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95P/Chiron

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95P/Chiron

2060 Chiron
95P/Chiron
Discovery
Discovered by Charles T. Kowal
Discovery date October 18, 1977
Designations
MPC designation 2060 Chiron
95P/Chiron
Pronunciation /ˈkaɪərən/
Named after Chiron
Alternative names 1977 UB
Minor planet category Centaur,[1] Comet
Adjective Chironean, Chironian
Orbital characteristics[2]
Epoch June 18, 2009 (JD 2455000.5)
Aphelion 18.891 AU (Q)
2,826 Gm
Perihelion 8.5114 AU (q)
1,273 Gm
Semi-major axis 13.708 AU (2,050.7 Gm) (a)
Eccentricity 0.37911
Orbital period 50.76 a (18,539 d)
Average orbital speed 7.75 km/s
Mean anomaly 94.716° (M)
Inclination 6.9311°
Longitude of ascending node 209.31°
Argument of perihelion 339.98°
Physical characteristics
Dimensions

233 ± 14 km[3]

132–152 km[4]
Rotation period 0.2466 d (5.918 h)[2]
Albedo

0.075 ± 0.01[3]

0.11 ± 0.02 [4]
Temperature ~75 K
Spectral type B,Cb[2]
Apparent magnitude ~18.7[5]
15.6 (Perihelic opposition)
Absolute magnitude (H) 6.5[2]
Angular diameter 0.035" (max)[6]

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),[7] 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.

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.

Mike Brown lists it as a possible dwarf planet with a measured diameter of 233 km.[8]

Discovery and naming

Chiron was discovered on 18 October 1977 by Charles Kowal from images taken two weeks earlier at Palomar Observatory.[9] It was given the temporary designation of 1977 UB.[10] It was found near aphelion[9] and at the time of discovery it was the most distant known minor planet.[10] Chiron was even claimed as the tenth planet by the press.[11] Chiron was later found on several precovery images, going back to 1895, which allowed its orbit to be accurately determined.[9] 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.[9] 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.[9]

It was named 2060 Chiron in 1979[10] after Chiron, one of the centaurs; it was suggested that the names of other centaurs be reserved for objects of the same type.[9] The proposed symbol is ⚷.[proposed by who?]

Physical characteristics

The visible and near-infrared spectrum of Chiron is neutral,[10] and is similar to that of C-type asteroids and the nucleus of Halley's Comet.[12]

Size estimates for Chiron:[4]
Year Radius (km) Notes
1984 90 Lebofsky
1991 <186 IRAS
1994 74 Campins
1996 90 occultation
2007 117[3] Spitzer Space Telescope
2013 109[13] Herschel Space Observatory

The assumed size of an object depends on its absolute magnitude (H) and the albedo (the amount of light it reflects). In 1984 Lebofsky estimated Chiron to be about 180 km in diameter.[4] Estimates in the 1990s were closer to 150 km in diameter.[2][4] Occultation data from 1993 suggests a diameter of about 180 km.[4] The data from the Spitzer Space Telescope in 2007 suggests that Chiron is closer to 233 ± 14 km in diameter.[3] Therefore Chiron may be as large as 10199 Chariklo.[3]

Its rotational period is 5.917813 hours, a value determined by observing its distinct light curve.[10]

Cometary behavior

In February 1988, at 12 AU from the Sun, Chiron brightened by 75 percent.[14] This is behavior typical of comets but not asteroids. Further observations in April 1989 showed that Chiron had developed a cometary coma,[15] A tail was detected in 1993.[10] Chiron differs from other comets in that water is not a major component of its coma, because it is too far from the Sun for water to sublimate.[16]

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. The fact that Chiron is still active probably means it has not been in this orbit that long.[7]

Chiron is officially designated as both a comet and a minor planet, an indication of the sometimes fuzzy dividing line between the two classes of object. The term proto-comet has also been used. Being at least 130 km in diameter, it is unusually large for a comet nucleus.

Since the discovery of Chiron, other centaurs have been discovered, and nearly all are currently classified as minor planets but are being observed for possible cometary behavior. 60558 Echeclus has displayed a cometary coma and now also has the cometary designation 174P/Echeclus. After passing perihelion in early 2008, centaur 52872 Okyrhoe significantly brightened.[17]

Chiron is a Chiron-type comet with (TJupiter > 3; a > aJupiter).[2] Other Chiron-type comets include: 39P/Oterma, 165P/LINEAR, 166P/NEAT, and 167P/CINEOS. There are other non-centaurs that are classified as comets: 4015 Wilson–Harrington, 7968 Elst–Pizarro, and 118401 LINEAR.[18]

Orbit

Chiron's orbit was found to be highly

Chiron came to perihelion (closest point to the Sun) in 1996.[2]

Orbit
Neptune.
Chaotic Motion
near resonance with Saturn over the next 10,000+ years.

References

Notes

External links

  • 2060 Chiron at the JPL Small-Body Database
  • Physical parameters
  • Cometography
  • A single clone run of centaur 2060 Chiron showing how Chiron may someday become an active comet (Solex 10)
Periodic comets (by number)
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