Lunar Plasma Environment

The Moon has no global intrinsic magnetic field and thick atmosphere. These properties of the Moon significantly affect the interaction between the solar wind and the Moon. Recent in-situ measurements of low energy ions around the Moon by Kaguya (SELENE) have revealed dynamic aspect of the lunar plasma environment. Besides the solar wind, there exist four clearly distinguishable ion populations on the dayside of the Moon: (1) solar wind protons backscattered at the lunar surface, (2) solar wind protons reflected by magnetic anomalies on the lunar surface, (3) reflected/backscattered protons picked-up by the solar wind, 4) ions originating from the lunar surface/lunar exosphere. In the lunar wake region, two types of ion entry into the lunar wake (Type-I entry and Type-II entry) are observed. The newly obtained knowledge about the lunar plasma environment by Kaguya can be applied to the understanding of the plasma environment around non-magnetized solar system objects.