The moon Phobos, the larger of the two natural satellites of the planet Mars, is also thought to be a rubble pile bound together by a thin regolith crust about 100 m (330 ft) thick. A rubble-pile morphology may point towards an in situ origin of the Martian moons. Based on this, has been proposed that Phobos and Deimos may originate from a single destroyed moon. Alternatively, Phobos may have undergone repeated 'recycling,' having been torn apart into a ring before reaccreting and migrating outwards.