MID-INFRARED EMISSION SPECTROSCOPY AS A TOOL TO STUDY MARS

Mid-infrared (thermal infrared) emission spectroscopy (5-50 µm; 2000-200 cm^-1) is a useful tool for studying minerals because the majority of molecular vibrations of minerals occurs in this spectral range and each mineral offers a unique spectral signature. Using a spectral suite of minerals studied in the laboratory, mid-infrared remote-sensing data of Mars or other planetary bodies can be analyzed to study the surface mineralogy, as has been done from orbit with the high-spectral-resolution (143-band) Mars Global Surveyor Thermal Emission Spectrometer (TES) and from the surface as has been done with the Mars Exploration Rover Mini-TES instruments on the Spirit and Opportunity rovers. Mid-infrared data also have been acquired of Mars from orbit using the Mars Odyssey THEMIS (Thermal Emission Imaging System) instrument, a 9-band, high-spatial-resolution (~100 m/pixel) imaging spectrometer.

The data from these instruments have enabled specific minerals to be identified on Mars and their geologic environment at the time of formation to be deduced. For example, coarse gray hematite was identified at Meridiani Planum and was the first mineralogical evidence of water on Mars. Fe-sulfates identified in Gusev Crater clearly indicated that low-pH, high-acidity waters existed on Mars. Other current studies are utilizing TES and THEMIS data to investigate the composition and hydration state of sulfates in Juventae Chasma and to predict the Mg-Fe composition of olivine deposits on Mars, including the olivine in the basaltic dunes within Gale crater.