2060 Chiron is a minor planet in the outer Solar System. Discovered in 1977 by Charles T. Kowal (precovery images have been found as far back as 1895), it was the first-known member of a new class of objects now known as centaurs, with an orbit between Saturn and Uranus.
Although it was initially called an asteroid and classified as a minor planet, it was later found to exhibit behavior typical of a comet. Today it is classified as both, and accordingly it is also known by the cometary designation 95P/Chiron. Mike Brown lists it as a possible dwarf planet with a measured diameter of 233 km.
Chiron is named after the centaur Chiron in Greek mythology. It should not be confused with the Plutonian moon Charon, discovered the following year, in 1978.
Discovery and naming
Chiron was discovered on 18 October 1977 by Charles Kowal from images taken two weeks earlier at Palomar Observatory. It was given the temporary designation of 1977 UB. It was found near aphelion and at the time of discovery it was the most distant known minor planet. Chiron was even claimed as the tenth planet by the press. Chiron was later found on several precovery images, going back to 1895, which allowed its orbit to be accurately determined. It had been at perihelion in 1945 but was not discovered then because there were few searches being made at that time, and these were not sensitive to slow-moving objects. The Lowell Observatory’s survey for distant planets would not have gone down faint enough in the 1930s and did not cover the right region of the sky in the 1940s.
It was named 2060 Chiron in 1979 after Chiron, one of the centaurs; it was suggested that the names of other centaurs be reserved for objects of the same type. The proposed symbol is ⚷.
The visible and near-infrared spectrum of Chiron is neutral, and is similar to that of C-type asteroids and the nucleus of Halley’s Comet.
Chiron’s orbit was found to be highly eccentric (0.37), with perihelion just inside the orbit of Saturn and aphelion just outside the perihelion of Uranus (it does not reach the average distance of Uranus, however). According to the program Solex, Chiron’s closest approach to Saturn in modern times was in May 720, at just under 30 million kilometres. During this passage Saturn’s gravity caused Chiron’s semi-major axis to decrease from 14.4AU to 13.7AU.
It does not come nearly as close to Uranus; Chiron crosses Uranus’ orbit where the latter is farther than average from the Sun. It attracted considerable interest because it was the first object discovered in such an orbit, well outside the asteroid belt. Chiron is classified as a centaur, the first of a class of objects orbiting between the outer planets. Chiron is an SU object since its perihelion lies within Saturn’s zone of control and its aphelion lies within Uranus’ zone of control. Centaurs are not in stable orbits and over millions of years will eventually be removed by gravitational perturbation by the giant planets, moving to different orbits or leaving the Solar System altogether.