral resolution measurements of NH3and PH3lines on Jupiter in the 10.5- to 11.2-μm range are presented. Observations, recorded on January 21-23, 1991, cover the 10°-40°S latitude range and several longitudes including the Great Red Spot (GRS). Information on the temperature in the upper troposphere was retrieved from the continuum radiance at wavelengths around 12.8 and 17.8 μm. At all observed longitudes, the 200-mbar temperature field is minimum at latitudes of 20°-25°S near the location of the South Tropical Zone, in agreement with Voyager infrared retrievals. This minimum temperature is lower over the GRS than at other longitudes. The ammonia mixing ratio at ~380 mbar is not significantly enhanced over the GRS. The phosphine abundance probed at ~580 mbar is also not enhanced (within a precision of 10%), suggesting that this molecule is not a precursor of the reddish chromophores. The NH3abundance at 380 mbar varies highly with latitude and longitude, a possible consequence of the active jovian meteorology. At the resolution of our observations (~8000 km), the NH3humidity at this altitude ranges between 15 and 100% throughout the available data set. Above the cloud tops, the NH3mixing ratio in the 240-mbar region reaches a maximum near 15°-18°S and decreases by a factor of ~40 at latitudes 30°-35°S. This variation is not correlated with the 200-mbar temperature. It can be explained by a decrease of the eddy mixing coefficient near 240 mbar from ~4000 to ≤400 cm2sec-1between the two latitude ranges. The PH3mixing ratio near 580 mbar lies between 1.7 and 2.6 × 10-7in the observed regions. At all longitudes, PH3varies smoothly with latitude, decreasing by ~30% from 10° to 35°S. This variation may also reflect a decrease in the strength of the eddy mixing near 580 mbar or at deeper levels in the atmosphere. © 1998 Academic Press.
• Bézard, B., Griffith, C. A., & Kelly, D. M. (1997). Search for NH₃ in Jupiter's stratosphere ten months after SL9's collision. Icarus, 125(2), 331-339.
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  Abstract: We present high-resolution 11-μm NH3 observations of the Shoemaker-Levy 9 sites that were conducted on May 15-18, 1995 UT at the NASA Infrared Telescope Facility. No emission from stratospheric NH3 was detected at any location. The upper limit on the NH3 column density above 40 mbar is 6 × 1015 molecule cm-2, about 30 times less than that observed on July 20-31 1994 UT over the K site. Destruction of stratospheric NH3 indicates that shielding from ultraviolet radiation was not efficient over a period of several months. Latitudinal variations observed in the NH3 absorption line can be interpreted through variations in the tropospheric temperature field consistent with Voyager and ground-based observations. No change in tropospheric NH3 around impact latitude needs to be invoked to explain these variations. © 1997 Academic Press.
• Bézard, B., Griffith, C. A., Kelly, D. M., Lacy, J. H., Greathouse, T., & Orton, G. (1997). Thermal infrared imaging spectroscopy of Shoemaker-Levy 9 impact sites: Temperature and HCN retrievals. Icarus, 125(1), 94-120.
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  Abstract: We present high-resolution 8-14 μm observations of Shoemaker-Levy 9 sites conducted on July 20, 30, and 31 1994 UT at the NASA Infrared Telescope Facility. Stratospheric heating was detected from strong enhancements of methane emission near 8.1 μm over areas at least 15,000 km wide around the K site observed 23 hr after impact and around the L site 11 hr after impact. The intensity distribution between strong and weaker CH4lines implies that the stratospheric heating was primarily confined to pressures less than 500 μbar. The L site temperature increased by 80 ± 10 K at 5 μbar, but did not exceed 20 K around 1 mbar or 10 K around 10 mbar. The older K site was still 30 ± 5 K warmer than the surroundings at the 10-μbar level. The excess thermal energy stored in the upper jovian stratosphere was 3+3-1.5× 1026erg over the L site, and 2+2-1× 1026erg over the K site at the time of the observations. Comparison with numerical simulations indicates that a large fraction (
• Griffith, C. A., Bézard, B., Greathouse, T. K., Kelly, D. M., Lacy, J. H., & Noll, K. S. (1997). Thermal infrared imaging spectroscopy of Shoemaker-Levy 9 impact sites: Spatial and vertical distributions of NH₃, C₂H₄, and 10-μm dust emission. Icarus, 128(2), 275-293.
