Saturation and equilibrium conditions for impact cratering on the lunar surface: Criteria and implications

A model based on first principles and laboratory results is presented for describing and evaluating long term effects of meteoritic impact against the lunar surface. The evolution of the cratered surface and concomitant regolith is calculated and compared with observations and analyses of Lunar Orbiter photographs. It is indicated that most craters are of impact origin, but gross differences in the apparent ages of surfaces in various units and regions of the moon imply that endogenic processes also must have been active, probably since the beginning of Precambrian time and, perhaps, as recently as a few million years ago.