Identification of plumes of ice/gas mixture in the lunar polar region / Prof Makiko Ohtake (Institute for Planetary Materials, Okayama University)

Abstract: Condensation of water ice in the lunar polar region has been reported. However, the origin and amount of water remain unknown because of varying results among reported derived by different observation technique. Therefore, information on the migration mechanism of water is key for understanding the origin, amount, and delivery process of water to the Earth¡VMoon system. To solve the issue, we analyzed spectral data derived by SELENE/Kaguya Spectral Profiler (SP) at the lunar polar region and found the migration process observed as plumes of water ice/gas mixtures ejected from the lunar surface to space. The identified spectra having water and other volatile absorption were fund at the nonpermanent shadowed region during the nighttime when no illumination reached the lunar surface. And volatile materials were repeatedly identified in some locations and most of the plume events did not coincide with the major meteoroid streams. Based on the timing, duration, location, and temperature simulations we propose that impact events are not their main origin, but the volatile sublimation from the subsurface is the most plausible scenario. This finding is significant for understanding migration and distribution of the water ice at the lunar polar region.