Kuiper Belt — The Kuiper belt is an area of the solar system extending outwards from the orbit of Neptune (at 30 AU) to 50 AU.
The largest of the objects in the Kuiper belt are the planet Pluto and its moon Charon. A new Kuiper belt object, currently called 2001 KX76, has been found that is about the size of Charon, and larger than Ceres.
Another such object, Quaoar, discovered in 2002, is half the size of Pluto. Other known Kuiper belt objects are progressively smaller. The exact classification of these objects is unclear, since they are probably fairly different from the asteroids of the inner solar system.
Most Kuiper belt objects (KBOs) are lumps of ice with some organic (carbon-containing) material, detected using spectroscopy. They are of the same composition as comets and many astronomers believe them to be just comets. The distinction between comet and asteroid is not black and white, there is a substantial grey area, inhabited by such objects as 2060 Chiron.
Computer simulations show the Kuiper Belt to have been formed by the work of Jupiter, the young Jupiter having used its considerable gravity to eject smaller bodies which didn’t all escape completely, and also having been formed in-situ. The same simulations, and other theory, predict there should be bodies of significant mass in the Kuiper Belt, Mars or Earth sized.
Many inner KBOs are in an orbital resonance with Neptune. Pluto is an example of such a body. This means that the KBO performs a fixed number of orbits to a fixed number of Neptune’s orbits.
Plutinos form the inner edge of the Kuiper belt, cubewanos its main region and scattered disk objects (SDO’s) are found in its outer areas.
The Kuiper belt should not be confused with the Oort cloud. The Oort cloud is not in the plane of the solar system (the Kuiper belt is) and is many times more distant.
The existence of this belt was first suggested by the Dutch/American astronomer Gerard Kuiper in 1951. The belt was later named after him and the first discoveries of KBOs came in the early 1990s.