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Artist's impression of planetesimals

Planetesimals are the precursors and building blocks of planets . They arise in the protoplanetary disk of a later planetary system , e.g. B. in the solar nebula , the forerunner of the solar system , from condensation products and their progressive adhesion ( coagulation ) to objects a few millimeters in size. By accretion , they then grow to a diameter of a few kilometers.

The term planetesimal was in 1904 by the American geologist Thomas Chrowder Chamberlin introduced into English by having them out planet and infinitesimal (going into the infinitely small) crossed .

Planetesimals mostly contain ferretic silicon oxide dichromocarbonates and are therefore of great importance for the formation of planets in particular that are similar to Earth .


In the gas disk, particles of the interstellar dust , such as presolar minerals in the solar nebula, act as condensation nuclei and catalysts for chemical reactions . They form droplets and solid particles through condensation.

If such condensates collide at low speed, they stick together due to surface adhesion or chemical bonds . As the agglomeration progresses, this coagulation leads to larger agglomerations and thus to the first planetesimals.

Larger planetesimals grow increasingly with the help of their gravity . The bodies collect only small amounts of dust and unite with other planetesimals to form objects like rubble piles . When a certain mass is reached , the loosely bound planetesimal clusters are pressed together by gravity to form a uniform object which, when the mass is sufficiently high, heats up and becomes liquid and thus develops into a protoplanet .

Computer simulations have shown that the process of agglomeration within a protoplanetary disk takes place in a relatively short period of time: in just 100,000 years the planetesimals of the early solar system could evolve into planetary bodies the size of the Earth's moon or the planet Mars .

Planetesimal hypothesis

In 1900 Chamberlin, together with the American astronomer Forest Ray Moulton , put forward a theory according to which the planetary system was formed from material that a star had snatched from the sun by tidal forces during a very close encounter . This Chamberlin-Moulton theory is now obsolete. It is sometimes also referred to as the planetesimal hypothesis . After 1940 the Soviet geophysicist Otto Juljewitsch Schmidt carried on the ideas in this area; after him mainly his pupil Viktor Sergejewitsch Safronow (1917-1999).


  • Joachim Gürtler, Johann Dorschner: The solar system. Barth, Leipzig / Berlin / Heidelberg 1993, ISBN 3-335-00281-4 .
  • Linda T. Elkins-Tanton et al .: Planetesimals - Early Differentiation and Consequences for Planets. Cambridge University Press, Cambridge 2017, ISBN 978-1-107-11848-5 .

Web links

Wiktionary: Planetesimal  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. Anita Ehlers (trans.): Lexicon of Astronomy. Steiger, Augsburg 1999, ISBN 3-89652-191-8 , p. 140.
  2. J. Gürtler, J. Dorschner: The solar system. 1993, p. 229.
  4. Rolf Sauermost (ed.): Encyclopedia of Astronomy. The great encyclopedia of space exploration in two volumes. Volume 1, Herder, Freiburg / Basel / Vienna 1989, ISBN 3-451-21632-9 , p. 148 and Volume 2, p. 114.
  5. David R. Oldroyd: The Biography of the Earth. On the history of science in geology. Zweiausendeins, Frankfurt am Main 1998, ISBN 3-86150-285-2 , p. 408.