Low Energy Charged Particle Measurement by MAP-PACE Onboard KAGUYA

概要

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MAP-PACE (MAgnetic field and Plasma experiment - Plasma energy Angle and Composition Experiment) is one of the scientific instruments onboard the KAGUYA (SELENE) satellite. PACE consists of 4 sensors: ESA (Electron Spectrum Analyzer)-S1, ESA-S2, IMA (Ion Mass Analyzer), and IEA (Ion Energy Analyzer). ESA-S1 and S2 measure the distribution function of low energy electrons below 15keV, while IMA and IEA measure the distribution function of mass identified low energy ions below 28keV/q. Since KAGUYA is a three-axis stabilized spacecraft, a pair of electron sensors (ESA-S1 and S2) and a pair of ion sensors (IMA and IEA) are necessary for obtaining three-dimensional distribution function of electrons and ions. Low energy ion measurements on the lunar orbit have been realized more than 30 years after the Apollo period. In addition, nobody has ever measured the mass identified three-dimensional distribution function of low energy ions at 100km altitude. PACE discovered surprisingly active low energy ion environment around the Moon. Instead of being absorbed by the lunar surface, quite a large amount of solar wind ions are reflected back from the Moon. The reflected solar wind ions are accelerated above solar wind energy picked up by the electric field in the solar wind.