planetesimal

noun

plan·​e·​tes·​i·​mal ˌpla-nə-ˈte-sə-məl 

-zə-məl

: any of numerous small celestial bodies that may have existed at an early stage of the development of the solar system

Examples of planetesimal in a Sentence

Recent Examples on the Web

Using computer models to simulate Jupiter's early, rapid growth, the researchers discovered that its gravity whipped the planetesimals into a frenzy, causing the high-speed collisions that created the chondrules. —Stefanie Waldek, Space.com, 27 Aug. 2025

But scientists have always known that the first solid parts of planets, known as planetesimals, must form much earlier. —Eric Lagatta, USA Today, 18 July 2025

While astronomers have previously seen young discs that contain newborn, massive planets like Jupiter, it was not yet proven that the first solid parts of nascent planets, known as planetesimals, must form further back in time, at earlier stages, McClure said. —Julia Jacobo, ABC News, 17 July 2025

For example, the first mile-sized planetesimals in our solar system–which grew to become celestial bodies like Earth or Jupiter’s core–formed right after the condensation of these same crystalline minerals. —Laura Baisas, Popular Science, 16 July 2025

Word History

Etymology

planet + -esimal (as in infinitesimal)

First Known Use

1903, in the meaning defined above

Phrases Containing planetesimal

• planetesimal hypothesis

Rhymes for planetesimal

• hexadecimal
• decimal
• infinitesimal

Kids Definition

planetesimal

noun

plan·​e·​tes·​i·​mal ˌplan-ə-ˈtes-ə-məl 

-tez-

: one of numerous small solid heavenly bodies which may have existed at an early stage of the development of the solar system and from which the planets may have been formed