Properties of Electron Phase Space Holes in the Lunar Plasma Environment

The spatial distribution and amplitudes of electron phase space holes observed in the plasma environment near Earth's Moon are presented. When the Moon is in the solar wind, the overwhelming majority of holes in its vicinity occur in its wake, and we attribute them to an instability caused by distortion of the electron distribution by the wake, as predicted by theory. Approximately 30% of these wake holes are statistically correlated with observed magnetic discontinuities nearby, which implies that external effects can influence and trigger these wake instabilities, yet the wake is the determining factor. When the Moon is deep in the Earth's magnetotail, and no detectable lunar wake is present, the hole occurrence is greatly reduced and is distributed approximately homogeneously about the Moon, implicating a different production mechanism. Near the boundary of the magnetotail, homogeneously occurring holes are more frequent, showing that other instabilities associated with the magnetopause region are also active. These results demonstrate ways in which the Earth's Moon is a unique plasma physics laboratory where plasma wake physics and electron instabilities can be studied in detail.