ABSTRACT

The Thermal Emission Spectrometer (TES) on Mars Global Surveyor (MGS) mapped the surface, atmosphere, and polar caps of Mars from 1997 through 2006. TES provided the first global mineral maps of Mars, and showed that the surface is dominated by primary volcanic minerals (plagioclase feldspar, pyroxene, and olivine) along with high-silica, poorly crystalline materials. Differences in the abundances of these minerals were initially grouped into two broad compositional categories that correspond to basalt and basaltic andesite. Additional analysis has identified four surface compositional groups that are spatially coherent, revealing variations in the composition of the primary crust-forming magmas through time. In general, plagioclase, high-Ca clinopyroxene, and high-silica phases are the dominant mineral groups for most regions, with lesser amounts of orthopyroxene, olivine, and pigeonite. One of the fundamental results from the TES investigation was the identification of several large deposits of crystalline hematite, including those in Meridiani Planum, that were interpreted to indicate the presence of liquid water for extended periods of time. This interpretation led to the selection of Meridiani as the target for the Opportunity rover, the first time that a planetary landing site was selected on the basis of mineralogic information. Aqueous weathering may have formed some of the high-silica phases seen in TES spectra at high latitudes, and the Mars Express Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité (OMEGA) spectrometer has detected phyllosilicates and sulfates, typically formed by aqueous weathering and deposition, in several locations.

ABSTRACT

The Thermal Emission Imaging System (THEMIS) began mapping Mars in 2002 on the Mars Odyssey spacecraft. This instrument provides nine infrared and five visible surface-sensing and atmospheric bands, with spatial resolutions of 100 m in the IR and 18 m in the visible. THEMIS data have been used to investigate the composition and physical properties of the surface and polar ices, as well as to study atmospheric temperature, dust, and water vapor. THEMIS provides an excellent complement to the hyperspectral, 3–6 km spatial resolution Thermal Emission Spectrometer (TES) observations, and the two instruments have been used together to map the distribution of geologic units and to determine their detailed mineralogy. Among the major findings to date is the discovery of a diversity in volcanic compositions, from ultramafic olivine-rich basalts through basalts, dacite cones and flows, and granitic rocks uplifted by impact. These observations indicate that the Martian crust, while dominated by basalt, has undergone many of the processes of igneous differentiation that occur on Earth. THEMIS has not detected any carbonate outcrops at 100 m scales, suggesting that carbonate rocks have not formed on Mars and has also not detected any evidence for near-surface volcanic activity, liquid water, or ice that is close enough to the surface to produce a measurable thermal anomaly. THEMIS nighttime temperature measurements have shown the existence of exposed bedrock at 100 m to km scales, and layered materials of differing physical properties, with inferred differences in the processes that deposited or consolidated them.