Kuiper Belt
A region of the outer solar system populated by an estimated ten billion to one trillion rock-ice bodies known as Kuiper Belt objects (KBOs). It stretches from about 30 AU from the Sun (Neptune's distance) to at least 150 AU and forms an inner, flattened extension of the Oort cloud.
The Kuiper Belt is an older structure than the more spherical outer part of the Oort cloud. KBOs formed pretty much in their present locations – far enough out not to be tossed around by the giant planets – whereas the more distant Oort cloud objects actually formed closer to the Sun than KBOs and were then slung into their present huge orbits by gravitational interactions with Jupiter and the other gas giants.
The Kuiper Belt is thought to be the source of short-period comets and of centaurs. It is named after Gerard Kuiper who predicted its existence in 1951 but is also sometimes referred to as the Edgeworth-Kuiper belt, in recognition of the amateur astronomer Kenneth Edgeworth (1880-1972) who, in his only scientific paper, published in the Journal of the British Astronomical Association in 1942, was the first to suggest the existence of a region of comet-like objects beyond the outer planets.
The Oort Cloud contains billions of icy bodies in solar orbit. Occasionally, passing stars disturb the orbit of one of these bodies, causing it to come streaking into the inner solar system as a long-period comet. These comets have very large orbits and are observed in the inner solar system only once. In contrast, short-period comets take less than 200 years to orbit the Sun and they travel along the plane in which most of the planets orbit. They come from a region beyond Neptune called the Kuiper Belt, named for astronomer Gerard Kuiper, who proposed its existence in 1951.
In 1992, astronomers detected a reddish speck about 42 AU from the Sun-- the first time a Kuiper Belt object (or KBO for short) had been sighted. More than 1,000 KBOs have been identified since 1992. (They are sometimes called Edgeworth Kuiper Belt objects, acknowledging another astronomer who also is credited with the idea, or they are simply called transneptunian objects (TNOs.)
But these are more than distant curiosities. They are relatively pristine remnants of the nebula from which the entire solar system was formed. Their composition and distribution places important constraints on models of the early evolution of the solar system.
Information from: David Darling's encyclopedia and Solar System Exploration-JPL-NASA.
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