protoplanet
noun
pro·to·plan·et
ˈprō-tō-ˌpla-nət 
: 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
Examples of protoplanet in a Sentence
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It's thought to be the result of collisions with various protoplanets and other massive objects during the formation of the solar system billions of years ago, according to NASA.
—
Janet Loehrke, USA Today, 17 June 2026
Beyond the question of how an angrite-spawning protoplanet could have arisen so early on, the details of its demise are unknown.
—Jenna Ahart, Scientific American, 9 June 2026
Based on all of these factors, astronomers now believe NWA 12774 once belonged to a young protoplanet with a radius anywhere from 621 to 2,050 miles wide.
—Andrew Paul, Popular Science, 3 June 2026
And that Earth, about 50 million years after the Sun became a full-fledged star, actually collided with another large protoplanet, kicking up a cloud of debris that wound up creating our modern Earth-Moon system.
—Big Think, 17 Apr. 2026
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Janet Loehrke, USA Today, 17 June 2026
Beyond the question of how an angrite-spawning protoplanet could have arisen so early on, the details of its demise are unknown.
—Jenna Ahart, Scientific American, 9 June 2026
Based on all of these factors, astronomers now believe NWA 12774 once belonged to a young protoplanet with a radius anywhere from 621 to 2,050 miles wide.
—Andrew Paul, Popular Science, 3 June 2026
And that Earth, about 50 million years after the Sun became a full-fledged star, actually collided with another large protoplanet, kicking up a cloud of debris that wound up creating our modern Earth-Moon system.
—Big Think, 17 Apr. 2026
See All Example Sentences for protoplanet
Cite this Entry
“Protoplanet.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/protoplanet. Accessed 23 Jun. 2026.
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protoplanet
noun
pro·to·plan·et
ˈprōt-ō-ˌplan-ət
: a whirling mass of gas that rotates around a star and is believed to become a planet
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