J. L. Bandfield

Publications (27)135.99 Total impact

• Article: Mafic high inertia crater floors in the southern highlands: Implications for a widespread post-impact modification process on Mars

  C. S. Edwards, J. L. Bandfield, D. Rogers, P. R. Christensen
  [show abstract] [hide abstract]
  ABSTRACT: Understanding the history of impact crater modification and alteration can provide insights into planet scale processes that have occurred throughout Martian history. We have identified a unique class of Martian craters with flat, high thermal inertia floors, mafic mineralogies, and degraded morphologies. By using physical material properties in combination with morphologic and mineralogical data, it is possible to constrain the formation and modification history of these craters and better understand the crater modification processes, including post-impact volcanism, chemical weathering and hydrothermal alteration. This class of crater is prevalent throughout the southern highlands of Mars. The craters studied have degraded walls and rims, no central peak, no clearly visible ejecta deposits, an average diameter of ~52km (ranging in size from 18.5km to 179km), and occur almost exclusively in the southern highlands indicating an old formation age. The thermal inertia values derived from Thermal Emission Imaging System (THEMIS) measurements of crater floors are consistent with competent rocky material, while the walls and surrounding plains are composed of a less cohesive material. We have used THEMIS, Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), and Thermal Emission Spectrometer (TES) data to constrain the compositional variability of ~60 sites with the highest thermal inertia values. In general, the crater floors have higher abundances of mafic minerals (e.g. pyroxenes and olivine), while the surrounding plains have lower abundances of mafic minerals but show an increase in high-Si phase abundance. The composition, morphology, and distribution suggest that old, flat floored craters were resurfaced by a post-impact process that resulted in material significantly more mafic than the surrounding terrain. A possible formation mechanism may be related to inflationary volcanism associated with the impact [Schultz, 1976]. In this model, during the impact event, the crust is fractured providing a conduit for magma to erupt onto the surface and infill the original crater floor. The source of this magma is not well constrained and may be related to the unloading of the early Martian mantle and crust, resulting in partial melting of the underlying material. The mineralogy of these materials is consistent with a picritic basalt and indicates a primitive magma source, such as the Martian mantle. We have identified and characterized a unique class of Martian craters that has gone previously unstudied. If the distribution of this crater type is considered and the proposed model is correct, it is likely that inflationary volcanism is an important widespread process on Mars that has gone previously undocumented. This process could be responsible for extended periods of hydrothermal activity, a source of energy for altering materials, and may indicate high crustal heat flow early in Mars history. Schultz, P. H. (1976), Floor-fractured lunar craters, Earth, Moon, and Planets, 15(3).
  AGU Fall Meeting Abstracts. 11/2010; -1:1531.
• Source

  Available from: Oded Aharonson

  Article: Geologic context of in situ rocky exposures in Mare Serpentis, Mars: Implications for crust and regolith evolution in the cratered highlands

  A D Rogers, O Aharonson, J L Bandfield
  [show abstract] [hide abstract]
  ABSTRACT: Global acquisition of infrared spectra and high-resolution visible and infrared imagery has enabled the placement of compositional information within stratigraphic and geologic context. Mare Serpentis, a low albedo region located northwest of Hellas Basin, is rich in spectral and thermophysical diversity and host to numerous isolated exposures of in situ rocky material. Most martian surfaces are dominated by fine-grained particulate materials that bear an uncertain compositional and spatial relationship to their source. Thus location and characterization of in situ rock exposures is important for understanding the origin of highland materials and the processes which have modified those materials. Using spectral, thermophysical and morphologic information, we assess the local and regional stratigraphy of the Mare Serpentis surface in an effort to reconstruct the geologic history of the region. The martian highlands in Mare Serpentis are dominated by two interspersed surface units, which have distinct compositional and thermophysical properties: (1) rock-dominated surfaces relatively enriched in olivine and pyroxene, and depleted in high-silica phases, and (2) sediment or indurated material depleted in olivine and pyroxene, with relatively higher abundance of high-silica phases. This is a major, previously unrecognized trend which appears to be pervasive in the Mare Serpentis region and possibly in other highland areas. The detailed observations have led us to form two hypotheses for the relationship between these two units: either (1) they are related through a widespread mechanical and/or chemical alteration process, where less-mafic plains materials are derived from the mafic bedrock, but have been compositionally altered in the process of regolith formation, or (2) they are stratigraphically distinct units representing separate episodes of upper crust formation. Existing observations suggest that the second scenario is more likely. In this scenario, plains materials represent older, degraded, and possibly altered, "basement" rock, whereas the rocky exposures represent later additions to the crust and are probably volcanic in origin. These hypotheses should be further testable with decimeter-resolution imagery and meter-resolution short wavelength infrared spectra.
  Icarus 01/2009; 200:446-462. · 3.38 Impact Factor
• Source

  Available from: sunysb.edu

  Article: Chloride-bearing materials in the southern highlands of Mars.

