Geologic and Thermal Characterization of Oxia Planum Using Mars Odyssey THEMIS Data

Oxia Planum will be the landing site for the European Space Agency ExoMars 2022 "Rosalind Franklin" mission to conduct astrobiological and geological experiments investigating the region's past. Previous orbital short-wave infrared (SWIR, 1.0-2.6 mu m) spectroscopic studies reported widespread phyllosilicate detections in the region suggesting possible alteration of its original lithology by past aqueous activity. We used thermal infrared data (TIR, 6.8-14.8 mu m) from the Thermal Emission Imaging System to assess regional bulk composition and thermophysical properties. We coupled these assessments with SWIR spectral analyses from the Compact Reconnaissance Imaging Spectrometer for Mars and with high-resolution visible images to characterize the physical properties of the region. We cataloged four geologic units with varying spectral, thermophysical, and textural properties. The previously mapped phyllosilicate bearing materials are associated with our oldest mapped unit. This unit exhibits light/dark-toned interbedding and TIR spectral characteristics consistent with phyllosilicate dominated and/or intermediate volcanic lithologies; evidence for mafic materials is lacking. Superposing that unit is a thin patchy dark-toned unit that contains mafic signatures. Isolated locations within the region are superposed by a mechanically competent, rough unit that lacks mafic signatures and is interpreted as lava or well-cemented fluvial deposits. The uppermost mapped unit is an eroded fan of possible deltaic or alluvial origin, with an inferred surface composition of unconsolidated sediment. Finally, based on stratigraphic and cross-cutting relationships with ejecta from Kilkhampton crater nearby, we suggest that all units formed during or before the Early Hesperian period.