Planet formation is the growth of planets from material around a young star. Solid grains in a protoplanetary disk can collide and stick through protoplanetary dust coagulation, concentrate into planetesimals, and build planetary embryos. Their gravity modifies further encounters through gravitational focusing, while collisions can merge or fragment the bodies.
In core accretion, a growing solid core can acquire a gas envelope if the gas can cool and remain bound. Direct formation from a self-gravitating gas concentration is a distinct route involving gravitational instability of an astrophysical disk. Planetary migration and planetary scattering can subsequently change the orbits, so present location alone does not identify formation location. Planetary differentiation then reorganizes the material inside an assembled body.
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