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  Abstract: Spatially resolved spectroscopy of the Shoemaker-Levy 9 (SL9) sites traces the dynamical evolution of cometary material, upwelled tropospheric gas, and compounds produced when the plume splashed back upon the atmosphere. The emissions of impact-produced stratospheric NH3, C2H4, and dust were imaged at NASA's Infrared Telescope Facility, with Irshell (the U. Texas mid-IR echelle spectrometer) 21 hr and 6, 11, and 12 days following the K impact. The images covered a ~7 × 17″ region generally centered on the K site and were composed of 0.8 × 1 arcsec pixels, each containing a spectrum of resolution ~15,000. We find evidence for two sources of NH3. Most of the stratospheric NH3resided at ~20 mbar. A second reservoir existed above 1 mbar, with a column abundance ~120lower than that of the deeper source (2 ± 1 × 1017molecules cm-2above 40 mbar for the K site). The position of the high altitude NH3suggests that it rose and was quenched within the fireball and survived the splash. The 2 ± 1 × 1013g of low altitude NH3indicates that the K impact upwelled at least ~2 × 1016g of jovian gas from Jupiter's troposphere. Its altitude coincides with the level where static stability is maximum. The NH3lineshape 12 days following impact indicates a gradual depletion of the high altitude source, which suggests that NH3was partially shielded from UV radiation. Enhanced continuum emission observed around 908 and 948 cm-1and not at wavenumbers outside the silicate feature is consistent with 8 ± 4 × 1012g of cometary dust residing in the plume fallback region. The total mass of C2H4was found to be 1 ± 0.3 × 1012g and remained constant within error limits throughout the observations. The compounds above 1 mbar displayed differing horizontal coverages consistent with each molecule's role in a ballistic plume, having a range of temperatures. Ammonia at 20 mbar spread out with time; however, its coverage was never as extensive as that of the dark material seen in HST images. In contrast, the dust, C2H4, and HCN (B. Bézardet al.1997,Icarus125,94-120), observed at significantly lower pressures than NH3, covered a broader spatial extent, similar to the coverage of the ejecta blanket observed by HST. Six days following impact, the dust and C2H4spread 7° eastward of NH3, similar to the dark particulates. The quiescent behavior of the NH3at 20 mbar in contrast to the zonal drift of the dust indicates the presence of winds above 1 mbar that are disconnected from those in the lower stratosphere. © 1997 Academic Press.
• McKay, C. P., Martin, S. C., Griffith, C. A., & Keller, R. M. (1997). Temperature lapse rate and methane in Titan's troposphere. Icarus, 129(2), 498-505.
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  PMID: 11541736;Abstract: We have reanalyzed the Voyager radio occultation data for Titan, examining two alternative approaches to methane condensation. In one approach, methane condensation is facilitated by the presence of nitrogen because nitrogen lowers the condensation level of a methane/nitrogen mixture. The resulting enhancement in methane condensation lowers the upper limit on surface relative humidity of methane obtained from the Voyager occultation data from 0.7 to 0.6. We conclude that in this case the surface relative humidity of methane lies between 0.08 and 0.6, with values close to 0.6 indicated. In the other approach, methane is allowed to become supersaturated and reaches 1.4 times saturation in the troposphere. In this case, surface humidities up to 100% are allowed by the Voyager occultation data, and thus the upper limit must be set by other considerations. We conclude that if supersaturation is included, then the surface relative humidity of methane can be any value greater than 0.08 - unless a deep ocean is present, in which case the surface relative humidity is limited to less than 0.85. Again, values close to 0.6 are indicated. Overall, the tropospheric lapse rate on Titan appears to be determined by radiative equilibrium. The lapse rate is everywhere stable against dry convection, but is unstable to moist convection. This finding is consistent with a supersaturated atmosphere in which condensation - and hence moist convection - is inhibited. © 1997 Academic Press.
• Noll, K. S., Gilmore, D., Knacke, R. F., Womack, M., Griffith, C. A., & Orton, G. (1997). Carbon monoxide in Jupiter after comet shoemaker-levy 9. Icarus, 126(2), 324-335.
