Craters and Lunar Lua (Pits/Skylights) in Mare Tranquillitatis and Marius Hills Reveal Variations in Protolith Properties

Abstract We investigated the regolith parent rock (“protolith”) properties of Mare Tranquillitatis and Marius Hills on the Moon, utilizing lunar pit craters (“lua”) to contextualize observations of rock abundance and crater degradation. We discovered a significant difference in underlying materials: the region around the Tranquillitatis lua is characterized by a competent, dense, solidified basalt, whereas the region around the Marius Hills lua exhibits a more friable protolith, indicative of porous or vesicular volcanic deposits. These distinct protoliths directly influence rock evolution, with the Marius Hills region demonstrating higher initial rock excavation but also more rapid degradation of rocky ejecta and interiors, while the Mare Tranquillitatis region produces larger, more persistent blocks that resist fragmentation for longer periods. Consequently, the competent protolith of Mare Tranquillitatis makes its lua an ideal candidate for future lunar exploration missions, offering superior geotechnical integrity for potential subsurface habitats and enhanced protection from surface radiation and impact bombardment.