Lunar Early Impact Flux Revealed by Mare Buried Impact Craters

Abstract The ambiguity in the crater density of the lunar surface formed before ∼4.0 Ga, primarily resulting from extensive resurfacing processes such as mare volcanism and basin ejecta deposition, has led to long‐standing debates about the lunar early impact flux and chronology. Although several correction approaches have been proposed to improve the accuracy of the crater density estimation on the ancient surface, studies directly constraining these values through the recovery of buried impact craters remain limited. In this study, we aim to identify the buried craters covered by mare basalt flooding and re‐estimate the crater cumulative size‐frequency distributions of ancient basins and surfaces to provide more accurate constraints on the lunar impact flux before ∼4.0 Ga. We first conduct the gravity investigation using the high‐spatial‐resolution gravity model, revealing more than 300 buried craters with diameters less than 200 km. After compiling the crater catalog, we perform cumulative size‐frequency distribution measurements for basins with diameters greater than 650 km. The re‐estimated cumulative crater density, combined with the isotopic age of ancient basins, indicates a higher impact flux during the pre‐Nectarian and Nectarian periods than previous estimates. According to the updated crater density on the ancient surface, we established a new lunar impact flux model for the period of 3.5–4.5 Ga, which suggests that an impact spike likely began around the time of the Imbrium impact event.