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  Abstract: Observations of the carbon monoxide fundamental vibration-rotation band near 4.7 μm before and after the impacts of the fragments of Comet Shoemaker-Levy 9 showed no detectable changes in the R5 and R7 lines, with one possible exception. Observations of the G-impact site 21 hr after impact do not show CO emission, indicating that the heated portions of the stratosphere had cooled by that time. The large abundances of CO detected at the millibar pressure level by millimeter wave observations did not extend deeper in Jupiter's atmosphere. Predicted upwelling of shocked, O-rich material from below also did not occur. Combined with evidence for upwelling of N- and S-rich gas, our observations indicate that the comet fragments may not have penetrated to the H2O cloud. We find that CO concentrations in Jupiter's stratosphere may be higher than previously suspected, suggesting that some of the CO detected after the impacts may already have been present in Jupiter's stratosphere. © 1997 Academic Press.
• Lissauer, J. J., Wolk, S. J., Griffith, C. A., & Backman, D. E. (1996). The ε aurigae secondary: A hydrostatically supported disk. Astrophysical Journal Letters, 465(1 PART I), 371-384.
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  Abstract: Epsilon Aurigae is an F supergiant in a spectroscopic binary system that undergoes a flat-bottomed partial eclipse of 2 yr duration every 27 yr. The spectrum appears to be single-lined, aside from extra absorption features detected during and shortly after eclipse. Eclipse characteristics indicate that the secondary is a very elongated object 5-10 AU in dimension parallel to its orbit. Orbital characteristics and the spectral properties of the primary are consistent with two different models of the system, with the secondary having a mass of either ∼15 M⊙ or ∼4 M⊙. We have modeled the cool, dark secondary in the ε Aurigae system as a geometrically thin circumstellar disk of gas and dust (surrounding one or two unseen stars, at or near its center), which is rotationally supported about its short axis and pressure supported perpendicular to its midplane. We assume that the midplane of the disk is coplanar with the orbital plane of the system. The gross features of the eclipse light curve observed at any single wavelength are easily reproduced, using a variety of disk scale heights and optical depths, provided that we are viewing within ∼3° of the symmetry plane of the system. Central holes in the disk only affect the eclipse profile for models with low optical depth (and correspondingly large pressure scale height). The observed grayness of the eclipse in the visible and near-IR implies that the particles in the disk are significantly larger than those in the typical ISM. Either particles of radius ≲ 5 μm are almost completely absent, or the disk must be very opaque. If the disk is very opaque, then the observed eclipse depth implies a small scale height for the disk, equal to roughly 3% of the disk's radius at the outer edge. This is a factor of ∼ 1.5-2 smaller than the value expected for the low-mass model from hydrostatic balance with the disk temperature measured in the thermal-IR, suggesting that the high-mass model of the system is correct and/or the dust particles have settled into a thinner disk than the pressure-supported gas. We have also constructed a quasi-hydrodynamic model of the expansion of the material in the outermost edge of the disk secondary in response to the heating that it receives as it rotates into view of the luminous primary. Light curves computed using this model reproduce the basic features of absorption lines, which are observed to be deepest subsequent to the middle of the continuum eclipse and to persist after fourth contact. © 1996. The American Astronomical Society. All rights reserved.
• Bézard, B., Griffith, C., Lacy, J., & Owen, T. (1995). Non-Detection of Hydrogen Cyanide on Jupiter. Icarus, 118(2), 384-391.
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  Abstract: High spectral resolution observations of Jupiter performed at the NASA/Infrared Telescope Facility near 13.5 μm are presented. Two spectral ranges including the R(7) and R(11) lines of the v2 band of HCN were observed at high signal-to-noise. No evidence for HCN absorption in excess of 2% of the continuum was found, in contrast to the report by Tokunaga et al . (1981, Icarus 48, 283-289). An upper limit on the tropospheric HCN mixing ratio of 1 × 10-9 was derived, assuming a uniform value up to the tropopause. When HCN condensation in the upper troposphere is taken into account, only a looser upper limit around 1.2 × 10-8 can be set on the deep mixing ratio. The lack of emission cores at the position of the HCN lines provides an upper limit of 2 × 10-4 cm-amagat on the HCN column density in the stratosphere (corresponding to a maximum average mixing ratio of 8 × 10-10 above condensation level). A critical reanalysis of Tokunaga et al.'s observations is finally presented, leading to the conclusion that the previously reported detection of HCN is questionable. © 1995 Academic Press. All rights reserved.
• Griffith, C. A., & Zahnle, K. (1995). Influx of cometary volatiles to planetary moons: the atmospheres of 1000 possible Titans.. Journal of geophysical research, 100(E8), 16907-16922.
