Most known large icy moons belong to giant planets, whose orbits lie beyond the Solar System's frost line; the remainder (such as Charon and Dysnomia) formed around dwarf planets such as Pluto and , typically in large impacts not unlike the impact thought to have formed Earth's moon. In the case of icy gas giant satellites, an additional requirement is that a moon did not form in the inner region of a proto-satellite disk, which is too warm for ices to condense.
