The orbit of Jupiter's Moon Io is fairly elliptical, bringing the moon closer to and further from Jupiter every few days. Tides raised on Io by Jupiter alternately strengthen and weaken, stretching and compressing the satellite and causing its interior to heat up and melt. Some of this molten material reaches Io's surface through regularly-erupting volcanic vents that are ubiquitous on Io. Flowing lava continually "repaves" Io's surface erasing any earlier impact craters. Unlike every other solid body in the Solar System, Io has no known impact craters.