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