Peter H Smith

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• Clifford, S. M., Yoshikawa, K., Byrne, S., Durham, W., Fisher, D., Forget, F., Hecht, M., Smith, P., Tamppari, L., Titus, T., & Zurek, R. (2013). Introduction to the fifth Mars Polar Science special issue: Key questions, needed observations, and recommended investigations. Icarus, 225(2), 864-868.
• McKay, C. P., Stoker, C. R., Glass, B. J., Davé, A. I., Davila, A. F., Heldmann, J. L., Marinova, M. M., Fairen, A. G., Quinn, R. C., Zacny, K. A., Paulsen, G., Smith, P. H., Parro, V., Andersen, D. T., Hecht, M. H., Lacelle, D., & Pollard, W. H. (2013). The icebreaker life mission to mars: A search for biomolecular evidence for life. Astrobiology, 13(4), 334-353.
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  PMID: 23560417;Abstract: The search for evidence of life on Mars is the primary motivation for the exploration of that planet. The results from previous missions, and the Phoenix mission in particular, indicate that the ice-cemented ground in the north polar plains is likely to be the most recently habitable place that is currently known on Mars. The near-surface ice likely provided adequate water activity during periods of high obliquity, ∼5 Myr ago. Carbon dioxide and nitrogen are present in the atmosphere, and nitrates may be present in the soil. Perchlorate in the soil together with iron in basaltic rock provides a possible energy source for life. Furthermore, the presence of organics must once again be considered, as the results of the Viking GCMS are now suspect given the discovery of the thermally reactive perchlorate. Ground ice may provide a way to preserve organic molecules for extended periods of time, especially organic biomarkers. The Mars Icebreaker Life mission focuses on the following science goals: (1) Search for specific biomolecules that would be conclusive evidence of life. (2) Perform a general search for organic molecules in the ground ice. (3) Determine the processes of ground ice formation and the role of liquid water. (4) Understand the mechanical properties of the martian polar ice-cemented soil. (5) Assess the recent habitability of the environment with respect to required elements to support life, energy sources, and possible toxic elements. (6) Compare the elemental composition of the northern plains with midlatitude sites. The Icebreaker Life payload has been designed around the Phoenix spacecraft and is targeted to a site near the Phoenix landing site. However, the Icebreaker payload could be supported on other Mars landing systems. Preliminary studies of the SpaceX Dragon lander show that it could support the Icebreaker payload for a landing either at the Phoenix site or at midlatitudes. Duplicate samples could be cached as a target for possible return by a Mars Sample Return mission. If the samples were shown to contain organic biomarkers, interest in returning them to Earth would be high. © Mary Ann Liebert, Inc.
• Barger, L. K., Sullivan, J. P., Vincent, A. S., Fiedler, E. R., McKenna, L. M., Flynn-Evans, E. E., Gilliland, K., Sipes, W. E., Smith, P. H., Brainard, G. C., & Lockley, S. W. (2012). Learning to live on a Mars day: Fatigue countermeasures during the Phoenix Mars Lander mission. Sleep, 35(10), 1423-1435.
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  PMID: 23024441;PMCID: PMC3443769;Abstract: Study Objectives: To interact with the robotic Phoenix Mars Lander (PML) spacecraft, mission personnel were required to work on a Mars day (24.65 h) for 78 days. This alien schedule presents a challenge to Earth-bound circadian physiology and a potential risk to workplace performance and safety. We evaluated the acceptability, feasibility, and effectiveness of a fatigue management program to facilitate synchronization with the Mars day and alleviate circadian misalignment, sleep loss, and fatigue. Design: Operational field study. Setting: PML Science Operations Center. Participants: Scientific and technical personnel supporting PML mission. Interventions: Sleep and fatigue education was offered to all support personnel. A subset (n = 19) were offered a short-wavelength (blue) light panel to aid alertness and mitigate/reduce circadian desynchrony. They were assessed using a daily sleep/work diary, continuous wrist actigraphy, and regular performance tests. Subjects also completed 48-h urine collections biweekly for assessment of the circadian 6-sulphatoxymelatonin rhythm. Measurements and Results: Most participants (87%) exhibited a circadian period consistent with adaptation to a Mars day. When synchronized, main sleep duration was 5.98 ± 0.94 h, but fell to 4.91 ± 1.22 h when misaligned (P < 0.001). Self-reported levels of fatigue and sleepiness also significantly increased when work was scheduled at an inappropriate circadian phase (P < 0.001). Prolonged wakefulness (≥ 21 h) was associated with a decline in performance and alertness (P < 0.03 and P < 0.0001, respectively). Conclusions: The ability of the participants to adapt successfully to the Mars day suggests that future missions should utilize a similar circadian rhythm and fatigue management program to reduce the risk of sleepiness-related errors that jeopardize personnel safety and health during critical missions.
• Tamppari, L. K., Anderson, R. M., Archer Jr., P. D., Douglas, S., Kounaves, S. P., McKay, C. P., Ming, D. W., Moore, Q., Quinn, J. E., Smith, P. H., Stroble, S., & Zent, A. P. (2012). Effects of extreme cold and aridity on soils and habitability: McMurdo Dry Valleys as an analogue for the Mars Phoenix landing site. Antarctic Science, 24(3), 211-228.
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  Abstract: The McMurdo Dry Valleys are among the driest, coldest environments on Earth and are excellent analogues for the Martian northern plains. In preparation for the 2008 Phoenix Mars mission, we conducted an interdisciplinary investigation comparing the biological, mineralogical, chemical, and physical properties of wetter lower Taylor Valley (TV) soils to colder, drier University Valley (UV) soils. Our analyses were performed for each horizon from the surface to the ice table. In TV, clay-sized particle distribution and less abundant soluble salts both suggested vertical and possible horizontal transport by water, and microbial biomass was higher. Alteration of mica to short-order phyllosilicates suggested aqueous weathering. In UV, salts, clay-sized materials, and biomass were more abundant near the surface, suggesting minimal downward translocation by water. The presence of microorganisms in each horizon was established for the first time in an ultraxerous zone. Higher biomass numbers were seen near the surface and ice table, perhaps representing locally more clement environments. Currently, water activity is too low to support metabolism at the Phoenix site, but obliquity changes may produce higher temperatures and sufficient water activity to permit microbial growth, if the populations could survive long dormancy periods (∼106 years). © 2012 Antarctic Science Ltd.
• Mehta, M., Renno, N. O., Marshall, J., Grover, M. R., Sengupta, A., Rusche, N. A., Kok, J. F., Arvidson, R. E., Markiewicz, W. J., Lemmon, M. T., & Smith, P. H. (2011). Explosive erosion during the Phoenix landing exposes subsurface water on Mars. Icarus, 211(1), 172-194.
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  Abstract: While steady thruster jets caused only modest surface erosion during previous spacecraft landings on the Moon and Mars, the pulsed jets from the Phoenix spacecraft led to extensive alteration of its landing site on the martian arctic, exposed a large fraction of the subsurface water ice under the lander, and led to the discovery of evidence for liquid saline water on Mars. Here we report the discovery of the 'explosive erosion' process that led to this extensive erosion. We show that the impingement of supersonic pulsed jets fluidizes porous soils and forms cyclic shock waves which propagate through the soil and produce erosion rates more than an order of magnitude larger than that of other jet-induced processes. The understanding of 'explosive erosion' allows the calculation of bulk physical properties of the soils altered by it, provides insight into a new behavior of granular flow at extreme conditions and explains the rapid alteration of the Phoenix landing site's ground morphology at the northern arctic plains of Mars. © 2010 Elsevier Inc.
• Moores, J. E., Smith, P. H., & Boynton, W. V. (2011). Adsorptive fractionation of HDO on JSC MARS-1 during sublimation with implications for the regolith of Mars. Icarus, 211(2), 1129-1149.
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  Abstract: A chamber was constructed to simulate the boundary between the ice table, regolith and atmosphere of Mars and to examine fractionation between H2O and HDO during sublimation under realistic martian conditions of temperature and pressure. Thirteen experimental runs were conducted with regolith overlying the ice. The thickness and characteristic grain size of the regolith layer as well as the temperature of the underlying ice was varied. From these runs, values for the effective diffusivity, taking into account the effects of adsorption, of the regolith were derived. These effective diffusivities ranged from 1.8×10-4m2s-1 to 2.2×10-3m2s-1 for bare ice and from 2.4×10-11m2s-1 to 2.0×10-9m2s-1 with an adsorptive layer present. From these, latent heats of adsorption of 8.6±2.6kJmol-1 and 9.3±2.8kJmol-1 were derived at ice-surface temperatures above 223±8K and 96±28kJmol-1 and 104±31kJmol-1 respectively for H2O and HDO were derived at colder temperatures. For temperatures below 223K, the effective diffusivity of HDO was found to be lower than the diffusivity of H2O by 40% on average, suggesting that the regolith was adsorptively fractionating the sublimating gas with a fractionation factor of 1.96±0.74. Applying these values to Mars predicts that adsorbed water on the regolith is enriched in HDO compared to the atmosphere, particularly where the regolith is colder. Based on current observations, the D/H ratio of the regolith may be as high as 21±8 times VSMOW at 12°S and LS=357° if the regolith is hydrated primarily by the atmosphere, neglecting any hydration from subsurface ice. © 2010 Elsevier Inc.
• Smith, P. H. (2011). Digging mars. Scientific American, 305(5), 28-36.
• Smith, P. H. (2011). Digging mars.. Scientific American, 305(5), 46-54.
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  PMID: 22125861;
• Ellehoj, M. D., Gunnlaugsson, H. P., Taylor, P. a., Bean, K. M., Cantor, B. A., Gheynani, B. T., Drube, L., Fisher, D., Harri, A. M., Holstein-Rathlou, C., Lemmon, M. T., Madsen, M. B., Malin, M. C., Polkko, J., Smith, P. H., Tamppari, L. K., Weng, W., & Whiteway, J. (2010). Convective vortices and dust devils at the Phoenix Mars mission landing site. Journal of Geophysical Research E: Planets, 115(4).
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  Abstract: The Phoenix Mars Lander detected a larger number of short (∼20 s) pressure drops that probably indicate the passage of convective vortices or dust devils. Near-continuous pressure measurements have allowed for monitoring the frequency of these events, and data from other instruments and orbiting spacecraft give information on how these pressure events relate to the seasons and weather phenomena at the Phoenix landing site. Here 502 vortices were identified with a pressure drop larger than 0.3 Pa occurring in the 151 sol mission (Ls 76 to 148). The diurnal distributions show a peak in convective vortices around noon, agreeing with current theory and previous observations. The few events detected at night might have been mechanically forced by turbulent eddies caused by the nearby Heimdal crater. A general increase with major peaks in the convective vortex activity occurs during the mission, around Ls = 111. This correlates with changes in midsol surface heat flux, increasing wind speeds at the landing site, and increases in vortex density. Comparisons with orbiter imaging show that in contrast to the lower latitudes on Mars, the dust devil activity at the Phoenix landing site is influenced more by active weather events passing by the area than by local forcing. Copyright 2010 by the American Geophysical Union.
• Goetz, W., Pike, W. T., Hviid, S. F., Madsen, M. B., Morris, R. V., Hecht, M. H., Staufer, U., Leer, K., Sykulska, H., Hemmig, E., Marshall, J., Morookian, J. M., Parrat, D., Vijendran, S., Bos, B. J., Maarry, M. E., Keller, H. U., Kramm, R., Markiewicz, W. J., , Drube, L., et al. (2010). Microscopy analysis of soils at the Phoenix landing site, Mars: Classification of soil particles and description of their optical and magnetic properties. Journal of Geophysical Research E: Planets, 115(8).
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  Abstract: The optical microscope onboard the Phoenix spacecraft has returned color images (4 μm pixel-1) of soils that were delivered to and held on various substrates. A preliminary taxonomy of Phoenix soil particles, based on color, size, and shape, identifies the following particle types [generic names in brackets]: (1) reddish fines, mostly unresolved, that are spectrally similar to (though slightly darker than) global airborne dust [red fines], (2) silt- to sand-sized brownish grains [brown sand], (3) silt- to sand-sized black grains [black sand], and (4) small amounts of whitish fines, possibly salts [white fines]. Most particles have a saturation magnetization in the range 0.5-2 Am2 kg-1 as inferred from their interaction with magnetic substrates. The particle size distribution has two distinct peaks below 10 μm (fines) and in the range 20-100 μm (grains), respectively, and is different from that of ripple soils in Gusev crater. In particular medium to large sand grains appear to be absent in Phoenix soils. Most sand grains have subrounded shape with variable texture. A fractured grain (observed on sol 112) reveals evidence of micrometer-sized crystal facets. The brown sand category displays a large diversity in color including shiny, almost colorless particles. Potential source regions for these grains may be the Tharsis volcanoes or Heimdal crater (20 km east of the landing site). The black grains are suggested to belong to a more widespread population of particles with mafic mineralogy. The absence of black/brown composite grains is consistent with different formation pathways and source regions for each grain type. Copyright 2010 by the American Geophysical Union.
• Holstein-Rathlou, C., Gunnlaugsson, H. P., Merrison, J. P., Bean, K. M., Cantor, B. A., Davis, J. A., Davy, R., Drake, N. B., Ellehoj, M. D., Goetz, W., Hviid, S. F., Lange, C. F., Larsen, S. E., Lemmon, M. T., Madsen, M. B., Malin, M., Moores, J. E., Nørnberg, P., Smith, P., , Tamppari, L. K., et al. (2010). Winds at the phoenix landing site. Journal of Geophysical Research E: Planets, 115(5).
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  Abstract: Wind speeds and directions were measured on the Phoenix Lander by a mechanical anemometer, the so-called Telltale wind indicator. Analysis of images of the instrument taken with the onboard imager allowed for evaluation of wind speeds and directions. Daily characteristics of the wind data are highly turbulent behavior during midday due to daytime turbulence with more stable conditions during nighttime. From Ls ∼77°-123° winds were generally ∼4 m s-1 from the east, with 360° rotation during midday. From Ls ∼123°-148° daytime wind speeds increased to an average of 6-10 m s-1 and were generally from the west. The highest wind speed recorded was 16 m s-1 seen on Ls ∼147°. Estimates of the surface roughness height are calculated from the smearing of the Kapton part of the Telltale during image exposure due to a 3 Hz turbulence and nighttime wind variability. These estimates yield 6 ± 3 mm and 5 ± 3 mm, respectively. The Telltale wind data are used to suggest that Heimdal crater is a source of nighttime temperature fluctuations. Deviations between temperatures measured at various heights are explained as being due to winds passing over the Phoenix Lander. Events concerning sample delivery and frost formation are described and discussed. Two different mechanisms of dust lifting affecting the Phoenix site are proposed based on observations made with Mars Color Imager on Mars Reconnaissance Orbiter and the Telltale. The first is related to evaporation of the seasonal CO2 ice and is observed up to Ls ∼95°. These events are not associated with increased wind speeds. The second mechanism is observed after Ls ∼111° and is related to the passing of weather systems characterized by condensate clouds in orbital images and higher wind speeds as measured with the Telltale. Copyright 2010 by the American Geophysical Union.
• Kounaves, S. P., Stroble, S. T., Anderson, R. M., Moore, Q., Catling, D. C., Douglas, S., Mckay, C. P., Ming, D. W., Smith, P. H., Tamppari, L. K., & Zent, A. P. (2010). Discovery of natural Perchlorate in the Antarctic Dry Valleys and its global implications. Environmental Science and Technology, 44(7), 2360-2364.
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  PMID: 20155929;Abstract: In the past few years, it has become increasingly apparent that Perchlorate (ClO4-) is present on all continents, except the polar regions where it had not yet been assessed, and that it may have a significant natural source. Here, we report on the discovery of Perchlorate in soil and ice from several Antarctic Dry Valleys (ADVs) where concentrations reach up to 1100 μg/kg. In the driest ADV, Perchlorate correlates with atmospherically deposited nitrate. Far from anthropogenic activity, ADV Perchlorate provides unambiguous evidence that natural Perchlorate is ubiquitous on Earth. The discovery has significant implications for the origin of Perchlorate, its global biogeochemical interactions, and possible interactions with the polar ice sheets. The results support the hypotheses that Perchlorate is produced globally and continuously in the Earth's atmosphere, that it typically accumulates in hyperarid areas, and that it does not build up in oceans or other wet environments most likely because of microbial reduction on a global scale. © 2010 American Chemical Society.
• Moores, J. E., Lemmon, M. T., Smith, P. H., Komguem, L., & Whiteway, J. A. (2010). Atmospheric dynamics at the Phoenix landing site as seen by the Surface Stereo Imager. Journal of Geophysical Research E: Planets, 115(1).
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  Abstract: The Surface Stereo Imager has made observations of dust blowing aloft and clouds near the horizon at the Phoenix landing site. These subtle features are apparent because of the high signal-to-noise ratio of the camera which allows for the removal of a mean frame from multiple images captured in rapid succession and the ability to conduct simultaneous capture through different filters in each camera eye. By examining the ratios between two filters, it was possible to determine in a relative sense how the water ice content of the atmosphere changed over the mission and on a diurnal time scale. The direction of travel and speed of features aloft near the zenith has been inferred and agree well with the diurnal pattern of near-surface wind direction from the Telltale. Direct observation of cumulus-like cloud near the surface suggests convection of water vaporrich air, but only until midday, requiring a mechanism to inhibit cloud formation in the early afternoon. The spectral ratios agree well with the observation of cloud and indicate a general increase in water ice toward the end of the mission as well as a strong diurnal pattern. However, even in periods of high water ice content, there is still a great deal of variability and days when dense clouds are absent. Also, different cloud layers are occasionally observed moving in different directions, indicating occasional wind shear aloft. Features observed had estimated minimum optical depths up to 0.11. Copyright 2010 by the American Geophysical Union.
• Stoker, C. R., Zent, A., Catling, D. C., Douglas, S., Marshall, J. R., Archer, D., Clark, B., Kounaves, S. P., Lemmon, M. T., Quinn, R., Renno, N., Smith, P. H., & Young, S. M. (2010). Habitability of the phoenix landing site. Journal of Geophysical Research E: Planets, 115(6).
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  Abstract: The Phoenix mission's key objective was to search for a habitable zone. Mission results are used to evaluate habitability where Phoenix landed. A habitability probability (HI) is defined as the product of probabilities for the presence of liquid water (Plw), energy (Pe), nutrients (P ch), and a benign environment (Pb). Observational evidence for the presence of liquid water (past or present) includes clean ice at a polygon boundary, chemical etching of soil grains, and carbonate minerals. The presence of surface and near subsurface ice, along with thermodynamic conditions that support melting, suggest that liquid water is theoretically possible. Presently, unfrozen water can form only in adsorbed films or saline brines but more clement conditions recur periodically due to variations in orbital parameters. Energy to drive metabolism is available from sunlight, when semitransparent soil grains provide shielding from UV radiation and chemical energy from the redox couple of perchlorate and reduced iron. Nutrient sources including C, H, N, O, P, and S compounds are supplied by known atmospheric sources or global dust. Environmental conditions are within growth tolerance for terrestrial microbes. Surface soil temperatures currently reach 260 K and are periodically much higher, the pH is 7.8 and is well buffered, and the water activity is high enough to allow growth when sufficient water is available. Computation of HI for the sites visited by landers yields Phoenix, 0.47; Meridiani, 0.23; Gusev, 0.22; Pathfinder, 0.05; Viking 1, 0.01; Viking 2, 0.07. HI for the Phoenix site is the largest of any site explored, but dissimilar measurements limit the comparisons' confidence. © 2010 by the American Geophysical Union.
• Arvidson, R., Adams, D., Bonfiglio, G., Christensen, P., Cull, S., Golombek, M., Guinn, J., Guinness, E., Heet, T., Kirk, R., Knudson, A., Malin, M., Mellon, M., McEwen, A., Mushkin, A., Parker, T., IV, F. S., Seelos, K., Smith, P., , Spencer, D., et al. (2009). Mars Exploration Program 2007 Phoenix landing site selection and characteristics. Journal of Geophysical Research E: Planets, 114(3).
