Chiron

2060 Chiron (kye'-rən, IPA: /ˈkaɪrən/) is a planetoid in the outer solar system. Discovered in 1977 by Charles T. Kowal (precovery images have been found as far back as 1895),^[4] 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.

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^[5] 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.

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.

References

1. ^ ^{a b} Groussin (01/2004). Properties of the nuclei of Centaurs Chiron and Chariklo. Astronomy and Astrophysics, v.413, p.1163-1175 (2004). Retrieved on 2007-10-18.
2. ^ JPL Small-Body Database. Retrieved on 2007-01-11.
3. ^ Meech, Karen (19-FEB-1994). THE STRUCTURE OF THE INNER COMA OF COMET CHIRON: IMAGING THE EXOPAUSE. INSTITUTE FOR ASTRONOMY, UNIVERSITY OF HAWAII. Retrieved on 2007-10-19.
4. ^ Grayzeck, Ed (2003-12-11). The Chiron Perihelion Campaign. NASA Goddard Space Flight Center. Retrieved on 2007-10-18.
5. ^ Kowal (1979 pages= 249). "The discovery and orbit of /2060/ Chiron" (PDF). In: Dynamics of the solar system; Proceedings of the Symposium, Tokyo, Japan, May 23-26, 1978. (A79-36276 15-89) Dordrecht, D. Reidel Publishing Co., 1979, p. 245-250.. 

• Luu JX, Jewitt DC, Trujillo C. (2000). "Water Ice in 2060 Chiron and Its Implications for Centaurs and Kuiper Belt Objects". Astrophysical Journal 531 (2): L151-L154.  PMID 10688775. Preprint on arXiv.
• Fernandez Y.R., Jewitt DC, Sheppard S (2002). "Thermal Properties of Centaurs Asbolus and Chiron". Astrophysical Journal 123: 1050–1055.  Preprint on arXiv.
• Patrick Moore Guinness book of Astronomy ISBN 0-85112-375-9

External links

• Orbital simulation from JPL (Java) / Ephemeris

Donate to Wikimedia