Crossword clues for planetesimal
Wiktionary
n. (cx astronomy English) Any of many small, solid astronomical objects, that orbit a star and form protoplanets through mutual gravitational attraction
WordNet
n. one of many small solid celestial bodies thought to have existed at an early stage in the development of the solar system
Wikipedia
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 hypotheses, the Chamberlin–Moulton planetesimal hypothesis and that of Viktor Safronov, states that planets form out of cosmic dust grains that collide and stick to form larger and larger bodies. When the bodies reach sizes of approximately one kilometer, then they can attract each other directly through their mutual gravity, enormously aiding further growth into moon-sized protoplanets. This is how planetesimals are often defined. Bodies that are smaller than planetesimals must rely on Brownian motion or turbulent motions in the gas to cause the collisions that can lead to sticking. Alternatively, planetesimals may form in a very dense layer of dust grains that undergoes a collective gravitational instability in the mid-plane of a protoplanetary disk or via the concentration and gravitational collapse of swarms of larger particles in streaming instabilities. Many planetesimals eventually break apart during violent collisions, as may have happened to 4 Vesta and 90 Antiope, but a few of the largest planetesimals may survive such encounters and continue to grow into protoplanets and later planets.
It is generally thought that about 3.8 billion years ago, after a period known as the Late Heavy Bombardment, most of the planetesimals within the Solar System had either been ejected from the Solar System entirely, into distant eccentric orbits such as the Oort cloud, or had collided with larger objects due to the regular gravitational nudges from the giant planets (particularly Jupiter and Neptune). A few planetesimals may have been captured as moons, such as Phobos and Deimos (the moons of Mars) and many of the small high- inclination moons of the giant planets.
Planetesimals that have survived to the current day are valuable to science because they contain information about the formation of the Solar System. Although their exteriors are subjected to intense solar radiation that can alter their chemistry, their interiors contain pristine material essentially untouched since the planetesimal was formed. This makes each planetesimal a ' time capsule', and their composition might reveal the conditions in the Solar Nebula from which our planetary system was formed.
Usage examples of "planetesimal".
Around the fast-growing sun, grains of dust and ice had accreted into swarming planetesimals.
Or perhaps the meteorological abnormalities in the planetesimal ring bodies that orbit the seventeenth geochemical hybrid ventigrain of Ursalia VII?
Solar System was very young, and the crusts of Earth and other inner planets were still subject to bombardment from stray planetesimals - a ship came here.
In consequence of the inevitable intersection of the orbits of the planetesimals, nodes are formed where the flying particles meet, and at these nodes large masses are gradually accumulated.
It may be added that the authors of the theory do not insist upon the appulse of two suns as the only way in which the planetesimals may have originated, but it is the only supposition that has been worked out.
Even as an explanation of the spiral nebulæ, not as solar systems in process of formation, but as the birthplaces of stellar clusters, the Planetesimal Hypothesis would be open to many objections.
Battered by a supernova shock, the cloud quickly coalesced into planetesimals: loosely aggregated lumps of rock and ice that swam chaotically through the dark, like blind fish.
But for reasons that still were not entirely understood, star systems with poorly developed planetary systems also seemed to produce a large number of dark comets--and Inferno shared its star with only two planets barely large enough to qualify as gas giants, a wizened little asteroid belt, and the usual sorts of deep space debris--comets, asteroids, planetesimals, and so on.