Lunar ejecta as the missing piece to resolving lunar cratering asymmetry

¹ State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau 999078, China
² School of Astronomy and Space Science, Nanjing University, 163 Xianlin Avenue, Nanjing 210046, China
³ Key Laboratory of Modern Astronomy and Astrophysics in Ministry of Education, Nanjing University, China

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 22 January 2026
Accepted: 19 March 2026

Abstract

The leading-trailing asymmetry in lunar crater distribution provides a critical record of inner Solar System dynamics, yet the long-standing discrepancy between the observed higher asymmetry and lower theoretical predictions indicates a gap in our understanding of the impactor population. This paper hypothesizes that lunar impact ejecta, which can enter Earth-like orbits and later exit, constitute a component that had previously been unaccounted for. Using numerical simulations, we found that ~25% of escaped ejecta will re-impact the Earth-Moon system within 3 Myr, with about 1.2% striking the Moon. Crucially, these lunar impacts exhibit an extreme leading-trailing asymmetry, with a ratio of 5.9. Our results indicate that the assumption of lunar ejecta, comprising ~15% of total impactors can indeed explain the observed asymmetry, leading to their recognition as active agents shaping the lunar impact record. This work provides new constraints on our understanding of the impact environment of the Earth-Moon system, with direct relevance to the interpretation of lunar geology, the transport of lunar material to Earth, and ongoing space exploration missions.