Planetary Formation Constrained by Collisions between Millimeter-sized Lunar Particles and Lunar Surface from Chang’E-4 Mission

Abstract Exploring low-velocity collisions is crucial for unraveling intricate processes in planetary formation, particularly the bouncing barrier that impedes the aggregation of dust into sizable planetesimals. Observational data on extraterrestrial collision processes remain limited. Here, we quantify collision parameters for millimeter-sized lunar particles impacting the porous lunar surface at speeds ranging from 2.3 to 76.8 cm s −1 under lunar gravity, leveraging Chang’E-4 imagery. This study represents the first tangible acquisition of extraterrestrial collision data. Our findings reveal that speeds exceeding 7.0 ± 2.6 cm s −1 result in bouncing, yielding coefficients of restitution ranging from 0.51 to 0.80. In contrast to particle–particle collisions, interactions between lunar particles and the porous lunar surface exhibit a heightened sticking threshold speed, facilitating particles to overcome the bouncing barrier. Diminished coefficients of restitution expedite collapses, significantly reducing dust cloud collapse times. This implies that porous particles foster favorable conditions for overcoming the bouncing barrier and promoting growth. Our results unveil the conducive conditions enabling extraterrestrial samples to overcome the bouncing barrier, advancing our comprehension of planetary formation and providing crucial observational constraints for relevant theories.