Interpreting Thermal Inertia in Arabia Terra Through Crater Density Analysis

Abstract:

Thermal Inertia (TI) measurements have been extensively utilized to help differentiate sediments on Mars’ surface. Typically, higher TI (> 500 Jm^-2K^-1s^-1/2) correlates to more indurated surfaces (e.g., bedrock), and lower TIs (< 300 Jm^-2K^-1s^-1/2) indicate less cohesive/particulate materials (e.g., sand). However, the relationship between TI and the surface physical properties can be obscured due to effects of dust cover or surface heterogeneity. To determine how surface induration, dust cover, and TI are related in Mars’ dusty regions, we compared crater densities comprised of small craters (< 1 km diameter) and TI for craters hosting sedimentary mounds in the particularly dusty Arabia Terra region. Small crater distributions are an effective indicator of surface induration since craters in mechanically stronger surfaces erode more slowly compared to looser surfaces. Initial results comparing crater density maps to TI maps in four large crater basins, and ongoing work at six other locations demonstrate these very dusty, less cratered surfaces are generally associated with higher apparent TIs. One possible explanation for this trend is that dust is preferentially removed from actively eroding surfaces by aeolian activity, and on more resistant surfaces thicker dust deposits may accumulate in surface depressions resulting in a lower overall apparent surface TI. This work will provide a quantitative template for how to consider the context of surface induration in very dusty regions when interpreting TI. Insight into which surfaces host thick dust layers, and which surfaces are stripped of dust will constrain rock strength as well as the types of processes that could have formed those units.