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  Abstract: To ensure a successful touchdown and subsequent surface operations, the Mars Exploration Program 2007 Phoenix Lander must land within 65° to 72° north latitude, at an elevation less than -3.5 km. The landing site must have relatively low wind velocities and rock and slope distributions similar to or more benign than those found at the Viking Lander 2 site. Also, the site must have a soil cover of at least several centimeters over ice or icy soil to meet science objectives of evaluating the environmental and habitability implications of past and current near-polar environments. The most challenging aspects of site selection were the extensive rock fields associated with crater rims and ejecta deposits and the centers of polygons associated with patterned ground. An extensive acquisition campaign of Odyssey Thermal Emission Imaging Spectrometer predawn thermal IR images, together with ∼0.31 m/pixel Mars Reconnaissance Orbiter High Resolution Imaging Science Experiment images was implemented to find regions with acceptable rock populations and to support Monte Carlo landing simulations. The chosen site is located at 68.16° north latitude, 233.35° east longitude (areocentric), within a ∼50 km wide (N-S) by ∼300 km long (E-W) valley of relatively rock-free plains. Surfaces within the eastern portion of the valley are differentially eroded ejecta deposits from the relatively recent ∼10-km-wide Heimdall crater and have fewer rocks than plains on the western portion of the valley. All surfaces exhibit polygonal ground, which is associated with fracture of icy soils, and are predicted to have only several centimeters of poorly sorted basaltic sand and dust over icy soil deposits. Copyright 2008 by the American Geophysical Union.
• Bonitz, R. G., Shiraishi, L., Robinson, M., Arvidson, R. E., Chu, P. C., Wilson, J. J., Davis, K. R., Paulsen, G., Kusack, A. G., Archer, D., & Smith, P. (2009). NASA Mars 2007 phoenix lander robotic arm and icy soil acquisition device. Journal of Geophysical Research E: Planets, 114(3).
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  Abstract: The primary purpose of the Mars 2007 Phoenix Lander Robotic Arm (RA) and associated Icy Soil Acquisition Device (ISAD) is to acquire samples of Martian dry and icy soil (DIS) by digging, scraping, and rasping, and delivering them to the Thermal Evolved Gas Analyzer and the Microscopy, Electrochemistry, and Conductivity Analyzer. The RA will also position (1) the Thermal and Electrical Conductivity Probe (TECP) in the DIS; (2) the TECP at various heights above the surface for relative humidity measurements, and (3) the Robotic Arm Camera to take images of the surface, trench, DIS samples within the ISAD scoop, magnetic targets, and other objects of scientific interest within its workspace. The RA/ISAD will also be used to generate DIS piles for monitoring; conduct DIS scraping, penetration, rasping, and chopping experiments; perform compaction tests; and conduct trench cave-in experiments. Data from the soil mechanics experiments will yield information on Martian DIS properties such as angle of repose, cohesion, bearing strength, and grain size distribution. Copyright 2008 by the American Geophysical Union.
• Boynton, W. V., Ming, D. W., Kounaves, S. P., Young, S. M., Arvidson, R. E., Hecht, M. H., Hoffman, J., Niles, P. B., Hamara, D. K., Quinn, R. C., Smith, P. H., Sutter, B., Catling, D. C., & Morris, R. V. (2009). Evidence for calcium carbonate at the mars phoenix landing site. Science, 325(5936), 61-64.
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  PMID: 19574384;Abstract: Carbonates are generally products of aqueous processes and may hold important clues about the history of liquid water on the surface of Mars. Calcium carbonate (approximately 3 to 5 weight percent) has been identified in the soils around the Phoenix landing site by scanning calorimetry showing an endothermic transition beginning around 725°C accompanied by evolution of carbon dioxide and by the ability of the soil to buffer pH against acid addition. Based on empirical kinetics, the amount of calcium carbonate is most consistent with formation in the past by the interaction of atmospheric carbon dioxide with liquid water films on particle surfaces.
• Gunnlaugsson, H. P., Holstein-Rathlou, C., Merrison, J. P., Jensen, S. K., Lange, C. F., Larsen, S. E., Madsen, M. B., Nernberg, P., Bechtold, H., Hald, E., Iversen, J. J., Lange, P., Lykkegaard, F., Rander, F., Lemmon, M., Renno, N., Taylor, P., & Smith, P. (2009). Telltale wind indicator for the Mars Phoenix lander. Journal of Geophysical Research E: Planets, 114(3).
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  Abstract: The Telltale wind indicator is a mechanical anemometer designed to operate on the Martian surface as part of the meteorological package on the NASA Phoenix lander. It consists of a lightweight cylinder suspended by Kevlar fibers and is deflected under the action of wind. Imaging of the Telltale deflection allows the wind speed and direction to be quantified and image blur caused by its oscillations provides information about wind turbulence. The Telltale will primarily support surface operations by documenting the wind conditions to improve the efficiency of sample delivery to instruments on the lander deck. During the latter stages of the mission the Telltale investigation will focus on meteorological studies. Copyright 2008 by the American Geophysical Union.
• Hecht, M. H., Kounaves, S. P., Quinn, R. C., West, S. J., Young, S. M., Ming, D. W., Catling, D. C., Clark, B. C., Boynton, W. V., Hoffman, J., DeFlores, L. P., Gospodinova, K., Kapit, J., & Smith, P. H. (2009). Detection of perchlorate and the soluble chemistry of martian soil at the phoenix lander site. Science, 325(5936), 64-67.
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  PMID: 19574385;Abstract: The Wet Chemistry Laboratory on the Phoenix Mars Lander performed aqueous chemical analyses of martian soil from the polygon-patterned northern plains of the Vastitas Borealis. The solutions contained ∼10 mM of dissolved salts with 0.4 to 0.6% perchlorate (ClO4) by mass leached from each sample. The remaining anions included small concentrations of chloride, bicarbonate, and possibly sulfate. Cations were dominated by Mg2+ and Na +, with small contributions from K+ and Ca2+. A moderately alkaline pH of 7.7 ± 0.5 was measured, consistent with a carbonate-buffered solution. Samples analyzed from the surface and the excavated boundary of the ∼5-centimeter-deep ice table showed no significant difference in soluble chemistry.
• Hecht, M. H., Marshall, J., Pike, W. T., Staufer, U., Blaney, D., Braendlin, D., Gautsch, S., Goetz, W., Hidber, H. -., Keller, H. U., Markiewicz, W. J., Mazer, A., Meloy, T. P., Morookian, J. M., Mogensen, C., Parrat, D., Smith, P., Sykulska, H., Tanner, R. J., , Reynolds, R. O., et al. (2009). Microscopy capabilities of the microscopy, electrochemistry, and conductivity analyzer. Journal of Geophysical Research E: Planets, 114(3).
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  Abstract: The Phoenix microscopy station, designed for the study of Martian dust and soil, consists of a sample delivery system, an optical microscope, and an atomic force microscope. The combination of microscopies facilitates the study of features from the millimeter to nanometer scale. Light-emitting diode illumination allows for full color optical imaging of the samples as well as imaging of ultraviolet-induced visible fluorescence. The atomic force microscope uses an array of silicon tips and can operate in both static and dynamic mode. Copyright 2008 by the American Geophysical Union.
• Keller, H. U., Goetz, W., Hartwig, H., Hviid, S. F., Kramm, R., Markiewicz, W. J., Reynolds, R., Shinohara, C., Smith, P., Tanner, R., Woida, P., Woida, R., Bos, B. J., & Lemmon, M. T. (2009). Phoenix robotic arm camera. Journal of Geophysical Research E: Planets, 114(3).
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  Abstract: The Phoenix Robotic Arm Camera (RAC) is a variable-focus color camera mounted to the Robotic Arm (RA) of the Phoenix Mars Lander. It is designed to acquire both close-up images of the Martian surface and microscopic images (down to a scale of 23 μm/pixel) of material collected in the RA scoop. The mounting position at the end of the Robotic Arm allows the RAC to be actively positioned for imaging of targets not easily seen by the Stereo Surface Imager (SSI), such as excavated trench walls and targets under the Lander structure. Color information is acquired by. illuminating the target with red, green, and blue light-emitting diodes. Digital terrain models (DTM) can be generated from RAC images acquired from different view points. This can provide high-resolution stereo information about fine details of the trench walls. The large stereo baseline possible with the arm can also provide a far-field DTM. The primary science objectives of the RAC are the search for subsurface soil/ice layering at the landing site and the characterization of scoop samples prior to delivery to other instruments on board Phoenix. The RAC shall also provide low-resolution panoramas in support of SSI activities and acquire images of the Lander deck for instrument and Lander check out. The camera design was inherited from the unsuccessful Mars Polar Lander mission (1999) and further developed for the (canceled) Mars Surveyor 2001 Lander (MSLOl). Extensive testing and partial recalibration qualified the MSLOl RAC flight model for integration into the Phoenix science payload. Copyright 2008 by the American Geophysical Union.
• Kounaves, S. P., Hecht, M. H., West, S. J., Morookian, J., M., S., Quinn, R., Grunthaner, P., Wen, X., Weilert, M., Cable, C. A., Fisher, A., Gospodinova, K., Kapit, J., Stroble, S., Hsu, P., Clark, B. C., Ming, D. W., & Smith, P. H. (2009). The MECA wet chemistry laboratory on the 2007 Phoenix Mars Scout Lander. Journal of Geophysical Research E: Planets, 114(3).
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  Abstract: To analyze and interpret the chemical record, the 2007 Phoenix Mars Lander includes four wet chemistry cells. These Wet Chemistry Laboratories (WCLs), part of the Microscopy, Electrochemistry, and Conductivity Analyzer (MECA) package, each consist of a lower "beaker" containing sensors designed to analyze the chemical properties of the regolith and an upper "actuator assembly" for adding soil, water, reagents, and stirring. The beaker contains an array of sensors and electrodes that include six membranebased ion selective electrodes (ISE) to measure Ca2+, Mg2+, K +, Na+, NO3-/ClO4-, and NH4+; two ISEs for H+ (pH); a Ba2+ ISE for titrimetric determination of SO42-; two Li+ ISEs as reference electrodes; three solid crystal pellet ISEs for Cl-, Br-, and I-; an iridium oxide electrode for pH; a carbon ring electrode for conductivity; a Pt electrode for oxidation reduction potential (Eh); a Pt and two Ag electrodes for determination of Cl-, Br-, and I- using chronopotentiometry (CP); a Au electrode for identifying redox couples using cyclic voltammetry (CV); and a Au microelectrode array that could be used for either CV or to indicate the presence of several heavy metals, including Cu2+, Cd2+, Pb2+, Fe2/3+, and Hg2+ using anodic stripping voltammetry (ASV). The WCL sensors and analytical procedures have been calibrated and characterized using standard solutions, geological Earth samples, Mars simulants, and cuttings from a Martian meteorite. Sensor characteristics such as limits of detection, interferences, and implications of the Martian environment are also being studied. A sensor response library is being developed to aid in the interpretation of the data. Copyright 2009 by the American Geophysical Union.
• Leer, K., Bertelsen, P., Binau, C. S., Olsen, L. D., Drube, L., Falkenberg, T. V., Haspang, M. P., Madsen, M. B., Olsen, M., Sykulska, H., Vijendran, S., Pike, W. T., Staufer, U., Parrat, D., Lemmon, M., Hecht, M. H., Mogensen, C. T., Gross, M. A., Goetz, W., , Marshall, J., et al. (2009). Magnetic properties experiments and the Surface Stereo Imager calibration target onboard the Mars Phoenix 2007 Lander: Design, calibration, and science goals. Journal of Geophysical Research E: Planets, 114(3).
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  Abstract: The first NASA scout mission to Mars, Phoenix, launched 4 August will land in the northern part of Mars in the locality of 68°N and 233°E on 25 May 2008. Part, of the science payload is the Magnetic Properties Experiments (MPE) that consists of two main experiments: the Improved Sweep Magnet Experiment (ISWEEP) and 10 sets of two Microscopy, Electrochemistry, and Conductivity Analyzer (MECA) magnet substrates with embedded permanent magnets of different strength. The ISWEEP experiment is, as the name indicates, an improved version of the Sweep Magnet Experiments flown onboard the two Mars Exploration Rovers (MERs) Spirit and Opportunity. The sweep magnet is ring shaped and is designed to allow only nonmagnetic particles to enter a small circular area at the center of the surface of this structure. Results from this experiment have shown that on the MERs hardly any particles can be detected in the central area of this ring-shaped magnet. From this we have concluded that essentially all particles in the Martian atmosphere are magnetic in the sense that they are attracted to permanent magnets. In order to improve the sensitivity of the Sweep Magnet Experiment for detection of nonmagnetic or very weakly magnetic particles, the ISWEEP holds six ring-shaped magnets, somewhat larger than the sweep magnet of the MERs, and with six different background colors in the central area. The six different colors provide new possibilities for improved contrast between these background colors, i.e., any putative nonmagnetic particles should render these more easily detectable. The Surface Stereo Imager will also take advantage of the small clean areas in the ISWEEPs and use the presumably constant colors for radiometric calibration of images. The MECA magnets work as substrates in the MECA microscopy experiments; they are built to attract and hold magnetic particles from dust samples. The collected dust will then be examined by the optical microscope and the atomic force microscope in the MECA package. Copyright 2008 by the American Geophysical Union.
• Ming, D. W., Morris, R. V., Woida, R., Sutter, B., Lauer, H. V., Shinohara, C., Golden, D. C., Boynton, W. V., Arvidson, R. E., Stewart, R. L., Tamppari, L. K., Gross, M., & Smith, P. (2009). Mars 2007 Phoenix Scout mission Organic Free Blank: Method to distinguish Mars organics from terrestrial organics. Journal of Geophysical Research E: Planets, 114(3).
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  Abstract: The Organic Free Blank (OFB) for the Mars 2007 Phoenix Scout mission provides an organic carbon null sample to compare against possible Martian organic signatures obtained by the Thermal and Evolved Gas Analyzer (TEGA). Major OFB requirements are an organic carbon content of
• Rennó, N. O., Bos, B. J., Catling, D., Clark, B. C., Drube, L., Fisher, D., Goetz, W., Hviid, S. F., Keller, H. U., Kok, J. F., Kounaves, S. P., Leer, K., Lemmon, M., Madsen, M. B., Markiewicz, W. J., Marshall, J., McKay, C., Mehta, M., Smith, M., , Zorzano, M. P., et al. (2009). Possible physical and thermodynamical evidence for liquid water at the Phoenix landing site. Journal of Geophysical Research E: Planets, 114(10).
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  Abstract: The objective of the Phoenix mission is to determine if Mars' polar region can support life. Since liquid water is a basic ingredient for life, as we know it, an important goal of the mission is to determine if liquid water exists at the landing site. It is believed that a layer of Martian soil preserves ice by forming a barrier against high temperatures and sublimation, but that exposed ice sublimates without the formation of the liquid phase. Here we show possible independent physical and thermodynamical evidence that besides ice, liquid saline water exists in areas disturbed by the Phoenix Lander. Moreover, we show that the thermodynamics of freeze-thaw cycles can lead to the formation of saline solutions with freezing temperatures lower than current summer ground temperatures on the Phoenix landing site on Mars' Arctic. Thus, we hypothesize that liquid saline water might occur where ground ice exists near the Martian surface. The ideas and results presented in this article provide significant new insights into the behavior of water on Mars. Copyright 2009 by the American Geophysical Union.
• Smith, P. H., Tamppari, L. K., Arvidson, R. E., Bass, D., Blaney, D., Boynton, W. V., Carswell, A., Catling, D. C., Clark, B. C., Duck, T., DeJong, E., Fisher, D., Goetz, W., Gunnlaugsson, H. P., Hecht, M. H., Hipkin, V., Hoffman, J., Hviid, S. F., Keller, H. U., , Kounaves, S. P., et al. (2009). H₂0 at the phoenix landing site. Science, 325(5936), 58-61.
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  PMID: 19574383;Abstract: The Phoenix mission investigated patterned ground and weather in the northern arctic region of Mars for 5 months starting 25 May 2008 (solar longitude between 76.5° and 148°). A shallow ice table was uncovered by the robotic arm in the center and edge of a nearby polygon at depths of 5 to 18 centimeters. In late summer, snowfall and frost blanketed the surface at night; H2O ice and vapor constantly interacted with the soil. The soil was alkaline (pH = 7.7) and contained CaCO3, aqueous minerals, and salts up to several weight percent in the indurated surface soil. Their formation likely required the presence of water.
• Smith, P. H., Tamppari, L., Arvidson, R. E., Bass, D., Blaney, D., Boynton, W., Carswell, A., Catling, D., Clark, B., Duck, T., Dejong, E., Fisher, D., Goetz, W., Gunnlaugsson, P., Hecht, M., Hipkin, V., Hoffman, J., Hviid, S., Keller, H., , Kounaves, S., et al. (2009). Introduction to special section on the Phoenix Mission: Landing site characterization experiments, mission overviews, and expected science. Journal of Geophysical Research E: Planets, 114(3).
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  Abstract: Phoenix, the first Mars Scout mission, capitalizes on the large NASA investments in the Mars Polar Lander and the Mars Surveyor 2001 missions. On 4 August 2007, Phoenix was launched to Mars from Cape Canaveral, Florida, on a Delta 2 launch vehicle. The heritage derived from the canceled 2001 lander with a science payload inherited from MPL and 2001 instruments gives significant advantages. To manage, build, and test the spacecraft and its instruments, a partnership has been forged between the Jet Propulsion Laboratory, the University of Arizona (home institution of principal investigator P. H. Smith), and Lockheed Martin in Denver; instrument and scientific contributions from Canada and Europe have augmented the mission. The science mission focuses on providing the ground truth for the 2002 Odyssey discovery of massive ice deposits hidden under surface soils in the circumpolar regions. The science objectives, the instrument suite, and the measurements needed to meet the objectives are briefly described here with reference made to more complete instrument papers included in this special section. The choice of a landing site in the vicinity of 68°N and 233°E balances scientific value and landing safety. Phoenix will land on 25 May 2008 during a complex entry, descent, and landing sequence using pulsed thrusters as the final braking strategy. After a safe landing, twin fan-like solar panels are unfurled and provide the energy needed for the mission. Throughout the 90-sol primary mission, activities are planned on a tactical basis. Copyright 2008 by the American Geophysical Union.
• Whiteway, J. A., Komguem, L., Dickinson, C., Cook, C., Illnicki, M., Seabrook, J., Popovici, V., Duck, T. J., Davy, R., Taylor, P. A., Pathak, J., Fisher, D., Carswell, A. I., Daly, M., Hipkin, V., Zent, A. P., Hecht, M. H., Wood, S. E., Tamppari, L. K., , Renno, N., et al. (2009). Mars water-ice clouds and precipitation. Science, 325(5936), 68-70.
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  PMID: 19574386;Abstract: The light detection and ranging instrument on the Phoenix mission observed water-ice clouds in the atmosphere of Mars that were similar to cirrus clouds on Earth. Fall streaks in the cloud structure traced the precipitation of ice crystals toward the ground. Measurements of atmospheric dust indicated that the planetary boundary layer (PBL) on Mars was well mixed, up to heights of around 4 kilometers, by the summer daytime turbulence and convection. The water-ice clouds were detected at the top of the PBL and near the ground each night in late summer after the air temperature started decreasing. The interpretation is that water vapor mixed upward by daytime turbulence and convection forms ice crystal clouds at night that precipitate back toward the surface.
• Holcomb, C. T., Allen, S. L., Makowski, M. A., Jayakumar, R. J., Gu, M. F., Lerner, S., Morris, K. L., Latkowski, J., Moller, J. M., Meyer, W., Ellis, R., Geer, R., Behne, D., Chipman, R., Smith, P., & McClain, S. (2008). An overview of the motional Stark effect diagnostic on DIII-D and design work for an ITER MSE. AIP Conference Proceedings, 988, 214-217.
