Lunar subsurface charging: GCR and SEP effects

The phenomenon of galactic cosmic rays (GCRs) and solar energetic particles (SEPs)-induced internal charging and discharging within the lunar subsurface has been addressed. As GCRs and SEPs penetrate the lunar subsurface, a finite amount of charge develops at each depth up to the maximum penetration depth—it creates a depth profile of the charge distribution, and induces a localized electric field. The subsurface electrical conductivity may further rearrange this distribution by dissipating these charges over time. The volume charge density and electric field profiles are derived by simultaneously solving continuity and Poisson's equations. In lunar permanently shadowed regions, GCR creates a steady-state electric field of 320 and 115 V m−1 during periods of solar minima and maximum values, respectively. For SEPs, the model predicts both positive and negative electric fields beneath the surface on the order of approximately 107 V m−1 at specific depths with potential significance of dielectric breakdown that contributes to space weathering on the Moon.