Increased small impactor flux on the Moon as inferred from regolith thickness at the Chang'E-5 Region.

Abstract

Knowledge of the small impactor flux on the Moon can provide critical insights into lunar geological evolution and the dynamics of the inner solar system. However, it cannot be directly deciphered from the observed populations of small craters due to their rapid degradation. Impact-generated lunar regolith records the contribution from historical impacts of various sizes and is particularly sensitive to sub-hectometer craters, providing a unique means to estimate the small impactor flux. Here we estimate the distribution of regolith thickness in the Chang'E-5 landing region (the youngest radiometric-dated homogeneous mare unit) through both statistics of fresh crater morphology and regolith evolution simulations using different impact flux hypotheses. The large median regolith thickness of 3.6±0.3 m derived from crater morphology can be attributed solely to a higher production rate of small lunar craters at sub-hectometer scales, which is 1.2-1.6 times higher than previously estimated. Such an increased small impactor flux may occur at ∼600 Ma and indicate recent asteroid breakup events, or could have persisted over the past 2 Ga, as a result of the preferential delivery of small impactors through the Yarkovsky and YORP effects.