Plasma and Electric Environment Within Lunar Pits and Caves Exposed to the Solar Wind

Abstract We have assessed the plasma and electric environment within a lunar pit and its connected subsurface cave utilizing plasma simulations. It is shown that adjacent illuminated and shadowed regions along the interior walls of the pit induce differential charging, exceeding the levels typically observed on open planar surfaces. Within the illuminated sectors, the incident solar wind (SW) proton flux dominates over the electron counterpart. In this regime, photo‐emitted and secondary electrons imported from adjacent illuminated surfaces suppress excessive positive charging by acting as negative charge carriers to compensate for the scarce SW electrons. Deep inside the cave, a residual population of SW electrons induces significant negative charging despite their small flux. The relative significance of minor current components, such as ion‐induced secondary electrons and protons scattered off the lunar regolith, is also enhanced therein. The local equilibrium potential is thus governed by the current balance of these multi‐species particle populations.