Protoplanet

A protoplanet is a growing planetary body within a planet-forming system. It has accumulated enough mass for gravity to strongly influence subsequent collisions and accretion, while its final orbit, composition and mass may still change substantially.

Accreting a small mass $\Delta m$ onto a body of mass $M$ and radius $R$ can release energy of order $GM\Delta m/R$. Heating, melting and chemical differentiation can therefore accompany growth. A protoplanet may continue to accumulate, merge with another body, lose material or be scattered; the name describes a stage of evolution rather than guaranteeing a particular final planet.