RIMFAX GROUND PENETRATING RADAR OBSERVATIONS OF THE WESTERN FAN, JEZERO CRATER, MARS

The Mars 2020 rover Perseverance carries the RIMFAX GPR instrument, collecting subsurface soundings over a full frequency range of 150-1200 MHz, every ~10 cm along its entire traverse within Jezero Crater. Roughly 4 km of data was collected in ~80 drives on and along the front of the western fan and its contact with the crater floor, and ~5 km has been collected in ~35 drives on the upper fan to date. This work presents a summary of RIMFAX findings at the western fan, including major subsurface strata, structures, and characteristics of the subsurface, set in the context of current geologic models.

The fan is confirmed to be younger than surrounding (likely igneous) crater floor materials, with the latter diving beneath onlapping sediments of the fan in the Cape Nukshak section. The relationship is more complex at the very toe of the Hawksbill Gap section, though the fan-crater floor interface is fairly flat and distinct in the more fanwards subsusrface. The stack of layers exposed in the fan front up to Hogwallow Flats are nearly horizontal. In contrast, Rockytop and higher materials slope downwards towards the fan edge, indicating a different episode of emplacement. Within the curvilinear Tenby Formation, steep dips and truncations of layer sets are apparent in select profile sections, allowing the intricate relationships of curvilinear surface sets to be extended to the subsurface. A likely broad erosional trough is apparent high in the Tenby Formation (beneath Emerald Lake), and potential evidence for buried narrower rilles may also exist. Parts of the subsurface here appear relatively featureless, especially where the upper near-surface is highly scattering, likely due to high concentrations of cobbles and boulders that are seen covering neighboring areas of the surface. RIMFAX subsurface GPR results have significantly augmented and illuminated more traditional rover surface observations, in a fundamentally new way over previous Mars rover missions.