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Kuiper Belt

visible comets, CCDs, Kuiper Belt Objects, KBOs, Kuiper Belt Object

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Kuiper Belt (pronounced KY-per), a collection of frozen objects made of ice, dust, and rock that orbit the Sun in the outer solar system. The belt extends from just beyond the orbit of the planet Neptune to well beyond the orbit of Pluto. The objects in the Kuiper Belt are called Kuiper Belt Objects (KBOs) and range in size from clumps of ice and dust up to planetary bodies larger than Pluto. The orbits of these objects show that the belt is actually disk-shaped.

Nearly 1,000 Kuiper Belt Objects have been found. Astronomers estimate that more than 100,000 KBOs larger than 50 km (30 mi) in diameter may exist. The Kuiper Belt therefore is far more extensive and contains far more large objects than the asteroid belt, a region of rocky debris between the orbits of Mars and Jupiter. Including the billions of comets believed to orbit in the Kuiper Belt, scientists estimate that the beltís total mass is about 1 to 3 percent the mass of Earth.

The small icy bodies in the Kuiper Belt sometimes turn into visible comets when their orbits are disturbed to bring them into the inner solar system. When the nucleus of a comet comes near enough to the Sun, heat causes the object to give off gas and dust as a coma and a tail. The Kuiper Belt is considered the likely source of short-period comets, which orbit the Sun in the main plane of the solar system in periods shorter than 200 years. The largest KBOs have planetlike properties, including a rounded shape from effects of their own gravity and an inner structure that likely has separated into a rocky core surrounded by layers of ice. Dozens of such planetlike objects may orbit in the Kuiper Belt.

The existence of the Kuiper Belt was first predicted during the mid-20th century, most notably by Dutch American astronomer Gerard Kuiper. Kuiper and other astronomers expected that a debris belt, similar to the asteroid belt of rocky material that orbits the Sun between Mars and Jupiter but composed of icy material, might lie beyond Neptune. The first searches for the Kuiper Belt, however, were unsuccessful. Astronomers now know the early searches failed because the photographic technology in use at the time was not sensitive enough to find KBOs. By the late 1980s, astronomers had access to a kind of electronic camera called a charge-coupled device (CCD). CCDs are much more sensitive than traditional photography, allowing them to detect fainter objects. In 1992 astronomers Jane Luu and David Jewitt found the first Kuiper Belt Object. This KBO, designated 1992QB1, is more than 1,000 times fainter than Pluto.


Stern, S. Alan, B.A., B.S., M.S., Ph.D.

Director, Department of Space Studies, Southwest Research Institute.

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