Degradation at the InSight Landing Site, Homestead Hollow, Mars: Constraints from Rock Heights and Shapes

Rock heights and three-dimensional shapes around the InSight lander in Homestead hollow, Mars, provide new constraints on modification of the degraded 27 m in diameter impact crater and are a tool for characterizing degradation on regolith-covered lava plains on Mars. Decreasing average rock height and increasing percentage of fragments where height comprises the short axis from outside to within the hollow supports significant ejecta deflation accompanied by infilling of the interior. Rock relief outside the hollow is compared with expectations of pristine ejecta thickness and indicates up to ~40 cm of near-rim early deflation (decreasing to a few cm out to one diameter) can account for the predicted eolian component of infilling and that other eolian infilling sources are not required. Scattered rocks in the hollow are ejecta from subsequent nearby impacts and their mostly buried expression is consistent with subsequent long-term degradation estimated to be 10⁻⁴ m/Myr. Basalt rock shapes at InSight are likely similar to basalt rock shapes on Earth, but appear more platy, bladed, and elongate in a triangular form factor plot and more discoidal and bladed in an axes ratio plot. Nevertheless, addition of 10 cm to near rim rock heights to account for continued partial embedding in ejecta would result in rock shapes quite similar to terrestrial rocks. Consistency between degradation estimates based on current rock relief and rock shape after accounting for partial embedding in ejecta indicates up to ~30-40 cm early (~0.1 Ga) near-rim deflation was followed by much lesser long-term degradation