Intensity and origin of the ancient lunar magnetic field

Abstract

There is now strong evidence that the Moon possessed a magnetic field between 4000 and 3200 Ma ago. The evidence for and origin of this field are discussed, and determinations of its intensity described. It is tentatively concluded that the field decreased from an initial intensity of about 1 G (10-4 T) during the above time interval, and the implications of the initial intensity and its decay for the origin of the field are discussed.