Irradiation and accretion of solids in space based on observations of lunar rocks and grains

Abstract

Clues to a wide range of questions relating to the origin and evolution of the solar system and dynamic physical and electromagnetic processes occurring concurrently and in the past in our galaxy have been provided by a study of the lunar samples. This information is deduced from a variety of complementary physical and chemical evidence. In this presentation, greatest emphasis is laid on information based on the cosmogenic effects, i.e. those arising from interactions of low energy cosmic rays with lunar surface materials. This information is generally not obtainable from examinations of meteorite samples, except in the case of certain types termed gas-rich meteorites, due to loss of their surface regions by atmospheric ablation. The present discussions will concern the nature of experimental data to date and implications thereof to the charged particle environment of the Moon, ancient magnetic fields and the nature of, time scales involved in the irradiation and accretion of solids in space, based on lunar regolith dynamics. It becomes clear that there does not yet exist any consensus on the absolute values of charged particle or the meteorite fluxes, and also about the details of the evolution of the lunar regolith. This would be expected also considering that one is dealing with phenomena which range in size/energy scales over many orders of magnitude and that the techniques used for the studies were only recently developed in many cases. The complex history of evolution of lunar material is slowly being understood and it is a hope that a great deal of quantitative information will soon be available which will in turn allow discussion of evolution of solid bodies in the solar system.