Schematic diagram showing the orientation between water ice (blue), regolith (brown circles), and salts (gray circles) in the standard Knudsen diffusion water ice loss model (left panel), the salts-alone model where the ice-table depth controls the amount of salt from which water vapor can escape (middle panels) and combined model where the two pressures between water-ice-derived vapor and salt-derived water vapor equal the saturation vapor pressure at the ice/regolith interface.