Plasma wake simulations and object charging in a shadowed lunar crater during a solar storm

• Published in: Journal of Geophysical Research: Planets 2012-10, Vol.117 (E10), p.n/a
• Main Authors: Zimmerman, M. I., Jackson, T. L., Farrell, W. M., Stubbs, T. J.
• Format: Article
• Language: English
• Subjects: astronaut; Astronauts; Computer simulation; Debye length; Electron energy; Electrons; Equivalent circuits; Implantation; Ion flux; Ion fluxes; Ions; lunar crater; Lunar craters; Lunar topography; Lunar wake; Mach number; Moon; Morphology; Planetology; Planets; plasma expansion; Plasma physics; plasma wake; Plasmas (physics); Solar storms; Solar wind; Solar wind ions; Space; Spatial distribution; Specific heat; Storms; Topography; Tribo charging; tribocharging; volatiles; Weather
• ISSN: 0148-0227; 2169-9097; 2156-2202; 2169-9100
• DOI: 10.1029/2012JE004094

Within a permanently shadowed lunar crater the horizontal flow of solar wind is obstructed by upstream topography, forming a plasma wake that electrostatically diverts ions toward the crater floor and generates a surface potential that can reach kilovolts. In the present work kinetic plasma simulations are employed to investigate the morphology of a lunar crater wake during passage of a solar storm. Results are cast in terms of leading dimensionless ratios including the ion Mach number, ratio of crater depth to plasma Debye length, peak secondary electron yield, and electron temperature versus electron impact energy at peak secondary yield. This small set of ratios allows generalization to a much wider range of scenarios. The kinetic simulation results are fed forward into an equivalent‐circuit model of a roving astronaut. In very low‐plasma‐current environments triboelectric charging of the astronaut suit becomes effectively perpetual, representing a critical engineering concern for roving within shadowed lunar regions. Finally, simulated ion fluxes are used to explore sputtering and implantation processes within an idealized crater. It is suggested that the physics of plasma miniwakes formed in the vicinity of permanently shadowed topography may play a critical role in modulating the enigmatic spatial distribution of volatiles at the lunar poles. Key Points Solar storms modulate lunar wake morphology Astronaut charging may become perpetual in PSRs Solar wind ions get into polar craters and affect volatile balance