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protoplanet

American

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

noun

Astronomy.

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

protoplanet British

/ ˌprəʊtəʊˈplænɪt /

noun

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

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Etymology

Origin of protoplanet

First recorded in 1945–50; proto- + planet

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

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

The chaos would have influenced the size, location, and composition of the rocky planets, and many researchers believe it could also explain why a Mars-size protoplanet crashed into Earth around this time, creating the Moon.

From Science Magazine • Apr. 16, 2024

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

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023