Water ice in primitive asteroids?

A short review of the literature dealing with possible signatures of ice in some asteroids is presented. The subject is poorly developed, even if in the last decade several authors started a spectroscopic survey of asteroids in the visible and near-infrared wavelengths in order to find ice features on asteroid spectra. Aqueous alteration of the mineral assemblages has been claimed for a number of B-, F- and for more than 50% of the observed C-type asteroids. The compositional and, consequently, the thermal structure of the asteroid belt supports the hypothesis that ices of volatile elements should be more abundant in the external region of the belt, where pristine materials have not undergone drastic modification processes after the accumulation in the planetesimal swarms between those of Mars and of Jupiter. As of today, there is no evidence of any water, water ice or aqueous alteration materials on the D-type asteroids, which are considered the least altered objects