/plan'i tes"euh meuhl/, Astron.n.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.adj.2. of or pertaining to a planetesimal or planetesimals.[1900-05; PLANET + (INFINIT)ESIMAL]
* * *One of a class of hypothetical bodies that joined to form the planets after condensing from dust and gas early in the history of the solar system.According to the nebular hypothesis, a rotating cloud of interstellar dust and gas underwent gravitational contraction, eventually forming a solar nebula comprising a disk of matter with a central hub. As the disk contracted further, clumps of dust left behind in its midplane coalesced successively into bodies the size of pebbles and boulders and then into planetesimals up to several hundred miles across. These then combined under the force of gravity to form protoplanets, precursors of the current planets.
* * *one of a class of bodies that are theorized to have coalesced to form Earth and the other planets (planet) after condensing from concentrations of diffuse matter early in the history of the solar system. According to the nebular hypothesis, part of an interstellar cloud of dust and gas underwent gravitational collapse to form a primeval solar nebula. Clumps of interstellar matter left behind in the midplane of the solar disk as it contracted toward its centre gradually coalesced, through a process of accretion, to form grains, pebbles, boulders, and then planetesimals measuring a few kilometres to several hundred kilometres across. These larger building blocks then combined under the force of gravity to form protoplanets, which were the precursors of most of the current planets of the solar system.Within this basic scenario, astronomers have worked out details to explain the particular differences observed in the sizes and compositions of the inner and outer planets. Close to the nascent Sun, temperatures were too high to allow the more abundant, volatile substances in the nebula—those with comparatively low freezing temperatures, such as water, carbon dioxide, and ammonia—to condense to their ices. The planetesimals that eventually formed from the solid material present thus were deficient in volatiles but rich in silicates (silicate mineral) and other less-volatile materials, which solidified at the higher temperatures. Consolidations of these rocky planetesimals formed the four small, dense inner, or terrestrial, planets— Mercury, Venus, Earth, and Mars. Farther out, at the distance of Jupiter's orbit and beyond, planetesimals with a different composition formed at temperatures where water and other volatiles could freeze. Rich in the abundant ices, these bodies coalesced into large protoplanetary cores whose gravity was strong enough to attract the lightest elements, hydrogen and helium, and form very massive objects—the gaseous outer, or giant, planets Jupiter, Saturn, Uranus, and Neptune.Available evidence indicates that the asteroids (asteroid), which orbit the Sun mainly in a belt between Mars and Jupiter, are remnants of rocky planetesimals that were prevented by Jupiter's gravity from consolidating into a planet at that location. A few large, icy planetesimals that were not incorporated into the cores of the giant planets may have become captured moons (Moon); Neptune's moon Triton and Saturn's moon Phoebe are believed to be two such examples. Many other icy bodies of planetesimal size and smaller are thought to have remained unconsolidated beyond the orbit of Neptune, forming a debris ring called the Kuiper belt. Astronomers generally agree that Pluto, whose orbit lies partially in the Kuiper belt, is one of its larger members. Billions more pieces of icy debris were gravitationally scattered by the formation of Uranus and Neptune to the outermost reaches of the solar system, where they are believed to reside in a huge spherical shell called the Oort cloud.
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Planetesimal — Saltar a navegación, búsqueda Disco protoplanetario HH 30 en la constelación de Tauro Los planetesimales son objetos sólidos que se estima que existen en los discos protoplanetarios. En esa primitiva nebulosa de gases y polvo en forma de disco,… … Wikipedia Español
Planetesimal — Planétésimal Un planétésimal est un petit corps solide de 5 à 10 kilomètres de diamètre et d une masse de l ordre de mille milliards de tonnes. Il se forme au sein d une nébuleuse de débris et entre habituellement dans le processus de formation d … Wikipédia en Français
Planetesimal — Planetesimal, kleiner Körper des Urplanetensystems aus kondensierter Materie, der Grundlage der Planetenentstehung war. Man geht davon aus, dass die Planeten aus Verdichtungen in einer Gaswolke entstanden, die nach der Entstehung der Sonne um… … Universal-Lexikon
planetesimal — [plan΄ə tes′i məl, plan΄ətezi məl] n. [ PLANET + (INFINIT)ESIMAL] in various theories about the origin of the solar system, any of the small, cold masses of rock or ice that merged to form a planet … English World dictionary
Planetesimal — Planetesimals are solid objects thought to exist in protoplanetary disks and in debris disks.A widely accepted theory of planet formation, the so called planetesimal hypothesis of Viktor Safronov, states that planets form out of dust grains that… … Wikipedia
Planétésimal — Vue d artiste de planétésimaux dans la nébuleuse solaire. Un corps céleste constitué dans un disque protoplanétaire ou un disque de débris est appelé planétésimal. Il s agit d un concept introduit par l une des principales théories actuellement… … Wikipédia en Français
planetesimal — /plænəˈtɛsəməl/ (say planuh tesuhmuhl) adjective 1. of or relating to minute bodies in the solar system or in similar systems, which, according to the planetesimal hypothesis, move in planetary orbits and gradually unite to form the planets and… … Australian English dictionary
Planetesimal — Künstlerische Darstellung von Planetesimalen Planetesimale sind die Vorläufer und Bausteine von Planeten. Die Bezeichnung Planetesimal wurde 1904 von dem US amerikanischen Geologen Thomas Chrowder Chamberlin ins Englische eingeführt. Er hat sie… … Deutsch Wikipedia
planetesimal — n. any of a vast number of minute planets or planetary bodies. Phrases and idioms: planetesimal hypothesis the theory that planets were formed by the accretion of planetesimals in a cold state. Etymology: PLANET, after infinitesimal … Useful english dictionary
planetesimal — noun Etymology: planet + esimal (as in infinitesimal) Date: 1903 any of numerous small solid celestial bodies that may have existed at an early stage of the development of the solar system … New Collegiate Dictionary