Solar wind proton reflection at the lunar surface: Low energy ion measurement by MAP‐PACE onboard SELENE (KAGUYA)

Interaction between the solar wind and objects in the solar system varies largely according to the settings, such as the existence of a global intrinsic magnetic field and/or thick atmosphere. The Moon's case is characterized by the absence of both of them. Low energy ion measurements on the lunar orbit is realized more than 30 years after the Apollo period by low energy charged particle analyzers MAP‐PACE on board SELENE(KAGUYA). MAP‐PACE ion sensors have found that 0.1%∼1% of the solar wind protons are reflected back from the Moon instead of being absorbed by the lunar surface. Some of the reflected ions are accelerated above solar wind energy as they are picked‐up by the solar wind convection electric field. The proton reflection that we have newly discovered around the Moon should be a universal process that characterizes the environment of an airless body.