  M M Osterloo, V E Hamilton, J L Bandfield, T D Glotch, A M Baldridge, P R Christensen, L L Tornabene, F S Anderson
  [show abstract] [hide abstract]
  ABSTRACT: Chlorides commonly precipitate during the evaporation of surface water or groundwater and during volcanic outgassing. Spectrally distinct surface deposits consistent with chloride-bearing materials have been identified and mapped using data from the 2001 Mars Odyssey Thermal Emission Imaging System. These deposits are found throughout regions of low albedo in the southern highlands of Mars. Geomorphologic evidence from orbiting imagery reveals these deposits to be light-toned relative to their surroundings and to be polygonally fractured. The deposits are small (< approximately 25 km(2)) but globally widespread, occurring in middle to late Noachian terrains with a few occurrences in early Hesperian terrains. The identification of chlorides in the ancient southern highlands suggests that near-surface water was available and widespread in early Martian history.
  Science 03/2008; 319(5870):1651-4. · 31.20 Impact Factor
• Article: Discovery and Distribution of Chloride-Bearing Deposits in the Ancient Cratered Terrain of Mars From THEMIS

  M. M. Osterloo, F. S. Anderson, V. E. Hamilton, T. D. Glotch, A. M. Baldridge, P. R. Christensen, J. L. Bandfield, L. L. Tornabene
  [show abstract] [hide abstract]
  ABSTRACT: We have identified and mapped a number of spectrally distinct deposits (~250) in mid-infrared data acquired by the 2001 Odyssey Thermal Emission Imaging System (THEMIS). These deposits are interpreted to contain a chloride salt component based on their spectral signatures in THEMIS and Mars Global Surveyor Thermal Emission Spectrometer (TES) data. Thermal inertia derived from THEMIS nighttime observations, indicate that the chloride-bearing materials are possibly cemented or indurated. Individually, most chloride-bearing deposits are small in area (<~25 km2), but they are globally widespread, as we have identified them throughout low albedo regions of the southern highlands of Mars. These regions correspond to mid-to-late Noachian terrains, as well as early Hesperian ridged plains units. The chloride-bearing deposits commonly occur in topographic lows relative to the surrounding terrain, and some appear to follow channel-like outlines. Less typically we observe them in small crater floors. Images acquired by the Mars Orbiter Camera (MOC) and the High Resolution Imaging Science Experiment (HiRISE) indicate geomorphology consistent with formation in an evaporitic environment. HiRISE imagery (at 25.3 cm/pixel) over a large exposure in Terra Sirenum shows the chloride-bearing materials to be light-toned and highly fractured. The fracturing is sub-polygonal and is similar to desiccation cracks in evaporitic environments. Cross cutting relationships indicate that the chloride-bearing materials are older than the surrounding basaltic materials, and commonly appear to have been exposed by erosion. In the HiRISE image we observe additional occurrences of chloride materials within the regional terrain, indicating that the chloride deposits are likely more extensive than what is discernable at THEMIS IR scales. The origin and diagenesis of each chloride deposit is likely complex, however it is probable that water played a role in each instance, either via direct precipitation of ground water or standing water, or via efflorescence from evaporative pumping, volcanic out gassing, or atmospheric-surface interactions. Many chloride salts are extremely hygroscopic and can be further modified by fluctuations in humidity. Identification of a hygroscopic chloride could indicate brine activity subsequent to initial deposition. The identification of another water-related material in the ancient cratered terrain of Mars is further evidence that Mars once had a hydrologic cycle (albeit possibly short in duration) that was more active than at present.
  AGU Fall Meeting Abstracts. 11/2007; -1:1563.
• Article: Evidence for magmatic evolution and diversity on Mars from infrared observations

