Thermophysical Characterization of the Tharsis Plateau Low-Inertia Layer from TES and THEMIS Observations

The surface of Mars can be divided into a few major surface types based on thermal inertia, albedo, and rock abundance measurements. The surfaces on the planet with the lowest thermal inertia, lowest rock abundance, and relatively high albedo represent a very fine-grained, poorly indurated, high albedo material. In order to completely blanket the geologically varied underlying materials and display such uniformly low thermal inertia, the surface layer must be at least a few centimeters thick, and is likely to be much thicker. The Tharsis-Amazonis region contains some of the brightest non-ice surfaces on the planet, often with morphologies that are uncoupled from the albedo and thermal inertia trends, suggesting that a regional or global process is responsible for the development of the relatively uniform low inertia layer. The Thermal Emission Spectrometer (TES) has provided well-calibrated datasets for characterizing the thermophysical properties of this low-inertia materials. THEMIS thermal infrared and visible images have been used to study the link between surface morphology and small-scale thermophysical characteristics, providing a better understanding of the physical nature of the units differentiated with TES observations. There are a few distinct surfaces in the Tharsis region that have anomalously low albedo and high thermal inertia, including sites in Noctis Labyrinthus, the Arsia Mons/Oti Fossae thermal anomaly, the scarp of Olympus Mons, and a small number of isolated impact craters throughout the region. These anomalous surfaces typically have distinct boundaries and contain evidence that they have resulted from current or recent aeolian activity constrained by morphologic features. The sites investigated provide insight into the uniform, widespread, low inertia unit, but most are not actual windows into underlying material. Dunes and other distinct morphologic features can be seen on top of the low intertia layer. The relationships seen among all the high inertia features in Tharsis provide some evidence that the low inertia unit may be more competent than previously determined, and probably significantly more complicated.