Centaur (planetoid) - Definition

The centaurs are a class of icy planetoids that orbit the Sun between Jupiter and Neptune, named after the mythical race of centaurs.

The first centaur to be discovered, 2060 Chiron was found to display a coma upon its approach to perihelion, and is now officially classified as both a comet (95/P Chiron) and an asteroid, although it is far larger than a typical comet and there is some lingering controversy. Other centaurs are being monitored for comet-like activity.

Centaurs are not in stable orbits and will eventually be removed from the solar system by the giant planets. Dynamical studies of their orbits indicate that centaurs are probably an intermediate orbital state of objects transitioning from the Kuiper Belt to the Jupiter Family of short period comets. Objects may be perturbed from the Kuiper Belt whereupon they become Neptune-crossing and interact gravitationally with that planet. They then become classed as centaurs, but their orbits are chaotic, evolving relatively rapidly as the centaur makes repeated close approaches to one or more of the outer planets. Some centaurs will evolve into Jupiter-crossing orbits whereupon their perihelia may become reduced into the inner solar system and they may be reclassified as active comets in the Jupiter Family if they display cometary activity. Centaurs will thus ultimately collide with the Sun or a planet or else they may be ejected into interplanetary space after a close approach to one of the planets (particularly Jupiter).

No centaur has yet been photographed up close by a spacecraft, although there is evidence that Saturn's moon Phoebe, imaged by the Cassini probe in 2004, may be a captured centaur. In addition, the Hubble Space Telescope has gleaned some information about the surface features of 8405 Asbolus.

Well-known centaurs include:

External links

• List of Centaurs and Scattered-Disk Objects (http://cfa-www.harvard.edu/iau/lists/Centaurs.html)