Definition of protoplanet in English:

protoplanet

Line breaks: proto|planet
Pronunciation: /ˈprəʊtəʊˌplanɪt
 
/

noun

Astronomy
A large body of matter in orbit around the sun or a star and thought to be developing into a planet: this analysis supported the view that the moon originated from a glancing collision between the earth and another protoplanet 4,500 million years ago
More example sentences
  • Learning more about the protoplanet won't be fast or easy.
  • The protoplanet candidate orbits about 70 times further from its star than Earth does from the Sun.
  • It isn't clear how the latest suspected protoplanet is being formed.

Origin

1940s: from proto- + planet.

Definition of protoplanet in:

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