Evidence for impact melt sheets in lunar highland smooth plains and implications for polar landing sites

Smooth plains units attributed to fluidized basin ejecta occur over much of the lunar highlands. We examined 4-20 km diameter Imbrian- and Eratosthenian-period craters in the southern highlands that have high 12.6-cm wavelength radar backscatter and circular polarization ratios associated with their interior walls but not with their proximal ejecta. Of these craters, about 70% occur on or very near deposits of Imbrian highland plains. We propose that melt-rich ejecta from basin-forming impact events, near the top of the stratigraphic section, supplies fragmental material that is exposed in the interior wall regolith of these small craters. These results support previous interpretations of 70-cm radar data, which provide insight on the near-surface morphology and rock provenance in proposed smooth plains landing sites such as that of Chandrayaan-2.