Leicester University Physics Department

The Kuiper Belt

Quaoar

picture : artist's impression of Quaoar, coutesy of NASA

Solar System Index

The Sun

Mercury

Venus

Earth

The Moon

Mars

Jupiter

Saturn

Uranus

Neptune

Pluto

The Kuiper Belt

Introduction

The Kuiper Belt is a disc beyond the orbit of Neptune, and Pluto's orbit travels through it. It is a collection of icy debris approximately 12 to 15 billion kilometres from our Sun. Gerard Kuiper, who gave his name to the belt, hypothesized that such a collection of objects, if found to exist, would mark the edge of our solar system. The region could also be a source of comets.

Kuiper Belt Objects

The Kuiper Belt is believed to consist of the debris that never became massive enough to form planets during the creation of the solar system. Several individual Kuiper Belt Objects, or KBOs, have been observed over the years. (Image courtesy of NASA).

The origins of Pluto

Pluto, now a dwarf planet, can perhaps be thought of as the largest Kuiper Belt Object. Other such bodies include Neptune's satellites Triton and Nereid, and Saturn's moon Phoebe. The eccentricities of their orbits suggest that they may have once been part of the Kuiper Belt and have since been captured by their respective planets.

Quaoar

Since the first KBOs (not including Pluto) were discovered in 1992, several have been imaged including one particularly fascinating specimen, Quaoar.

Quaoar was discovered in 2002 when it was imaged by the Hubble Space Telescope. It is a small icy body approximately half the size of Pluto, and at the time it was the largest object to be discovered in the solar system since the ninth planet. It has a comet-like composition, but it is 100 million times greater in volume. It also has an almost perfectly circular orbit.

The name, Quaoar, (phonetic: kwa-whar) was bestowed upon it by its discoverers in honour of a North American tribal god.

Sedna

Sedna In March 2004, researchers at the California Institute of technology (Caltech) discovered a body orbiting the sun that is three times further away from the Earth than Pluto. This puts it well beyond the bounds of the Kuiper Belt as far as we know, and yet it is approximately three-quarters of the size of Pluto, larger than Quaoar. What is it doing so far away from the Sun? (Artist's impression courtesy of NASA).

Scientists believe that Sedna (named after an Inuit goddess) may not be related to the Kuiper Belt, but may be the first evidence of an 'inner Oort Cloud'. The Oort Cloud, named after Jan Oort, is a spherical cloud surrounding out solar system from which many comets originate. The edge of the Oort cloud is the furthest the Sun's physical influence can be said to extend. However, Sedna is ten times closer than the predicted distance of the Oort Cloud.

One hypothesis is that Sedna was originally much closer to the Sun, but was pulled further away under the gravitational influence of another star.

Sedna became even more curious after its discovery. Its orbital speed suggested to scientists that Sedna should have a satellite, but when the Hubble Space Telescope imaged it no trace of a moon could be seen.

Whatever Sedna may be, it was the largest object to date discovered in the solar system since Pluto in 1930 - until a body at least as large as Pluto, but three times further away from the Sun, was discovered in 2005.

This object is now known as Eris, rather aptly named after the Greek goddess of discord as its discovery finally brought about Pluto's reclassification. It is also a dwarf planet along with Pluto and Ceres, a large asteroid from the belt between Mars and Jupiter.