Mars Global Surveyor Thermal Emission Spectrometer experiment: Investigation description and surface science results

The Thermal Emission Spectrometer (TES) investigation on Mars Global Survey or (MGS) is aimed at determining (1) the composition of surface minerals, r ocks, and ices; (2) the temperature and dynamics of the atmosphere; (3) the properties of the atmospheric aerosols and clouds; (4) the nature of the p olar regions; and (5) the thermophysical properties of the surface material s. These objectives are met using an infrared (5.8- to 50-mum) interferomet ric spectrometer, along with broadband thermal (5.1- to 150-mum) and visibl e/near-IR (0.3- to 2.9-mum) radiometers. The MGS TES instrument weighs 14.4 7 kg, consumes 10.6 W when operating, and is 23.6 X 35.5 X 4.0.0 cm in size . The TES data are calibrated to a 1-sigma precision of 2.5(-6) X 10(-8) W cm(-2) sr(-1)/cm(-1), 1.6 X 10(-6) W cm(-2) sr(-1), and similar to0.5 K in the spectrometer, visible/near-IR bolometer, and IR bolometer, respectively . These instrument subsections are calibrated to an absolute accuracy of si milar to4 X 10(-8) W cm(-2) sr(-1)/cm(-1) (0.5 K at 280 K), 1-2%, and simil ar to1-2 K., respectively. Global mapping of surface mineralogy at a spatia l resolution of 3 km has shown the following: (1) The mineralogic compositi on 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 limi ted regions under ambient or hydrothermal conditions; these deposits are in terpreted to be in-place sedimentary rock formations and indicate that liqu id water was stable near the surface for a long period of time. (3) There i s no evidence for large-scale (tens of kilometers) occurrences of moderate- grained (> 50-mum) carbonates exposed at the surface at a detection limit o f similar to 10%. (4) Unweathered volcanic minerals dominate the spectral p roperties of dark regions, and weathering products, such as clays, have not been observed anywhere above a detection limit of similar to 10%; this lac k of evidence for chemical weathering indicates a geologic history dominate d by a cold, dry climate in which mechanical, rather than chemical, weather ing was the significant form of erosion and sediment production. (5) There is no conclusive evidence for sulfate minerals at a detection limit of simi lar to 15%. The polar region has been studied with the following major conc lusions: (1) Condensed CO2 has three distinct end-members, from fine-graine d crystals to slab ice. (2) The growth and retreat of the polar caps observ ed 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 s lab CO2 ice throughout its sublimation. (4) Regional atmospheric dust is co mmon in localized and regional dust storms around the margin and interior o f the southern cap. Analysis of the thermophysical properties of the surfac e shows that (1) the spatial pattern of albedo has changed since Viking obs ervations, (2) a unique cluster of surface materials with intermediate iner tia and albedo occurs that is distinct from the previously identified low-i nertia/bright and high-inertia/dark surfaces, and (3); localized patches of high-inertia material have been found in topographic lows and may have bee n formed by a unique set of aeolian, fluvial, or erosional processes or may be exposed bedrock.