  P. R. Christensen, H. Y. McSween, J. L. Bandfield, S. W. Ruff, A. D. Rogers, V. E. Hamilton, N. Gorelick, M. B. Wyatt, B. M. Jakosky, H. H. Kieffer, M. C. Malin, J. E. Moersch
  [show abstract] [hide abstract]
  ABSTRACT: Compositional mapping of Mars at the 100-metre scale with the Mars Odyssey Thermal Emission Imaging System (THEMIS) has revealed a wide diversity of igneous materials. Volcanic evolution produced compositions from low-silica basalts to high-silica dacite in the Syrtis Major caldera. The existence of dacite demonstrates that highly evolved lavas have been produced, at least locally, by magma evolution through fractional crystallization. Olivine basalts are observed on crater floors and in layers exposed in canyon walls up to 4.5 km beneath the surface. This vertical distribution suggests that olivine-rich lavas were emplaced at various times throughout the formation of the upper crust, with their growing inventory suggesting that such ultramafic (picritic) basalts may be relatively common. Quartz-bearing granitoid rocks have also been discovered, demonstrating that extreme differentiation has occurred. These observations show that the martian crust, while dominated by basalt, contains a diversity of igneous materials whose range in composition from picritic basalts to granitoids rivals that found on the Earth.
  Nature 07/2005; 436(7050):504-509. · 36.28 Impact Factor
• Article: Mineral Composition and Abundance of the Rocks and Soils at Gusev and Meridiani from the Mars Exploration Rover Mini-TES Instruments

  P. R. Christensen, M. B. Wyatt, T. D. Glotch, A D Rogers, S Anwar, R. E. Arvidson, J. L. Bandfield, D. L. Blaney, C Budney, W. M. Calvin
  [show abstract] [hide abstract]
  ABSTRACT: The Miniature Thermal Emission Spectrometer (Mini-TES) has provided remote measurements of mineralogy, thermophysical properties, and atmospheric temperature profile and composition of the outcrops, rocks, spherules, and soils surrounding the Spirit and Opportunity Rovers. The mineralogy of volcanic rocks provides insights into the composition of the source regions and the nature of martian igneous processes. Carbonates, sulfates, evaporites, and oxides provide information on the role of water in the surface evolution. Oxides, such as crystalline hematite, provide insight into aqueous weathering processes, as would the occurrence of clay minerals and other weathering products. Diurnal temperature measurements can be used to determine particle size and search for the effects of sub-surface layering, which in turn provide clues to the origin of surficial materials through rock disintegration, aeolian transport, atmospheric fallout, or induration. In addition to studying the surface properties, Mini-TES spectra have also been used to determine the temperature profile in the lower boundary layer, providing evidence for convective activity, and have determined the seasonal trends in atmospheric temperature and dust and cloud opacity.
  02/2005;
• Article: Mineralogy at Meridiani Planum from the Mini-TES Experiment on the Opportunity Rover.

  P R Christensen, M B Wyatt, T D Glotch, A D Rogers, S Anwar, R E Arvidson, J L Bandfield, D L Blaney, C Budney, W M Calvin, [......], A T Knudson, H Y McSween, G L Mehall, L K Mehall, J E Moersch, R V Morris, M D Smith, S W Squyres, S W Ruff, M J Wolff
  [show abstract] [hide abstract]
  ABSTRACT: The Miniature Thermal Emission Spectrometer (Mini-TES) on Opportunity investigated the mineral abundances and compositions of outcrops, rocks, and soils at Meridiani Planum. Coarse crystalline hematite and olivine-rich basaltic sands were observed as predicted from orbital TES spectroscopy. Outcrops of aqueous origin are composed of 15 to 35% by volume magnesium and calcium sulfates [a high-silica component modeled as a combination of glass, feldspar, and sheet silicates (approximately 20 to 30%)], and hematite; only minor jarosite is identified in Mini-TES spectra. Mini-TES spectra show only a hematite signature in the millimeter-sized spherules. Basaltic materials have more plagioclase than pyroxene, contain olivine, and are similar in inferred mineral composition to basalt mapped from orbit. Bounce rock is dominated by clinopyroxene and is close in inferred mineral composition to the basaltic martian meteorites. Bright wind streak material matches global dust. Waterlain rocks covered by unaltered basaltic sands suggest a change from an aqueous environment to one dominated by physical weathering.
  Science 01/2005; 306(5702):1733-9. · 31.20 Impact Factor
• Article: Removing the Shock from the Thermal Emission Spectra of Shocked Terrestrial and Martian Basalts

