Comments on “Is the Moon really as smooth as a billiard ball?…”

Hapke and Cassidy (1978), in describing their ideas concerning sputter deposition, have criticised a number of aspects of a model for chemical fractionation and metallic iron production which is based on preferential sputtering. Questions referring to the fate of sputtered atoms, the surface roughness of the moon and the existence of metal rich layers may all be answered. Doubts may be expressed concerning the validity of some arguments used by Hapke and Cassidy since the regolith in their model is predominantly static with only episodic turnover. Some effects associated with gardening and comminution processes, and solar wind irradiation angle need to be considered. Chemical fractionation and metallic iron formation at the lunar surface is likely to be a complex process; preferential sputtering, sputter deposition and agglutination may all be involved.