Ceres is possibly a surviving protoplanet ( planetary embryo ) , which formed 4 @.@ 57 billion years ago in the asteroid belt . Although the majority of inner Solar System protoplanets ( including all lunar- to Mars @-@ sized bodies ) either merged with other protoplanets to form terrestrial planets or was ejected from the Solar System by Jupiter , Ceres is thought to have survived relatively intact . An alternative theory propose that Ceres formed in the Kuiper belt and later migrated to the asteroid belt . The discovery of ammonia salts in Occator crater support an origin in the outer Solar System . Another possible protoplanet , Vesta , is less than half the size of Ceres ; it suffered a major impact after solidifying , losing ~ 1 % of its mass .