[ 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

British Dictionary definitions for planetesimal hypothesis

planetesimal hypothesis

/ (ˌplænɪˈtɛsɪməl) /


the discredited theory that the close passage of a star to the sun caused many small bodies (planetesimals) to be drawn from the sun, eventually coalescing to form the planets

Word Origin for planetesimal hypothesis

C20: planetesimal, from planet + infinitesimal
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Science definitions for planetesimal hypothesis


[ 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.
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