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  Abstract: The advanced tokamak research program at DIII-D relies critically on the measurement of the current density profile. This was made possible by the development of a Motional Stark Effect (MSE) polarimeter that was first installed in 1992. Three major upgrades have since occurred, and improvements in our understanding of critical performance issues and calibration techniques are ongoing. In parallel with these improvements, we have drawn on our DIII-D experience to begin studies and design work for MSE on burning plasmas and ITER. This paper first reviews how Motional Stark Effect polarimetry (MSE) is used to determine the tokamak current profile. It uses the DIII-D MSE system as an example, and shows results from the latest upgrade that incorporates an array of channels from a new counter-Ip injected neutral beam. The various calibration techniques presently used are reviewed. High-leverage or unresolved issues affecting MSE performance and reliability in ITER are discussed. Next, we show a four-mirror collection optics design for the two ITER MSE views. Finally, we discuss measurements of the polarization properties of a few candidate mirrors for the ITER MSE. Work supported by the U.S. Department of Energy under W-7405-ENG-48. © 2008 American Institute of Physics.
• Moores, J. E., Pelletier, J. D., & Smith, P. H. (2008). Crack propagation by differential insolation on desert surface clasts. Geomorphology, 102(3-4), 472-481.
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  Abstract: In the southwest U.S., cracks in alluvial fan surface clasts have a preferred orientation independent of rock fabric and shape. In this paper, we show that differential insolation of incipient cracks of random orientations predicts a distribution of crack orientations consistent with field observations. In this model, crack growth by hydration and/or thermal weathering is primarily a function of local water content at the crack tip. Crack tips that experience minimal solar insolation maintain a greater average moisture and, hence, weather more rapidly than cracks that experience greater solar insolation. To show this, we used a numerical radiative transfer code to quantify the solar insolation of rectangular cracks at 35° N. latitude with a range of depths and orientations. The amount of solar energy reaching the bottom of each crack was calculated at 5-min intervals over the day for several days of the year to determine hourly, daily, seasonal, and annual energy deposition as a function of crack depth and orientation. By assuming that only crack orientations that effectively shield their interiors and minimize their water loss are able to grow, the pattern of cracks produced by the model is consistent with field observations. The annual average insolation, which controls water retention, is associated with the two primary modes of crack orientation. The effect of daily recharge by summer rains of the North American monsoon system is consistent with the observed deviations from these primary modes. Model results suggest that both the annual average insolation and the daily pattern of rainfall is recorded in the preferred crack orientations of surface clasts in the southwest U.S.
• Schuerger, A. C., Fajardo-Cavazos, P., Clausen, C. A., Moores, J. E., Smith, P. H., & Nicholson, W. L. (2008). Slow degradation of ATP in simulated martian environments suggests long residence times for the biosignature molecule on spacecraft surfaces on Mars. Icarus, 194(1), 86-100.
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  Abstract: Prelaunch planetary protection protocols on spacecraft are designed to reduce the numbers and diversity of viable bioloads on surfaces in order to mitigate the forward contamination of planetary surfaces. In addition, there is a growing appreciation that prelaunch spacecraft cleaning protocols will be required to reduce the levels of biogenic signature molecules on spacecraft to levels that will not compromise life-detection experiments on landers. The biogenic molecule, adenosine triphosphate (ATP) was tested for long-term stability under simulated Mars surface conditions of high UV flux, low temperature, low pressure, Mars atmosphere, and clear-sky dust loading conditions. Data on UV-induced ATP degradation rates were then extrapolated to a diversity of global conditions using a radiative transfer model for UV on Mars. The UV-induced degradation of ATP tested at 4.1 W m-2 UVC (200-280 nm), -10 °C, 7.1 mb, 95% CO2 gas composition, and an atmospheric opacity of τ = 0.1 yielded a half-life for ATP of 1342 kJ m-2; or extrapolated to approximately 22 sols on equatorial Mars with an atmospheric opacity of τ = 0.5. Temperature was found to moderately affect ATP degradation rates under martian conditions; tests at -80 or 20 °C yielded ATP half-lives of 2594 or 1183 kJ m-2, respectively. The ATP degradation rates reported here are over 10 orders of magnitude slower than the UV-induced biocidal rates reported in the literature on the inactivation of strongly UV-resistant bacterial spores from Bacillus pumilus SAFR-032 [Schuerger, A.C., Richards, J.T., Newcombe, D.A., Venkateswaran, K.J., 2006. Icarus 181, 52-62]. Extrapolating results to global Mars conditions, residence times for a 99% reduction of ATP on spacecraft surfaces ranged from 158 sols on Sun-exposed surfaces to approximately 32,000 sols for the undersides of landers similar to Viking. However, spacecraft materials greatly affected the survival times of ATP under martian conditions. Stainless steel was found to enhance the UV degradation of ATP by over 2 orders of magnitude compared to ATP-doped iridited aluminum, graphite, and astroquartz coupons. Extrapolating these results to global conditions, ATP on stainless steel might be expected to persist between 2 and 320 sols for upper and lower surfaces of landers. Liquid chromatography-mass spectrometry data supported the conclusion that UV irradiation acted to remove the γ-phosphate group from ATP, and no evidence was observed for the UV-degradation of d-ribose or adenine moieties. Long residence times for ATP on spacecraft materials under martian conditions suggest that prelaunch cleaning protocols may need to be strengthened to mitigate against possible ATP contamination of life-detection experiments on Mars landers. © 2007 Elsevier Inc. All rights reserved.
• Banerjee, D. P., Misselt, K. A., Su, K. Y., Ashok, N. M., & Smith, P. S. (2007). Spitzer observations of V4332 sagittarii: Detection of alumina dust. Astrophysical Journal, 666(1 PART 2), L25-L28.
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  Abstract: We present broadband 24, 70, and 160 μm photometry and 5-35 and 55-90 μm spectra of the eruptive variable V4332 Sgr from Spitzer observations. The distinguishing feature of the 5-35 μm spectrum is an unusually broad absorption feature near 10 μm at the position generally associated with silicate-rich dust. Through radiative transfer modeling, we show that this broad feature cannot arise from silicates alone but requires the inclusion of alumina (Al 2O3) as a dust condensate. The case for including Al 2O3 is further strengthened by the presence of the AlO radical, a potentially important molecule in forming Al2O 3. The present detection indicates that porous alumina manifests itself through a broadening of the 9.7 μm silicate feature and additionally displays, on the shoulder of the silicate feature, a component at ∼11.5 μm. We discuss how further observations of V4332 Sgr may have the potential of verifying some general predictions of the dust condensation process. © 2007. The American Astronomical Society. All rights reserved. Printed in U.S.A.
• Moores, J. E., Smith, P. H., Tanner, R., Schuerger, A. C., & Venkateswaran, K. J. (2007). The shielding effect of small-scale martian surface geometry on ultraviolet flux. Icarus, 192(2), 417-433.
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  Abstract: The atmosphere of Mars does little to attenuate incoming ultraviolet (UV) radiation. Large amounts of UV radiation sterilize the hardiest of terrestrial organisms within minutes, and chemically alter the soil such that organic molecules at or near the surface are rapidly destroyed. Thus the survival of any putative martian life near the surface depends to a large extent on how much UV radiation it receives. Variations in small-scale geometry of the surface such as pits, trenches, flat faces and overhangs can have a significant effect on the incident UV flux and may create "safe havens" for organisms and organic molecules. In order to examine this effect, a 1-D radiative transfer sky model with 836 meshed points (plus the Sun) was developed which includes both diffuse and direct components of the surface irradiance. This model derives the variation of UV flux with latitude and an object's Geometric Shielding Ratio (a ratio which describes the geometry of each situation). The best protection is offered by overhangs with flux reduced to a factor of 1.8 ± 0.2 × 10-5 of the unprotected value, a reduction which does not vary significantly by latitude. Pits and cracks are less effective with a reduction in UV flux of only up to 4.5 ± 0.5 × 10-3 for the modeled scenarios; however, they are more effective for the same geometric shielding ratio than overhangs at high latitudes due to the low height of the Sun in the sky. Lastly, polar faces of rocks have the least effective shielding geometry with at most a 1.1 ± 0.1 × 10-1 reduction in UV flux. Polar faces of rocks are most effective at mid latitudes where the Sun is never directly overhead, as at tropical latitudes, and never exposes the back of the rock, as at polar latitudes. In the most favorable cases, UV flux is sufficiently reduced such that organic in-fall could accumulate beneath overhanging surfaces and in pits and cracks. As well, hardy terrestrial microorganisms such as Bacillus pumilus could persist for up to 100 sols on the outer surfaces of typical spacecraft or several tens of martian years in the most shielded surface niches.
• Plemmons, D., Wilcher, K., Tamppari, L., Smith, P., & Peach, L. (2007). Spectroscopic plume analysis of the phoenix mars lander hydrazine monopropellant thrusters. Collection of Technical Papers - 43rd AIAA/ASME/SAE/ASEE Joint Propulsion Conference, 7, 6874-6879.
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  Abstract: Emission testing was performed on two hydrazine monopropellant thrusters to characterize the products of the catalytic decomposition of the hydrazine fuel. These thrusters are part of the landing system on NASA's Phoenix Mars Lander. Gas samples were extracted during engine testing and analyzed using a Fourier transform infrared spectrometer. The spectrometer was calibrated to measure hydrazine, ammonia, and water vapor. The results of the emissions test reported in this paper compare favorably with theoretical predictions.
• Smith, P. H. (2007). The phoenix mission to Mars. Proceedings of SPIE - The International Society for Optical Engineering, 6694.
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  Abstract: After a picture-perfect launch to Mars on August 4, 2007 (see fig. 1), the Phoenix mission will land near 70° N on the northern lowlands on May 25, 2008 and perform an in situ investigation of the ice layer discovered by the Mars Odyssey scientists in 2002. Mars undergoes climate change through obliquity and orbital variations on time periods of 50,000 years. By analyzing the minerals, aqueous chemistry, and grain shapes of the soil associated with the ice, Phoenix will determine whether the ice has ever melted and modified the soil properties. Since water is a necessary substance for life on Earth, a major question for the mission is whether the northern plains represent a habitable zone on Mars. Besides water, the Phoenix team will assess the organic content of the soil and ice as well as the abundances of biologically active elements. Finally, the transport of water through soils and atmosphere is measured using a Canadian meteorological station supplemented by probes to evaluate soil conductivity.
• Soderblom, L. A., Tomasko, M. G., Archinal, B. A., Becker, T. L., Bushroe, M. W., Cook, D. A., Doose, L. R., Galuszka, D. M., Hare, T. M., Howington-Kraus, E., Karkoschka, E., Kirk, R. L., Lunine, J. I., McFarlane, E. A., Redding, B. L., Rizk, B., Rosiek, M. R., See, C., & Smith, P. H. (2007). Topography and geomorphology of the Huygens landing site on Titan. Planetary and Space Science, 55(13), 2015-2024.
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  Abstract: The Descent Imager/Spectral Radiometer (DISR) aboard the Huygens Probe took several hundred visible-light images with its three cameras on approach to the surface of Titan. Several sets of stereo image pairs were collected during the descent. The digital terrain models constructed from those images show rugged topography, in places approaching the angle of repose, adjacent to flatter darker plains. Brighter regions north of the landing site display two styles of drainage patterns: (1) bright highlands with rough topography and deeply incised branching dendritic drainage networks (up to fourth order) with dark-floored valleys that are suggestive of erosion by methane rainfall and (2) short, stubby low-order drainages that follow linear fault patterns forming canyon-like features suggestive of methane spring-sapping. The topographic data show that the bright highland terrains are extremely rugged; slopes of order of 30° appear common. These systems drain into adjacent relatively flat, dark lowland terrains. A stereo model for part of the dark plains region to the east of the landing site suggests surface scour across this plain flowing from west to east leaving ∼100-m-high bright ridges. Tectonic patterns are evident in (1) controlling the rectilinear, low-order, stubby drainages and (2) the "coastline" at the highland-lowland boundary with numerous straight and angular margins. In addition to flow from the highlands drainages, the lowland area shows evidence for more prolific flow parallel to the highland-lowland boundary leaving bright outliers resembling terrestrial sandbars. This implies major west to east floods across the plains where the probe landed with flow parallel to the highland-lowland boundary; the primary source of these flows is evidently not the dendritic channels in the bright highlands to the north. © 2007 Elsevier Ltd. All rights reserved.
• Arvidson, R. E., Squyres, S. W., Anderson, R. C., F., J., Blaney, D., Brückner, J., Cabrol, N. A., Calvin, W. M., Carr, M. H., Christensen, P. R., Clark, B. C., Crumpler, L., Marais, D. D., Souza, J. d., d'Uston, C., Economou, T., Farmer, J., Farrand, W. H., Folkner, W., , Golombek, M. P., et al. (2006). Overview of the Spirit Mars Exploration Rover Mission to Gusev Crater: Landing site to Backstay Rock in the Columbia Hills. Journal of Geophysical Research E: Planets, 111(2).
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  Abstract: Spirit landed on the floor of Gusev Crater and conducted initial operations on soil-covered, rock-strewn cratered plains underlain by olivine-bearing basalts. Plains surface rocks are covered by wind-blown dust and show evidence for surface enrichment of soluble species as vein and void-filling materials and coatings. The surface enrichment is the result of a minor amount of transport and deposition by aqueous processes. Layered granular deposits were discovered in the Columbia Hills, with outcrops that tend to dip conformably with the topography. The granular rocks are interpreted to be volcanic ash and/or impact ejecta deposits that have been modified by aqueous fluids during and/or after emplacement. Soils consist of basaltic deposits that are weakly cohesive, relatively poorly sorted, and covered by a veneer of wind-blown dust. The soils have been homogenized by wind transport over at least the several kilometer length scale traversed by the rover. Mobilization of soluble species has occurred within at least two soil deposits examined. The presence of monolayers of coarse sand on wind-blown bedforms, together with even spacing of granule-sized surface clasts, suggests that some of the soil surfaces encountered by Spirit have not been modified by wind for some time. On the other hand, dust deposits on the surface and rover deck have changed during the course of the mission. Detection of dust devils, monitoring of the dust opacity and lower boundary layer, and coordinated experiments with orbiters provided new insights into atmosphere-surface dynamics. Copyright 2006 by the American Geophysical Union.
• Hanifin, J. P., Stewart, K. T., Smith, P., Tanner, R., Rollag, M., & Brainard, G. C. (2006). High-intensity red light suppresses melatonin. Chronobiology International, 23(1-2), 251-268.
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  PMID: 16687299;Abstract: Early studies on rodents indicated that the long-wavelength portion of the spectrum (orange- and red-appearing light) could influence circadian and neuroendocrine responses. Since then, both polychromatic and analytic action spectra in various rodent species have demonstrated that long-wavelength light is very weak, if not entirely inactive, for regulating neurobehavioral responses. Since testing of monochromatic light wavelengths above 600 nm is uncommon, many researchers have assumed that there is little to no effect of red light on the neuroendocrine or circadian systems. The aims of the following studies were to test the efficacy of monochromatic light above 600 nm for melatonin suppression in hamsters and humans. Results in hamsters show that 640nm monochromatic light at 1.1 × 1017 photons/cm2 can acutely suppress pineal melatonin levels. In normal healthy humans, equal photon density exposures of 1.9 × 1018 photons/cm2 at 460, 630, and 700 nm monochromatic light elicited a significant melatonin suppression at 460 nm and small reductions of plasma melatonin levels at 630 and 700 nm. These findings are discussed relative to the possible roles of classical visual photoreceptors and the recently discovered intrinsically photosensitive retinal ganglion cells for circadian phototransduction. That physiology, and its potential for responding to red light, has implications for domestic applications involving animal care, the lighting of typical human environments, and advanced applications such as space exploration. Copyright © Taylor & Francis Group, LLC.
• Lorenz, R. D., Lemmon, M. T., & Smith, P. H. (2006). Seasonal evolution of Titan's dark polar hood: Midsummer disappearance observed by the Hubble Space Telescope. Monthly Notices of the Royal Astronomical Society, 369(4), 1683-1687.
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  Abstract: Titan, Saturn's largest moon, has a dense organic-laden atmosphere that displays dramatic seasonal variations in composition and appearance. Here we document the evolution of the dark polar hood, first seen in 1980 by Voyager 1 around the north pole, and report quantitative measurements of the hood's disappearance from the south pole in 2002-2003 using previously unpublished observations with the Hubble Space Telescope Advanced Camera for Surveys (HST/ACS). These data support a model of the hood as a transient structure associated with downwelling during polar winter. © 2006 RAS.
• Saito, J., Miyamoto, H., Nakamura, R., Ishiguro, M., Michikami, T., Nakamura, A. M., Demura, H., Sasaki, S., Hirata, N., Honda, C., Yamamoto, A., Yokota, Y., Fuse, T., Yoshida, F., Tholen, D. J., Gaskell, R. W., Hashimoto, T., Kubota, T., Higuchi, Y., , Nakamura, T., et al. (2006). Detailed images of asteroid 25143 Itokawa from Hayabusa. Science, 312(5778), 1341-1344.
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  PMID: 16741110;Abstract: Rendezvous of the Japanese spacecraft Hayabusa with the near-Earth asteroid 25143 Itokawa took place during the interval September through November 2005. The onboard camera imaged the solid surface of this tiny asteroid (535 meters by 294 meters by 209 meters) with a spatial resolution of 70 centimeters per pixel, revealing diverse surface morphologies. Unlike previously explored asteroids, the surface of Itokawa reveals both rough and smooth terrains. Craters generally show unclear morphologies. Numerous boulders on Itokawa's surface suggest a rubble-pile structure.
• Spanovich, N., Smith, M. D., Smith, P. H., Wolff, M. J., Christensen, P. R., & Squyres, S. W. (2006). Surface and near-surface atmospheric temperatures for the Mars Exploration Rover landing sites. Icarus, 180(2), 314-320.
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  Abstract: Downward-looking spectra of the martian surface from the Miniature Thermal Emission spectrometer (Mini-TES), onboard each of the two Mars Exploration Rovers, are modeled in order to retrieve surface and near-surface atmospheric temperatures. By fitting the observed radiance in the vicinity of the 15-μm CO2 absorption feature, the surface temperature and the near-surface atmospheric temperature, approximately 1.1 m above the surface, are determined. The temperatures from the first 180 sols (martian days) of each surface mission are used to characterize the diurnal dependence of temperatures. The near-surface atmospheric temperatures are consistently 20 K cooler than the surface temperatures in the warmest part of each sol, which is 1300-1400 LTST (local true solar time) depending on the location. Seasonal cooling trends are seen in the data by displaying the temperatures as a function of sol. Long ground stares, 8.5 min in duration, show as much as 8 K fluctuation in the near-surface atmospheric temperatures during the early afternoon hours when the near-surface atmosphere is unstable. © 2005 Elsevier Inc. All rights reserved.
• Squyres, S. W., Arvidson, R. E., Bollen, D., F., J., Brückner, J., Cabrol, N. A., Calvin, W. M., Carr, M. H., Christensen, P. R., Clark, B. C., Crumpler, L., Marais, D. D., d'Uston, C., Economou, T., Farmer, J., Farrand, W. H., Folkner, W., Gellert, R., Glotch, T. D., , Golombek, M. P., et al. (2006). Overview of the Opportunity Mars Exploration Rover Mission to Meridiani Planum: Eagle Crater to Purgatory Ripple. Journal of Geophysical Research E: Planets, 111(12).
