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

Objects of this size are referred to as planetesimals — objects similar in size to many of the asteroids and comets in our solar system but much smaller than a dwarf planet like Pluto. —Prabhat Ranjan Mishra, Interesting Engineering, 20 Dec. 2025

Young star systems like Fomalhaut are estimated to be a hub of such violent collisions as space rocks, asteroids, and larger planetesimals, objects smaller than dwarf planets, slam into each other. —Robert Lea, Space.com, 18 Dec. 2025

As detailed in a study published today in the journal Science, researchers describe the aftermath of two separate collisions between two small, rocky cosmic objects called planetesimals. —Andrew Paul, Popular Science, 18 Dec. 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

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