Complex geology of two large impact craters in Tyrrhena Terra, Mars: Detailed analysis using MEX HRSC camera data

Abstract

Tyrrhena Terra, located just north of the roughly 200 km Hellas impact basin, is a typical region of the ancient cratered southern highlands on Mars. Its base material is a mixture of Hellas ejecta, prebasin remnants, and highland terrain, all later saturated with smaller (<200 km) impact craters. Fluvial and lacustrine deposits, erosion, tectonic movements, volcanic materials and aeolian processes have subsequently modified the region further. In this study we take a closer look at two adjacent unnamed craters in Tyrrhena Terra, located at 24.5°S, 80.8°E (crater “A”) and 23.9°S, 79.3°E (crater “B”). The craters are covered by the ∼20–80 m/pixel Mars Express High Resolution Stereo Color imager (HRSC) multispectral data, which together with MOC, THEMIS, and MOLA data sets allows us to make very detailed analysis of the area. We describe several identified geological and geomorphological units with their individual characteristics (e.g., morphology, color, cratering records, and elevation differences) and interpret their individual evolution. The crater floors show several unique material types of both depositional and erosional origin. Crater A has a large 200 m high central massif and a central peak ring as well as a unique low‐lying terrain type, “honeycomb terrain,” with narrow 50–200 m high ridges and intervening pits. Additionally, both craters exhibit erosional features similar to each other and nearby craters, indicating episodes of deposition of various material types in both craters. We find that the crater pair reveals many characteristics which are typical of the N Hellas rim but are not found elsewhere.