Impact into lunar regolith inhibits high-velocity ejection of large blocks

Our data suggest that the presence of a layer of regolith covering the lunar surface results in a portion of the high-velocity ejection phase occurring in the fine-grained regolith, reducing the population of large blocks available for ejection at high velocities. This conclusion is supported by a study of boulder distributions around 10 lunar craters. The boulder ejection velocities were calculated by applying crater ejecta scaling relations and assuming a ballistic trajectory. Regolith depths were estimated by analyzing the morphology of small craters (tens of meters in diameter). Because both meteorites and distant secondary craters are produced by solid fragments within the highest-velocity ejecta, we conclude that less regolith cover at the impact site will favor the formation of meteorites and distant secondary craters.