Induced magnetosphere of the Moon. 1. Theory

An analytic solution for the magnetic field in the space defined by a spherical moon and its downstream cylindrical cavity formed by the solar wind is derived for interplanetary magnetic fields both parallel and perpendicular to the cavity axis. By superposition, the solution is obtained for arbitrary orientations of the interplanetary field. The theory is quasi-static and is formulated in terms of a scalar magnetic potential. Thus the moon model consists of a core of arbitrary size and infinite electrical conductivity surrounded by a nonconducting shell; the cavity volume is assumed to be nonconducting. The variation of the magnetic field on the lunar surface, both on the sunlit and on the dark side hemispheres, and on the cavity boundary is presented for various values of core radius. The solution yields the distribution of currents on the lunar sunlit surface and the surface of the cavity. Theoretical transfer functions are presented and their variations with position on the lunar surface and with core size are discussed.