5:15 PM - 7:15 PM
[PPS08-P11] Anticipated Micro-scale Electrostatic Structures formed on the Rough Lunar Surface exposed to Space Plasma
Keywords:Moon, Space plasma, Surface charging, Electrostatic environment
Preparation for lander exploration of the Moon is rapidly increasing, hence, there is a strong and urgent demand for accurate understanding of the electrostatic environment of the lunar surface and assess any potential hazard it might pose. 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 an insulating and rough regolith surface significantly alters the charging conditions. The topography effects not only cause a change in the value of the equilibrium, it can also significantly alter the current equilibration regime itself. Even a commonly accepted ordering of plasma current magnitudes, i.e., Jpe > Je > Ji, where Jpe, Je, and Ji represent photoelectron, background electron, and ion currents to an uncharged surface, respectively, 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; Nakazono and Miyake, 2025]. Deep depressions, which can be expected to exist on irregular lunar surfaces, exhibit a charging state caused by an anomalous current magnitude ordering in which Ji > Je.
The distinctive feature of the ion-driven charging is that surface patches with positive charges develop only in the depths of the depression. The shallow surface in the vicinity of the depression exhibits a pronounced accumulation of negative charges, as incoming electrons are preferentially collected at these locations. This indicates a peculiar charging effect as the consequence of localized charge separation that is generated by the specific surface morphology. Based on the results, we argue that the electrostatic environment near the lunar surface will be characterized by localized deviations from the spatially averaged potential. This perspective would be important because the potential difference over a small distance indicates an intense electrostatic field. Human activities on the Moon will take place in just such a complex electrostatic environment. This talk will summarize our current understanding the electrostatic charging environment on the Moon, and discuss the direction of future charging studies for upcoming lunar missions.
The distinctive feature of the ion-driven charging is that surface patches with positive charges develop only in the depths of the depression. The shallow surface in the vicinity of the depression exhibits a pronounced accumulation of negative charges, as incoming electrons are preferentially collected at these locations. This indicates a peculiar charging effect as the consequence of localized charge separation that is generated by the specific surface morphology. Based on the results, we argue that the electrostatic environment near the lunar surface will be characterized by localized deviations from the spatially averaged potential. This perspective would be important because the potential difference over a small distance indicates an intense electrostatic field. Human activities on the Moon will take place in just such a complex electrostatic environment. This talk will summarize our current understanding the electrostatic charging environment on the Moon, and discuss the direction of future charging studies for upcoming lunar missions.