Definition of protoplanet
: a hypothetical whirling gaseous mass within a giant cloud of gas and dust that rotates around a sun and is believed to give rise to a planet
protoplanetaryplay \ˌprō-tō-ˈpla-nə-ˌter-ē\ adjective
Recent Examples of protoplanet from the Web
Eventually, some accrete enough mass to form protoplanets.
That sharp divide likely comes from the planet formation process, Fulton said: Planets' rocky cores form from smaller pieces, and then the protoplanet's gravity attracts hydrogen and helium gas.
Though that’s not part of Dawn’s current mission, excitement about the potential for life on the protoplanet could one day fuel future exploration—and a better understanding of what once happened on Earth.
The idea is that a large protoplanet called Theia bumped into Earth about 4.4 billion years ago, knocking off a moon-sized cloud of debris that eventually coalesced into our favorite satellite.
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First Known Use of protoplanet
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Britannica.com: Encyclopedia article about protoplanet
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