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planetesimal

[plan-i-tes-uh-muh l] /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.
adjective
2.
of or pertaining to a planetesimal or planetesimals.
Origin
1900-1905
1900-05; planet + (infinit)esimal
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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British Dictionary definitions for planetesimal hypothesis

planetesimal hypothesis

/ˌplænɪˈtɛsɪməl/
noun
1.
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
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
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planetesimal hypothesis in Science
planetesimal
  (plān'ĭ-těs'ə-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 © 2002. Published by Houghton Mifflin. All rights reserved.
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