Noun
English Wikipedia has an article on:protoplanetWikipedia
protoplanet (plural protoplanets)
An astronomical object, approximately the size of the Moon, formed from the mutual gravitational attraction of planetesimals; they are thought to collide with each other and slowly form planets
Because of this, some scientists refer to Vesta as a protoplanet. Source: Internet
Vesta's differentiation is one of the reasons why scientists consider it a protoplanet. Source: Internet