Kinetic simulations of kilometer-scale minimagnetosphere formation on the Moon

Abstract Kinetic simulations are used to examine the solar wind’s interaction with a 3 km wide region of strong crustal dipole magnetization on the Moon. In contrast with recent hybrid and implicit particle-in-cell simulations of magnetic anomalies that have aimed to resolve electric fields over several tens of kilometers, kinetic simulations reveal a much smaller scale regime in which magnetically driven ion-electron separation can generate a kV potential difference over a height of less than 200m. The resulting electric field structure varies considerably between dawn and noon (when the solar wind flows, respectively, horizontally across the surface and vertically down from above) and is strong enough to reflect some ions back into space, consistent with spacecraft observations. Ion velocity and energy distributions are extracted near the surface and are used to derive maps of ion flux and impact energy, and the effects on sputtering and defect formation within the regolith are discussed. However, considerable uncertainty remains in how the surface ion flux evolves throughout a lunar day and how the plasma-surface-magnetic field interaction changes with respect to different magnetic topologies. 1