The presence of volatiles near the lunar poles is considered. The chemical composition of a lunar atmosphere temporarily produced by comet impact is analyzed during the day and night. C-rich and long-period comets are insufficient sources of water ice on the Moon. O-rich short-period comets deliver significant amounts of H2O, CO2, SO2, and S to the Moon. An observable amount of polar hydrogen can be delivered to the Moon by a single impact of an O-rich short-period comet with diameter of 5 km in the form of water ice. The areas where CO2 and SO2 ices are stable against a thermal sublimation are estimated to be 300 and 1500 km2, respectively. If water ice exists in the 2cm top regolith layer, CO2 and SO2 ices can be stable in the coldest parts of permanently shaded craters. The delivery rate of elemental sulfur near the poles is estimated to be 106 g yr-1. The sulfur content is estimated to be as high as 1 wt % in the polar regions. The SELENE gamma-ray spectrometer can detect sulfur polar caps on the Moon if the sulfur content is higher than 1 wt %. This instrument can check the presence of hydrogen and minerals with the unusual chemical composition at the lunar poles.
|ジャーナル||Publications of the Astronomical Society of Japan|
|出版ステータス||Published - 2003|
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