Stratigraphy of Ice and Ejecta Deposits at the Lunar Poles

Abstract

Water ice has been delivered to the lunar poles from different sources over billions of years, but this accumulation was punctuated by large impacts that excavated dry regolith from depth and emplaced it in layers over the poles. Here, we model the resulting stratigraphies of ice and ejecta deposits in the lunar polar regions. Large polar craters were age dated, and their ejecta distributions calculated with standard scaling relations. We then created a Monte Carlo model for ice deposition and ejecta emplacement. Typical model runs showed that deposits in older cold traps (>4 Ga) are divided into two zones: buried ice-rich gigaton deposits and younger more gardened mantles. The latter are consistent with small crater morphometry measurements, but the existence of substantial ice buried at great depths is more difficult to confirm. Rare outlier model runs included Mercury-like cases with significant deposition events in recent history (<200 Ma).