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Chiron, icy small body orbiting the Sun in the outer solar system among the giant planets. Once thought to be the most distant known asteroid, Chiron is now believed to have the composition of a comet nucleus—i.e., a mixture of water ice, other frozen gases, organic material, and silicate dust.
Chiron was discovered in 1977 by the American astronomer Charles Kowal and classified as an asteroid with the number 2060. It is about 200 km (125 miles) in diameter and travels in an unstable, eccentric orbit that crosses that of Saturn and passes just inside that of Uranus with a period of 50.45 years. In 1989 American astronomers Karen Meech and Michael Belton detected a fuzzy luminous cloud around Chiron. Such a cloud, termed a coma, is a distinguishing feature of comets and consists of gases and entrained dust escaping from the cometary nucleus when sunlight causes its ices to sublimate. Given Chiron’s large distance from the Sun, the sublimating ices are likely far more volatile substances than water ice, such as carbon monoxide and carbon dioxide. On the basis of that discovery, Chiron was reclassified as a comet. Additional study of historical observations showed that Chiron was active in the past, including at the time of its discovery in 1977. Subsequently, additional asteroid-size icy bodies in orbits that cross those of the outer planets were discovered and given the class name Centaur objects. Several of them have also displayed sporadic cometlike activity.
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comet: The modern eraNamed 2060 Chiron, it is about 200 km (120 miles) in diameter and has a low-inclination orbit that stretches from 8.3 AU (inside the orbit of Saturn) to 18.85 AU (just inside the orbit of Uranus). Because it can make close approaches to those two giant planets,…
asteroid: Asteroids in unusual orbits…of Phaethon and Hidalgo is Chiron, which, following its discovery in 1977, was classified as an asteroid, (2060) Chiron. In 1989 the object was observed to have a dusty coma surrounding it, and in 1991 the presence of cyanogen radicals was detected, a known constituent of the gas comas of…
solar system: The small bodies…but the Centaur object called Chiron—originally classified as a distant asteroid but now known to show characteristics of a comet—has a diameter estimated to be about 200 km (125 miles). Other bodies of this size and much larger—e.g., Pluto and Eris—have been observed in the Kuiper belt. Most of the…