  S. P. Wright, J. L. Bandfield, P. R. Christensen, J. R. Johnson
  [show abstract] [hide abstract]
  ABSTRACT: An abundance of impact craters on the martian surface and shock effects in the martian meteorites indicate that the surface of Mars has been shocked. The thermal infrared (TIR) spectra of plagioclase feldspars experimentally shocked to various pressures have enabled the amount of shock to be correlated with changes in the TIR spectra [Johnson et al., 2002, 2003]. With these, estimates on the amount of shocked plagioclase feldspar on the martian surface has been investigated [Johnson et al., in press]. However, in relation to the use of shocked plagioclase feldspars as end-members for the deconvolution of remote TIR data, similar work need to be performed on the laboratory spectra of shocked rocks and subsequent deconvolutions with these shocked mineral end-members. In this work, laboratory TIR spectra of a shocked terrestrial basalt and it unshocked counterpart are deconvolved and compared to assess the possibility of removing the spectral contribution of shocked plagioclase feldspar from a shocked martian basalt spectrum. It has been suggested that the modal abundances of martian meteorite Los Angeles [Rubin et al., 2000] are similar to mineral abundances derived from the deconvolution of Thermal Emission Spectrometer (TES) Surface Type 1 (ST1) [Bandfield, 2002]. TIR spectra of shocked basalt from Lonar Crater, India were collected and deconvolved with an end-member library containing experimentally shocked calcic plagioclase feldspars [Johnson et al., 2002]. The deconvolution-derived mineral abundances were compared to those from deconvolutions of unshocked basalt, and it was determined that the spectrum of the original, unshocked bulk rock could be replicated by removing from the spectrum of a shocked basalt the shocked plagioclase end-member spectrum (scaled by its abundance). The same methodology was performed on another shocked basalt, martian meteorite Los Angeles. The TIR spectra of Los Angeles was deconvolved with an end-member library containing shocked plagioclase feldspar (An75), revealing an abundance of maskelynite (~46%) that closely matches modal abundances from petrographic studies (~45%) [Rubin et al., 2000]. TIR spectra of shocked intermediate calcic plagioclase feldspars such as those found in Los Angeles (An56-38) do not exist and therefore are not contained within the spectral library used here. A mean percentage of 46% of the shocked plagioclase feldspar end-member was removed from the bulk rock spectra of Los Angeles and replaced with unshocked labradorite. Similar to the Lonar Crater basalts, this should recreate the spectra of the pre-impact, unshocked basalt. This end-member replacement results in a TIR spectrum of a basalt with a Christiansen feature moved to lower wavenumbers, agreeing with previous work that suggested the position of this feature varies with the amount of shock [Johnson et al., 2002]. The new "unshocked" Los Angeles TIR spectrum is not an exact match for ST1, but it is more similar to TES spectra than a shocked Los Angeles spectrum is. Whereas laboratory TIR spectra of shergottites provide poor matches to orbital TES data [Hamilton et al., 2003], using this unshocked basalt spectrum as an end-member might provide additional constraints on the source region of Los Angeles. Further, it is suggested here that TIR spectra be acquired for various experimentally shocked end members of plagioclase feldspar solid solution series for better deconvolutions of shocked rocks.
  AGU Fall Meeting Abstracts. 11/2004; -1:0954.
• Source

  Available from: Deanne Rogers

  Article: Initial results from the Mini-TES experiment in Gusev Crater from the Spirit Rover.

  P R Christensen, S W Ruff, R L Fergason, A T Knudson, S Anwar, R E Arvidson, J L Bandfield, D L Blaney, C Budney, W M Calvin, [......], H Y McSween, G L Mehall, L K Mehall, J E Moersch, R V Morris, A D Rogers, M D Smith, S W Squyres, M J Wolff, M B Wyatt
  [show abstract] [hide abstract]
  ABSTRACT: The Miniature Thermal Emission Spectrometer (Mini-TES) on Spirit has studied the mineralogy and thermophysical properties at Gusev crater. Undisturbed soil spectra show evidence for minor carbonates and bound water. Rocks are olivinerich basalts with varying degrees of dust and other coatings. Dark-toned soils observed on disturbed surfaces may be derived from rocks and have derived mineralogy (+/-5 to 10%) of 45% pyroxene (20% Ca-rich pyroxene and 25% pigeonite), 40% sodic to intermediate plagioclase, and 15% olivine (forsterite 45% +/-5 to 10). Two spectrally distinct coatings are observed on rocks, a possible indicator of the interaction of water, rock, and airfall dust. Diurnal temperature data indicate particle sizes from 40 to 80 microm in hollows to approximately 0.5 to 3 mm in soils.
  Science 09/2004; 305(5685):837-42. · 31.20 Impact Factor
• Article: Mini-TES Observations of the Gusev and Meridiani Landing Sites

