TWENTY YEARS OF EXPLORING SILICATE ALTERATION MINERALOGY ON MARS IN THE THERMAL INFRARED

Decades of research carried out with Thermal Emission Spectrometer (TES) and Thermal Emission Imaging System (THEMIS) data have revealed much about the alteration history of Mars. But while the spectral signatures of minerals on the planet might often add linearly, the journey itself has been anything but linear as we have shifted from information to knowledge to understanding of how alteration mineralogy manifests in thermal infrared data. This talk will highlight the clues to martian alteration processes on Mars made with thermal infrared data, most of which were originally discovered by Josh Bandfield. Because thermal emission spectra were rarely applied to studying altered rock types in years before the TES and THEMIS instruments arrived at Mars, some of the signatures of silicate alteration in the data have been challenging to interpret. But in-depth laboratory research using thermal emission spectroscopy applied to weathered rocks, hydrothermally altered rocks, sedimentary rocks and other altered rock types has revealed thermal emission spectroscopy as a powerful tool to explore many types of altered rocks, especially those with thin coatings and rinds. The technique is particularly well suited to detect and map short range order and amorphous silicates, which are seemingly abundant materials on Mars. Among Bandfield’s many discoveries are the detection of fine grained carbonates in the martian dust, mapping of aluminous silica at high latitudes, identification of quartz, and the recognition of alkali feldspars. Through years of contemplation, lab analyses, and comparison of thermal emission data to near infrared reflectance data have revealed much about the meaning of TES and THEMIS data with regard to aqueous alteration on Mars, some outstanding questions remain. This presentation reviews the history of alteration on Mars as seen from the perspective of emitted radiation.