Impacts into the lunar permanently shadowed regions

Abstract

Water ice is preserved on the permanently shadowed regions (PSRs) of Moon’s south pole, which have witnessed multiple impacts. It is unclear how impacts disturb the volatiles present within PSRs. Here, we mapped the extent of craters within PSRs located between 85° and 90°S. A small-scale crater population model was developed, and we estimated ~24 million craters of 1–20 m diameter in PSRs >1 km2. We report that ~74% of PSRs are unaffected by impacts. However, the impact gardening process, including vertical mixing of ice with ejecta, may influence them and help preserve potential ice deposits. From iSALE-2D simulations in a PSRs-like environment, we found that craters >200 m can excavate/redistribute shallow ice, allowing it to get trapped within cold traps, while ice is lost within crater cavities. The study implies that small craters within the PSR likely disturbed the buried ice, and gardening in crater-free PSRs facilitates vertical mixing of ice, which is a potential target for future lunar missions.