| Astrophysics (Index) | About |
The term protoplanet, a term used in planet formation discussions, naturally refers to objects in a system that will later evolve into planets. (The definition of planet does vary: for some purposes it is based on the object's structure whereas for others, it also includes the object's effect on the surrounding system, specifically, the object's ability to protect a "lane" around its orbit.)
The term protoplanet is also more-specifically used for objects that have already become more planet-like for showing planetary differentiation, i.e., having developed internal layers, implying stratification of a melted interior at some point in their history. Some asteroids, such as Ceres, Pallas, and Vesta fit this description.
However, the above usages are not universal: the term protoplanet is also sometimes used for any object within any stage of the formation of a single planet, or that is within some particular specified stage.