Detection of Crater Ejecta in Venus Tessera Terrain using Magellan SAR Data

Abstract:

Tesserae, areas of high radar backscatter with a highly deformed morphology, are hypothesized to be some of the oldest materials on the surface of Venus, while parabolic crater ejecta deposits are some of the youngest geologic features. Recently, Earth-based radar data were used to make the first detailed maps of crater ejecta deposits within tessera terrains, such as Alpha Regio. In this work, we analyze tesserae using Magellan radar image data based on this new understanding of surface properties, with the goal of extending the technique for identifying crater deposits beyond the coverage of the Earth-based data. Our goals are to define stratigraphic relationships, determine whether there is a non-uniform distribution of crater ejecta within the tesserae, and identify uncontaminated tessera regions as possible future landing sites. We first present detections of ejecta in tesserae from Magellan images of craters also observed in the Earth-based data, then show several tessera regions that have only Magellan coverage but apparently similar surface mantling deposits. Tellus Tessera contains a concentration of low radar backscatter surfaces, in its center and southwest, interpreted as fine-grained ejecta deposits from Bernhardt crater. At Sudenitsa Tessera, located on the northern edge of the Beta-Atla-Themis region, several low backscatter tessera areas occur that are not associated with any obvious impact crater. This suggests that the low-backscatter ejecta were sourced from a crater that was resurfaced in the recent (likely less than 50-100 Ma) past. From these analyses it is evident that crater parabola deposits are non-uniformly distributed in tesserae, and future landing site selection will need to account for the presence of these deposits. Fine-grained deposits in the tesserae may also preserve evidence of ejecta after the parent crater is buried by plains-forming lavas.