Influence of Magnetospheric Plasma Environment on Surface Charging of the Lunar South Pole

Abstract

The lunar south pole is a key candidate region for future lunar exploration and base construction, but its charging characteristics under real topographic conditions and dynamic plasma environments remain insufficiently understood. A high-fidelity terrain model of the lunar south pole spanning 86°S-90°S was constructed from optimized LRO/LOLA elevation data. Surface charging evolution over half a lunar orbital cycle was then simulated with a finite element-BP neural network scheme, using lunar-phase-dependent plasma inputs encompassing plasma parameters of solar wind and diverse Earth magnetospheric zones. The results show that south polar topography strongly regulates surface charging. Higher potentials appear on windward terrains, whereas lower potentials occur in shielded leeward regions, leading to enhanced local electric fields at the tops of uplands and crater floor-wall boundaries. Significant potential differences between the crests and the middle of the downstream walls of various craters indicate that these regions are highly terrain-sensitive. When the Moon passes through Earth's magnetosphere, surface potential and electric field are roughly symmetric around 0° lunar phase. From the solar wind to the plasma sheet, surface potential generally decreases while electric field magnitude rises. Only in the narrow magnetotail lobe adjacent to the plasma sheet does the potential temporarily increase and the electric field weaken. In the plasma sheet, the surface potential can decrease to approximately -1000 V, and the domain's peak electric field reaches about 5 V/m. These findings provide references for landing site selection, rover path planning, and electrostatic protection of lunar surface equipment.