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  Abstract: The Mars Exploration Rover Opportunity touched down at Meridiani Planum in January 2004 and since then has been conducting observations with the Athena science payload. The rover has traversed more than 5 km, carrying out the first outcrop-scale investigation of sedimentary rocks on Mars. The rocks of Meridiani Planum are sandstones formed by eolian and aqueous reworking of sand grains that are composed of mixed fine-grained siliciclastics and sulfates. The siliciclastic fraction was produced by chemical alteration of a precursor basalt. The sulfates are dominantly Mg-sulfates and also include Ca-sulfates and jarosite. The stratigraphic section observed to date is dominated by eolian bedforms, with subaqueous current ripples exposed near the top of the section. After deposition, interaction with groundwater produced a range of diagenetic features, notably the hematite-rich concretions known as "blueberries." The bedrock at Meridiani is highly friable and has undergone substantial erosion by wind-transported basaltic sand. This sand, along with concretions and concretion fragments eroded from the rock, makes up a soil cover that thinly and discontinuously buries the bedrock. The soil surface exhibits both ancient and active wind ripples that record past and present wind directions. Loose rocks on the soil surface are rare and include both impact ejecta and meteorites. While Opportunity's results show that liquid water was once present at Meridiani Planum below and occasionally at the surface, the environmental conditions recorded were dominantly arid, acidic, and oxidizing and would have posed some significant challenges to the origin of life. Copyright 2006 by the American Geophysical Union.
• Tomasko, M. G., Archinal, B., Becker, T., Bézard, B., Bushroe, M., Combes, M., Cook, D., Coustenis, A., Bergh, C. D., Dafoe, L. E., Doose, L., Douté, S., Eibl, A., Engel, S., Gliem, F., Grieger, B., Holso, K., Howington-Kraus, E., Karkoschka, E., , Keller, H. U., et al. (2005). Rain, winds and haze during the Huygens probe's descent to Titan's surface. Nature, 438(7069), 765-778.
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  PMID: 16319829;Abstract: The irreversible conversion of methane into higher hydrocarbons in Titan's stratosphere implies a surface or subsurface methane reservoir. Recent measurements from the cameras aboard the Cassini orbiter fail to see a global reservoir, but the methane and smog in Titan's atmosphere impedes the search for hydrocarbons on the surface. Here we report spectra and high-resolution images obtained by the Huygens Probe Descent Imager/Spectral Radiometer instrument in Titan's atmosphere. Although these images do not show liquid hydrocarbon pools on the surface, they do reveal the traces of once flowing liquid. Surprisingly like Earth, the brighter highland regions show complex systems draining into flat, dark lowlands. Images taken after landing are of a dry riverbed. The infrared reflectance spectrum measured for the surface is unlike any other in the Solar System; there is a red slope in the optical range that is consistent with an organic material such as tholins, and absorption from water ice is seen. However, a blue slope in the near-infrared suggests another, unknown constituent. The number density of haze particles increases by a factor of just a few from an altitude of 150 km to the surface, with no clear space below the tropopause. The methane relative humidity near the surface is 50 per cent. © 2005 Nature Publishing Group.
• Farrell, W. M., Smith, P. H., Delory, G. T., Hillard, G. B., Marshall, J. R., Catling, D., Hecht, M., Tratt, D. M., Renno, N., Desch, M. D., Cummer, S. A., Houser, J. G., & Johnson, B. (2004). Electric and magnetic signatures of dust devils from the 2000-2001 MATADOR desert tests. Journal of Geophysical Research E: Planets, 109(3), E03004 1-13.
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  Abstract: Dust devils are significant meteorological phenomena on Mars: They are ubiquitous, continually gardening the Martian surface, and may be the primary atmospheric dust-loading mechanism in nonstorm seasons. Further, dust grains in the swirling dust devils may become electrically charged via triboelectric effects. Electrical effects associated with terrestrial dust devils have been reported previously, but these were isolated measurements (electric fields only) with no corroborating measurements. To study the fluid and electrical forces associated with dust devils, NASA's Human Exploration and Development of Space (HEDS) enterprise sponsored a set of desert field tests with a suite of mutually compatible and complementary instruments in order to determine the relationship between electric, magnetic, and fluid forces. The project (originally a selected flight project) was entitled "Martian ATmosphere And Dust in the Optical and Radio" (MATADOR). In this work, we present a number of interesting examples of the electromagnetic nature of the dust devil. We also describe potential hazards of the dust devil and how similar devil- and storm-related forces on Mars might affect any human occupation. Copyright 2004 by the American Geophysical Union.
• Herkenhoff, K. E., Squyres, S. W., Arvidson, R., Bass, D. S., III, J. B., Bertelsen, P., Cabrol, N. A., Gaddis, L., Hayes, A. G., Hviid, S. F., Johnson, J. R., Kinch, K. M., Madsen, M. B., Maki, J. N., McLennan, S. H., McSween, H. Y., Rice Jr., J. W., Sims, M., Smith, P. H., , Soderblom, L. A., et al. (2004). Textures of the soils and rocks at Gusev crater from Spirit's Microscopic Imager. Science, 305(5685), 824-826.
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  PMID: 15297663;Abstract: The Microscopic Imager on the Spirit rover analyzed the textures of the soil and rocks at Gusev crater on Mars at a resolution of 100 micrometers. Weakly bound agglomerates of dust are present in the soil near the Columbia Memorial Station. Some of the brushed or abraded rock surfaces show igneous textures and evidence for alteration rinds, coatings, and veins consistent with secondary mineralization. The rock textures are consistent with a volcanic origin and subsequent alteration and/or weathering by impact events, wind, and possibly water.
• Herkenhoff, K. E., Squyres, S. W., Arvidson, R., Bass, D. S., III, J. B., Bertelsen, P., Ehlmann, B. L., Farrand, W., Gaddis, L., Greeley, R., Grotzinger, J., Hayes, A. G., Hviid, S. F., Johnson, J. R., Jolliff, B., Kinch, K. M., Knoll, A. H., Madsen, M. B., Maki, J. N., , McLennan, S. M., et al. (2004). Evidence from opportunity's microscopic imager for water on Meridiani Planum. Science, 306(5702), 1727-1730.
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  PMID: 15576607;Abstract: The Microscopic Imager on the Opportunity rover analyzed textures of soils and rocks at Meridiani Planum at a scale of 31 micrometers per pixel. The uppermost millimeter of some soils is weakly cemented, whereas other soils show little evidence of cohesion. Rock outcrops are laminated on a millimeter scale; image mosaics of cross-stratification suggest that some sediments were deposited by flowing water. Vugs in some outcrop faces are probably molds formed by dissolution of relatively soluble minerals during diagenesis. Microscopic images support the hypothesis that hematite-rich spherules observed in outcrops and soils also formed diagenetically as concretions.
• Lemmon, M. T., Wolff, M. J., Smith, M. D., Clancy, R. T., Banfield, D., Landis, G. A., Ghosh, A., Smith, P. H., Spanovich, N., Whitney, B., Whelley, P., Greeley, R., Thompson, S., III, J. B., & Squyres, S. W. (2004). Atmospheric imaging results from the Mars exploration rovers: Spirit and opportunity. Science, 306(5702), 1753-1756.
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  PMID: 15576613;Abstract: A visible atmospheric optical depth of 0.9 was measured by the Spirit rover at Gusev crater and by the Opportunity rover at Meridiani Planum. Optical depth decreased by about 0.6 to 0.7% per sol through both 90-sol primary missions. The vertical distribution of atmospheric dust at Gusev crater was consistent with uniform mixing, with a measured scale height of 11.56 ± 0.62 kilometers. The dust's cross section weighted mean radius was 1.47 ± 0.21 micrometers (μm) at Gusev and 1.52 ± 0.18 μm at Meridiani. Comparison of visible optical depths with 9-μm optical depths shows a visibie-to-infrared optical depth ratio of 2.0 ± 0.2 for comparison with previous monitoring of infrared optical depths.
• Lorenz, R. D., Smith, P. H., & Lemmon, M. T. (2004). Seasonal change in Titan's haze 1992-2002 from Hubble Space Telescope observations. Geophysical Research Letters, 31(10), L10702 1-4.
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  Abstract: Images from the Hubble Space Telescope (HST) document the seasonal migration of haze in Titan's atmosphere. Image profiles show darkening of the north relative to the south at 439 nm (blue) but no change at 619 nm. The limb profile at 889 nm has inverted, becoming north-bright, a variation consistent with haze transport towards the winter hemisphere by winds. The complex altitude-time variation of the north-south haze differences are indicated in resolved spectra acquired with the Space Telescope Imaging Spectrograph (STIS): the continuum slope of a north/south ratio spectrum changes sign, becoming red, between 2000 and 2002, although the 889 nm band had already reversed by 2000, suggesting the haze distribution changes most rapidly at high altitudes. Copyright 2004 by the American Geophysical Union.
• Renno, N. O., Abreu, V. J., Koch, J., Smith, P. H., Hartogensis, O. K., A.R., H., Burose, D., Delory, G. T., Farrell, W. M., Watts, C. J., Garatuza, J., Parker, M., & Carswell, A. (2004). MATADOR 2002: A pilot field experiment on convective plumes and dust devils. Journal of Geophysical Research E: Planets, 109(7), E07001 1-10.
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  Abstract: Recent research suggests that mineral dust plays an important role in terrestrial weather and climate, not only by altering the atmospheric radiation budget, but also by affecting cloud microphysics and optical properties. In addition, dust transport and related Aeolian processes have been substantially modifying the surface of Mars. Dusty convective plumes and dust devils are frequently observed in terrestrial deserts and are ubiquitous features of the Martian landscape. There is evidence that they are important sources of atmospheric dust on both planets. Many studies have shown that on a small scale, dust sourcing is sensitive to a large number of factors, such as soil cover, physical characteristics, composition, topography, and weather. We have been doing comparative studies of dust events on Earth and Mars in order to shed light on important physical processes of the weather and climate of both planets. Our 2002 field campaign showed that terrestrial dust devils produce heat and dust fluxes two and five orders of magnitude larger than their background values. It also showed that charge separation within terrestrial dust devils produces strong electric fields that might play a significant role in dust sourcing. Since Martian dust devils and dust storms are stronger and larger than terrestrial events, they probably produce even stronger fluxes and electric fields. Copyright 2004 by the American Geophysical Union.
• Smith, M. D., Wolff, M. J., Lemmon, M. T., Spanovich, N., Banfield, D., Budney, C. J., Clancy, R. T., Ghosh, A., Landis, G. A., Smith, P., Whitney, B., Christensen, P. R., & Squyres, S. W. (2004). First atmospheric science results from the Mars exploration rovers Mini-TES. Science, 306(5702), 1750-1753.
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  PMID: 15576612;Abstract: Thermal infrared spectra of the martian atmosphere taken by the Miniature Thermal Emission Spectrometer (Mini-TES) were used to determine the atmospheric temperatures in the planetary boundary layer and the column-integrated optical depth of aerosols. Mini-TES observations show the diurnal variation of the martian boundary layer thermal structure, including a near-surface superadiabatic layer during the afternoon and an inversion layer at night. Upward-looking Mini-TES observations show warm and cool parcels of air moving through the Mini-TES field of view on a time scale of 30 seconds. The retrieved dust optical depth shows a downward trend at both sites.
• Smith, P. H. (2004). The Phoenix mission to Mars. IEEE Aerospace Conference Proceedings, 1, 337-341.
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  Abstract: Like the bird of ancient mythology, the Phoenix mission is reborn out of fire; a new mission is born from the embers of previous missions. Phoenix returns to flight the Mars Surveyor Program's 2001 (MSP'01) lander that was mothballed in 2000; at that time, the project was 25% through its final test period. In addition, a diverse scientific payload has been chosen from the instruments from the Mars Polar Lander and the MSP'01 missions. This complement of spacecraft and payload will perform a scientific analysis of the Martian arctic soils and weather to unravel the history of water in all its phases and assess the potential for biology.
• Squyres, S. W., Arvidson, R. E., III, J. B., Brückner, J., Cabrol, N. A., Calvin, W., Carr, M. H., Christensen, P. R., Clark, B. C., Crumpler, L., Marais, D. D., D'Uston, C., Economou, T., Farmer, J., Farrand, W., Folkner, W., Golombek, M., Gorevan, S., Grant, J. A., , Greeley, R., et al. (2004). The Spirit Rover's Athena science investigation at Gusev crater, Mars. Science, 305(5685), 794-799.
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  PMID: 15297657;Abstract: The Mars Exploration Rover Spirit and its Athena science payload have been used to investigate a landing site in Gusev crater. Gusev is hypothesized to be the site of a former take, but no clear evidence for lacustrine sedimentation has been found to date. Instead, the dominant lithology is basalt, and the dominant geologic processes are impact events and eolian transport. Many rocks exhibit coatings and other characteristics that may be evidence for minor aqueous alteration. Any lacustrine sediments that may exist at this location within Gusev apparently have been buried by lavas that have undergone subsequent impact disruption.
• Squyres, S. W., Arvidson, R. E., III, J. B., Brückner, J., Cabrol, N. A., Calvin, W., Carr, M. H., Christensen, P. R., Clark, B. C., Crumpler, L., Marais, D. D., D'Uston, C., Economou, T., Farmer, J., Farrand, W., Folkner, W., Golombek, M., Gorevan, S., Grant, J. A., , Greeley, R., et al. (2004). The opportunity Rover's athena science investigation at Meridiani Planum, Mars. Science, 306(5702), 1698-1703.
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  PMID: 15576602;Abstract: The Mars Exploration Rover Opportunity has investigated the landing site in Eagle crater and the nearby plains within Meridiani Planum. The soils consist of fine-grained basaltic sand and a surface lag of hematite-rich spherules, spherule fragments, and other granules. Wind ripples are common. Underlying the thin soil layer, and exposed within small impact craters and troughs, are flat-lying sedimentary rocks. These rocks are finely laminated, are rich in sulfur, and contain abundant sulfate salts. Small-scale cross-lamination in some locations provides evidence for deposition in flowing liquid water. We interpret the rocks to be a mixture of chemical and siliciclastic sediments formed by episodic inundation by shallow surface water, followed by evaporation, exposure, and desiccation. Hematite-rich spherules are embedded in the rock and eroding from them. We interpret these spherules to be concretions formed by postdepositional diagenesis, again involving liquid water.
• Thomas, N., Lüthi, B., Hviid, S. F., Keller, H. U., Markiewicz, W. J., Blümchen, T., Basilevsky, A. T., Smith, P. H., Tanner, R., Oquest, C., Reynolds, R., Josset, J. -., Beauvivre, S., Hofmann, B., Rüffer, P., & Pillinger, C. T. (2004). The microscope for Beagle 2. Planetary and Space Science, 52(9), 853-866.
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  Abstract: The microscope for the Beagle 2 lander, which was launched as part of the European Space Agency's Mars Express mission on 2 June 2003, will provide images of the Martian surface at around 6 μm resolution. It will provide optical images of the surface of Mars at a resolution 5 times higher than any other experiment currently planned. The device has a working distance of 12 mm and uses a set of 12 light-emitting diodes which surround the aperture to illuminate the sample in four colours. The target is brought into focus using a stepper motor. This article describes the scientific objectives and the design of the microscope. It also discusses initial results from ground calibration exercises which were designed to validate the system and describes aspects of its operation. © 2004 Elsevier Ltd. All rights reserved.
• Ferri, F., Smith, P. H., Lemmon, M., & Rennó, N. O. (2003). Dust devils as observed by Mars Pathfinder. Journal of Geophysical Research E: Planets, 108(12), 7-1.
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  Abstract: Dust devils are localized meteorological phenomena frequently observed in terrestrial dry lands and desert landscapes as well as on Mars. They are low-pressure, warm core vortices that form at the bottom of convective plumes and loft dust from the surface. They move with the speed of the ambient wind and are tilted by wind shears. The Mars Pathfinder detected dust devils as dust plumes in the Imager for Mars Pathfinder images and as low-pressure convective vortices in the meteorological Mars Pathfinder Atmospheric Structure Investigation/Meteorology (ASI/MET) experiment data. The Pathfinder data have been analyzed in terms of dust devil size, spatial distribution, and frequency of occurrence. The results show that the Pathfinder imaging and MET observations are consistent with each other and with the observations made by the Viking 1 Orbiter and Mars Global Surveyor. The dust devil's ability to loft dust into the atmosphere has been investigated and a thermodynamic theory for dust devils has been used to calculate their physical parameters relevant to dust transport. The dust devils observed in an active day provide a pumping rate larger than the dust-settling rate derived from the optical obscuration of the Pathfinder rover solar panels. Therefore dust devils are a major factor in transporting dust from the surface to the atmosphere at the Pathfinder site. Copyright 2003 by the American Geophysical Union.
• Tratt, D. M., Hecht, M. H., Catling, D. C., Samulon, E. C., & Smith, P. H. (2003). In situ measurement of dust devil dynamics: Toward a strategy for Mars. Journal of Geophysical Research E: Planets, 108(11), 2-1.
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  Abstract: An intensive 3-day dust devil investigation was conducted near Eloy, Arizona, during June of 2001. The goal was to evaluate strategies for observing dust devils on Mars by studying the physics of terrestrial dust devils. As part of this campaign, an instrumented vehicle outfitted with wind, temperature, and pressure sensors was used to intercept and penetrate numerous dust devils. Defined analysis of meteorological fields was only possible with knowledge of the whole body motion of a dust devil. One such data set analyzed revealed a dust devil structure characterized by a tangential wind proportional to radius, r, inside the warm, low-pressure core of a dust devil, and proportional to r-1/2 outside the core. We discuss the implications for optimum measurement strategies. Copyright 2003 by the American Geophysical Union.
• Kuhlman, K. R., Hecht, M. H., Brinza, D. E., Feldman, J. E., Fuerstenau, S. D., Friedman, L., Kelly, L., Oslick, J., Polk, K., Moller, L. E., Trowbridge, K., Sherman, J., Marshall, A., Diaz, A. L., Waldron, A., Lewis, C., Gyulai, C., Powell, G., Meloy, T., & Smith, P. (2002). SNOOPY: Student nanoexperiments for outreach and observational planetary inquiry. IEEE Aerospace Conference Proceedings, 1, 317-325.
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  Abstract: Student nanoexperiments for outreach and observational planetary inquiry (SNOOPY) is an example of directly involving students and teachers in planetary science missions. The SNOOPY Project evolved from the Mars Environmental Compatibility Assessment (MECA) Student Nanoexperiment Project, a partnership between MECA, The Planetary Society and Visionary Products, Inc. The MECA instrument suite, developed at the Jet Propulsion Laboratory, was scheduled for launch aboard the canceled Mars Surveyor Lander 2001. Students 18 years of age and younger were invited to propose experiments that were consistent with MECA's Mission: to help us better understand how humans will be able to live on Mars. Two nanoexperiments were chosen for flight, the Angle of Repose of Martian Dust and Contradistinctive Copper. These experiments addressed the behavior of windblown Martian dust on surfaces and the oxidation of copper. The SNOOPY paradigm for planetary science experiments could be used on a variety of future space exploration missions. © 2002 IEEE.
• Lemmon, M. T., Smith, P. H., & Lorenz, R. D. (2002). Methane abundance on Titan, measured by the Space Telescope Imaging Spectrograph. Icarus, 160(2), 375-385.
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  Abstract: Although methane is the dominant absorber in Titan's reflection spectrum, the amount of methane in the atmosphere has only been determined to an order of magnitude. We analyzed spectra from the Space Telescope Imaging Spectrograph, looking at both a bright surface region (700-km radius) and a dark surface region. The difference between the spectra of the two regions is attributed to light that has scattered off the surface, and therefore made a round-trip through all of Titan's methane. Considering only absorption, the shape of the difference spectrum provides an upper limit on methane abundance of 3.5 km-am. Modeling the multiple scattering in the atmosphere further constrains the methane abundance to 2.63 ± 0.17 km-am. In the absence of supersaturation and with a simplified methane vertical profile, this corresponds to a surface methane-mole fraction near 3.8% and a relative humidity of 0.32. With supersaturation near the tropopause, the surface methane mole fraction could be as low as 3%. © 2002 Elsevier Science (USA).
• Tomasko, M. G., Buchhauser, D., Bushroe, M., Dafoe, L. E., Doose, L. R., Eibl, A., Fellows, C., McFarlane, E., Prout, G. M., Pringle, M. J., Rizk, B., See, C., Smith, P. H., & Tsetsenekos, K. (2002). The descent imager/spectral radiometer (DISR) experiment on the huygens entry probe of titan. Space Science Reviews, 104(1-4), 469-551.
