Investigating crater rim thermal inertia variations on Mars: A case study in Tisia Valles

Abstract

Impact craters across Mars, that are otherwise similar, commonly exhibit vastly different thermal inertia values on their rims. We focused on the Tisia Valles region because the terrain is mostly flat, and craters of various ages are present within the same target geologic unit. We present an investigation of two hypotheses for why these thermal inertia variations exist. The first hypothesis is that crater rim thermal inertia is affected by crater degradation state, and the second hypothesis is that thermal inertia is affected by the amount of regolith mantling the rims, regardless of degradation state. To investigate the first hypothesis, we used a series of multilevel regression analyses to test for correlations between crater rim thermal inertia and depth-diameter ratio, rim irregularity, and radii variation, which are indicators of crater degradation state. To investigate the second hypothesis, we tested for a correlation between thermal inertia and mantled crater rim percentage, which is indicative of the amount of regolith atop the rims. Our results did not support the first hypothesis but did support the second hypothesis. Therefore, we concluded that regolith rim mantling affects crater rim thermal inertia variations in the Tisia Valles region. Crater degradation may not have an effect on rim thermal inertia because regolith is transported down the crater rim slopes faster than local regolith is produced from erosion in this region. An implication of this work is that the spatial extent of regolith-rich regions near Tisia Valles can be mapped using the spatial extent of proximal craters with low thermal inertia rims. Additionally, the timing of mantling events can be quantified by comparing counts of craters with high thermal inertia rims to those of low thermal inertia rims within a region.