Possibility of inverse sheath in the lunar nightside due to secondary electron emission

Abstract

This study assesses the plasma sheath formation on the night side of the Moon when exposed to highly energetic ambient plasma. The calculations indicate that the secondary electron emission (SEE) due to highly energetic plasma electrons leads to the formation of the inverse sheath around the positively charged lunar surface on the night side, where a traditional Debye sheath with a high negative surface potential is anticipated. Analytical formulation of Debye sheath and inverse sheath formation is given considering Maxwellian plasma and secondary electrons and cold ions. For a given SEE yield, a temperature regime is predicted where the inverse sheath is possible.