A 3D hybrid simulation study of the electromagnetic field distributions in the lunar wake

As a consequence of its lack of a thick atmosphere and an ionosphere, the interaction of the solar wind with the Moon is characterized by the direct impact of the solar wind on its sunward hemisphere. This absorption effect produces a near-vacuum in the wake immediately behind the Moon. The absence of a global magnetosphere and the low electrical conductivity further leads to the free passage of the interplanetary magnetic field (IMF) through the lunar interior. This classic scenario of the solar wind�Moon interaction was established by the very first plasma measurements in the lunar environment made by the Explorer 35 spacecraft (Lyon et al., 1967; Schubert and Lichtenstein, 1974). The wake region is gradually filled in by the diffusion of solar wind protons into the zone of density depletion. As described in the early analyses by Michel (1968) and Whang and Ness (1970), the expansion of the solar wind plasma into the wake is accompanied by rarefaction waves. At the same time, the magnetometer experiment on Explorer 35 detected the existence of a field reduction zone at the wake boundary surrounding the central region, with magnetic field enhancement up to a factor of 1.4 in comparison to the value in the ambient solar wind (Colburn et al., 1967). Some of these features were repeatedly observed at different distances in the lunar wake by the Win