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Planetesimals are small bodies of rock and/or ice that form by accretion in the protoplanetary disks of protostellar systems. These small objects continue to accrete and merge until finally a planetary system is formed.

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 collide and stick to form larger and larger bodies.

Planetesimal Compositions in Exoplanet Systems
ApJ, accepted
arxiv ...

planetesimal Term given to objects in the early solar system that had reached the size of small moons, at which point their gravitational fields were strong enough to begin to influence their neighbors.

The planetesimal hypothesis is a theory about the formation of the Solar System. It was proposed by Thomas Chrowder Chamberlain (Sept. 25, 1843 - Nov. 15, 1928), an American geologist and teacher.

~S - Hypothetical solid celestial body that accumulated during the last stages of accretion. These bodies, from ~1-100 km in size, formed in the early solar system by accretion of dust (rock) and ice (if present) in the central plane of the solar nebula.

A small body of primordial dust and ice from which the planets were formed.
A hot ionized gas.

a rocky and/or icy body, a few to several tens of kilometers in size, that was produced in the solar nebula.
a geological term denoting the time in Earth history prior to 570 million years ago.

~s: Bodies ranging in size from meters up to hundreds of kilometers in diameter that formed during the process that formed the planets by accretion. Most ~s accreted to form the planets.

~: One of the small bodies that formed from the solar nebula and eventually grew into protoplanets.
plastic: A material with the properties of a solid but capable of flowing under pressure.

Asteroid-sized solid bodies that are hypothesized to form when the protosolar nebula collapsed into a disk and fragmented. Most of the ~s subsequently accumulated into planets.
Planetocentric Coordinates ...

~ - A primordial solar system body of intermediate size that accreted with other ~s to form planets and satellites
Planetology - The comparative study of the properties of planets
Plasma - A fully or partially ionized gas ...

A small body of rock and/or ice - under 10 kilometers (6 miles) across - formed during the early stages of the solar system. ~s are the building blocks of planets, but many never combined to form large bodies. Asteroids are one example of ~s.
Protoplanet ...

~s within the region which would become the asteroid belt were too strongly perturbed by Jupiter's gravity to form a planet. Instead they continued to orbit the Sun as before, while occasionally colliding.

A ~ is a small object that orbits the Sun. ~s are thought to have formed when the Solar System itself formed, and they were perhaps the building blocks from which the planets were built.

~ - (n.)
A small (diameter up to several hundred kilometers) solar-system body of the type that first condensed from the solar nebula. ~s are thought to have been the principal bodies that combined to form the planets.
plasma - (n.) ...

A solid object that is believed to exist in protoplanetary disks and in debris disks. ~s are formed from small dust grains that collide and stick together and are the building blocks that eventually form planets in new planetary systems.
A low plain.

Icy ~s formed in the outer solar system.
Composition Mainly ice and dust Orbits Highly elliptical, taking them very close to the Sun and back out into deep space, often far beyond the orbit of Pluto. Orbit duration Less than 200 years to more than several millions of years.
Short-period ...

Large ~s were created as the new Sun's heat acted on nearby metal grains and chunks of rock during formation of the Solar System.

The Colliding ~s Theory: The interaction of earth-orbiting and Sun-orbiting ~s (very large chunks of rocks like asteroids) early in the history of the Solar System led to their breakup. The Moon condensed from this debris.

Comets are icy ~s usually from 1 to 50 km across and containing bits of fragile dust resembling carbonaceous chondrite material. They probably formed among the outer planets and were ejected into the Oort cloud, from which they occasionally reenter the inner solar system.

~s small solid bodies believed to have formed during the condensing stage of the solar nebula. plasma hot ionized gas that is electrically conductive. plate tectonics the motions of large segments of the Earth's surface, having the form of plates, over the mantle.

~s (Galileo Project Glossary - JPL) Primordial bodies of intermediate size that accreted into planets or asteroids. planetocentric (NASA SP-7, 1965) 1. Of or pertaining to a planet's center of mass.
2. Of or pertaining to the planet as a center of a system.

Within these disks, ~s collide and agglomerate into larger protoplanetary bodies that eventually form planets.

The theory by which ~s are assumed to collide with one another and coalesce, eventually sweeping up enough material to form the planets. [Silk90]
A subgiant of spectral type B5, about 35 pc distant. ( Eridani) [H76]
Achilles ...

Some of the initial ~s get ejected out beyond the orbit of Pluto to form the nuclei of the comets. The young sun continues to heat things up, and blows excess gas and dust out of the solar system.

