Terrestrial-origin O+ ions below 1 keV near the Moon measured with the Kaguya satellite

Abstract In this study, we investigated terrestrial-origin O + ions below 1 keV around the Moon using data from the Kaguya satellite between December 2007 and June 2009. These terrestrial-origin low-energy O + ions were identified based on three parameters: the periodicity of O + ion count enhancement corresponding to Kaguya’s 2-h orbital period, the count ratio of O + ions to Na + and Al + ions, and the direction of ion bulk velocity in the Sun–Earth direction. We identified three intervals that included such O + ions: 14:30–20:30 UT on June 19, 2008, 19:00 UT on July 16, 2008 to 03:00 UT on July 17, 2008, and 14:00–24:00 UT on June 7, 2009. These intervals were found in the dawn sector, the dusk sector, and the midnight to dawn sector within the magnetotail, respectively. We examined the relation between geomagnetic storm conditions and increases in terrestrial-origin O + ion counts and found that all three intervals occurred during the late recovery phase of moderate/weak magnetic storms. Since moderately/weakly disturbed conditions (Dst = –40 nT to –20 nT) account for approximately 21% of the total time between 1957 and 2016, we suggest that low-energy O + ions from the Earth have a non-negligible impact on the ion composition and the ion mass density in the lunar plasma environment. Graphical abstract