2060 Chiron

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2060 Chiron
95P/Chiron
Discovery
Discovered by:	Charles T. Kowal
Discovery date:	October 18, 1977
Alternative names:	1977 UB
Minor planet category:	Centaur, Comet
Orbital characteristics
Epoch May 10, 2005 (JD 2453500.5)
Aphelion distance:	2.826 Gm (18.891 AU)
Perihelion distance:	1.263 Gm (8.449 AU)
Semi-major axis:	2.045 G m (13.670 AU)
Eccentricity:	0.382
Orbital period:	18461.347 d (50.54 a)
Avg. orbital speed:	7.75 km/s
Mean anomaly:	65.733°
Inclination:	6.935°
Longitude of ascending node:	209.231°
Argument of perihelion:	339.606°
Physical characteristics
Dimensions:	132-142 km 1
Mass:	2.4-3.0×10¹⁸ kg
Mean density:	2.0? g/cm³
Equatorial surface gravity:	0.037-0.040 m/s²
Escape velocity:	0.070-0.075 km/s
Rotation period:	0.2466 d (5.918 h) 2
Albedo:	0.10?
Temperature:	~75 K
Spectral type:	B,Cb [1]
Absolute magnitude:	6.5

2060 Chiron (kye'-rən, IPA: /ˈkaɪrən/) is a planetoid in the outer solar system. Discovered in 1977 by Charles T. Kowal, it was the first known member of a new class of objects now known as Centaurs, with an orbit between those of Saturn and Uranus.

Although it was initially classified as an asteroid, later dispute arose as to whether it was an asteroid or actually a comet. Today it is classified as both, and accordingly it is also known by the cometary designation 95P/Chiron.

Chiron is named after the centaur Chiron in Greek mythology. It should not be confused with the largest moon of Pluto named Charon, discovered in 1978.

1 Orbit
2 Physical characteristics
3 References
4 External links

[edit] Orbit

Chiron's orbit was found to be highly eccentric, with perihelion just inside the orbit of Saturn and aphelion just inside the orbit of Uranus (thus, it crosses Saturn's orbit, but not that of Uranus). It attracted considerable interest because it was the first object discovered in such an orbit, well outside the asteroid belt. Chiron is now classified as a Centaur, the first of a class of objects orbiting between the outer planets. Centaurs are not in stable orbits and will eventually be removed by gravitational perturbation by the giant planets, moving to different orbits or leaving the solar system altogether.

It has been calculated that in 1664 BC Chiron approached Saturn to within approximately 16 million kilometres; only 3 million km further away than Saturn's largest outer moon Phoebe, and within the orbital radii of many of Saturn's newly discovered minor satellites. Chiron is probably a refugee from the Kuiper belt.

[edit] Physical characteristics

In 1988 it was found that Chiron was undergoing an outburst in brightness (by about one magnitude), which is behaviour typical of comets but not asteroids. Further observations in 1989 showed that Chiron had developed a cometary coma. At the time of its discovery, Chiron was close to aphelion, whereas the observations showing a coma were done closer to perihelion, perhaps explaining why no cometary behavior had been seen earlier.

Chiron is officially designated as both a comet and an asteroid, an indication of the sometimes fuzzy dividing line between the two classes of object. The term proto-comet has also been used. At approximately 180km across, it is unusually large for a comet nucleus.

Since the discovery of Chiron, quite a few other Centaurs have been discovered, and nearly all are currently classified as asteroids but are being observed for possible cometary behavior. As of March 2006, only one has been observed to have a cometary coma: 60558 Echeclus, which now also has the cometary designation 174P/Echeclus.

There are also three other non-Centaur asteroids that are also classified as comets: 4015 Wilson-Harrington, 7968 Elst-Pizarro, and 118401 LINEAR. The Centaur 60558 Echeclus is also cross-listed as comet 174P/Echeclus.