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  PMID: 11539417;Abstract: We use a Monte Carlo model to simulate impact histories of possible Titans, Callistos, and Ganymedes. Comets create or erode satellite atmospheres, depending on their mass and velocity distributions: faster and bigger comets remove atmophiles; slower or smaller comets supply them. Mass distributions and the minimum total mass of comets passing through the Saturn system were derived from the crater records of Rhea and Iapetus. These were then scaled to give a minimum impact history for Titan. From this cometary population, of 1000 initially airless Titans, 16% acquired atmospheres larger than Titan's present atmosphere (9 x 10(21) g), and more than half accumulated atmospheres larger than 10(21) g. In contrasts to the work of Zahnle et al. (1992), we find that, in most trials, Callisto acquires comet-based atmospheres. Atmospheres acquired by Callisto and, especially, Ganymede are sensitive to assumptions regarding energy partitioning into the ejecta plume. If we assume that only the normal velocity component heats the plume, the majority of Ganymedes and half of the Callistos accreted atmospheres smaller than 10(20) g. If all the impactor's velocity heats the plume, Callisto's most likely atmosphere is 10(17) g and Ganymede's is negligible. The true cometary flux was most likely larger than that derived from crater records, which raises the probability that Titan, Ganymede, and Callisto acquired substantial atmospheres. However, other loss processes (e.g., sputtering by ions swept up by the planetary magnetic field, solar UV photolysis of hydrocarbons) are potentially capable of eliminating small atmospheres over the age of the solar system. The dark material on Callisto's surface may be a remnant of an earlier, now vanished atmosphere.
• Orton, G., A'Hearn, M., Baines, K., Deming, D., Dowling, T., Goguen, J., Griffith, C., Hammel, H., Hoffmann, W., Hunten, D., Jewitt, D., Kostiuk, T., Miller, S., Noll, K., Zahnle, K., Achilleos, N., Dayal, A., Deutsch, L., Espenak, F., , Esterle, P., et al. (1995). Collision of comet Shoemaker-Levy 9 with Jupiter observed by the NASA Infrared Telescope Facility. Science, 267(5202), 1277-1282.
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  PMID: 7871423;Abstract: The National Aeronautics and Space Administration (NASA) Infrared Telescope Facility was used to investigate the collision of comet Shoemaker-Levy 9 with Jupiter from 12 July to 7 August 1994. Strong thermal infrared emission lasting several minutes was observed after the impacts of fragments C, G, and R. All impacts warmed the stratosphere and some the troposphere up to several degrees. The abundance of stratospheric ammonia increased by more than 50 times. Impact-related particles extended up to a level where the atmospheric pressure measured several millibars. The north polar near-infrared aurora brightened by nearly a factor of 5 a week after the impacts.
• Griffith, C. A. (1993). Evidence for surface heterogeneity on Titan. Nature, 364(6437), 511-514.
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  Abstract: UNLIKE all other planetary satellites, Saturn's moon Titan has a massive atmosphere1-8. At visible wavelengths, a thick stratospheric haze hides the surface from view. The emission from Titan in the infrared is largely from methane, nitrogen and hydrogen also in the stratosphere4. In the near-infrared, however, the extinction from haze decreases, and narrow windows exist in which the atmosphere absorbs only weakly9-14, and through which we might therefore catch a glimpse of the surface. Within two of these windows, Lemmon et al.15,16 recently observed a difference in Titan's albedo when the satellite was at eastern and western elongation with respect to Saturn. Although these observations could be taken to imply that Titan's surface is heterogeneous (and therefore is not covered by a global methane-ethane ocean as predicted previously7), they could also be explained by transient clouds. Here I present observations from two more rotational periods which record the same albedo difference, indicating that the heterogeneity is most unlikely to be associated with transient features and must be intrinsic to the surface. These results also imply that Titan is locked in a synchronous orbit about Saturn.
• Griffith, C. A., Bézard, B., Owen, T., & Gautier, D. (1992). The tropospheric abundances of NH₃ and PH₃ in Jupiter's great red spot, from Voyager IRIS observations. Icarus, 98(1), 82-93.
