The Kuiper Belt

The Kuiper Belt

The Kuiper Belt is a thick ecliptic band which contains over 200 million small, icy objects. These objects, known as the Kuiper Belt Objects or trans- Neptunians, were discovered in 1992 by Jewitt and Lu. The first Kuiper Belt Object discovered in 1992, is QB1 (1992) and is 150 miles wide. The Kuiper Belt is about 30 AU to 50 AU away from the Sun. The Kuiper Belt is very important because of two specific things; the first being, Kuiper Belt Objects are remnants from the earliest phases of the solar system and are tens of millions of years old and secondly, that the Kuiper Belt is the source of short-period comets.

The Kuiper Belt is named after Gerald Kuiper, an American scientist with a special interest in astronomy. He wrote a paper in 1951 that mentioned objects out beyond Pluto. He predicted that there must be a cloud of dust and debris out past the main area of the solar system, i.e. out past Pluto (Jewitt "The Kuiper Belt"). His hypothesis was reinforced in the 1980s by computer simulations. The simulations predicted that a belt of debris would naturally form around the edge of the solar system. There is some dispute as to who really predicted the Kuiper belt first. Kenneth Edgeworth wrote a paper in 1943 and then another 1949 in which he seemed to indirectly predict the belt. Kuiper did not cite any of his work. This will be a never-ending dispute (Stern 52). Gerard Kuiper was also responsible for discovering Saturn's largest moon, Titan in 1944, Uranus's fifth moon, Miranda, in 1948, and Neptune's second moon, Nereid in 1949.

Classical Kuiper Belt Objects are between 37 and 59 AU from Earth. They mainly have a semi-major axis between 42 - 48 AU. They are categorized as 'classical' because their orbits have small eccentricities that are expected of objects formed by accumulation of mass in a cool disk.

Scattered Kuiper Belt Objects are defined by large, eccentric, looping inclined orbits. There distance from the Earth is about 35 AU. They were first discovered at the University of Hawaii using a 2.2 - m telescope on Mauna Kea. Further research has proved that they have a certain, distinct population in the Kuiper Belt. Scattered Kuiper Belt Objects have an orbit which is affected by Neptune and its gravitational pull. They form a large circle around the classical Kuiper Belt Objects, but their population is uncertain.

The Kuiper Belt is believed to be a reservoir for short-period comets. Short- period comets have orbital periods of less than 200 years. Comets are objects, rich in ice, which become very prominent when heat from the Sun causes their composition to liquefy. The most visible part of a comet is the coma and the tail. It is believed that short-period comets were made in the Kuiper Belt because of the high content of water and carbon monoxide in the nucleus that must be formed at low temperatures. It is believed that these comets are fragments of Kuiper Belt Objects that were chipped off by collisions. It is possible, if this is correct, that the short-period comets' nuclei would have the same compositions as the Kuiper Belt Object it came from. As it turns out, the comets are greatly modified by thermal and physical effects which mean that the comets are very different from the original region they were in.

Long-period comets are those with orbital periods over two hundred years. They are very interesting because their orbits are normally very large, but even more so because they show no sign of preferred direction. Fifty percent of the long-period comets are retrograde. Jan Oort realized that these comets must be just entering the solar system, to not have been affected and modified by the gravitational pull of the major planets. It is believed that there may be as many as a trillion comets in the Oort cloud, but it is unproved because the comets are so small and at such a great distance, that no one can be completely sure. Although the Oort cloud is located out much further than the Kuiper Belt, it seems as though the Oort cloud objects were formed closer than those in the Kuiper Belt. Small planets may have been ejected by gravitational encounters with larger planets and sent sailing deep into the solar system where they began to amass in what we know call the Oort cloud. The Oort cloud is some 30 trillion km from the Sun. The cloud has a dense core where many icy comets are and they tend to gradually spread out and replenish the rest of the cloud. It is believed that the comets in the cloud were formed in different places in the solar system, which means at different temperatures, which would account for the compositional diversity observed. Hale- Bopp was a recent comet that originated in the Oort cloud.

About ј of the Kuiper Belt Objects are Plutinos. The word Plutinos means "little Plutos." The objects were named this because they complete two orbits around the Sun in the time it takes Neptune to complete three orbits.

This is the same resonance, 3:2, which Pluto has. There are approximately 1,400 Plutinos that are larger than 100 km in diameter. They have orbits that closely follow and sometimes even cross Neptune's orbit (Jewitt "The Kuiper Belt"). Plutinos contrast w/ cubewanos. The objects called cubewanos make-up sixty to seventy percent of the Kuiper Belt Objects and never cross orbits with Neptune. These objects were too discovered by Jewitt and Lu (Trujillo 424).

Binaries are very scarce in the Kuiper Belt. There are only eight that have been documented so far. It is believed that binaries were formed by collisions because this would offer a source of natural friction. This friction would produce enough kinetic energy to create the necessary gravitational capture of another Kuiper Belt Object. Granted this is a speculation, but one with a lot of support to back it up and prove its probability. The best known binary is the Earth and its Moon. This was probably caused by an impact which ejected mass from the Earth; the mass was then caught by Earth's gravitational pull and was eventually formed into the Moon we now see. This does not seem likely to have formed the Kuiper Belt Object binaries because the masses are too small. They were more likely created by low velocity collisions between different Kuiper Belt Objects, which can result in peanut shaped binaries or the collisions may not cause enough energy to be lost, so no binaries are formed at all (Jewitt "The Kuiper Belt"). All the Kuiper Belt binaries have diameters over 100 km. Since Kuiper Belt Objects with diameters over 100 km are more so rare, it is hard to believe that the belt always had such a lack of objects of that size, and that binaries between them were able to be created. The speculation is