planetesimal

American  

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

noun

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

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adjective

1. of or relating to a planetesimal or planetesimals.

planetesimal Scientific  

/ plăn′ĭ-tĕs′ə-məl /

1. Any of innumerable small bodies of accreted gas and dust thought to have orbited the Sun during the formation of the planets.

2. ◆ 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.

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Etymology

Origin of planetesimal

First recorded in 1900–05; planet + (infinit)esimal

Example Sentences

After billions of years, two major planetesimal belts remain: the asteroid belt between Mars and Jupiter and the Kuiper belt beyond the giant planets.

From Science Daily • Dec. 6, 2025

"In this model, 'Oumuamua began as an icy planetesimal that was irradiated at low temperatures by cosmic rays during its interstellar journey, and experienced warming during its passage through the Solar System."

From Salon • Mar. 26, 2023

“This provides further support that Oumuamua originated as a planetesimal relic broadly similar to solar system comets.”

From New York Times • Mar. 22, 2023

“Now more and more people are talking about a planetesimal source,” says Myriam Telus, a planetary scientist from the University of California, Santa Cruz.

From Scientific American • Dec. 8, 2020

Possibly the planetesimal hypothesis of Chamberlin and Moulton affords the true explanation, as the result of a rupture due to excessive tidal strain.

From Astronomy: The Science of the Heavenly Bodies by Todd, David Peck