In planetary science, planetary differentiation is the process of separating out different parts of a planetary body where the planetary body develops into distinct layers. The denser materials of a planet sink to the center, while less dense materials rise to the surface. Such a process usually creates a core and mantle. Sometimes a crust forms on top of the mantle. The process of planetary differentiation has happened on planets, dwarf planets, the asteroid 4 Vesta, and natural satellites (such as the Moon).