[ plan-i-tes-uh-muh l ]
/ ˌplæn ɪˈtɛs ə məl /


one of the small celestial bodies that, according to one theory (planetesimal hypothesis), were fused together to form the planets of the solar system.


of or relating to a planetesimal or planetesimals.

Origin of planetesimal

First recorded in 1900–05; planet + (infinit)esimal Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for planetesimal

Science definitions for planetesimal

[ plăn′ĭ-tĕsə-məl ]

Any of innumerable small bodies of accreted gas and dust thought to have orbited the Sun during the formation of the planets.♦ The theory that explains the formation of the solar system in terms of the aggregation of such bodies is known as the planetesimal hypothesis. According to this theory, first proposed in 1900, the planetesimals formed within a spiral disk of dust and gas surrounding a central nucleus. Their gravitational attraction eventually caused the planetesimals to coalesce into protoplanetary disks from which larger objects such as planets, asteroids, and satellites were formed, while the nucleus coalesced into the Sun.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.