Possibility of the Presence of S, SO₂, and CO₂ at the Poles of the Moon

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.