Oort cloud

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Related to Oort cloud: Kuiper belt, Sedna

Oort cloud:

see cometcomet
[Gr.,=longhaired], a small celestial body consisting mostly of dust and gases that moves in an elongated elliptical or nearly parabolic orbit around the sun or another star. Comets visible from the earth can be seen for periods ranging from a few days to several months.
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Oort cloud

(oort, ort) (Öpik–Oort cloud) A cloud of comets that move in orbits round the Sun with perihelia in the range 5–50 AU and aphelia in a zone with heliocentric distances between 30 000 and 100 000 AU, i.e. in a zone far beyond Pluto's orbit. Since the nearest star to the Sun – Proxima Centauri – is 270 000 AU away these comets can be perturbed by passing stars; this changes their orbits and send them in closer toward our Sun (or out toward the perturbing star). These perturbed comets have periods of hundreds of thousands of years. The Oort cloud is so distant that it acts as a refrigerated cometary reservoir.

The existence of a distant long-lived cloud of comets was first suggested in 1932 by Ernst Öpik. The same idea was proposed in 1950 by J.H. Oort who thought that comets originated from the disintegration of a planet some time in the early history of the Solar System. After this the major planets, Jupiter in particular, drove the majority of the comets either into the inner Solar System, where they decayed, or into the outer regions. Of this latter group 98% would have been lost from the Solar System, only 2% remaining in the Oort cloud. The number of comets in the cloud is uncertain but it could be somewhere in the range 1011 to 1012 with a total mass in the region of 1028 grams. The orbits are oriented at random. A cometary cloud of radius 100 000 AU has a half life of at least 1.1 × 109 years. The existence of the cloud shows up very clearly when the number distribution of comets is considered as a function of the reciprocal of the semimajor axes of the orbits. See also Kuiper belt.

References in periodicals archive ?
Astro Lords: Oort Cloud provides captivating gameplay as well as the ability to continue playing from the last checkpoint, even on a browser or different platforms (Windows, Mac OS, Linux).
The 'original' barycentric value of 1/a indicates that it is not a new comet from the Oort Cloud.
It suggests that virtually all the dust must be coming from short-period comets, with a very small contribution from Oort Cloud members and only about 10% from the asteroid belt.
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Even farther out is the Oort cloud, a region of comets and, perhaps, still more planet-like objects.
They are believed to originate from the Oort Cloud, named after the Dutch astronomer, Jan Oort.
These comets were flung out into the almost-perfect icebox we call the Oort Cloud.
A typical comet in the Oort Cloud is circuiting the Sun at the leisurely pace of about a hundred meters per second, around 220 miles an hour.
All previous D/H measurements were of comets that hail from the far more distant Oort cloud, a shell of ice fragments that envelops the solar system.
Siding Spring is the first comet from our solar system's Oort Cloud to be studied up close.
What's more, their work indicates the potential presence of an enormous planet, perhaps up to 10 times the size of Earth, not yet seen, but possibly influencing the orbit of 2012 VP113, as well as other inner Oort cloud objects.