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

This crystalline material was the first solid matter in the solar system, and was bound together by gravity to create mile-wide planetesimals, the seeds of the terrestrial planets like Earth and the cores of solar system gas giants like Jupiter. —Robert Lea, Space.com, 16 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

In this way, vast amounts of iron and nickel alloys were trapped deep inside these planetesimals, forever hidden from direct scrutiny. —IEEE Spectrum, 27 Dec. 2021

Instead, the researchers suggest this gas was originally locked in solid minerals like quartz within asteroid-size planetesimals that crashed into the young planet. —Sharmila Kuthunur, Space.com, 4 June 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