Statistical Study of Moon-originating Ions in the Solar Wind

When the Moon was in the solar wind, Kaguya frequently observed ions originating from the Moon. To examine their statistical properties, we analyzed Kaguya low-energy particle data obtained from January 2008 to June 2009. These Moon-originating ions were mainly detected on the lunar far side, with energies ranging from 20 to 300 eV. At the time of their creation at or near the lunar surface, the ions are expected to have energies of only a few eV or less. Consequently, the ions observed by Kaguya are energized by a factor of 10 to 100. Time-of-flight (TOF) analyses indicate that these ions consist of C⁺, O⁺, Na⁺, Al⁺, K⁺, and Ar⁺. We found a pronounced asymmetry between the Northern and Southern Hemispheres in the detection rate of Moon-originating ions. These ions are concentrated mainly at high northern latitudes. To investigate the energization and asymmetric spatial distribution of Moon-originating ions, we perform test-particle simulations and discuss where and how the ions are energized and what produces the asymmetry.