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  Abstract: The payload of the Huygens Probe into the atmosphere of Titan includes the Descent Imager/Spectral Radiometer (DISR). This instrument includes an integrated package of several optical instruments built around a silicon charge coupled device (CCD) detector, a pair of linear InGaAs array detectors, and several individual silicon detectors. Fiber optics are used extensively to feed these detectors with light collected from three frame imagers, an upward and downward-looking visible spectrometer, an upward and downward looking near-infrared spectrometer, upward and downward looking violet phtotometers, a four-channel solar aerole camera, and a sun sensor that determines the azimuth and zenith angle of the sun and measures the flux in the direct solar beam at 940 nm. An onboard optical calibration system uses a small lamp and fiber optics to track the relative sensitivity of the different optical instruments relative to each other during the seven year cruise to Titan. A 20 watt lamp and collimator are used to provide spectrally continuous illumination of the surface during the last 100 m of the descent for measurements of the reflection spectrum of the surface. The instrument contains software and hardware data compressors to permit measurements of upward and downward direct and diffuse solar flux between 350 and 1700 nm in some 330 spectral bands at approximately 2 km vertical resolution from an alititude of 160 km to the surface. The solar aureole camera measures the brightness of a 6° wide strip of the sky from 25 to 75° zenith angle near and opposite the azimuth of the sun in two passbands near 500 and 935 nm using vertical and horizontal polarizers in each spectral channel at a similar vertical resolution. The downward-looking spectrometers provide the reflection spectrum of the surface at a total of some 600 locations between 850 and 1700 nm and at more than 3000 locations between 480 and 960 nm. Some 500 individual images of the surface are expected which can be assembled into about a dozen panoramic mosaics covering nadir angles from 6° to 96° at all azimuths. The spatial resolution of the images varies from 300 m at 160 km altitude to some 20 cm in the last frames. The scientific objectives of the experiment fall into four areas including (1) measurement of the solar heating profile for studies of the thermal balance of Titan; (2) imaging and spectral reflection measurements of the surface for studies of the composition, topography, and physical processes which form the surface as well as for direct measurements of the wind profile during the descent; (3) measurements of the brightness and degree of linear polarization of scattered sunlight including the solar aureole together with measurements of the extinction optical depth of the aerosols as a function of wavelength and altitude to study the size, shape, vertical distribution, optical properties, sources and sinks of aerosols in Titan's atmosphere; and (4) measurements of the spectrum of downward solar flux to study the composition of the atmosphere, especially the mixing ratio profile of methane throughout the descent. We briefly outline the methods by which the flight instrument was calibrated for absolute response, relative spectral response, and field of view over a very wide temperature range. We also give several examples of data collected in the Earth's atmosphere using a spare instrument including images obtained from a helicopter flight program, reflection spectra of various types of terrain, solar aureole measurements including the determination of aerosol size, and measurements of the downward flux of violet, visible, and near infrared sunlight. The extinction optical depths measured as a function of wavelength are compared to models of the Earth's atmosphere and are divided into contributions from molecular scattering, aerosol extinction, and molecular absorption. The test observations during simulated descents with mountain and rooftop venues in the Earth's atmosphere are very important for driving out problems in the calibration and interpretion of the observations to permit rapid analysis of the observations after Titan entry.
• Keller, H. U., Hartwig, H., Kramm, R., Koschny, D., Markiewicz, W. J., Thomas, N., Fernades, M., Smith, P. H., Reynolds, R., Lemmon, M. T., Weinberg, J., Marcialis, R., Tanner, R., Boss, B. J., Oquest, C., & Paige, D. A. (2001). The MVACS Robotic Arm Camera. Journal of Geophysical Research E: Planets, 106(E8), 17609-17621.
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  Abstract: The Robotic Arm Camera (RAC) is one of the key instruments newly developed for the Mars Volatiles and Climate Surveyor payload of the Mars Polar Lander. This lightweight instrument employs a front lens with variable focus range and takes images at distances from 11 mm (image scale 1:1) to infinity. Color images with a resolution of better than 50 μm can be obtained to characterize the Martian soil. Spectral information of nearby objects is retrieved through illumination with blue, green, and red lamp sets. The design and performance of the camera are described in relation to the science objectives and operation. The RAC uses the same CCD detector array as the Surface Stereo Imager and shares the readout electronics with this camera. The RAC is mounted at the wrist of the Robotic Arm and can characterize the contents of the scoop, the samples of soil fed to the Thermal Evolved Gas Analyzer, the Martian surface in the vicinity of the lander, and the interior of trenches dug out by the Robotic Arm. It can also be used to take panoramic images and to retrieve stereo information with an effective baseline surpassing that of the Surface Stereo Imager by about a factor of 3. Copyright 2000 by the American Geophysical Union.
• Mogensen, C. T., Knudsen, J. M., Madsen, M. B., Bertelsen, P., Hviid, S. F., Hargraves, R. B., Smith, P., & Paige, D. A. (2001). Magnetic Properties Experiments on the Mars Polar Lander. Journal of Geophysical Research E: Planets, 106(E8), 17579-17587.
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  Abstract: The Mars Polar Lander carries an instrument package called the Magnetic Properties Experiments. This package consists of one magnet array, one tip-plate magnet, and three Thermal and Evolved Gas Analyzer (TEGA) magnets. The magnet array and the tip-plate magnet are identical to those flown on Mars Pathfinder and will be passively exposed to airborne dust. The TEGA magnets are a new addition to the package designed to study actively sampled material collected from three different depths in the trench that will be dug by the robotic arm soil sampler. Copyright 2001 by the American Geophysical Union.
• Reynolds, R. O., Smith, P. H., Bell, L. S., & Keller, H. U. (2001). The design of mars lander cameras for Mars Pathfinder, Mars Surveyor '98 and Mars Surveyor '01. IEEE Transactions on Instrumentation and Measurement, 50(1), 63-71.
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  Abstract: The Mars Pathfinder, Mars Surveyor '98, and Mars Surveyor '01 lander designs all utilize charged coupled device (CCD)-based cameras to conduct scientific investigations, assist with navigation of surface rovers and/or confirm sample acquisition and delivery by robotic arms (RAs). The extreme temperature and pressure environment of the Martian surface, the vibration and shock experienced during launch and landing, and the tight volume, mass, and power budgets challenge the designer and scientist alike to develop instruments and associated electronics that will function properly to provide the desired data. This paper provides an overview of the optical and mechanical design of two of the camera configurations, as well as a detailed description of the camera electronics. The cameras described are a gimbal-mounted stereo multi-spectral imager with 1 mrad/pixel resolution, and a variable focus robotic arm camera (RAC) capable of 23-μm/pixel resolution and provided with a self-contained three-color illumination system. The electronics, housed in the cameras and in separate enclosures, utilizes such subsystems as Field Programmable Gate Arrays (FPGAs) for digital control, VME bus-mapped video memory, and multiplexed stepper motor select/phase driver circuitry. © 2001 IEEE.
• Smith, P. H., Reynolds, R., Weinberg, J., Friedman, T., Lemmon, M. T., Tanner, R., Reid, R. J., Marcialis, R. L., Bos, B. J., Oquest, C., Keller, H. U., Markiewicz, W. J., Kramm, R., Gliem, F., & Rueffer, P. (2001). The MVACS Surface Stereo Imager on Mars Polar Lander. Journal of Geophysical Research E: Planets, 106(E8), 17589-17607.
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  Abstract: The Surface Stereo Imager (SSI), a stereoscopic, multispectral camera on the Mars Polar Lander, is described in terms of its capabilities for studying the Martian polar environment. The camera's two eyes, separated by 15.0 cm, provide the camera with range-finding ability. Each eye illuminates half of a single CCD detector with a field of view of 13.8° high by 14.3° wide and has 12 selectable filters between 440 and 1000 nm. The f/18 optics have a large depth of field, and no focusing mechanism is required; a mechanical shutter is avoided by using the frame transfer capability of the 528 x 512 CCD. The resolving power of the camera, 0.975 mrad/pixel, is the same as the Imager for Mars Pathfinder camera, of which it is nearly an exact copy. Specially designed targets are positioned on the Lander; they provide information on the magnetic properties of wind-blown dust, and radiometric standards for calibration. Several experiments beyond the requisite color panorama are described in detail: contour mapping of the local terrain, multispectral imaging of interesting features (possibly with ice or frost in shaded spots) to study local mineralogy, and atmospheric imaging to constrain the properties of the haze and clouds. Eight low-transmission filters are included for imaging the Sun directly at multiple wavelengths to give SSI the ability to measure dust opacity and potentially the water vapor content. This paper is intended to document the functionality and calibration of the SSI as flown on the failed lander. Copyright 2001 by the American Geophysical Union.
• Stoker, C. R., Cabrol, N. A., Roush, T. R., Moersch, J., Aubele, J., Barlow, N., III, E. B., Bishop, J., Chapman, M., Clifford, S., Cockell, C., Crumpler, L., Craddock, R., Hon, R. D., Foster, T., Gulick, V., Grin, E., Horton, K., Hovde, G., , Johnson, J. R., et al. (2001). The 1999 Marsokhod rover mission simulation at Silver Lake, California: Mission overview, data sets, and summary of results. Journal of Geophysical Research E: Planets, 106(E4), 7639-7663.
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  Abstract: We report on a field experiment held near Silver Lake playa in the Mojave Desert in February 1999 with the Marsokhod rover. The payload (Descent Imager, PanCam, Mini-TES, and Robotic Arm Camera), data volumes, and data transmission/receipt windows simulated those planned for the Mars Surveyor mission selected for 2001. A central mast with a pan and tilt platform at 150 cm height carried a high-resolution color stereo imager to simulate the PanCam and a visible/near-infrared fiberoptic spectrometer (operating range 0.35-2.5 μm). Monochrome stereo navigation cameras were mounted on the mast and the front and rear of the rover near the wheels. A field portable infrared spectroradiometer (operating range 8-14 μm) simulated the Mini-TES. A Robotic Arm Camera, capable of close-up color imaging at 23 μm/pixel resolution, was used in conjunction with the excavation of a trench into the subsurface. The science team was also provided with simulated images from the Mars Descent Imager and orbital panchromatic and multispectral imaging of the site obtained with the French SPOT, airborne Thermal Infrared Mapping Spectrometer, and Landsat Thematic Mapper instruments. Commands sequences were programmed and sent daily to the rover, and data returned were limited to 40 Mbits per communication cycle. During the simulated mission, 12 commands were uplinked to the rover, it traversed ∼90 m, six sites were analyzed, 11 samples were collected for laboratory analysis, and over 5 Gbits of data were collected. Twenty-two scientists, unfamiliar with the location of the field site, participated in the science mission from a variety of locations, accessing data via the World Wide Web. Remote science interpretations were compared with ground truth from the field and laboratory analysis of collected samples. Using this payload and mission approach, the science team synergistically interpreted orbital imaging and infrared spectroscopy, descent imaging, rover-based imaging, infrared spectroscopy, and microscopic imaging to deduce a consistent and largely correct interpretation of the geology, mineralogy, stratigraphy, and exobiology of the site. Use of imaging combined with infrared spectroscopy allowed source outcrops to be identified for local rocks on an alluvial fan. Different lithologies were distinguished both near the rover and at distances of hundreds of meters or more. Subtle differences such as a contact between dolomite and calcite were identified at a distance of 0.5 km. A biomarker for endolithic microbiota, a plausible life form to be found on Mars, was successfully identified. Microscopic imaging of soils extracted from the surface and subsurface allowed the mineralogy and fluvial history of the trench site to be deduced. The scientific productivity of this simulation shows that this payload and mission approach has high science value and would contribute substantially to achieving the goals of Mars exploration. Copyright 2001 by the American Geophysical Union.
• Yingst, R. A., Smith, P. H., Lemmon, M. T., Marcialis, R. L., Rice Jr., J. W., & Weinberg, J. D. (2001). DIRTCam in the desert: The Silver Lake field test of the Robotic Arm Camera. Journal of Geophysical Research E: Planets, 106(E4), 7721-7732.
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  Abstract: The Robotic Arm Camera (RAC) is a panchromatic imager included as part of the Mars Volatiles and Climate Surveyor (MVACS) science experiment on Mars Polar Lander and on the Mars 2001 lander. It is designed to take both panoramic and microscopic images in order to gather data on the morphology and mineralogy of surface materials. In order to demonstrate these capabilities, a field test was conducted at Silver Lake playa in the Mojave Desert. The test consisted of going to a remote site unknown to the science team and providing that team with a data set of RAC panoramic, anaglyph, and microscopic images similar to what would be available during an actual landing. With only this information the science team attempted a determination of the position and the geology of the field test site. Using panoramic and anaglyph images provided by RAC, in conjunction with overflight images simulating data from a descent camera, the landing site for the field test was determined within 50 m of the actual site as lying near both a playa and an alluvial fan. Images of samples from the surface and within the trench revealed grain morphology, texture, and mineralogy indicating a soil dominated by quartz and feldspar, interspersed with a minor mafic component. Grain-size distribution was bimodal, with small, rounded to subrounded grains dominant at lower depths and larger, more angular grains more plentiful near the surface. This mineralogy is confirmed by the geology of the site and the data provided by the descent images and mid-IR measurements. RAC has demonstrated its ability to image the local geology and identify the major mineralogic components of an unknown site. These abilities will be crucial in understanding both the macroscopic and the microscopic geology of future Mars landing sites. This test also has demonstrated the crucial link between RAC data and complementary data sets such as context images and compositional data that can support the mineralogic observations made by RAC. Copyright 2001 by the American Geophysical Union.
• Sullivan, R., Greeley, R., Kraft, M., Wilson, G., Golombek, M., Herkenhoff, K., Murphy, J., & Smith, P. (2000). Results of the Imager for Mars Pathfinder windsock experiment. Journal of Geophysical Research E: Planets, 105(E10), 24547-24562.
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  Abstract: The Imager for Mars Pathfinder (IMP) windsock experiment measured wind speeds at three heights within 1.2 m of the Martian surface during Pathfinder landed operations. These wind data allowed direct measurement of near-surface wind profiles on Mars for the first time, including determination of aerodynamic roughness length and wind friction speeds. Winds were light during periods of windsock imaging, but data from the strongest breezes indicate aerodynamic roughness length of 3 cm at the landing site, with wind friction speeds reaching 1 m/s. Maximum wind friction speeds were about half of the threshold-of-motion friction speeds predicted for loose, fine-grained materials on smooth Martian terrain and about one third of the threshold-of-motion friction speeds predicted for the same size particles over terrain with aerodynamic roughness of 3 cm. Consistent with this, and suggesting that low wind speeds prevailed when the windsock array was not imaged and/or no particles were available for aeolian transport, no wind-related changes to the surface during mission operations have been recognized. The aerodynamic roughness length reported here implies that proposed deflation of fine particles around the landing site, or activation of duneforms seen by IMP and Sojourner, would require wind speeds >28 m/s at the Pathfinder top windsock height (or >31 m/s at the equivalent Viking wind sensor height of 1.6 m) and wind speeds >45 m/s above 10 m. These wind speeds would cause rock abrasion if a supply of durable particles were available for saltation. Previous analyses indicate that the Pathfinder landing site probably is rockier and rougher than many other plains units on Mars, so aerodynamic roughness length elsewhere probably is less than the 3-cm value reported for the Pathfinder site. Copyright 2000 by the American Geophysical Union.
• Titov, D. V., Markiewicz, W. J., Thomas, N., Keller, H. U., Tomasko, M. G., Lemmon, M., & Smith, P. H. (2000). On the optical studies of the atmospheric water vapour from the surface of Mars. Planetary and Space Science, 48(15), 1423-1427.
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  Abstract: Remote observations of the atmospheric water vapour from the Mars orbit were usually carried out to study its global distribution and variability. Measurements of the water vapour abundance onboard the landers have recently become an important complement to the orbital sounding. Narrow-band filter photometry and spectroscopy of the solar radiation from the surface of the planet proved to be a powerful tool in the study of atmospheric water. The Imager for Mars Pathfinder (IMP) was the first instrument to measure its amount from the surface. The Surface Stereo Imager (SSI) onboard the Mars Polar Lander (MPL) was to follow but the spacecraft was lost at landing. Nevertheless significant expertise in the optical measurements of atmospheric H2O was gained during these missions. This paper summarizes this experience emphasizing the radiative transfer aspects of the problem. The results of this study could be of importance for future missions to Mars. © 2000 Elsevier Science Ltd. All rights reserved.
• Gaddis, L. R., Kirk, R. L., Johnson, J. R., Soderblom, L. A., Ward, A. W., Barrett, J., Becker, K., Decker, T., Blue, J., Cook, D., Eliason, E., Hare, T., Howington-Kraus, E., Isbell, C., Lee, E. M., Redding, B., Sucharski, R., Sucharski, T., Smith, P. H., & Britt, D. T. (1999). Digital mapping of the Mars Pathfinder landing site: Design, acquisition, and derivation of cartographic products for science applications. Journal of Geophysical Research E: Planets, 104(E4), 8853-8868.
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  Abstract: The Imager for Mars Pathfinder (IMP) acquired more than 16,000 images and provided panoramic views of the surface of Mars at the Mars Pathfinder landing site in Ares Vallis. This paper describes the stereoscopic, multispectral IMP imaging sequences and focuses on their use for digital mapping of the landing site and for deriving cartographic products to support science applications of these data. Two-dimensional cartographic processing of IMP data, as performed via techniques and specialized software developed for ISIS (the U.S.Geological Survey image processing software package), is emphasized. Cartographic processing of IMP data includes ingestion, radiometric correction, establishment of geometric control, coregistration of multiple bands, reprojection, and mosaicking. Photogrammetric processing, an integral part of this cartographic work which utilizes the three-dimensional character of the IMP data, supplements standard processing with geometric control and topographic information [Kirk et al., this issue]. Both cartographic and photogrammetric processing are required for producing seamless image mosaics and for coregistering the multispectral IMP data. Final, controlled IMP cartographic products include spectral cubes, panoramic (360° azimuthal coverage) and planimetric (top view) maps, and topographic data, to be archived on four CD-ROM volumes. Uncontrolled and semicontrolled versions of these products were used to support geologic characterization of the landing site during the nominal and extended missions. Controlled products have allowed determination of the topography of the landing site and environs out to ∼60 m, and these data have been used to unravel the history of large- and small-scale geologic processes which shaped the observed landing site. We conclude by summarizing several lessons learned from cartographic processing of IMP data. Copyright 1999 by the American Geophysical Union.
• Golombek, M. P., Anderson, R. C., Barnes, J. R., III, J. B., Bridges, N. T., Britt, D. T., Brückner, J., Cook, R. A., Crisp, D., Crisp, J. A., Economou, T., Folkner, W. M., Greeley, R., Haberle, R. M., Hargraves, R. B., Harris, J. A., Haldemann, A. F., Herkenhoff, K. E., Hviid, S. F., , Jaumann, R., et al. (1999). Overview of the Mars Pathfinder Mission: Launch through landing, surface operations, data sets, and science results. Journal of Geophysical Research E: Planets, 104(E4), 8523-8553.
