MAPPING OF ROCKY EJECTA CRATERS IN INSIGHT LANDING SITES IN WESTERN ELYSIUM PLANITIA

Impact craters with rocky ejecta blankets were mapped in four potential InSight landing sites in western Elysium Planitia to understand their degradational sequence and to characterize their potential landing hazard.

Five morphologic classifications of rocky ejecta craters were defined based on the preservation of the crater rim, crater interior and ejecta blankets in HiRISE images. Class 1 craters are the freshest craters and are distinguished by a well-defined, prominent crater rim. Class 1 crater interiors show minimal infill and few signs of fresh eolian bed forms. The ejecta blanket extends about one diameter from the crater rim and is very rocky, suggesting little accumulation of sediment. The rocky ejecta blanket covers 75-100% of a one-diameter annulus around the crater.

Crater classes 2 through 4 show increasing degradation of the crater rims (becoming rounder), shallower, with increasing sediment infill, and decreasing area covered by rocks within the ejecta blanket.

Class 5 represents the most degraded craters. Crater rims are rounded and the crater floor is shallow and smooth having been filled in with sediment (without obvious bed forms). Ejecta blankets are not continuous around class 5 craters with rocks covering only 10%-40% of the one diameter annulus around the crater.

Mapping of all rocky ejecta craters in western Elysium Planitia shows that the craters themselves cover 1.7% and their rocky ejecta cover 4.6% of the area mapped in HiRISE images. Class 1 and 2 craters and their ejecta blankets are the best preserved and the most rockiest: these craters cover 0.7% and their rocky ejecta 2.7% of the area. Class 3-5 craters cover 1% and their rocky ejecta cover 1.9% of the mapped area.