Starting in 1992, astronomers have become aware of a vast population of small bodies orbiting the sun beyond Neptune. There are at least 70, 000 "trans-Neptunians" with diameters larger than 100 km in the radial zone extending outwards from the orbit of Neptune (at 30 AU) to 50 AU. Observations show that the trans-Neptunians are mostly confined within a thick band around the ecliptic, leading to the realization that they occupy a ring or belt surrounding the sun. This ring is generally referred to as the Kuiper Belt.

The Kuiper Belt holds significance for the study of the planetary system on at least two levels. First, it is likely that the Kuiper Belt objects are extremely primitive remnants from the early accretional phases of the solar system. The inner, dense parts of the pre-planetary disk condensed into the major planets, probably within a few millions to tens of millions of years. The outer parts were less dense, and accretion progressed slowly. Evidently, a great many small objects were formed. Second, it is widely believed that the Kuiper Belt is the source of the short-period comets. It acts as a reservoir for these bodies in the same way that the Oort Cloud acts as a reservoir for the long-period comets.

Occasionally the orbit of a Kuiper Belt object will be disturbed by the interactions of the giant planets in such a way as to cause the object to cross the orbit of Neptune. It will then very likely have a close encounter with Neptune sending it out of the solar system or into an orbit crossing those of the other giant planets or even into the inner solar system.

There are presently nine known objects orbiting between Jupiter and Neptune (including 2060 Chiron (aka 95 P/Chiron) and 5145 Pholus). The IAU has designated this class of objects as Centaurs. These orbits are not stable. These objects are almost certainly "refugees" from the Kuiper Belt. Their future fate is not known. Some of these show some cometary activity (i.e., their images are a little fuzzy indicating the presence of a diffuse coma). The largest of these is Chiron which is about 170 km in diameter, 20 times larger than Comet Halley. If it ever is perturbed into an orbit that approaches the Sun it will be a truly spectacular comet.

Several Kuiper Belt objects have been discovered recently including 1992 QB1 and 1993 SC. They appear to be small icy bodies similar to Pluto and Triton (but mostly smaller). There are more than 800 known trans-Neptunian objects (as of early 2004). Many orbit in 3:2 resonance with Neptune (as does Pluto). Colour measurements of some of the brightest have shown that they are unusually red. In late 2002, a Kuiper Belt object over 1000 km in diameter was discovered and provisionally designated 2002 LM60 "Quaoar". In early 2004 an even larger one, 2004 DW, was found (its size isn't well known yet, but it's almost certainly smaller than Pluto). And in late 2005 the discovery of 2003 UB313 (now officially named "Eris") was announced; it is very likely somewhat larger than Pluto.

It is estimated that there are at least 35, 000 Kuiper Belt objects greater than 100 km in diameter, which is several hundred times the number (and mass) of similar sized objects in the main asteroid belt.

Some astronomers believe that Neptune's moon Triton, and Pluto and its moon Charon are merely the largest examples of Kuiper Belt objects (Pluto can still be considered a member of the Kuiper Belt in addition to its classification as a "dwarf planet").

Solar System Links & Resources

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Kuiper Belt Links & Resources

Kuiper Belt Wealth of information about Kuiper Belt Objects, including ephemerides for those who would like to observer them along with a number of movies and images. New Horizons: NASA's Pluto/Kuiper Belt Mission News about Pluto and the Pluto/Kuiper Belt mission that will fly by Pluto in 2015. Distant EKOs The Distant EKOs Newsletter is dedicated to the dissemination of research relevant to the Kuiper belt. The goal is to provide researchers with easy and rapid access to current observational and theoretical studies of the Kuiper belt, directly related objects (e.g., Pluto, Centaurs), and other areas of research that are explicitly applied to the Kuiper belt. A Deep Ecliptic Survey for Kuiper Belt Objects Astronomers are using the KPNO Mosaic camera with the Mayall 4-metre telescope to identify Kuiper Belt Objects (KBOs, also known as Trans-Neptunian Objects). The goals of their survey are to answer several fundamental scientific questions. What We Know About Pluto, Charon and the Kuiper Belt NASA site providing inforamtion on what's currently known about Kuiper Belt Objects. Kuiper Belt Movie Lynne Allen and Gary Bernstein, formerly of the UM Astronomy Department, observed several square degrees of the sky in order to discover very faint KBOs, in an effort to learn more about the formation of the Solar System. This movie shows the appearance of a small patch of the sky observed over 2 nights in May, 1998 as part of this project. Moons Over the Kuiper Belt In the not-too-distant past, the planet Pluto was thought to be an odd bird in the outer reaches of the solar system because it has a moon, Charon, that was formed much like Earth's own moon was formed. But Pluto is getting a lot of company these days. Of the four largest objects in the Kuiper belt, three have one or more moons. Frequently Asked Questions About Quaoar Quaoar is a newly discovered Kuiper Belt object, found in June 2002 by Chad Trujillo and Mike Brown at Caltech in Pasadena. It's half the diameter of Pluto (about 1/8 the volume), and 1.6 billion kilometers (1 billion miles) further away than Pluto. Frequently Asked Questions About 2004 DW 2004 DW is a newly discovered Kuiper belt object, found in images taken Feb 17 2004 (nearly 74 years to the day after Pluto was discovered). 2004 DW is one of the largest Kuiper Belt objects currently known. Initial indications are that it may be over half the diameter of Pluto, larger than Quaoar, and 2.4 billion kilometers (1.5 billion miles) further away than Pluto. The discovery of 2003 UB313, the 10th planet The new planet, colloquially named 'Xena', is the most distant object ever seen in orbit around the sun, even more distant than Sedna, the planetoid discovered almost 2 years ago. It is almost 10 billion miles from the sun and more than 3 times more distant than the next closest planet, Pluto and takes more than twice as long to orbit the sun as Pluto. Sedna Sedna is the coldest most distant place known in the solar system; possibly the first object in the long-hypothesized Oort cloud. List Of Transneptunian Objects This list is updated daily, except for the few days surrounding the preparation of each batch of MPCs. It is also updated as and when new objects are discovered.

Kuiper Belt eBooks & Articles

The Edge of the Solar System An account of a detection experiment to locate Kuiper Belt objects along the ecliptic. No objects were found beyond 65AU. Kuiper Belt Articles A list of 465 online articles and papers (dating from 1995 to 1999) about Kuiper Belt Objects.