Plasma electron temperature variability in lunar surface potential and in electric field under average solar wind conditions

Abstract

The Moon is immersed in plasma environment. The most interesting challenge of the lunar plasma– field environment is that it is alternatively dominated by the extended but variable outer atmosphere of the Earth – the magnetosphere – and by the extended but highly variable solar atmosphere – the solar wind. Understanding the plasma environment and its interaction with the lunar surface will be beneficial to both manned and robotic surface exploration activities and to scientific investigations. Presented is a preliminary map of variations of lunar surface electric potential over the day side and night side using probe equations and a discussion on dust dynamics in this E-field structure using the data from Electron Reflectometer in Lunar Prospector spacecraft during 1998–1999. On the day side, potential is around 5V and on the night side it reaches up to −82V. On the night side region, only highly energetic electrons can overcome this large negative potential. The variation at electron temperature (Te) strongly reflects in the surface potential. The potential reaches to a value of −82V for Te=58eV. Surface charging causes the electrostatic transport of charged dust grains. Dust grain size of 0.1μm shows a levitation height of 4.92m on lunar day side, 748m on terminator region and 3.7km on the night side. The radius of maximum sized grain to be lofted, Rmax, peaks at the terminator region (Rmax=0.83μm). At the transition region dust levitation is almost absent. This region is most suited for exploration activities as the region is free from hazards caused by lunar dust.