At the news conference, which was held at NASA's Ames Research Center in Moffett Field, Calif., Feldman and other scientists described the observations and analyses that led them to conclude that crystals of water ice are scattered in small quantities throughout lunar soil in craters at the north and south poles that have regions permanently shaded from sunlight.
Scientists believe that water reaches the moon from impacting comets.
If a water molecule lands in one of these cold spots it becomes trapped, adhered to some particle of soil. Over the millenia, as the moon gets pummeled by a continual rain of small meteorites, the soil gets turned over and the ice crystals are mixed throughout. The data that point to the presence of water come from a neutron spectrometer developed and built at Los Alamos in partnership with the Southwest Research Institute. The question still to be pinned down is how much water is present. The first estimates based on a month's worth of data, and to be refined as Lunar Prospector continues its mission, is about one percent water in a given volume of soil.