The Lunar Polar Icy Regolith and Possible Moonflows

The Lunar CRater Observation and Sensing Satellite (LCROSS) experiment, which created a crater 27 meters in size, showed that up to 6 percent water appear to be present in the permanently shadowed region (PSR) of Cabeus crater. Past independent theoretical analyses have concluded that some water molecules released elsewhere on the lunar surface can migrate to permanently shadowed areas. The estimated amount of ice, ice fragments, and other volatiles located in the polar regions in and beneath the regolith at depths of several meters may be still affected by significant uncertainties. Data from the Kaguya mission provide strong evidence for active plumes of water vapor erupting from polar regions outside the PSRs to heights of several km. These plumes appear to originate from subsurface ice located beneath the regolith surface at depths of approximately 20 cm. On the other hand, the polar highlands exhibit a relative deficit of craters larger than 25 meters, which may be caused by impact-melted ice lubricating regolith that flowed into initial crater depressions. At both the north and south poles of the Moon, signs of possible short-lived flows of liquid water-bearing material "moonflows" are presented in this work. Limited hydrous alteration of regolith ultra-fines to phyllosilicates may have occurred as these moonflows cooled.