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  PMID: 11540935;Abstract: To investigate the chemistry and dynamics of Jupiter's Great Red Spot (GRS), the tropospheric abundances of NH3 and PH3 in the GRS are determined and compared to those of the surrounding region, the South Tropical Zone (STZ). These gases well up from deep in the atmosphere, and, in the upper troposphere, are depleted by condensation (in the case of NH3), chemical reactions, and UV photolysis. At Jupiter's tropopause, the chemical lifetimes of NH3 and PH3 are comparable to the time constant for vertical transport over the atmospheric scale height. The distributions of these gases are therefore diagnostic of the rate of vertical transport in the upper troposphere and lower stratosphere. Three groups of Voyager IRIS spectra are analyzed, two of the STZ and one of the GRS. The two groups of STZ spectra are defined on the basis of their radiances at 602 and 226 cm-1, which reflect, respectively, the temperature near 150 mbar and the cloud opacity in the 300-600 mbar region. One selection of STZ spectra is chosen to have the same radiance as does the GRS at 226 cm-1. The other STZ selection has a significantly greater radiance, indicative of reduced cloudiness. Variations in the abundances of NH3 and PH3 are determined within the STZ, as a background for our studies of the GRS. Within the uncertainty of our measurements (-55% and +75%), the PH3 mixing ratio at 600 mbar is 3 × 10-7, the same for all three selections. The NH3 mixing ratio profile in the pressure region between 300 and 600 mbar is the same within error (-25% and +50% at 300 mbar) for both STZ selections. In the GRS, however, NH3 is significantly depleted at 300 mbar, with an abundance of 25% that derived for the STZ selections. Since the GRS is believed to be a region of strong vertical transport, our finding of a depletion of NH3 below the tropopause within the GRS is particularly unexpected. One of the STZ selections has a temperature-pressure profile similar to that of the GRS below the 300-mbar level; therefore, condensation at this level does not easily explain the low NH3 abundance in the GRS. All samples are taken at essentially the same latitude; photolysis and/or charged particle precipitation is probably not directly responsible either. The observed NH3 depletion may have a dynamical origin or result from some unidentified chemical processes at work in the GRS. © 1992.
• Toon, O. B., McKay, C. P., Griffith, C. A., & Turco, R. P. (1992). A physical model of Titan's aerosols. Icarus, 95(1), 24-53.
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  PMID: 11538397;Abstract: Microphysical simulations of Titan's stratospheric haze show that aerosol microphysics is linked to organized dynamical processes. The detached haze layer may be a manifestation of 1 cm sec-1 vertical velocities at altitudes above 300 km. The hemispherical asymmetry in the visible albedo may be caused by 0.05 cm sec-1 vertical velocities at altitudes of 150 to 200 km, we predict contrast reversal beyond 0.6 μm. Tomasko and Smith's (1982, Icarus 51, 65-95) model, in which a layer of large particles above 220 km altitude is responsible for the high forward scattering observed by Rages and Pollack (1983, Icarus 55, 50-62), is a natural outcome of the detached haze layer being produced by rising motions if aerosol mass production occurs primarily below the detached haze layer. The aerosol's electrical charge is critical for the particle size and optical depth of the haze. The geometric albedo, particularly in the ultraviolet and near infrared, requires that the particle size be near 0.15 μm down to altitudes below 100 km, which is consistent with polarization observations (Tomasko and Smith 1982, West and Smith 1991, Icarus 90, 330-333). Above about 400 km and below about 150 km Yung et al.'s (1984, Astrophys. J. Suppl. Ser. 55, 465-506) diffusion coefficients are too small. Dynamical processes control the haze particles below about 150 km. The relatively large eddy diffusion coefficients in the lower stratosphere result in a vertically extensive region with nonuniform mixing ratios of condensable gases, so that most hydrocarbons may condense very near the tropopause rather than tens of kilometers above it. The optical depths of hydrocarbon clouds are probably less than one, requiring that abundant gases such as ethane condense on a subset of the haze particles to create relatively large, rapidly removed particles. The wavelength dependence of the optical radius is calculated for use in analyzing observations of the geometric albedo. The lower atmosphere and surface should be visible outside of regions of methane absorption in the near infrared. Limb scans at 2.0 μm wavelength should be possible down to about 75 km altitude. © 1992.
• Griffith, C. A., Owen, T., & Wagener, R. (1991). Titan's surface and troposphere, investigated with ground-based, near-infrared observations. Icarus, 93(2), 362-378.
