Anticipated electrical environment within permanently shadowed lunar craters

• Published in: Journal of Geophysical Research. B. Solid Earth 2010-03, Vol.115 (E3), p.n/a
• Main Authors: Farrell, W. M., Stubbs, T. J., Halekas, J. S., Killen, R. M., Delory, G. T., Collier, M. R., Vondrak, R. R.
• Format: Article
• Language: English
• Subjects: Craters; Earth sciences; Earth, ocean, space; Exact sciences and technology; Lunar craters; Moon; Mountains; Obstacles; Obstructions; Planetology; Planets; Solar wind; Surface chemistry; surface potential; Voids
• ISSN: 0148-0227; 2169-9097; 2156-2202; 2169-9100
• DOI: 10.1029/2009JE003464

Shadowed locations near the lunar poles are almost certainly electrically complex regions. At these locations near the terminator, the local solar wind flows nearly tangential to the surface and interacts with large‐scale topographic features such as mountains and deep large craters. In this work, we study the solar wind orographic effects from topographic obstructions along a rough lunar surface. On the leeward side of large obstructions, plasma voids are formed in the solar wind because of the absorption of plasma on the upstream surface of these obstacles. Solar wind plasma expands into such voids, producing an ambipolar potential that diverts ion flow into the void region. A surface potential is established on these leeward surfaces in order to balance the currents from the expansion‐limited electron and ion populations. We find that there are regions near the leeward wall of the craters and leeward mountain faces where solar wind ions cannot access the surface, leaving an electron‐rich plasma previously identified as an “electron cloud.” In this case, some new current is required to complete the closure for current balance at the surface, and we propose herein that lofted negatively charged dust is one possible (nonunique) compensating current source. Given models for both ambipolar and surface plasma processes, we consider the electrical environment around the large topographic features of the south pole (including Shoemaker crater and the highly varied terrain near Nobile crater), as derived from Goldstone radar data. We also apply our model to moving and stationary objects of differing compositions located on the surface and consider the impact of the deflected ion flow on possible hydrogen resources within the craters.