First direct detection of ions originating from the Moon by MAP-PACE IMA onboard SELENE (KAGUYA)

The Moon has no global intrinsic magnetic field and only has a very thin atmosphere. Ion measurements made from lunar orbit provide us with information regarding interactions between the solar wind and planetary surface, the surface composition through secondary ion mass spectrometry and the source and loss mechanisms of planetary tenuous atmosphere. An ion energy mass spectrometer MAP-PACE IMA onboard a lunar orbiter SELENE (KAGUYA) has detected low-energy ions at 100-km altitude. The MAP-PACE measurements have elucidated that the ions originate from the lunar surface and exosphere and that the ions are at least composed of He⁺, C⁺, O⁺, Na⁺ and K⁺. Following the discovery of the lunar Na and K exospheres by the ground-based observation, MAP-PACE IMA have found the He, C and 0 exospheres around the Moon.