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  Abstract: Mars Pathfinder successfully landed at Ares Vallis on July 4, 1997, deployed and navigated a small rover about 100 m clockwise around the lander, and collected data from three science instruments and ten technology experiments. The mission operated for three months and returned 2.3 Gbits of data, including over 16,500 lander and 550 rover images, 16 chemical analyses of rocks and soil, and 8.5 million individual temperature, pressure and wind measurements. Pathfinder is the best known location on Mars, having been clearly identified with respect to other features on the surface by correlating five prominent horizon features and two small craters in lander images with those in high-resolution orbiter images and in inertial space from two-way ranging and Doppler tracking. Tracking of the lander has fixed the spin pole of Mars, determined the precession rate since Viking 20 years ago, and indicates a polar moment of inertia, which constrains a central metallic core to be between 1300 and ∼2000 km in radius. Dark rocks appear to be high in silica and geochemically similar to anorogenic andesites; lighter rocks are richer in sulfur and lower in silica, consistent with being coated with various amounts of dust. Rover and lander images show rocks with a variety of morphologies, fabrics and textures, suggesting a variety of rock types are present. Rounded pebbles and cobbles on the surface as well as rounded bumps and pits on some rocks indicate these rocks may be conglomerates (although other explanations are also possible), which almost definitely require liquid water to form and a warmer and wetter past. Airborne dust is composed of composite silicate particles with a small fraction of a highly magnetic mineral, interpreted to be most likely maghemite; explanations suggest iron was dissolved from crustal materials during an active hydrologic cycle with maghemite freeze dried onto silicate dust grains. Remote sensing data at a scale of a kilometer or greater and an Earth analog correctly predicted a rocky plain safe for landing and roving with a variety of rocks deposited by catstrophic floods, which are relatively dust free. The surface appears to have changed little since it formed billions of years ago, with the exception that eolian activity may have deflated the surface by ∼3-7 cm, sculpted wind tails, collected sand into dunes, and eroded ventifacts (fluted and grooved rocks). Pathfinder found a dusty lower atmosphere, early morning water ice clouds, and morning near-surface air temperatures that changed abruptly with time and height. Small scale vortices, interpreted to be dust devils, were observed repeatedly in the afternoon by the meteorology instruments and have been imaged. Copyright 1999 by the American Geophysical Union.
• Johnson, J. R., Kirk, R., Soderblom, L. A., Gaddis, L., Reid, R. J., Britt, D. T., Smith, P., Lemmon, M., Thomas, N., F., J., Bridges, N. T., Anderson, R., Herkenhoff, K. E., Maki, J., Murchie, S., Dummel, A., Jaumann, R., Trauthan, F., & Arnold, G. (1999). Preliminary results on photometric properties of materials at the Sagan Memorial Station, Mars. Journal of Geophysical Research E: Planets, 104(E4), 8809-8830.
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  Abstract: Reflectance measurements of selected rocks and soils over a wide range of illumination geometries obtained by the Imager for Mars Pathfinder (IMP) camera provide constraints on interpretations of the physical and mineralogical nature of geologic materials at the landing site. The data sets consist of (1) three small "photometric spot" subframed scenes, covering phase angles from 20° to 150°; (2) two image strips composed of three subframed images each, located along the antisunrise and antisunset lines (photometric equator), covering phase angles from ∼0° to 155°; and (3) full-image scenes of the rock "Yogi," covering phase angles from 48° to 100°. Phase functions extracted from calibrated data exhibit a dominantly backscattering photometric function, consistent with the results from the Viking lander cameras. However, forward scattering behavior does appear at phase angles >140°, particularly for the darker gray rock surfaces. Preliminary efforts using a Hapke scattering model are useful in comparing surface properties of different rock and soil types but are not well constrained, possibly due to the incomplete phase angle availability, uncertainties related to the photometric function of the calibration targets, and/or the competing effects of diffuse and direct lighting. Preliminary interpretations of the derived Hapke parameters suggest that (1) red rocks can be modeled as a mixture of gray rocks with a coating of bright and dark soil or dust, and (2) gray rocks have macroscopically smoother surfaces composed of microscopically homogeneous, clear materials with little internal scattering, which may imply a glass-like or varnished surface. Copyright 1999 by the American Geophysical Union.
• Kirk, R. L., Howington-Kraus, E., Hare, T., Dorrer, E., Cook, D., Becker, K., Thompson, K., Redding, B., Blue, J., Galuszka, D., Lee, E. M., Gaddis, L. R., Johnson, J. R., Soderblom, L. A., Ward, A. W., Smith, P. H., & Britt, D. T. (1999). Digital photogrammetric analysis of the IMP camera images: Mapping the Mars Pathfinder landing site in three dimensions. Journal of Geophysical Research E: Planets, 104(E4), 8869-8887.
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  Abstract: This paper describes our photogrammetric analysis of the Imager for Mars Pathfinder data, part of a broader program of mapping the Mars Pathfinder landing site in support of geoscience investigations. This analysis, carried out primarily with a commercial digital photogrammetric system, supported by our in-house Integrated Software for Imagers and Spectrometers (ISIS), consists of three steps: (1) geometric control: simultaneous solution for refined estimates of camera positions and pointing plus three-dimensional (3-D) coordinates of ∼103 features sitewide, based on the measured image coordinates of those features; (2) topographic modeling: identification of ∼3 × 105 closely spaced points in the images and calculation (based on camera parameters from step 1) of their 3-D coordinates, yielding digital terrain models (DTMs); and (3) geometric manipulation of the data: combination of the DTMs from different stereo pairs into a sitewide model, and reprojection of image data to remove parallax between the different spectral filters in the two cameras and to provide an undistorted planimetric view of the site. These processes are described in detail and example products are shown. Plans for combining the photogrammetrically derived topographic data with spectrophotometry are also described. These include photometric modeling using surface orientations from the DTM to study surface microtextures and improve the accuracy of spectral measurements, and photoclinometry to refine the DTM to single-pixel resolution where photometric properties are sufficiently uniform. Finally, the inclusion of rover images in a joint photogrammetric analysis with IMP images is described. This challenging task will provide coverage of areas hidden to the IMP, but accurate ranging of distant features can be achieved only if the lander is also visible in the rover image used. Copyright 1999 by the American Geophysical Union.
• Lorenz, R. D., Lemmon, M. T., Smith, P. H., & Lockwood, G. W. (1999). Seasonal Change on Titan Observed with the Hubble Space Telescope WFPC-2. Icarus, 142(2), 391-401.
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  Abstract: Recent observations with the Wide-Field Planetary Camera (WFPC-2) on the Hubble Space Telescope (HST) show an unexpectedly rapid change in the atmospheric albedo contrast between the north and south hemispheres. In 1994 at blue wavelengths, the north was around 15% brighter than the south, and was expected to fall to about 12% in 1997, but has dropped to only 6% brighter. At some other wavelengths, the contrast has reversed, which was not expected until 2002. The interhemispheric contrast has a time dependence that varies with wavelength; contrast changes in blue lag behind changes in violet and yellow/red. The rapid change and the phase variation with wavelength are consistent with ground-based photometry. A physical model of the transport of high-altitude dark haze by meridional winds is a better description of Titan's behavior than the simple sinusoidal models used to date. Investigation with a radiative transfer model indicates that haze number density changes above 160-km altitude are compatible with the observed hemispheric albedo difference, and require particles >0.1 μm in radius. © 1999 Academic Press.
• Maki, J. N., Lorre, J. J., Smith, P. H., Brandt, R. D., & Steinwand, D. J. (1999). The color of Mars: Spectrophotometric measurements at the Pathfinder landing site. Journal of Geophysical Research E: Planets, 104(E4), 8781-8794.
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  Abstract: We calculate the color of the Martian sky and surface directly using the absolute calibration of the Mars Pathfinder (MPF) lander camera, which was observed to be stable during the mission. The measured colors of the Martian sky and surface at the Pathfinder site are identical to the Viking sites, i.e., a predominantly yellowish brown color with only subtle variations. These colors are distributed continuously and fall into five overlapping groups with distinct average colors and unique spatial characteristics: shadowed soil, soil, soil/rock mixtures, rock, and sky. We report that the primary difference between the sky color and the color of the rocks is due to a difference in brightness. Measurements of the sky color show that the sky reddens away from the Sun and toward the horizon and that the sky color varies with time of day and is reddest at local noon. We present a true color picture of the Martian surface and color enhancement techniques that increase image saturation, maximize color discriminability while preserving hue, and eliminate brightness variations while preserving the chromaticity of the scene. Although Mars has long been called the "red" planet, quantitative measurements of the surface color from telescopic and surface observations indicate a light to moderate yellowish brown color. The Pathfinder camera measurements presented here support the claim that the red planet is not red but indeed yellowish brown. Copyright 1999 by the American Geophysical Union.
• Markiewicz, W. J., Sablotny, R. M., Keller, H. U., Thomas, N., Titov, D., & Smith, P. H. (1999). Optical properties of the Martian aerosols as derived from Imager for Mars Pathfinder midday sky brightness data. Journal of Geophysical Research E: Planets, 104(E4), 9009-9017.
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  Abstract: The Imager for Mars Pathfinder (IMP) obtained data on the midday sky brightness in filters centered at 443.6, 481.0, 670.8, 896.1 and 965.3 nm. Useful data sets were returned on sols 27, 40, 56, 65, 68, 74, and 82. Data from sol 56 were fitted with multiple scattering radiative transfer calculations, to extract the size distribution, optical properties and shape of the aerosols suspended in the atmosphere. The derived effective radius of the particles is about 1.71 + 0.29/ - 0.26μm with an effective variance of veff = 0.25 + 0.05/ - 0.1. The estimated values of the refractive index and shape parameters are close to those derived from Viking and Phobos data. This in turn implies that dust plays a significant and relatively constant role in the energy budget of the Martian atmosphere over the last two decades. Estimates of the optical depth agree well with those obtained independently from direct IMP imaging of the Sun. The derived single scattering phase function is more compatible with plate (clay) like particles rather than equal dimensional particles. The presented analysis assumes a simple single-component dust atmosphere. The data-model residuals exhibit, albeit weak, wavelength dependence. This dependence can be interpreted as an indication that during the time the analyzed images were taken, the dust particle distribution was bimodal or that the Martian atmosphere contained a second component, possibly submicron ice particles, in the aerosol's population. Copyright 1999 by the American Geophysical Union.
• Reid, R. J., Smith, P. H., Lemmon, M., Tanner, R., Burkland, M., Wegryn, E., Weinberg, J., Marcialis, R., Britt, D. T., Thomas, N., Kramm, R., Dummel, A., Crowe, D., Bos, B. J., III, J. B., Rueffer, P., Gliem, F., Johnson, J. R., Maki, J. N., , Herkenhoff, K. E., et al. (1999). Imager for Mars Pathfinder (IMP) image calibration. Journal of Geophysical Research E: Planets, 104(E4), 8907-8925.
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  Abstract: The Imager for Mars Pathfinder returned over 16,000 high-quality images from the surface of Mars. The camera was well-calibrated in the laboratory, with
• Smith, P. H., & Lemmon, M. (1999). Opacity of the Martian atmosphere measured by the Imager for Mars Pathfinder. Journal of Geophysical Research E: Planets, 104(E4), 8975-8985.
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  Abstract: The Imager for Mars Pathfinder (IMP) has obtained 1733 images of the Sun during its 83-sol mission starting on July 4, 1997, which have been used to determine the atmospheric opacity at wavelengths of 450, 670, 883, and 989 nm. Solar images were obtained hourly between 0700 and 1700 hours, allowing detection of changes within a sol as well as from one sol to another. Atmospheric opacities were similar to those determined by the Viking landers: τ= 0.4-0.5 in all filters early in the mission (near Ls 145) increasing to τ = 0.6 late in the mission (near Ls 185). Opacity was variable in the mornings, especially in the blue filter; less variability was seen in the afternoons and in the longer wavelength filters. We conclude that submicron water ice particles with opacities as large as 0.14 in blue light are the cause of the diurnal variations. Orbital observations of the limb have been modeled by water ice detached hazes above a dust layer. Using this model, detached hazes of small particles provide the extra limb brightening that is observed by images in the UV taken by the Hubble Space Telescope. Thus the presence of about one-half optical depth of dust during the interval between Viking and Pathfinder is consistent with UV observations, suggesting that Viking- and Pathfinder-like dust conditions are typical for northern subtropical latitudes. Copyright 1999 by the American Geophysical Union.
• Thomas, N., Britt, D. T., Herkenhoff, K. E., Murchie, S. L., Semenov, B., Keller, H. U., & Smith, P. H. (1999). Observations of Phobos, Deimos, and bright stars with the Imager for Mars Pathfinder. Journal of Geophysical Research E: Planets, 104(E4), 9055-9068.
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  Abstract: The Imager for Mars Pathfinder (IMP) was used to observe several objects during the Martian night. The satellites, Phobos and Deimos, were observed on two occasions each, through the IMP geological filters covering the wavelength range 440 nm to μm. The observations were converted to geometric albedo using triaxial ellipsoid models of the satellites and phase functions derived from Viking Orbiter images. The spectral slopes over the full wavelength range were 7.9(±0.5)% (100 nm)-1 and 9.6(±0.6)% (100 nm)-1, respectively, referenced to 600 nm. In the Deimos spectra, some evidence for decreased reddening toward the trailing hemisphere was found. The geometric albedoes of Phobos and Deimos were found to be 0.065 (±0.010) and 0.068 (±0.009), respectively, averaged over 440 and 600 nm, in good agreement with previous measurements. The nighttime optical depth was investigated using observations of stars. A mean value of 0.56 (±0.09) was determined from measurements at different airmass. A possible maximum in the optical depth near 0200 local time was found, which may result from condensation during the night. A measurement of the egress of Phobos from eclipse was made. Modeling of the light curve gave a scale height for the scatterers of 10-15 km. The exact time of the eclipse reappearance over the limb could be reconstructed from the measurements and was in reasonable accord with predictions, although a small modification to the predicted position of Phobos of 6.8 (±6.0) km would have produced better agreement. Copyright 1999 by the American Geophysical Union.
• Titov, D. V., Markiewicz, W. J., Thomas, N., Keller, H. U., Sablotny, R. M., Tomasko, M. G., Lemmon, M. T., & Smith, P. H. (1999). Measurements of the atmospheric water vapor on Mars by the Imager for Mars Pathfinder. Journal of Geophysical Research E: Planets, 104(E4), 9019-9026.
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  Abstract: The Imager for Mars Pathfinder (IMP) was the first instrument to measure the atmospheric water on Mars from its surface. It took the images of the Sun through the Martian atmosphere in five narrowband filters, two in the 0.94 μm H2O band and three in the continuum around it. The observations were carried out in the mornings and in the evenings when the Sun was between 3° and 8° above the horizon. The absorption due to the atmospheric water vapor did not exceed 2%. An average column density of 6±4 precipitated microns (pr μm) was derived from the IMP data. The dependence of the observed H2O transmittance on Sun elevation tentatively implies that the water vapor is not uniformly mixed in the atmosphere but is rather confined to a layer 1-3 km thick near the surface. IMP observations also indicate a horizontal inhomogeneity of the layer but show no significant morning-to-evening variations of the water vapor amount. Copyright 1999 by the American Geophysical Union.
• Tomasko, M. G., Doose, L. R., Lemmon, M., Smith, P. H., & Wegryn, E. (1999). Properties of dust in the Martian atmosphere from the Imager on Mars Pathfinder. Journal of Geophysical Research E: Planets, 104(E4), 8987-9007.
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  Abstract: The Imager for Mars Pathfinder (IMP) returned sequences of images of the Martian sky characterizing the size distribution, optical constants, and nature of the aerosols suspended in the atmosphere of Mars. These sequences were executed when the solar elevation angle was approximately 15° and consisted of images near the elevation of the Sun, spanning a range in azimuth from about 4° to 180° from the Sun. Images were obtained at four wavelengths from 444 to 965 nm. From one sequence of observations, results are shown from a comparison of absolute photometry of the Martian sky with multiple scattering models. Results include the following. (1) The geometric cross-section-weighted mean particle radius is 1.6 ± 0.15 μm almost independent of the assumed width (variance) of the size distribution. (2) The imaginary refractive index shows a steep increase with wavelength from 670 nm to shorter wavelengths, and a shallow increase toward longer wavelengths, consistent with the reflection spectrum observed by IMP for Martian soil. (3) For each assumed variance, two parameters governing the slope and curvature of the portion of the phase function due to internally transmitted light are found uniquely as functions of wavelength. (4) The variance of the gamma size distribution is difficult to constrain from these observations alone. The shape of the single scattering phase functions derived from the IMP observations is compared to laboratory measurements of powder samples. One sample of irregular particles has a single scattering phase function quite similar to that derived for Mars. Overall, the results for the mean cross-section-weighted size and imaginary refractive index as a function of wavelength are in remarkably good agreement with the revised analysis by Pollack et al. [1995] of the observations made by the Viking lander 20 years earlier. Copyright 1999 by the American Geophysical Union.
• Kramm, J. R., Thomas, N., Keller, H. U., & Smith, P. H. (1998). The CCD imager electronics for the mars pathfinder and mars surveyor cameras. IEEE Transactions on Instrumentation and Measurement, 47(5), 1112-1118.
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  Abstract: The Mars pathfinder stereo camera and both cameras on the Mars surveyor lander use CCD detectors for image acquisition. The frame transfer type CCD's were produced by Loral for space applications under contract from MPAE. A detector consists of two sections of 256 lines and 512 columns each. Pixels in the image section contain an anti-blooming structure to remove excessive charge from overexposure. The storage section is covered by a metal mask. Rapid charge transfer allows operation without shutter. The CCD's are qualified for operations at very low temperatures. In the course of the development, the performance of the CCD detectors was significantly improved by a technological change in the substrate grounding. For several reasons, the design of the cameras require a separation of the CCD's from the readout electronics. The electronics were designed to operate the CCD's via a cable of up to 4 m length without performance loss. Low read noise and a resolution of 12 bits could be achieved with a very low power consumption of approximately 1.1 W. © 1998 IEEE.
• Kramm, J., Thomas, N., Keller, H., & Smith, P. H. (1998). CCD imager electronics for the Mars Pathfinder and Mars Surveyor cameras. Conference Record - IEEE Instrumentation and Measurement Technology Conference, 1, 574-579.
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  Abstract: The Mars Pathfinder stereo camera and both cameras on the Mars Surveyor Lander use CCD detectors for image acquisition. The frame transfer type CCDs were produced by Loral for space applications under contract from MPAE. A detector consists of two sections of 256 lines and 512 columns each. Pixels in the image section contain an anti-blooming structure to remove excessive charge from overexposure. The storage section is covered by a metal mask. Rapid charge transfer allows operation without shutter. The CCDs are qualified for operations at very low temperatures. In the course of the development, the performance of the CCD detectors was significantly improved by a technological change in the substrate grounding. For several reasons, the design of the cameras require a separation of the CCDs from lite readout electronics. The electronics was designed to operate the CCDs via a cable of up to 4 m length without performance loss. Low read noise and a resolution of 12 bits could be achieved with a very low power consumption of approximately 1.1 watts.
• Smith, P. H. (1998). Imager for Mars Pathfinder experiment (IMP): A multispectral stereo imaging system. Proceedings of SPIE - The International Society for Optical Engineering, 3295, 4-9.
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  Abstract: On Independence Day 1997 Mars Pathfinder bounced to a stop on the Ares-Tiu Vallis floodplain and began returning the first pictures from the surface of Mars in 20 years. The IMP camera took panoramas first in a stowed position (about seated height) and after day 2 from a deployed height of 1.85 m (about standing height). The eye separation of the stereoscopic camera (15 cm) allowed a humanistic view of the surrounding terrain. Months of calibration payed off in producing color images with the 5 visible filters; color was extended into the near IR with 10 additional filters three of which were doubled on each eye for stereo views. Because of low data rates from the direct transmission to Earth, the resolution was limited to 1 mrad/pixel and the FOV was fixed at 14 degrees square. The pointing motors allowed the camera to point in any direction and a complete panorama required 120 images per color. The mission lasted 83 sols (martian days of 24 hours and 39 minutes) and returned over 16,000 image frames. The science goals included contour mapping the site to study the geomorphology and multispectral imaging to sort out the mineralogy of the rocks and soils. In addition, the camera was used to help guide the Sojourner rover using virtual reality visualization techniques.
• Smith, P. H., Gliem, F., Rueffer, P., & Hviid, S. (1998). Erratum: Results from the Mars Pathfinder camera (Science (December 5, 1977) (1758)). Science, 280(5367), 1177-.
• Burkland, M. K., Wellman, J. B., Smith, P. H., Crowe, D. G., Tanner, R. D., & Reynolds, R. O. (1997). Computer modeling of the imager for Mars Pathfinder. Proceedings of SPIE - The International Society for Optical Engineering, 3132, 86-97.
