 Some impacts by big space rocks may punch through the crust, allowing more water to reach the surface. And a recent study by scientists at the University of Texas found that an impact doesn't have to go all the way through the ice. If it rams halfway through, it can melt enough ice for the warm water to melt the rest of the way to the ocean. That may allow some of the ocean water to reach the surface, helping Europa keep its youthful appearance.