Ceres is a surviving protoplanet (planetary embryo) that formed 4.56 billion years ago, the only one surviving in the inner Solar System, with the rest either merging to form terrestrial planets or being ejected from the Solar System by Jupiter. However, its composition is not consistent with a formation in the asteroid belt. It seems rather that Ceres formed as a centaur, most likely between the orbits of Jupiter and Saturn, and was scattered into the asteroid belt as Jupiter migrated outward. The discovery of ammonia salts in Occator crater supports an origin in the outer Solar System. However, the presence of ammonia ices can be attributed to impacts by comets, and ammonia salts are more likely to be native to the surface.