  P. Christensen, R. Arvidson, J. L. Bandfield, D. Blaney, C. Budney, W. Calvin, S. Ciccolella, A. Fallacaro, R. Fergason, T. Glotch, [......], J. Moersch, R. Morris, D. Rogers, S. Ruff, A. Saddat, M. D. Smith, S. Squyres, M. Wolff, M. Wyatt, The Mer Scienceteam
  [show abstract] [hide abstract]
  ABSTRACT: Mini-TES observations have been acquired of both the Gusev and Meridiani landing sites. The most recent results from the surface mineralogy, thermophysical properties, and atmospheric observations will be discussed.
  02/2004; 35:2186.
• Article: THEMIS Observations of Atmospheric Aerosol Optical Depth

  M. D. Smith, J. L. Bandfield, P. R. Christensen, M. I. Richardson
  [show abstract] [hide abstract]
  ABSTRACT: We present results from the retrieval of atmospheric dust and water-ice optical depth from THEMIS infrared images. Data from THEMIS complements the concurrent MGS TES data by offering a later local time and much higher spatial resolution.
  06/2003; -1:3168.
• Source

  Available from: adsabs.harvard.edu

  Article: Searching for the source regions of martian meteorites using MGS TES: Integrating martian meteorites into the global distribution of igneous materials on Mars

  V. E. Hamilton, P. R. Christensen, McSween, H. Y., Jr, J. L. Bandfield
  [show abstract] [hide abstract]
  ABSTRACT: The objective of this study was to identify and map possible source regions for all 5 known martian meteorite lithologies (basalt, lherzolite, clinopyroxenite, orthopyroxenite, and dunite) using data from the Mars Global Surveyor Thermal Emission Spectrometer (MGS TES). We deconvolved the TES data set using laboratory spectra of 6 martian meteorites (Los Angeles, Zagami, ALH A77005, Nakhla, ALH 84001, and Chassigny) as end members, along with atmospheric and surface spectra previously derived from TES data. Global maps (16 pixels/degree) of the distribution of each meteorite end member show that meteorite-like compositions are not present at or above TES detectability limits over most of the planet's dust-free regions. However, we have confidently identified local-scale (100s­1000s km2) concentrations of olivine- and orthopyroxene-bearing materials similar to ALH A77005, Chassigny, and ALH 84001 in Nili Fossae, in and near Ganges Chasma, in the Argyre and Hellas basin rims, and in Eos Chasma. Nakhla-like materials are identified near the detection limit throughout the eastern Valles Marineris region and portions of Syrtis Major. Basaltic shergottites were not detected in any spatially coherent areas at the scale of this study. Martian meteorite-like lithologies represent only a minor portion of the dust-free surface and, thus, are not representative of the bulk composition of the ancient crust. Meteorite-like spectral signatures identified above TES detectability limits in more spatially restricted areas (<tens of km) are targets of ongoing analysis.
  Meteoritics & planetary science 05/2003; 38:871-885. · 2.72 Impact Factor
• Article: Mars Odyssey THEMIS-VIS: Surface-Atmosphere Separation and Derivation of Aerosol Properties

  T. H. McConnochie, Bell, J. F, III, M. J. Wolff, M. D. Smith, J. L. Bandfield, M. I. Richardson, P. R. Christensen
  [show abstract] [hide abstract]
  ABSTRACT: Scattering by atmospheric aerosols can contribute a substantial fraction of the visible-light radiance observed in any remote sensing of Mars. Our objective is to develop techniques to separate this aerosol component from the surface-reflectance component in Mars Odyssey's THEMIS Visible Imaging Subsystem (THEMIS-VIS) dataset. The primary purpose of this study is the production of accurate surface reflectance data in order to allow for reliable color and mineralogical unit mapping. The second principal goal is to study the feasibility of using VIS measurements to derive quantitative information about ice and dust aerosol properties such as particle size and optical depth.
  02/2003;
• Article: THEMIS Surface-Atmosphere Separation Strategy and Preliminary Results

  J. L. Bandfield, M. D. Smith, P. R. Christensen
  [show abstract] [hide abstract]
  ABSTRACT: Methods refined and adapted from the TES investigation are used to develop a surface-atmosphere separation strategy for THEMIS image analysis and atmospheric temperature and opacity retrievals. Additional information is contained in the original extended abstract.
  05/2002;
• Article: TES Observations of Chryse and Acidalia Planitiae: Multiple Working Hypotheses for Distributions of Surface Compositions

