Anomalous modes of lunar surface charging anticipated by numerical analysis

Preparations for the lander's exploration of the Moon are progressing rapidly, hence, there is an urgent need for an accurate understanding of the electrostatic environment of the lunar surface, in order to assess any potential hazards. The surface potential of the lunar dayside is on average a few to 10 V positive due to photoelectron emission in addition to the solar wind plasma precipitation. Recent studies, however, have shown that a rough, insulating regolith surface can significantly alter charging conditions. The topography effects not only cause a change in the equilibrium potential value, but they can also significantly alter the current balance regime itself. The commonly accepted ordering of plasma current magnitudes can be disrupted by considering certain classes of surface geometry. Our recent investigations have demonstrated such showcases [Miyake and Nishino, 2015; Nakazono and Miyake, 2023; 2025; Nakazono, Miyake, and Miloch, 2025]; deep depressions, which can be expected to exist on irregular lunar surfaces, exhibit a charging state caused by an anomalous ordering of plasma current magnitudes.

Our numerical study aims to explore and elucidate the detailed properties of such anomalous charging emerged on the rough surface of the Moon. We have performed parametric studies focusing on the dependence of the charging intensity on the solar wind conditions. Based on the results, we will discuss the conditions under which the localized, intense charging mechanism works (or not) on the airless planetary bodies. Furthermore, we will extend the discussion to recent inquiries into anomalous charging states under the influence of active potential perturbations induced by human activities on the Moon.