The gravity of the ~s tended to divide the solar nebula into ring-shaped zones. This process explains item (i) above. F. More massive ~s had stronger gravity and could pull in more of the surrounding solar nebula material.

In regions where the average velocity of the collisions was too high, the shattering of ~s tends to dominate over accretion, preventing the formation of planet-sized bodies.

Comets also are cosmic debris, probably ~s that originally resided in the vicinity of the orbits of Uranus and Neptune rather than in the warmer regions of the asteroid belt.

Rocky planets are thought to have formed from the accretion of dust into '~s,' the ~s into proto-planets and finally the proto-planets into planets. Many details of this sequence are still unknown, including the composition of the ~s.

It has an inner disc, with a radius between six and fifteen astronomical units (897 million to 2.2 billion kilometres); a ~ disc between 90 and 300 AU (13.4 billion to 44.8 billion kilometres) and an extended halo reaching out to 1000 AU (150 billion kilometres).

Most of these large objects, called ~s, ultimately combined to form the dense, rocky planets of the inner solar system (Mercury through Mars).

The Giant Impactor Theory (sometimes called The Ejected Ring Theory): This theory proposes that a ~ (or small planet) the size of Mars struck the Earth just after the formation of the solar system, ejecting large volumes of heated material from the outer layers of both objects.

Furthermore, the second authors mistakenly derive the collision rate appropriate for ~s *within* the dust belt while Fomalhaut b is located well outside of it.

TRAnsiting Planets and ~s Small Telescope
Danish 1.54-metre telescope
Télescope à Action Rapide pour les Objets Transitoires
ESO 1-metre Schmidt telescope
ESO 1.52-metre telescope
ESO 1-metre telescope
ESO 0.5-metre telescope
Coudé Auxiliary Telescope
MarLy 1-metre telescope ...

Current theories hold that the planets and moons formed from the blocks - called ~s - and their gravity later ejected the left over material from the solar system or to its outer reaches. If The HST could search the entire sky, it would find about 500,000 ~s.

"We will use ALMA to image the 'birth ring' of ~s that we believe orbits this young star. Only with ALMA, however, can we hope to discover clumps in these dusty asteroid belts, which can be the markers of unseen planets.

TNO stands for Trans Neptunian Object. These small ~s made of rock and ice orbit our Sun past the planet Neptune. They are Kuiper Belt objects left over from the formation of the solar system. Pluto may be a TNO, albeit a rather massive one.

What are comets?
A comet is a small world which scientists sometimes call a ~. They are made out of dust, and ice. Kind of like a dirty snow ball.
Where do they come from?
Comets come from two places: The Kuiper Belt, and the Oort Cloud. ...

The period since the Earth's formation from ~s, measured to be 4.6 billion years.
Age of the Universe
About 13 billion years, as determined by big bang model and age of oldest stars.

At this point, the solar system is composed only of solid, protoplanetary bodies and gas giants. The "~s" would slowly collide with each other and become more massive.

The planets were originally formed from ~s, sub-planetary bodies that accreted together during the first years of the solar system and no longer exist. The name is also sometimes used to refer to asteroids and comets in general, or to asteroids below 10km in diameter ...

An process involving the selective removal of atmospheric species from impacts of ~s.

The Moon - 1.5 light seconds from the Earth. Current evidence suggests that the moon may have been blasted away from the earth about 4.5 billion years ago when a Mars-sized "~" collided with the newly formed Earth. More info at Bill Arnett's "The Nine Planets". ...

A minor planet is a general term for small-bodies in our solar system not classified as comets. Asteroids and trans-Neptunian objects are considered minor planets. These objects may also be called ~s. We use the term "asteroid" to imply "minor planet" on this web-site.

25 times its current mass; but that early in the solar system's history, Mercury was struck by a ~ of approximately 1/6 that mass. The impact would have stripped away much of the original crust and mantle, leaving the core behind.

The reasons why some planets rotate as quickly as they do remain puzzling to planetary scientists. Most studies in this area have focused on the inner planets. Earth and Mars, which accumulated gradually from rocky ~s, most likely got...

it has to be orbiting a star, and not a satellite of another planet (several moons in the Solar System are bigger than Pluto); it has to be not massive enough to cause thermonuclear fusion (in which case it would classify as a star); and it must have cleared its neighbouring region of ~s ...

See also: See also: What is the meaning of Planet, Astro, Solar, Orbit, Earth?

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