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