Thermal Emission Spectrometer (TES) data from the Mars Global Surveyor (MCS) are used t o determine compositions and distributions of martian lowalbedo regions. Two surface spectral signatures are identified from low-albedo regions. Comparisons with spectra of terrestrial rock samples and deconvolution results indicate that the t w o compositions are a basaltic composition dominated by plagioclase feldspar and clinopyroxene and an andesitic composition dominated by plagioclase feldspar and volcanic glass. The distribution of the t w o compositions is split roughly along the planetary dichotomy. The basaltic composition is confined t o older surfaces, and the more silicic composition is concentrated in the younger northern plains.A major objective of the TES investigation is to determine and map the mineralogy of the martian surface in order to understand the formation and development of Mars. To understand present and past conditions on Mars, it is important to determine if the surface materials are, for example, volcanic, weathering products, or chemical precipitates. We demonstrate here that martian dark materials are volcanic and that they vary significantly across the planet. These findings can help lead to an understanding of planetary mechanisms such as the development of the martian crust, heat loss processes, bulk composition, magma differentiation, and source materials of the martian soil and dust.Previous studies have developed the methodology for separating the surface and atmospheric components of the emission of Mars

Abstract. The Thermal Emission Spectrometer (TES) investigation on Mars GlobalThe TES data are calibrated to a 1-o-precision of 2.5 -6 X 10 -8 W cm -2 sr-1/cm -•, 1.6 x 10 -6 W cm -2 sr -•, and -0.5 K in the spectrometer, visible/near-IR bolometer, and IR bolometer, respectively_. These instrument subsections are calibrated to an absolute accuracy of-4 x 10 -8 W cm -2 sr-•/cm -• (0.5 K at 280 K), 1-2%, and -1-2 K, respectively. Global mapping of surface mineralogy at a spatial resolution of 3 km has shown the following: (1) The mineralogic composition of dark regions varies from basaltic, primarily plagioclase feldspar and clinopyroxene, in the ancient, southern highlands to andesitic, dominated by plagioclase feldspar and volcanic glass, in the younger northern plains. (2) Aqueous mineralization has produced gray, crystalline hematite in limited regions under ambient or hydrothermal conditions; these deposits are interpreted to be in-place sedimentary rock formations and indicate that liquid water was stable near the surface for a long period of time. (3) There is no evidence for large-scale (tens of kilometers) occurrences of moderate-grained (>50-•m) carbonates exposed at the surface at a detection limit of -10%. (4) Unweathered volcanic minerals dominate the spectral properties of dark regions, and weathering products, such as clays, have not been observed anywhere above a detection limit of -10%; this lack of evidence for chemical weathering indicates a geologic history dominated by a cold, dry climate in which mechanical, rather than chemical, weathering was the significant form of erosion and sediment production. (5) There is no conclusive evidence for sulfate minerals at a detection limit of -15%. The polar region has been studied with the following major conclusions: (1) Condensed CO2 has three distinct end-members, from fine-grained crystals to slab ice. (2) The growth and retreat of the polar caps observed by MGS is virtually the same as observed by Viking 12 Martian years ago. (3) Unique regions have been identified that appear to differ primarily in the grain size of CO2; one south polar region appears to remain as black slab CO2 ice throughout its sublimation. (4) Regional atmospheric dust is common in localized and regional dust storms around the margin and interior of the southern cap. Analysis of the thermophysical properties of the surface shows that (1) the spatial pattern of albedo has changed since Viking observations, (2) a unique cluster of surface materials with intermediate inertia and albedo occurs that is distinct from the previously identified lowinertia/bright and high-inertia/dark surfaces, and (3) localized patches of high-inertia material have been found in topographic lows and may have been formed by a unique set of aeolian, fluvial, or erosional processes or may be exposed bedrock.• •Raytheon Santa Barbara Remote Sensing, Goleta, California. IntroductionThe Thermal Emission Spectrometer (TES) experiment is designed to address a wide range of science objectives, including the de...

Sedimentary rocks at Eagle crater in Meridiani Planum are composed of fine-grained siliciclastic materials derived from weathering of basaltic rocks, sulfate minerals (including magnesium sulfate and jarosite) that constitute several tens of percent of the rock by weight, and hematite. Cross-stratification observed in rock outcrops indicates eolian and aqueous transport. Diagenetic features include hematite-rich concretions and crystal-mold vugs. We interpret the rocks to be a mixture of chemical and siliciclastic sediments with a complex diagenetic history. The environmental conditions that they record include episodic inundation by shallow surface water, evaporation, and desiccation. The geologic record at Meridiani Planum suggests that conditions were suitable for biological activity for a period of time in martian history.