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

The Thermal Emission Spectrometer (TES) investigation on Mars Global Surveyor (MGS) is aimed at determining (1) the composition of surface minerals, rocks, and ices; (2) the temperature and dynamics of the atmosphere; (3) the properties of the atmospheric aerosols and clouds; (4) the nature of the polar regions; and (5) the thermophysical properties of the surface materials. These objectives are met using an infrared (5.8to 50m) interferometric spectrometer, along with broadband thermal (5.1to 150m) and visible/near-IR (0.3to 2.9m) radiometers. The MGS TES instrument weighs 14.47 kg, consumes 10.6 W when operating, and is 23.6 35.5 40.0 cm in size. The TES data are calibrated to a 1precision of 2.5 6 10 8 W cm 2 sr /cm , 1.6 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 10 8 W cm 2 sr /cm 1 (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 ( 50m) 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. Department of Geology, Arizona State University, Tempe, Arizona. U.S. Geological Survey, Flagstaff, Arizona. Malin Space Science Systems, San Diego, California. NASA Johnson Space Center, Houston, Texas. U.S. Geological Survey, Denver, Colorado. University of Colorado, Boulder, Colorado. Goddard Space Flight Center, Greenbelt, Maryland. Space Science Institute, Boulder, Colorado. Vernadsky Institute, Moscow, Russia. Ames Research Center, Moffett Field, California. Raytheon Santa Barbara Remote Sensing, Goleta, California. Copyright 2001 by the American Geophysical Union. Paper number 2000JE001370. 0148-0227/01/2000JE001370$09.00 JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 106, NO. E10, PAGES 23,823–23,871, OCTOBER 25, 2001