Rock Abundance on the Lunar Mare on Surfaces of Different Age: Implications for Regolith Evolution and Thickness

Abstract

AbstractThe growth of lunar regolith over time affects surface rock abundance, because larger, less frequent impacts are needed to penetrate thicker regolith developed on older surfaces and excavate rocks. On younger surfaces with thinner regolith, smaller, more frequent impacts are sufficient to excavate rocks. We quantify the correlation between observed rock abundances and age on the lunar surface by comparing Diviner rock abundance data to the surface ages of intercrater parts on the maria. Our observations show the expected negative correlation between age and rock abundance. The commonality of nonzero rock abundance values on ancient surfaces, combined with a simple Monte Carlo model of the rock excavation process, suggest that rocks reexcavated from the regolith volume contribute to the presently observed rock population on the lunar surface. The half‐life of meter‐scale surface rocks most consistent with our observations is 80 ± 20 Myr.