CHIRON DATADiscoverer : Charles Kowal Date : 01 November 1977 Satellites : 0 Diameter : 132±142 km. Polar Tilt : Unknown Period (P) : 50.794 years Synodic Period : 358.17 days Orbital Velocity : 7.75 kms-1 Distance : 13.89 AU or ‗9 km Perihelion (q) : 8.46 A.U. Aphelion (Q) : 18.91 A.U. Eccentricity (e) : 0.3836 Inclination (i) : 6.929o Mass : 2.7‗0.3 x 1018 kg. Mean Density : 2.0 g.cm-3? Sidereal Rotation : 5.918 hr. Mean Sidereal Rotation : 5.918 hr. Maximum Magnitude : 15.6 Minimum Magnitude : 19.6 |
CHIRON (2060) or 1977 UB is the closest and first of the Centaur-type Cb objects that is sometimes referred as a distant outer asteroid. Discovered by Charles Kowal on 01st November 1977, Chiron lies just within orbit at perihelion of Saturn and just outside that of Uranus at aphelion.
With the short orbital period of 50.78 years and having the mean solar distance of 13.89 AU, Chiron changes position more rapidly than the other more distant TBO’s. An highly eccentric orbit (e) of 0.382, finds that distances from the Sun between periastron to apastron may vary anywhere from 8.46 AU to 18.91 AU - a difference of almost 75%! The slight inclination of 6.94o means that Chiron follows the ecliptic similar to all the main planets. Physically, Chiron is only 163 kilometres across and is unusually dark. Detailed photometry has revealed the short rotation period of 5.92 hours.
This is certainly an unusual planetary body, as it shows characteristics similar to both comets and asteroids. Almost since the day of its discovery, Charon was found to have an unexpected very thin atmosphere of cyanogen (HCN) and other gases - similar to what has been found in comets. During opposition in 1988 and 1989, and likely for several years around perihelion, Charon was suddenly to brighten by just over one magnitude. Remarkably it then displayed characteristics of a cometary-like coma, making some to speculated that Chiron may be actually a very large distant comet or even, as some suggest, a proto-comet. For this reason Chiron shares its name as asteroid 2060 and also as comet 95P/Chiron!
Other examples of Centaur-type asteroids include 5335 Damocles, whose orbit ranges from just ouside of Mars’ to just beyond Uranus. Another is 5145 Pholus, that orbits between Saturn to just beyond Neptune. Since Kowal’s discover, many more Centaurs have been found, but all these planet-crossing orbits are unstable and suffer much from the gravitational perturbations from the outer planets. Like Charon, most Centaurs are more like comets, the distant Kuiper belt or even the other trans-Neptunian bodies.
Presently, yellowish Chiron is very faint at 18.5 magnitude, that varies by 0.3 magnitude between opposition and conjuction. In 2006-08, it remains close to the border of Carpicornus and Aquarius, and will cross into Pisces by 2014. Perihelion last occurred 14th February 1996, making the time of the next aphelion in early May 2020 (2020.48). At the Pisces opposition in 2020 the maximum magnitude peaks at 19.2, dropping to the minimum brightness of 19.6 magnitude. Like most of these small outer solar system bodies, they are almost totally invisible to amateur telescopes, but Chiron seem to be the exception. For only several years around 1996, Chiron reached its oppositions in Virgo where the magnitude just topped 15.6 magnitude. It was easily visible in dark skies using either in 35cm to 40cm telescopes as a faint star, whose movement could be detected over one or two nights. After about 2002, Chiron became more difficult to see, as the maximum brightness will drop below 17th magnitude. Amateurs will likely have their chances again in seeing Chiron probably between 2043 and 2048 AD, whose opposition again in Virgo becomes brightest around 2046 AD.
In ancient Greek mythology the principal leader of the mythical Centaurs - creatures who are half human and half horse. The Centaurs were established in the early history of the world, whose creation was made by the union of Cronus (Saturn) and the nymph Philyra. (Although to detailed for our discussion here, the detailed mythology of Cronus can be readed in Saturn : Part 2 and about the nymphs Neptune : Part 2.) Chiron, was unlike his often drunken and violent fellow Centaurs, as he was considered to be highly cultured and wise. He was often associated as a great healer and teacher, and being the son of Cronus, he was an immortal. However, he was eventually accidentally killed by a dropped poison arrow, and because of his charity and the healing of the sick, he was respectfully placed among the stars by the ancient Greeks as the constellation of Sagittarius. In more recent times, others associated him with the mainly southern constellation of Centaurus.
NOTE : Chiron should not to be confused with the similarly named Charon, the largest moon orbiting Pluto. Charon, which was found later in 1978.
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