A new Monte Carlo model of lunar megaregolith development

A new Monte Carlo model is used to examine the development of the lunar megaregolith through impact cratering processes. The computer code incorporates some of the techniques used in earlier models; however, it also solves some notable problems in those earlier models. The difficult problem of “edge effects” in computer modeling has been resolved in this model. Additionally, more recent morphological information on crater geometries and ejecta blanket geometry are included in this model along with current information on the crater production function. The morphologies now contribute to the evolving landscape such that each new impact encounters a more topographically realistic terrain. This improved model predicts greater minimum megaregolith thicknesses than did the earlier models. The increase results mainly from three factors: (1) our use of the observed lunar highlands crater size-frequency curve as the production function, (2) the retention of topographic information as cratering proceeds, and (3) the differences in the crater bowl and ejecta geometries. If the 25 km seismic horizon on the moon is attributable to the bottom of the crater-excavated material, then the highlands appear to have suffered a bombardment of two to five times the number of craters presently preserved on the surface.