  M. B. Wyatt, J. L. Bandfield, Mcsween, H. Y, P. R. Christensen, J. Moersch
  [show abstract] [hide abstract]
  ABSTRACT: A gradation of surface units represents either (1) an influx of basaltic sediment from southern highlands, deposited on andesitic volcanics, or (2) incompletely weathered basalt marking the geographic extent of submarine alteration of basaltic crust. Additional information is contained in the original extended abstract.
  05/2002;
• Article: Compositions of Low Albedo Intracrater Materials and Wind Streaks on Mars: Examination of MGS TES Data in Western Arabia Terra

  J. L. Bandfield, M. B. Wyatt, P. Christensen, Mcsween, H. Y
  [show abstract] [hide abstract]
  ABSTRACT: Basalt and andesite surface compositions are identified within individual low albedo intracrater features and adjacent dark wind streaks. High resolution mapping of compositional heterogeneities may help constrain origin hypotheses for these features. Additional information is contained in the original extended abstract.
  02/2001;
• Article: TES Observations of the Martian Surface and Atmosphere

  P. R. Christensen, H. H. Kieffer, J. C. Pearl, B. Conrath, M. C. Malin, R. C. Clark, R. V. Morris, J. L. Bandfield, M. D. Smith, M. D. Lane
  [show abstract] [hide abstract]
  ABSTRACT: The Thermal Emission Spectrometer (TES) instrument is a Fourier transform Michelson interferometer operating with 10 or 5 cm(exp -1) sampling in the thermal infrared spectral region from 1700 to 200 cm(exp -1) (-6 to 50 micrometers) where virtually all minerals have characteristic fundamental vibrational absorption bands. The TES data used in this paper are among the 6 x 10(exp 7) spectra collected during the early mapping phase of the Mars Global Surveyor (MGS) mission from southern hemisphere winter to early summer (aerocentric longitude, L(sub s), 107 deg to 297 deg. The methodology for separating the surface and atmospheric components of the radiance from Mars, which allows detailed analysis and interpretation of surface mineralogy, is described in previous paper. Additional information is contained in original extended abstract.
  09/2000;
• Source

  Available from: articles.adsabs.harvard.edu

  Article: Martian Surface Compositions from Mars Global Surveyor Thermal Emission Spectrometer Data: Mars Pathfinder Landing Site and Surrounding Regions

  M. B. Wyatt, J. L. Bandfield, McSween, H. Y., Jr, P. R. Christensen
  Meteoritics and Planetary Science Supplement. 06/2000; 35:171.
• Article: Mars' "White Rock" Feature Lacks Evidence of an Aqueous Origin

  S. W. Ruff, P. R. Christensen, R. N. Clark, H. H. Kieffer, M. C. Malin, J. L. Bandfield, B. M. Jakosky, M. D. Lane, M. T. Mellon, M. A. Presley
  [show abstract] [hide abstract]
  ABSTRACT: The Thermal Emission Spectrometer on board the Mars Global Surveyor has observed "White Rock" and the data do not indicate the presence of evaporite minerals. We suggest it is a deposit of compacted or weakly cemented aeolian sediment.
  04/2000;
• Article: A Review of Spatial and Seasonal Changes in Condensation Clouds Observed During Aerobraking by MGS TES

  J. C. Pearl, M. D. Smith, B. J. Conrath, J. L. Bandfield, P. R. Christensen
  [show abstract] [hide abstract]
  ABSTRACT: Successful operation of the Mars Global Surveyor spacecraft, beginning in September 1997, has permitted extensive infrared observations of condensation clouds during the martian southern summer and fall seasons (184 deg less than L(sub s) less than 28 deg). Initially, thin (normal optical depth less than 0.06 at 825/ cm) ice clouds and hazes were widespread, showing a latitudinal gradient. With the onset of a regional dust storm at L(sub s) = 224 deg, ice clouds essentially vanished in the southern hemisphere, to reappear gradually after the decay of the storm. The thickest clouds (optical depth approx. 0.6) were associated with major volcanic features. At L(exp s) = 318 deg, the cloud at Ascraeus Mons was observed to disappear between 21:30 and 09:30, consistent with historically recorded diurnal behavior for clouds of this type. Limb observations showed extended optically thin (depth less than 0.04) stratiform clouds at altitudes up to 55 km. A water ice haze was present in the north polar night at altitudes up to 40 km; this probably provided heterogeneous nucleation sites for the formation of CO2 clouds at altitudes below the 1 mbar pressure level, where atmospheric temperatures dropped to the condensation point of CO2.
  08/1999;