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  PMID: 11538707;Abstract: New observations of Titan's near-infrared spectrum (4000-5000 cm-1) combined with points taken from Fink and Larson's (1979) spectrum (4000-12500 cm-1) provide information on Titan's haze, possible clouds, surface albedo, and atmospheric abundance of H2. In the near-infrared, the main features in Titan's spectrum result from absorption of solar radiation by CH4. The strength of this absorption varies considerably with wavelength, allowing us to probe various atmospheric levels down to the surface itself by choosing specific wavelengths for analysis. At 4715 cm-1, the pressure-induced S(1) fundamental band of H2 lies in the wings of CH4 bands. Based on current values for the CH4 line parameters, Titan's spectrum can be best interpreted with a volume mixing ratio of H2 between 0.5 and 1.0%. Our observations suggest the existence of an optically thin CH4 cloud layer. The optical depths that we derive for Titan's haze and clouds are small enough to allow us to sense the surface of Titan at 4900, 6250, and 7700 cm-1. The most plausible interpretation of the albedos determined at these wavenumbers suggests a surface dominated by "dirty" water ice. A global ethane ocean is not compatible with these albedos. © 1991.

Proceedings Publications

• Fitzpatrick, M., & Griffith, C. (2020, jan). Mapping the Surface Methane Abundance on Titan. In American Astronomical Society Meeting Abstracts \#235, 235.
• Griffith, C. (2019, Sep). A corridor of exposed ice-rich bedrock across Titan's tropical region. In EPSC-DPS Joint Meeting 2019, 2019.
• Pearson, K., Griffith, C., Zellem, R. T., Koskinen, T., & Roudier, G. (2019, Jan). Constraints on the Na abundance of XO-2 b using ground-based mutli-object spectroscopy. In American Astronomical Society Meeting Abstracts \#233, 233.
• Waldmann, I., & Griffith, C. (2019, Sep). Mapping Saturn using deep learning. In EPSC-DPS Joint Meeting 2019, 2019.
• Martins-Filho, W. .., Griffith, C., Pearson, K., Waldmann, I., Alvarez-Candal, A. .., & Zellem, R. (2018, jan). Independent Component Analysis applied to Ground-based observations. In American Astronomical Society Meeting Abstracts \#231, 231.
• Griffith, C., Penteado, P., Neish, C., & M.~C, L. R. (2017, oct). Principal Component Analysis of Titan\rsquos surface composition at Middle Latitudes. In AAS/Division for Planetary Sciences Meeting Abstracts \#49, 49.
• Martins-Filho, W. .., Griffith, C., Pearson, K., Waldmann, I., Alvarez-Candal, A. .., & Zellem, R. (2017, oct). Independent Component Analysis applied to Ground-based observations. In AAS/Division for Planetary Sciences Meeting Abstracts \#49, 49.
• Pearson, K., Palafox, L., & Griffith, C. (2017, oct). Searching for Exoplanets using Artificial Intelligence. In AAS/Division for Planetary Sciences Meeting Abstracts \#49, 49.
• {Griffith}, C., {Penteado}, P., {Turner}, J., {Montiel}, N., {Schoenfeld}, A., {Lopes}, R., {Soderblom}, L., {Neish}, C., , J. (2016, oct). Spectral Trends of Titan's Tropical Surface. In AAS/Division for Planetary Sciences Meeting Abstracts, 48.
• {Pearson}, K., {Griffith}, C., , R. (2016, oct). Ground-based Multi-object Spectroscopy of XO-2b using a Systematic Wavelength Calibration. 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.
• {Ryleigh Fitzpatrick}, M., {Pearson}, K., {Griffith}, C., {Dunn}, M., {Montiel}, N., {Zellem}, R., {Calahan}, J., {Chance}, Q., {Henrici}, A., {Sanchez}, D., , . (2016, jan). A Study of the Effects of Underlying Assumptions in the Reduction of Multi-Object Photometry of Transiting Exoplanets. In American Astronomical Society Meeting Abstracts, 227.
• {Silva Martins-Filho}, W., {Griffith}, C., {Pearson}, K., {Waldmann}, I., {Biddle}, L., {Zellem}, R., , A. (2016, oct). Independet Component Analyses of Ground-based Exoplanetary Transits. In AAS/Division for Planetary Sciences Meeting Abstracts, 48.
• Ryleigh Fitzpatrick}, M., {Watson}, Z., {Zellem}, R., {Pearson}, K., {Griffith}, C., ". In American Astronomical Society Meeting Abstracts, 225.
• {Griffith}, C., {Penteado}, P., {Turner}, J., {Khamsi}, T., , N. (2015, nov). "{Spectral Maps of Titan{rsquo}s Surface}". In AAS/Division for Planetary Sciences Meeting Abstracts, 47.
