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

Rock shapes and heights around the InSight lander are examined to refine the degradation history of the 27 m‐diameter Homestead hollow. Results document decreasing average exposed rock height and increasing percentage of rocks where height comprises the short axis from outside to within the hollow and support prior models of ejecta deflation accompanied by hollow infilling. We estimate 0.3 m of deflation at the current rim that is realistic compared to rock relief, original ejecta thickness, and predicted aeolian contributions to infilling. We also find that shapes of embayed basalt rocks outside the hollow appear platy, bladed, and elongate in a triangular form factor plot, and more discoidal and bladed in an axes ratio plot. By contrast, expected shapes based on terrestrial studies of basalt rocks are mostly compact, compact platy, compact bladed, compact elongated, platy, bladed, and elongate in triangular form factor plots, and equant with lesser, but significant disc‐ and blade‐shaped rocks in axes ratio plots. We find addition of 10 cm to the heights of rocks near the hollow rim, to account for continued partial embedding in ejecta, yields the best match between observed and expected rock shapes. Exposure of small ejecta rocks in the hollow supports degradation rates of 10−4 m/Myr during most of hollow history. Results indicate that deflation from ejecta accompanied by downwind deposition in the hollow can account for the current degraded form of the crater. Our approach is a new tool for characterizing small crater degradation on regolith‐covered lava plains on Mars. Key Points: Rock heights and shapes at Homestead hollow indicate early transport of deflated ejecta sediments can account for infilling of the craterNear‐rim rock heights and shapes relative to the expected original versus remnant ejecta thickness indicates 30 cm deflation at the current rimExposure of later arriving, small ejecta rocks in the hollow supports very low estimates of degradation over most hollow history [ABSTRACT FROM AUTHOR]