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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 quotations examples
Tyrix, one of the largest objects in Thal's asteroid belt, is a metallic asteroid with an iron-nickel core under a rocky olivine mantle. It is possibly a remnant protoplanet prevented from forming into anything bigger by gravitational disturbances from Xerceo.
2012, BioWare, Mass Effect 3 (Science Fiction), Redwood City: Electronic Arts, PC, scene: Tyrix