Europa
Europa, the brightest of Jupiter’s Galilean satellites, may have a surface of thin ice crust overlying water or softer ice, with large-scale fracture and ridge systems appearing in the crust. Europa has a density about three times that of water, suggesting it is a mixture of silicate rock and some water. Very few impact craters are visible on the surface, implying a continual resurfacing process, perhaps by the production of fresh ice or snow along cracks and cold glacier-like flows.