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  Abstract: A modified camera model of the Imager for Mars Pathfinder (IMP), initially developed at NASA's Jet Propulsion Laboratory (JPL), was used for calibration of the camera's optical and mechanical pointing parameters at the Lunar & Planetary Laboratory of the University of Arizona (UofA). These parameters were determined by comparing images of calibrated and surveyed geometric targets in the laboratory to the camera model predictions. Results of the calibration were applied to system testing of the IMP integrated with the Lander spacecraft at JPL to determine the pointing accuracy of the IMP and the relative orientation of the camera and Lander coordinate systems. The camera model achieves a 1σ pointing error in azimuth of 0.6 milliradians (mrad) and 6.0 mrad in elevation. The stereoscopic range finding error of the IMP is 1 mm at a range of 1 m to 10 cm at 10 m based on the camera model and the determined parameters. ©2004 Copyright SPIE - The International Society for Optical Engineering.
• Golombek, M. P., Cook, R. A., Economou, T., Folkner, W. M., Haldemann, A. F., Kallemeyn, P. H., Knudsen, J. M., Manning, R. M., Moore, H. J., Parker, T. J., Rieder, R., Schofield, J. T., Smith, P. H., & Vaughan, R. M. (1997). Overview of the Mars Pathfinder Mission and assessment of landing site predictions. Science, 278(5344), 1743-1748.
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  PMID: 9388167;Abstract: Chemical analyses returned by Mars Pathfinder indicate that some rocks may be high in silica. Implying diffentiated parent materials. Rounded pebbles and cobbles and a possible conglomerate suggest fluvial processes that imply liquid water in equilibrium with the atmospher and thus a warmer and wetter past. The moment of inertia indicates a central metallic core of 1300 to 2000 kilometers in radius. Composite airborne dust particles appear magnetized by freeze-dried maghemite stain or cement that may have been leached from crustal materials by an active hydrologic cycle. Remote-sensing data at a scale of generally greater than ~1 kilometer and an Earth analog correctly predicted a rocky plain safe for landing and roving with a variety of rocks deposited by catastrophic floods that are relatively dust-free.
• Hviid, S. F., Madsen, M. B., Gunnlaugsson, H. P., Goetz, W., Knudsen, J. M., Hargraves, R. B., Smith, P., Britt, D., Dinesen, A. R., Mogensen, C. T., Olsen, M., Pedersen, C. T., & Vistisen, L. (1997). Magnetic properties experiments on the Mars Pathfinder lander: Preliminary results. Science, 278(5344), 1768-1770.
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  PMID: 9388172;Abstract: Many of the particles currently suspended in the martian atmosphere are magnetic, with an average saturation magnetization of about 4 A-m2/kg (amperes times square meters per kilogram). The particles appear to consist of claylike aggregates stained or cemented with ferric oxide (Fe2O3); at least some of the stain and cement is probably maghemite (γ-Fe2O3). The presence of the 'y phase would imply that Fe2+ ions leached from the bedrock, passing through a state as free Fe2+ ions dissolved in liquid water. These particles could be a freeze-dried precipitate from ground water poured out on the surface. An alternative is that the magnetic particles are titanomagnetite occurring in palagonite and inherited directly from a basaltic precursor.
• Lorenz, R. D., Smith, P. H., Lemmon, M. T., Karkoschka, E., Lockwood, G. W., & Caldwell, J. (1997). Titan's north-south asymmetry from HST and Voyager imaging: Comparison with models and ground-based photometry. Icarus, 127(1), 173-189.
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  Abstract: New measurements of Titan's hemispheric brightness asymmetry from HST images from 260 to 1040 nm show that the contrast is strongest near 450 nm (blue) and, with the opposite sign, at 889 nm (methane band). Comparison with a full Titan year of disk-integrated albedo data indicates that the seasonal cycle in asymmetry is smooth, but is insufficient to explain the variation in albedo, and a twice-per-year global albedo enhancement 50% larger than the hemispheric asymmetry amplitude is required, as noted by other workers. We also report measurements of limb-darkening (strongest at red wavelengths) and note that the transition zone between the "hemispheres" lies in the northern, brighter hemisphere at present. Comparison of models to the HST data set indicates that a change in aerosol number density above 70 km, and largely below 120 km, is the likely mechanism and is probably driven by aerosol transport by meridonal and vertical winds. © 1997 Academic Press.
• Smith, P. H., III, J. B., Bridges, N. T., Britt, D. T., Gaddis, L., Greeley, R., Keller, H. U., Herkenhoff, K. E., Jaumann, R., Johnson, J. R., Kirk, R. L., Lemmon, M., Maki, J. N., Malin, M. C., Murchie, S. L., Oberst, J., Parker, T. J., Reid, R. J., Sablotny, R., , Soderblom, L. A., et al. (1997). Results from the Mars Pathfinder camera. Science, 278(5344), 1758-1765.
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  PMID: 9388170;Abstract: Images of the martian surface returned by the Imager for Mars Pathfinder (IMP) show a complex surface of ridges and troughs covered by rocks that have been transported and modified by fluvial, aeolian, and impact processes. Analysis of the spectral signatures in the scene (at 440- to 1000-nanometer wavelength) reveal three types of rock and four classes of soil. Upward- looking IMP images of the predawn sky show thin, bluish clouds that probably represent water ice forming on local atmospheric haze (opacity ~0.5). Haze particles are about 1 micrometer in radius and the water vapor column abundance is about 10 precipitable micrometers.
• Smith, P. H., Tomasko, M. G., Britt, D., Crowe, D. G., Reid, R., Keller, H. U., Thomas, N., Gliem, F., Rueffer, P., Sullivan, R., Greeley, R., Knudsen, J. M., Madsen, M. B., Gunnlaugsson, H. P., Hviid, S. F., Goetz, W., Soderblom, L. A., Gaddis, L., & Kirk, R. (1997). The imager for Mars Pathfinder experiment. Journal of Geophysical Research E: Planets, 102(E2), 4003-4025.
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  Abstract: The imager for Mars Pathfinder (IMP), a stereoscopic, multispectral camera, is described in terms of its capabilities for studying the Martian environment. The camera's two eyes, separated by 15.0 cm, provide the camera with range-finding ability. Each eye illuminates half of a single CCD detector with a field of view of 14.4 × 14.0° and has 12 selectable filters. The f/18 optics have a large depth of field, and no focussing mechanism is required; a mechanical shutter is avoided by using the frame transfer capability of the 512 × 512 CCD. The resolving power of the camera, 0.98 mrad/pixel, is approximately the same as the Viking Lander cameras; however, the signal-to-noise ratio for IMP greatly exceeds Viking, approaching 350. This feature along with the stable calibration of the filters between 440 and 1000 nm distinguishes IMP from Viking. Specially designed targets are positioned on the Lander; they provide information on the magnetic properties of wind-blown dust, measure the wind vectors, and provide radiometric standard reflectors for calibration. Also, eight low-transmission filters are included for imaging the Sun directly at multiple wavelengths, giving IMP the ability to measure dust opacity and potentially the water vapor content. Several experiments beyond the requisite color panorama are described in detail: contour mapping of the local terrain, multispectral imaging of the surrounding rock and soil to study local mineralogy, viewing of three wind socks, measuring atmospheric opacity and water vapor content, and estimating the magnetic properties of wind-blown dust. This paper is intended to serve as a guide to understanding the scientific integrity of the IMP data that will be returned from Mars starting on July 4, 1997. Copyright 1997 by the American Geophysical Union.
• Thomas, N., Keller, H. U., Markiewicz, W. J., & Smith, P. H. (1997). Observations of Martian aerosols with the Imager for Mars Pathfinder. Advances in Space Research, 19(8), 1271-1276.
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  Abstract: The Imager for Mars Pathfinder (IMP) is a powerful tool for the analysis of Martian atmospheric aerosol content. This paper illustrates the capabilities of the IMP for this purpose and discusses some of the measurements that can be performed. The optical depth (by day and by night), sky brightness, atmospheric water content, the solar aureole structure, icy haloes, and cloud measurements can all be investigated by the IMP. A discussion of nighttime optical depth measurements is presented. The potential synergism between IMP atmospheric measurements and imaging of atmospheric phenomena from an orbiter is also briefly described. © 1997 COSPAR. Published by Ebevier Science Ltd.
• Greenberg, A. E., Wiktor, S. Z., DeCock, K. M., Smith, P., Jaffe, H. W., T.J., J. D., Kanki, P. J., Eisen, G., Travers, K. U., Marlink, R. G., Essex, M. E., C.-, C. H., & MBoup, S. (1996). HIV-2 and natural protection against HIV-1 infection. Science, 272(5270), 1959-1960.
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  PMID: 8658172;
• Smith, P. H., Lemmon, M. T., Lorenz, R. D., Sromovsky, L. A., Caldwell, J. J., & Allison, M. D. (1996). Titan's surface, revealed by HST imaging. Icarus, 119(2), 336-349.
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  Abstract: We present for the first time relative albedo maps of Titan's surface. The maps were made from images taken by the Hubble Space Telescope's planetary camera (295 km per pixel) through atmospheric windows at 940 and 1080 nm. Coverage at all longitudes and between 45°S and 60°N was obtained with 14 orbits from 4-18 October 1994. Each image is characterized by haze with both limb effects (brightening) and a large north-south contrast. Subtracting an averaged image from each frame removes haze effects and reveals surface features of ∼10% maximum contrast. Many features are clearly visible in multiple images and in both filters, but the surface map is dominated by a large, bright, roughly rectangular feature centered at 110°W, 10°S and elongated in an east-west direction (4000 × 2500 km2): this feature and others indicate the diversity of Titan's surface. We consider the origin of the bright feature in an otherwise dark landscape and suggest that highland washing by methane rainfall is a likely mechanism. © 1996 Academic Press, Inc.
• Tomasko, M. G., Doose, L. R., Smith, P. H., Fellows, C., Rizk, B., See, C., Bushroe, M., McFarlane, E., Wegryn, E., Frans, E., Clark, R., Prout, M., & Clapp, S. (1996). Descent imager/spectral radiometer (DISR) instrument aboard the Huygens probe of Titan. Proceedings of SPIE - The International Society for Optical Engineering, 2803, 64-74.
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  Abstract: The Huygen's probe of the atmosphere of Saturn's moon Titan includes one optical instrument sensitive to the wavelengths of solar radiation. The goals of this investigation fall into four broad areas: 1) the measurement of the profile of solar heating to support an improved understanding of the thermal balance of Titan and the role of the greenhouse effect in maintaining Titan's temperature structure; 2) the measurement of the size, vertical distribution, and optical properties of the aerosol and cloud particles in Titan's atmosphere to support studies of the origin, chemistry, life cycles, and role in the radiation balance of Titan played by these particles; 3) the composition of the atmosphere, particularly the vertical profile of the mixing ratio of methane, a condensable constituent in Titan's atmosphere; and 4) the physical state, composition, topography, and physical processes at work in determining the nature of the surface of Titan and its interaction with Titan's atmosphere. In order to accomplish these objectives, the Descent Imager/Spectral Radiometer (DISR) instrument makes extensive use of fiber optics to bring the light from several different sets of foreoptics to a silicon CCD detector, to a pair of InGaAs linear array detectors, and to three silicon photometers. Together these detectors permit DISR to make panoramic images of the clouds and surface of Titan, to measure the spectrum of upward and downward streaming sunlight from 350 to 1700 nm at a resolving power of about 200, to measure the reflection spectrum of ≥ 3000 locations on the surface, to measure the brightness and polarization of the solar aureole between 4 and 30 degrees from the sun at 500 and 935 nm, to separate the direct and diffuse downward solar flux at each wavelength measured, and to measure the continuous reflection spectrum of the ground between 850 and 1600 nm using an onboard lamp in the last 100 m of the descent.
• Crowe, D. G., & Smith, P. H. (1995). Calibration of the imager for Mars pathfinder (IMP). Proceedings of the Color Imaging Conference: Color Science, Systems, and Applications, 172-173.
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  Abstract: Calibration for true color is available through absolute spectroradiometric calibration at each of 17 different wavelengths. This allows the 12-bit data in each wavelength to be used in conjunction with a calibration of the display medium to present an approximation to the absolute spectral radiance of Mars.
• Crowe, D. G., & Smith, P. H. (1995). Calibration of the imager for mars pathfinder (IMP). Final Program and Proceedings - IS and T/SID Color Imaging Conference, 172-173.
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  Abstract: Calibration of the imager for Mars pathfinder (IMP) was presented. The 12-bit data in each wavelength was allowed to be used in conjunction with a calibration of the display medium to present an approximation to the absolute spectral radiance of Mars. The highest level of precision achievable with the Flight Model hardware in radiometric, spectroradiometric, and geometric data collection was achieved.
• Reynolds, R. O., Smith, P. H., Crowe, D. G., Bigler, M., & Pollard, M. (1995). Design of a stereo multispectral CCD camera for Mars Pathfinder. Proceedings of SPIE - The International Society for Optical Engineering, 2542, 197-206.
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  Abstract: The Imager for Mars Pathfinder is a stereo multispectral CCD camera designed to support a variety of science experiments from the Martian surface. The camera combines a straightforward imaging system based on a pair of Cooke triplets, fold optics, and a divided 512 by 256 pixel CCD with a complement of spectral and solar filters on two filter wheels. Aluminum and titanium component mountings on an aluminum optical bench provide for a complete pointing and imaging system having a mass of less than 3 kg. The az-el gimbal utilizes gearhead stepper motors to provide a field of regard of 370 degrees in azimuth and 156 degrees in elevation, in support of stereo and monoscopic panoramas and atmospheric studies. This paper discusses mechanical aspects of the optical component mountings and adjustments, as well as structural and mechanical aspects of the gimbal.
• Smith, P. H. (1995). Imager for Mars pathfinder (IMP) experiment. Proceedings of the Color Imaging Conference: Color Science, Systems, and Applications, 169-171.
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  Abstract: IMP will land on the surface of Mars on July 4, 1997 and take the first pictures of the outflow delta of the Ares Valles river system. The imager is a multi-spectral, stereo camera with 12 filters per eye and a separation between the eyes of 15 cm. The imager rests on a pop-up mast 80 cm above the lander and 1.5 m above the surface and has full pointing ability. IMP will provide the mapping and orientation capabilities needed by the Pathfinder Rover, contouring the local topography. Several targets on the lander enhance the ability of the camera to study Mars: magnetic targets of varying strength will collect the magnetic component of the wind-blown dust, calibration targets allow spectra to be normalized for nearby rocks, and windsocks show the direction, speed, and vertical gradient of the local wind. Several science goals are being addressed with this experiment including the geology and weathering of the local terrain, the absorption properties of the atmosphere, the magnetic strength of the windblown dust, and the wind vectors.
• Smith, P. H. (1995). The imager for mars pathfinder (IMP)experiment. Final Program and Proceedings - IS and T/SID Color Imaging Conference, 169-171.
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  Abstract: IMP will land on the surface of Mars on July 4, 1997 and take the first pictures of the outflow delta of the Ares Valles river system. The imager is a multi-spectral, stereo camera with 12 filters per eye and a separation between the eyes of 15 cm. The imager rests on a pop-up mast 80 cm above the lander and 1.5 m above the surface and has full pointing ability. IMP will provide the mapping and orientation capabilities needed by the Pathfinder Rover, contouring the local topography. Several targets on the lander enhance the ability of the camera to study Mars: magnetic targets of varying strength will collect the magnetic component of the windblown dust, calibration targets allow spectra to be normalized for nearby rocks, and windsocks show the direction, speed, and vertical gradient of the local wind. Several science goals are being addressed with this experiment including the geology and weathering of the local terrain, the absorption properties of the atmosphere, the magnetic strength of the windblown dust, and the wind vectors.
• Mcmillan, R. S., Moore, T. L., Perry, M. L., & Smith, P. H. (1994). Long, accurate time series measurements of radial velocities of solar-type stars. Astrophysics and Space Science, 212(1-2), 271-280.
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  Abstract: We have been measuring changes in the radial velocities (RV's) of solar-type stars to search for gravitational perturbations by planets. We transmit violet starlight through a Fabry-Perot etalon interferometer and sense changes in Doppler shift from changes in the fluxes of light on the slopes of stellar absorption lines. Our data now span 6 years. Our observations of the Sun showed earlier that both our technique and the profiles of solar photospheric violet absorption lines can be stable enough to reveal planetary perturbations. We now carry this validation to the spectra of other near-solar-type stars. Annual averages of our RV's of σ Draconis and β Virginis are stable to ±6 m s-1. The slope of our five-year series of RV's of ξ Bootis A is consistent with the star's well-determined visual astrometric orbit about ξ Bootis B. The Fabry-Perot technique of Doppler shift measurement is fully capable of detecting perturbations due to planets with masses and orbits similar to those of Jupiter. © 1994 Kluwer Academic Publishers.
• Mcmillan, R. S., Moore, T. L., Perry, M. L., & Smith, P. H. (1993). Radial velocity observations of the sun at night. Astrophysical Journal Letters, 403(2), 801-809.
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  Abstract: We have measured the Doppler shift of the solar spectrum for 5 yr to help demonstrate our ability to detect planets orbiting other stars. The sunlit surface of the Moon provides nighttime access to the solar spectrum integrated over the solar disk, as if the Sun were being observed at a stellar distance. The standard deviation of our 486 lunar observations spanning 4.9 yr is ± 7.8 m s-1, consistent with our short-term internal precision and external calibration accuracy. Long-term periodic errors in the instrument are ± 4 m s-1. An artificial signal with a period of 2.5 yr and semiamplitude 8 m s-1 stands well above the noise periodogram of the instrument. Since calibration error and internal precision account for the scatter of the reduced data, there is little room left for long-period variations intrinsic to the Sun. The data series runs from 1987 April through 1992 February, during which daily sunspot counts increased an order of magnitude and are now well past the maximum of activity of Cycle 22. Nevertheless, our observations of the Moon indicate the Doppler shift of the integrated disk of the solar photosphere in violet absorption lines has varied less than ± 4 m s-1 over this interval. This suggests that the spectra of solar-type stars can be stable enough to reveal the Doppler shifts induced by planets with Jupiter's mass and orbital period.
• Caldwell, J., Cunningham, C. C., Anthony, D., White, H. P., Groth, E. J., Hasan, H., Noll, K., Smith, P. H., Tomasko, M. G., & Weaver, H. A. (1992). Titan: Evidence for seasonal change-A comparison of Hubble space telescope and voyager images. Icarus, 97(1), 1-9.
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  Abstract: Images of Titan were obtained by the Hubble Space Telescope (HST) on 26 August 1990. Comparison with Voyager 1 and Voyager 2 images obtained 10 and 9 years earlier shows that the seasonal hemispheric brightness asymmetry has reversed near 440 and 550 nm wavelengths, with the northern hemisphere now being brighter. An additional, noisy HST image at 889 nm wavelength, for which there are no analogous Voyager data, suggests that the southern hemisphere may have been brighter than the northern at that wavelength in 1990. © 1992.
• Pope, S. K., Tomasko, M. G., Williams, M. S., Perry, M. L., Doose, L. R., & Smith, P. H. (1992). Clouds of ammonia ice: Laboratory measurements of the single-scattering properties. Icarus, 100(1), 203-220.
