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

protoplanetary

ˌprō-tō-ˈpla-nə-ˌter-ē 

adjective

Examples of protoplanet in a Sentence

Recent Examples on the Web

Ryugu is believed to have once been part of a larger protoplanet, but was blasted off due to an impact at some point in the solar system's history. —Keith Cooper, Space.com, 1 July 2025

These disks are common around younger stars like RIK 113, and will eventually condense due to the star's gravitational pressure, forming larger objects that will create the beginnings of a planet, known as a protoplanet. —Kenna Hughes-Castleberry, Space.com, 11 June 2025

But back then, only the young protoplanets beyond the ice line were cold enough to have it. —Lucas Brefka, The Conversation, 19 May 2025

Early in the history of the solar system, a massive protoplanet plowed into a young Earth. —Nola Taylor Tillman, Space.com, 8 May 2025

Word History

First Known Use

1949, in the meaning defined above

Rhymes for protoplanet

• pomegranate
• gannet
• granite
• planet
• intranet

Kids Definition

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

protoplanetary

ˌprōt-ō-ˈplan-ə-ˌter-ē 

adjective