Ultraviolet photodesorption from water ice

The absolute desorption yield of low temperature (35–100 K) water ice under irradiation with Lyman-α (121.6 nm) photons. and its dependence on ice temperature and irradiation dose are measured. It is found that photodesorption can account for the absence of ice on grains in diffuse interstellar clouds, is an important factor determining the life of ice mantles in molecular clouds, and exceeds solar wind ion erosion and sublimation of ice grains in the outer solar system.