By varying the mass of icy spheres which collide with large ice blocks, we have determined the mass dependence of energy loss in such collisions. We find, at commercial deep freeze temperatures, that collisions at 1 cm/s become quite inelastic for small iceballs and that the rate at which elasticity decreases with decreasing mass roughly coincide with that predicted by a viscous dissipation model. If such a mass dependence persists at much lower temperatures, it could lead to very large effects in planetary ring systems (rings and dust, ice, surfaces, origin, and evolution). ¿ American Geophysical Union 1996