• {Zellem}, R., {Griffith}, C., {Lewis}, N., {Swain}, M., , H. (2015, jan). "{Constraining the Thermal Structure, Abundances, and Dynamics of the Exoplanet HD 209458b}". In American Astronomical Society Meeting Abstracts, 225.
• Teske, J., Cuha, K., Smith, V., Schuler, S., & Griffith, C. (2014, Fall). The Role of Oxygen Abundances in Exoplanet Host Star C/O Ratios: A Case Study of 55 Cnc. In IAU Symposium, 299, 307-308.
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  In: Exploring the Formation and Evolution of Planetary Systems, Proceedings of the International Astronomical Union
• {Griffith}, C., {Turner}, J., {Penteado}, P., {Khamsi}, T., , J. (2014, nov). "{Spectral Characteristics of Titan's Surface}". In AAS/Division for Planetary Sciences Meeting Abstracts, 46.
• {Khamsi}, T., {Griffith}, C., , L. (2014, nov). "{Titan{rsquo}s Haze Uncertainties and their Effects on Derived Surface Albedos}". In AAS/Division for Planetary Sciences Meeting Abstracts, 46.
• {Pearson}, K., {Zellem}, R., , C. (2014, nov). "{Exoplanet Observation from the Vattican Observatory}". In AAS/Division for Planetary Sciences Meeting Abstracts, 46.
• {Zellem}, R., {Griffith}, C., {Lewis}, N., {Swain}, M., , H. (2014, nov). "{Constraining the Thermal Structure, Abundances, and Dynamics of the Exoplanet HD 209458b}". In AAS/Division for Planetary Sciences Meeting Abstracts, 46.

Poster Presentations

• Pearson, K., Zellem, R., & Griffith, C. (2014, Fall). Near-UV and Optical Observations of the transiting hot Jupiter WASP-1b. AAS Meeting #223American Astronomical Society.
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  #347.16
• Teske, J., Cunha, K., Schuler, S., Griffith, C., & Smith, V. (2014, Fall). Diamonds in the Rough: A Cautionary Tale of C/O Ratios in Exoplanet Host Stars. AAS Meeting #223American Astronomical Society.
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  #207.01
• Zellem, R., Lewis, N., Knutson, H., Griffith, C., Fortnet, J., Showman, A., Cowan, N., Agol, E., Burrows, A., Charbonneau, D., Deming, D., Laughlin, G., & Langton, J. (2014, Fall). The Spitzer/IRAC 4.5 micron full-orbit phase curve of the hot Jupiter HD 209458b. AAS Meeting #223American Astronomical Society.
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  #105.08
• 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
• Griffith, C. (2013, Fall). Titan's Spectacular Volte-Face. DPS meeting #45American Astronomical Society.
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  #308.01
• Griffith, C. A. (2013, Fall). Cassini PSG. Cassini PSG. Sardinia, Italy.
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  Date: 06/13
• Griffith, C. A. (2013, Fall). Royal Society (London). Royal Society (London).
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  Date: 03/12
• Griffith, C., Turner, J., Zellem, R., Tinetti, G., & Teske, J. (2013, September). Interpreting low spectral resolution data of transiting exoplanets. European Planetary Science Congress 2013. London, UK.
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  Dates: 09/08-09/13
• Karkoschka, E., Griffith, C., & See, C. (2013, Fall). Titan's Seasonal North-South Asymmetry Separated into two Components. DPS meeting #45American Astronomical Society.
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  #305.05
• 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, L., 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: 09/08-09/13
• Turner, J., Smart, B., Hardegree-Ullman, K., Griffith, C., Biddle, L., Carleton, T., Crawford, B., De, L., Donnels, M., Guvenen, B., Guvenen, B., Hofmann, R., McGraw, A., Nieberding, M., Robertson, A., Scott, A., Small, L., Smith, C., Teske, J., , Towner, A., et al. (2013, Fall). Constraining The Magnetic Fields Of Transiting Exoplanets Through Ground-based Near-UV And Optical Observations. AAS Meeting #221American Astronomical Society.
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  #343.28
• Turner, J., Smart, B., Pearson, K., Biddle, L., Cates, I., Berube, M., Thompson, R., Smith, C., Teske, J., Hardegree-Ullman, K., Robertson, A., Crawfod, B., Zellem, R., Nieberding, M., Raphael, B., Tombleson, R., Cook, K., Hoglund, S., Hofmann, R., , Jones, C., et al. (2013, Fall). Constraining the Magnetic Fields of Transiting Exoplanets through Ground-based Near-UV Observations. DPS meeting #45American Astronomical Society.