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  Abstract: This work presents scattering measurements and photographs of ammonia ice crystals grown at temperatures from 130 to 180 K. The prime candidate for the material making up the visible clouds of Jupiter and Saturn is ammonia ice. Spacecraft observations of these planets have constrained the single-scattering properties of the cloud particles. To further investigate the nature of these particles, ammonia ice crystals were grown at temperatures occuring at the relevant levels of the atmospheres of Jupiter and Saturn. The experimental apparatus used to make these measurements has a glass-walled cylindrical chamber which permits measurement of the scattered light over a wide range of scattering angles and a temperature control system which uses a liquid nitrogen reservoir combined with heaters. The chamber is illuminated by a tungsten lamp through a rapidly spinning filter/polarizer wheel which yields measurements of intensity and linear polarization in each of three colors. A photographic record of the crystals is obtained with a microscope objective, and six linear array detectors measure the scattered light. Representative scattering measurements and photographs are presented, showing a variety of phase functions and crystal shapes. The data cannot be reproduced by theoretical calculations for ammonia clouds composed purely of cubic, tetrahedral, or octahedral crystals. The data appear similar to microwave analog measurements of the scattering by a mix of particles shapes and also by fluffy particles. The ammonia measurements fall into two groups: one has wavelength-dependent polarization and for size parameters up to about seven the scattering properties can be fit by Mie theory. The second group has wavelength-independent phase functions, implying size parameters of 10 to 50, and has a characteristic signature of polarization varying from - 10% to +10%. The data can be used to rule out some models for Jupiter's and Saturn's atmospheres and to guide future modeling efforts. For Jupiter, models with a cloud of ammonia crystals of size parameter equal to about 5 (in the red) are suggested. For Saturn, a model is suggested that has a thin layer of small ammonia crystals (in the Mie range) over a thicker ammonia cloud with the wavelength-independent polarization that is characteristic of larger crystals. © 1992.
• West, R. A., & Smith, P. H. (1991). Evidence for aggregate particles in the atmospheres of Titan and Jupiter. Icarus, 90(2), 330-333.
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  Abstract: Calculations of the optical properties of aggregate particles are able to resolve a persistent problem in understanding the shape and size of haze aerosols in the atmospheres of Titan and Jupiter. Most of the photometric and polarimetric observations for Titan can be explained by the presence of aggregate particles whose mean projected area is equal to that of a sphere with radius 0.14 μm, containing monomers with mean radii near 0.06 μm. An additional mode of smaller particles is needed to fit ultraviolet data. Aggregate particles can also account for the observed optical properties of Jupiter's high altitude haze. Knowledge of the size and shape of the particles will allow for more precise estimates of the sedimentation rates and provide a key constraint on the coupled surface/atmosphere evolution of Titan. © 1991.
• McMillan, R. S., Smith, P. H., Perry, M. L., Moore, T. L., & Merline, W. J. (1990). Long-term stability of a Fabry-Perot interferometer used for measurement of stellar Doppler shift. Proceedings of SPIE - The International Society for Optical Engineering, 1235 pt 2, 601-609.
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  Abstract: We are measuring temporal changes of the Doppler shifts of stars with the aid of a Fabry-Perot interferometer. A combination of design features permits unusually good precision and accuracy. First, an optical fiber feeds starlight from the telescope focus to the object plane of the collimator of a cross-dispersed echelle spectrograph. The length and scrambling properties of the fiber isolate the interferometer, and thereby the velocity metric, from environmental conditions and the effects of guiding and seeing. The etalon, in parallel light between the collimator and the echelle grating, is tuned by tilting to allow the transmitted orders of constructive interference to fall on the desired wavelengths. The spectral resolution and the absolute wavelength metric are defined by the interferometer, not by the placement of the spectrum on the detector. This avoidance of mapping CCD pixel position into radial velocity is a fundamental feature that enhances accuracy. Finally, the spectrograph spatially separates the interference orders onto a CCD. Changes of the velocity of a star are sensed by detecting changes in the relative intensities of those interference orders that lie on the steep slopes of line profiles. The parameters of the interferometer are measured frequently by observing emission lines from an iron-argon hollow cathode lamp. Years of use show that with such calibration, observations of stars can be reduced to the same velocity reference with an accuracy of ±10 m/s. This corresponds to ±33 ppb in the effective spacing of the etalon plates.
• McMillan, R. S., Smith, P. H., Frecker, J. E., Merline, W. J., & Perry, M. L. (1986). FABRY-PEROT INTERFEROMETER FOR ACCURATE MEASUREMENT OF TEMPORAL CHANGES IN STELLAR DOPPLER SHIFT.. Proceedings of SPIE - The International Society for Optical Engineering, 627(pt 1), 2-19.
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  Abstract: We are making accurate observations of the changes in Doppler shift of stellar absorption lines. The scrambling of incident light by an optical fiber and the stability of wavelength calibration by a tilt-tunable Fabry-Perot etalon provide immunity to systematic errors. A cross-dispersed echelle spectrograph spatially separates the orders of constructive interference transmitted through the etalon. Selecting several echelle diffraction orders in the vicinity of 4250-4750 A, which are imaged on a CCD, about 350 points on the profile of the stellar spectrum are sampled by successive orders of interferometric transmission through the etalon. At 4300 A each interference order is 47 milliangstroms wide and the sample points are 0. 64 A apart, causing distinct, widely-spaced monochromatic images of the entrance aperture to be formed in the focal plane of the camera.
• Smith, P. H. (1986). The vertical structure of the Jovian atmosphere. Icarus, 65(2-3), 264-279.
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  Abstract: An inhomogeneous atmospheric model, which includes both polarizing aerosols and methane gas, has been developed for the equatorial and tropical regions of Jupiter consistent with the Pioneer polarimetry and photometry data as well as the methane-band data of West (1979a, Icarus 38, 12-33). A two-cloud model with an overlying stratospheric haze has been used to explain the relative strengths of weak and strong methane bands. The upper cloud, assumed to be composed primarily of ammonia crystals, is denser in the zones (5-8 optical depths) than the belts (3-4 optical depths) when viewed in red light. There is also a compositional difference; an increase in the concentration of the unknown chromophore lowers the blue albedo in the belts. Otherwise, belts and zones are remarkably similar. The cloudtops are found between 200 and 230 mbar and the cloud extends down to the saturated vapor pressure of ammonia at 700 mbar; a haze of 0.3 ± 0.1 optical depths overlies all regions. For all the regions studied, the polarization measurements are best fit with a negatively polarizing ammonia cloud (-20%) beneath a positively polarizing haze (40-50%). Unlike the nearby features, the Equatorial Region and the Great Red Spot have a negative polarization at 80° phase angle implying less gas above the clouds in these regions, a conclusion supported by the increased brightness at 8900 Å. Tables are presented giving the preferred model parameters for each region studied. © 1986.
• Tomasko, M. G., Doose, L. R., & Smith, P. H. (1985). The absorption of solar energy and the heating rate in the atmosphere of Venus. Advances in Space Research, 5(9), 71-79.
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  Abstract: The Solar Flux Radiometer (LSFR) experiment on the large probe of the Pioneer Venus (PV) mission made detailed measurements of the vertical profile of the upward and downward broadband flux of sunlight at a solar zenith angle of 65.7°. These data have been combined with cloud particle size distribution measurements on the PV mission to produce a forward-scattering model of the Venus clouds. The distribution of clouds at high altitudes is constrained by measurements from the PV orbiter. Below the clouds the visible spectrum and flux levels are consistent with Venera measurements at other solar zenith angles. The variations in the optical parameters with height and with wavelength are summarized in several figures. The model is used to evaluate the solar heating rate at cloud levels as a function of altitude, solar longitude, and latitude for use in dynamical studies. © 1985.
• Smith, P. H., & Tomasko, M. G. (1984). Photometry and polarimetry of Jupiter at large phase angles. II. Polarimetry of the South Tropical Zone, South Equatorial Belt, and the polar regions from the Pioneer 10 and 11 missions. Icarus, 58(1), 35-73.
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  Abstract: The imaging photopolarimeter (IPP) experiment on the Pioneer 10 and 11 missions to Jupiter measured the intensity and linear polarization of red and blue sunlight reflected from the planet over a range of phase angles inaccessible from the Earth. We give an overview of the polarization data obtained in the two Jupiter encounters at phase angles from 43° to 117° and briefly describe the photometry data from the Pioneer 11 encounter at phase angles between 34° and 80° which partially fill a gap in the phase coverage from Pioneer 10 (M. G. Tomasko, R. A. West, and N. D. Castillo, 1978, Icarus 33, 558-592). The polarimetry and photometry of the South Tropical Zone (STrZ), the north component of the South Equatorial Belt (SEBn), and a north-south cut extending to the south pole are given in detailed tables. Comparison of the data to multiple-scattering models yields several details of the distribution and single-scattering properties of the clouds and aerosols on Jupiter. The observed polarization in blue light at latitudes less than about 40° shows only small variations between belts and zones. Simple models indicate that the tops of the belt and zone clouds are reached at nearly the same pressure level of about 320 mb and that the polarization differences are a result of the lower cloud albedo in the belt. The optical thickness of the belt as well as the zone clouds at this level must be at least 1.5 to prevent the polarization produced by underlying gas from being seen in the data. The polarization rises abruptly toward the limb and terminator in red light, indicating a haze of positively polarizing particles with an optical thickness of a few tenths at a pressure level of about 120 mb. The polarization in both colors increases abruptly from latitudes north of 40°N and south of 48°S to values as high as 60% at high latitudes. This effect is not due to a longer slant path but must be due to a large increase in the optical thickness of the polarizing haze at high latitudes. There is some indication that the size of the haze aerosols grows with increasing latitude as well. The photometry data indicate little change in the brightness of planetary features in the year between the two Pioneer encounters. Photometric models that fit the Pioneer 10 data fit the Pioneer 11 data remarkably well with essentially the same phase functions. Using a two-cloud model, we find that our models best fit the limb darkening at 12° phase when the belt absorbers are evenly distributed in both the clouds. There is no evidence for rainbow-like bumps on the single-scattering phase functions in the range of scattering angles from 120° to 140° as might result from scattering by spherical particles. © 1984.
• Rages, K., Pollack, J. B., & Smith, P. H. (1983). SIZE ESTIMATES OF TITAN'S AEROSOLS BASED ON VOYAGER HIGH-PHASE-ANGLE IMAGES.. Journal of Geophysical Research, 88(A11), 8721-8728.
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  Abstract: Limits on the physical properties of the scattering haze near the top of Titan's atmosphere are derived from data obtained from seven high-phase-angle images from Voyager 1 and 2. From the ratio of the intensities observed at two different high phase angles, an estimate can be made of the forward scattering lobe of the single-scattering phase function. By comparing the forward scattering estimate with diffraction lobes from particles of different radii, it is concluded that the average radius of the particles found in the upper few tenths of an optical depth exceeds 0. 19 mu m. Judging from data observed at four different phase angles, the haze particles probably have a refractive index near 1. 6 and a mean size of approximately 0. 5 mu m, if the widths of their diffraction peaks are close to those for equal volume spheres.
• Tomasko, M. G., & Smith, P. H. (1982). Photometry and polarimetry of Titan: Pioneer 11 observations and their implications for aerosol properties. Icarus, 51(1), 65-95.
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  Abstract: The preliminary measurements by Pioneer 11 of the limb darkening and polarization of Titan at red and blue wavelenghts (M. G. Tomasko, 1980, J. Geophys. Res., 85, 5937-5942) are refined and the measurements of the brightness of the integrated disk at phase angles from 22 to 96° are reduced. At 28° phase, Titan's reflectivity in blue light at southern latitudes is as much as 25% greater than that at northern latitudes, comparable to the values observed by Voyager 1 (L. A. Sromovsky et al., 1981, Nature (London), 292, 698-702). In red light the reflectivity is constant to within a few percent for latitudes between 40°S and 60°N. Titan's phase coefficient between 22 and 96° phase angle averages about 0.014 magnitudes/degree in both colors-a value considerably greater than that observed at smaller phase from the Earth. Comparisons of the data with vertically homogeneous multiple-scattering models indicate that the single-scattering phase functions of the aerosols in both colors are rather flat at scattering angles between 80 and 150° with a small peak at larger scattering (i.e., small phase) angles. The models indicate that the phase integral, q, for Titan in both red and blue light is about 1.66 ± 0.1. Together with Younkin's value for the bolometric geometric albedo scaled to a radius of 2825 km, this implies an effective temperature in equilibrium with sunlight of 84 ± 2°K, in agreement with recent thermal measurements. The single-scattering polarizations produced by the particles at 90° scattering angle are quite large, >85% in blue light and >95% in red. A vertically homogeneous model in which the particles are assumed to scatter as spheres cannot simultaneously match the polarization observations in both colors for any refractive index. However, the observed polarizations are most sensitive to the particle properties near optical depth 1 2 in each color, and so models based on single scattering by spheres can be successful over a range of refractive indices if the size of the particles increases with depth and if the cross section of the particles increases sufficiently rapidly with decreasing wavelenght. For example, with nr = 1.70, the polarization (and the photometry) are reproduced reasonably well in both colors when the area-weighted average radous of the particles, α, is given by α = (0.117 μm)(τred/0.5)0.217. While this model does not reproduce the large increase in brightness from 129 to 160° phase observed by Voyager 1, the observed increase is determined by the properties of the particles in the top few hundredths of an optical depth. Thus the addition of a very thin layer of forward-scattering aerosols on top of the above model offers one way of satisfying both the Pioneer 11 and Voyager 1 observations. Of course, other models, using bimodal size distributions or scattering by nonspherical particles, may also be capable of reproducing these data. © 1982.
• Hamaker, R. W., Putney, Z. C., Ayers, R. L., & Smith, P. H. (1981). Degradation mechanism for silicon p⁺-n junctions under forward bias. Solid State Electronics, 24(11), 1001-1008.
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  Abstract: Leakage current degradation has been observed during forward bias stressing of silicon integrated p+-n junctions. Detailed characterization results of the anomalous leakage behavior are discussed in this paper. From these results an electric field-enhanced impurity diffusion mechanism has been proposed to explain both the strong temperature and forward bias dependencies on leakage current time-to-saturation. An activation energy has been determined for this mechanism (0.48±0.04 eV) and is in good agreement with that previously determined for diffusion of interstitial copper in p-type silicon. Subsequent Secondary Ion Mass Spectrometer elemental analysis has confirmed the presence of copper near the surface of the epitaxial layer containing the p+-n device. © 1981.
• Gehrels, T., Baker, L. R., Beshore, E., Blenman, C., Burke, J. J., Castillo, N. D., DaCosta, B., Degewij, J., Doose, L. R., Fountain, J. W., Gotobed, J., KenKnight, C. E., Kingston, R., McLaughlin, G., McMillan, R., Murphy, R., Smith, P. H., Stoll, C. P., Strickland, R. N., , Tomasko, M. G., et al. (1980). Imaging photopolarimeter on Pioneer Saturn. Science, 207(4429), 434-439.
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  Abstract: An imaging photopolarimeter aboard Pioneer 11, including a 2.5-centimeter telescope, was used for 2 weeks continuously in August and September 1979 for imaging, photometry, and polarimetry observations of Saturn, its rings, and Titan. A new ring of optical depth
• Tomasko, M. G., Doose, L. R., & Smith, P. H. (1979). Absorption of sunlight in the atmosphere of Venus. Science, 205(4401), 80-82.
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  Abstract: In this report the fluxes measured by the solar flux radiometer (LSFR) of the Pioneer Venus large probe are compared with calculations for model atmospheres. If the large particles of the middle and lower clouds are assumed to be sulfur, strong, short-wavelength absorption results in a net flux profile significantly different from the LSFR net flux measurements. Models in which the smallest particles are assumed to be sulfur gave flux profiles consistent with the measurements if an additional source of absorption is included in the upper cloud. The narrowband data from 0.590 to 0.665 micrometer indicate an absorption optical depth of about 0.05 below the cloud bottom. The broadband data imply that either this absorption extends over a considerable wavelength interval (as might be the case for dust) or that a very strong absorption band lies on one side of the narrowband filter (as suggested by early Venera II and Venera 12 reports). Thermal balance calculations based on the measured visible fluxes indicate high surface temperature for reasonable assumptions of cloud opacity and water vapor abundance. The lapse rate becomes convective within the middle cloud. For water mixing ratios of 2.0 × 10-4 below the clouds we find a subadiabatic region extending from the cloud bottom to altitudes near 35 kilometers. Copyright © 1979 AAAS.
• Tomasko, M. G., Doose, L. R., Palmer, J., Holmes, A., Wolfe, W., Castillo, N. D., & Smith, P. H. (1979). Preliminary results of the solar flux radiometer experiment aboard the Pioneer Venus multiprobe mission. Science, 203(4382), 795-797.
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  Abstract: The solar flux radiometer aboard the Pioneer Venus large probe operated successfully during its descent through the atmosphere of Venus. Upward, downward, and net fluxes from 0.4 to 1.0 micrometers were obtained at more than 390 levels between 185 millibars (at an altitude of ∼ 61 kilometers) and the surface. Fluxes from 0.4 to 1.8 micrometers were also obtained between 185 millibars and about the level at which the pressure was 2 atmospheres. Data from 80 to 185 millibars should be available after additional decoding by the Deep Space Network. Upward and downward intensities in a narrower band from 0.59 to 0.66 micrometers were also obtained throughout the descent in order to constrain cloud properties. The measurements indicate three cloud regions above the 1.3-atmosphere level (at an altitude of ∼ 49 kilometers) and a clear atmosphere beneath that level. At the 67° solar zenith of the probe entry site, some 15 watts per square meter are absorbed at the surface by a dark ground, which implies that about 2 percent of the solar energy incident on the planet is absorbed at the ground. Copyright © 1979 AAAS.
• Sari, S. O., Smith, P., & Oona, H. (1978). Near IR absorption in films of silicon containing oxygen. Journal of Physics and Chemistry of Solids, 39(9), 957-960.
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  Abstract: A novel reflectance effect has been used to extract new information about oxygen impurity states in silane-vapor-deposited silicon films. A comparison to IR measurements in crystalline silicon yields a substantial wavelength shift of the characteristic 9-μm oxygen transition and may suggest increased film impurity absorption in comparison to the bulk. By combining these experiments with measurements of film oxygen impurity concentration using X-ray emission spectroscopy, values for the oscillator strengths of the prominent oxygen lines in the near IR can be obtained. Interpretation of these data is given. © 1978.
• Bergeron, D. L., Putney, Z. C., Smith, P. H., & Stephens, G. B. (1977). HOT ELECTRON RELIABILITY EFFECTS IN LATERAL PNP TRANSISTORS.. Annual Proceedings - Reliability Physics (Symposium), 10-15.
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  Abstract: A failure mechanism of bipolar lateral PNP transistors in medium voltage integrated circuits has been observed. The failure mechanism is characterized by inversion layer conduction between emitter and collector of the devices resulting from the trapping of hot electrons in the dielectric. A model of the mechanism is developed which explains the observed temperature and voltage acceleration.
• Sari, S. O., Smith, P. H., & Gurev, H. S. (1977). Observation of an oxygen resonance in reflectivity from weakly absorbing thin silicon layers. Physical Review B, 15(10), 4817-4821.
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  Abstract: A bulk polariton has been discovered in silicon films deposited by silane vapor deposition on substrates of highly reflecting silver. From reflectivity measurements, resonances at 8.3 and 10 μm are examined using a simple model. Properties of the observed transitions, due to impurity oxygen in silicon, have been determined by an analysis of our spectra for semiconductor layers of increasing thickness between 1.5 and 6 μm. © 1977 The American Physical Society.
• Smith, P., & Gurev, H. (1977). Silicon dioxide as a high temperature stabilizer for silver films. Thin Solid Films, 45(1), 159-168.
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  Abstract: Silver films cannot at present be used as high temperature reflectors because of severe agglomeration in the presence of oxygen at temperatures in excess of 200 °C. Cr2O3, Al2O3, SiO3 and CrOx were tested for their effectiveness as thin barrier layers, and SiO2 is the best of those tested. The use of SiO2 allows the process of hole healing to compete with the normal hole growth process. Hole healing does not last indefinitely but is superseded by a slower rate hole growth process with an activation energy of 49 kcal mol-1. Because of this last mechanism, stabilized silver is less than 1% transmitting after 50 h at 650 °C in air, whereas bare silver agglomerates to 66% transmittance after only 3 min under the same conditions. Therefore 500 Å SiO2 films can be used as long term stabilizers for silver films in oxygen atmospheres with temperatures of up to 650 °C. © 1977.