protoplanet

American  

[proh-toh-plan-it] / ˈproʊ toʊˌplæn ɪt /

noun

Astronomy.

1. the collection of matter, in the process of condensation, from which a planet is formed.

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protoplanet British  

/ ˌprəʊtəʊˈplænɪt /

noun

1. a planet in its early stages of evolution by the process of accretion

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Etymology

Origin of protoplanet

First recorded in 1945–50; proto- + planet

Example Sentences

About 4.5 billion years ago, a dramatic event transformed the young Earth when a large protoplanet known as Theia struck our planet.

From Science Daily • Nov. 23, 2025

A giant collision between the young Earth and a smaller protoplanet has long been the prevailing theory for the Moon’s formation.

From Scientific American • Nov. 2, 2023

Perhaps, the new study suggests, those clumps came from the protoplanet that smashed into Earth, leading to the moon’s formation.

From National Geographic • Nov. 1, 2023

The most popular theory says that about 4.5 billion years ago, a Mars-size protoplanet slammed into Earth.

From New York Times • Nov. 1, 2023

For decades, scientists have wondered whether Psyche could be the denuded metal core of a larger protoplanet.

From Science Magazine • Oct. 13, 2023