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  #113.13
• Turner, J., Teske, J., Mueller, M., & Griffith, C. (2013, Fall). Optical Observations of the Transiting Exoplanet GJ 1214b. AAS Meeting #222American Astronomical Society.
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  #217.05
• Zellem, R., Griffith, C., Swain, M., Deroo, P., Waldmann, I., & Drossart, P. (2013, September). Ground-based Near-infrared Spectroscopy of HD 209458b. European Planetary Science Congress 2013. London, UK.
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  Dates: 09/08-09/13
• 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
• Griffith, C. A. (2012, Fall). Observatoire de Paris/Meudon. Observatoire de Paris/Meudon.
• 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
• 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, Fall). 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: 03/19-03/23; 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., Jauman, R., Stephan, K., Buratti, B., , Clark, R., et al. (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; LPI Contribution No. 1673; Page Number: p.81-82
• 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
• Stofan, E., Lunine, J., Lorenz, R., Aharonson, O., Bierhaus, E., Clark, B., Griffith, C., Harri, A., Karkoschka, E., Kirk, R., Mahaffy, P., Newman, C., Ravine, M., Trainer, M., Tuertle, E., Waite, H., Yelland, M., Zarnecki, J., & Hayes, A. (2012, Fall). Constraining the Role of Seas and Lakes in Titan's Climate: The Titan Mare Explorer Mission. Comparative Climatology of Terrestrial Planets. Boulder, CO.
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  Dates: 06/25-06/28; LPI Contribution No. 1675; id.8039
• Teske, J., Schuler, S., & Griffith, C. (2012, Fall). C/O Ratios of Stars with Transiting Hot Jupiters: Connecting Stars to Planets. DPS meeting #44American Astronomical Society.
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  #113.13
• Turner, J., Griffith, C., & Penteado, P. (2012, Fall). Preliminary Results Of Titan's Tropical Surface Albedo Using Cassini Vims Measurements. DPS meeting #44American Astronomical Society.
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  #312.17
• Turner, J., Griffith, C., Teske, J., Crawford, B., Robertson, A., Smart, B., Hardegree-Ullman, K., & Zellem, R. (2012, Fall). Detecting The Magnetic Field Of The Transiting Exoplanet Wasp-12b Through Ground-based And Space-based Near-UV And Optical Observations. AAS Meeting #220American Astronomical Society.
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  #129.01
• Turner, J., Griffith, C., Zellem, R., Hardegree-Ullman, K., & Richardson, L. (2012, Fall). Detecting The Magnetic Fields Of The Transiting Exoplanets Corot-1b And Wasp-3b. AAS Meeting #219American Astronomical Society.
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  #339.08
• Zellem, R., Griffith, C., Deroo, P., Swain, M., Waldmann, I., & Zhao, M. (2012, Fall). Near-infrared Transmission and Emission Spectra of HD 209458b: Demonstrating Palomar/TripleSpec's Capability for Exoplanet Spectroscopy. DPS meeting #44American Astronomical Society.
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  #113.12

Others

• Griffith, C. (2018). A global map of Titans tropospheric methane abundance near Northern Solstice.
• Müller-Wodarg, I., Griffith, C., Lellouch, E., & Cravens, T. (2014, Fall). Titan.
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  Location: Cambridge, UK; Publisher: Cambridge University Press
• {Griffith}, C. (2014). "{Elementary Abundances of Planetary Systems}".
• Lewis, N., Knutson, H., Cowan, N., Zellem, R., Griffith, C., Fortney, J., & Showman, A. (2013, Fall). Dynamic Studies of Exoplanet Atmospheres: Revisiting the 3.6 micron Phase Curve of HD209458b.
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  Spitzer Proposal: ID #10118
• Silverman, J., Foley, R., Filippenko, A., Ganeshalingam, M., Barth, A., Chornock, R., Griffith, C., Kong, J., Lee, N., Leonard, D., Matheson, T., Miller, E., Steele, T., Barris, B., Bloom, J., Cobb, B., Coil, A., Desroches, L., Gates, E., , Ho, L., et al. (2013, Fall). Berkeley supernova Ia program. I. (Silverman+, 2012). VizieR On-line Data Catalog: J/MNRAS/425/1789.
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  Originally published in: 2012MNRAS.425.1789S