Ancient Impact Melt Near the Lunar South Pole: Distribution, Provenance, and Sampling Strategy

Abstract

Due to a lack of pre-Nectarian samples associated with specific impacts in the Apollo suite, the early Solar System's impact chronology is poorly constrained. We investigate where Artemis and other south polar lunar missions could sample impactites to determine the ages of pre-Nectarian craters, focusing on the ancient craters Haworth, Shoemaker, and Faustini. We examine similarly sized non-polar analogue craters containing mappable impact melt features and find no patterns that could be used to predict where similar deposits may have once existed in the south polar region. We also create a model of the ejecta stratigraphy of craters that post-date the South Pole-Aitken basin, from which we predict how younger, smaller craters may excavate ancient, buried impact melt to the surface. We find that, at most, primary impact melt from a source crater will comprise no more than 2%–3% of material at the surface above its buried rim, and <1% elsewhere. Furthermore, disruption of the ejecta stratigraphy by ballistic sedimentation and surface mixing due to impact gardening will make sampling specific sources more difficult. We conclude that determining the provenance of ancient impact melt samples will be difficult, but that sampling near the rim of a given source—such as in the “Haworth” Artemis candidate landing region—will maximize the chances of success.