95P/Chiron (0095P)
Type: Periodic
Perihelion date: 27 August 2046
Perihelion distance (q): 8.5
Aphelion distance (Q) : 18.9
Period (years): 50.7
Eccentricity (e): 0.38
Inclination (i): 6.9
JPL Orbit diagram
COBS lightcurve
Atlas
Chiron was discovered on 18 October 1977 by Charles Kowal from images taken two
weeks earlier at Palomar Observatory. It was given the temporary designation of 1977
UB. It was found near aphelion and at the time of discovery it was the most distant
known minor planet, even claimed as the tenth planet by the press.
Chiron was later found on several precovery images, going back to 1895, which
allowed its orbit to be accurately determined.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. 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.
It was named in 1979 after Chiron, one of the centaurs; it was suggested that the
names of other centaurs be reserved for objects of the same type. Chiron's orbit was
found to be highly eccentric (0.37), with perihelion just inside the orbit of Saturn and
aphelion just outside the perihelion of Uranus (it does not reach the average distance
of Uranus, however).
According to the program Solex, Chiron's closest approach to Saturn in modern times
was around May 720, when it came within 30.5±2.0 million km of Saturn. During this
passage Saturn's gravity caused Chiron's semi-major axis to decrease from
14.55±0.12 AU to 13.7 AU. It does not come nearly as close to Uranus; Chiron
crosses Uranus's orbit where the latter is farther than average from the Sun.
Chiron attracted considerable interest because it was the first object discovered in
such an orbit, well outside the asteroid belt. Chiron is classified as a centaur, the first
of a class of objects orbiting between the outer planets. Chiron is a Saturn-Uranus
object because its perihelion lies in Saturn's zone of control and its aphelion lies in
that of Uranus. Centaurs are not in stable orbits and will be removed by gravitational
perturbation by the giant planets over a period of millions of years, moving to different
orbits or leaving the Solar System altogether. Chiron is probably a refugee from the
Kuiper belt and will probably become a short-period comet in about a million years.
The visible and near-infrared spectrum of Chiron is neutral, and is similar to that of C-
type asteroids and the nucleus of Halley's Comet. 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. Estimates in the
1990s were closer to 150 km in diameter. Occultation data from 1993 suggests a
diameter of about 180 km. Combined data from the Spitzer Space Telescope in 2007
and the Herschel Space Observatory in 2011 suggests that Chiron is 218 ± 20 km in
diameter. Its rotational period is 5.917813 hours, a value determined by observing its
distinct light curve.
In February 1988, at 12 AU from the Sun, Chiron brightened by 75 percent. This is
behavior typical of comets but not asteroids. Further observations in April 1989
showed that Chiron had developed a cometary coma. A tail was detected in 1993.
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. 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 its current
orbit very long.
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,
52872 Okyrhoe significantly brightened. Other Chiron-type comets include:
39P/Oterma, 165P/LINEAR, 166P/NEAT, and 167P/CINEOS. There are also non-
centaurs that are classified as comets, such as 4015 Wilson-Harrington, 7968 Elst-
Pizarro, and 118401 LINEAR.
Chiron is suspected to have two rings, similar to the better-established rings of
Chariklo. Based on unexpected occultation events observed in stellar-occultation data
obtained on 7 November 1993, 9 March 1994, and 29 November 2011, which were
initially interpreted as resulting from jets associated with Chiron's comet-like activity,
Chiron's rings are proposed to be 324 (± 10) km in radius and sharply defined. Their
changing appearance at different viewing angles can largely explain the long-term
variation in Chiron's brightness and hence estimates of Chiron's albedo and size.
Moreover, it can, by assuming that the water ice is in Chiron's rings, explain the
changing intensity of the infrared water-ice absorption bands in Chiron's spectrum,
including their disappearance in 2001 (when the rings were edge-on). Also, the
geometric albedo of Chiron's rings as determined by spectroscopy is consistent with
that used to explain Chiron's long-term brightness variations.
Observations (VEMag = visual equivalent magnitude)
Date
10x10 mag
Error
VEmag
Coma '
15-Aug-15
17.96
0.04
17.8
0.2
22-Aug-15
17.88
0.04
17.6
0.2
06-Sep-15
17.78
0.02
17.7
0.2
16-Sep-15
17.73
0.02
17.5
0.2
30-Oct-15
17.92
0.03
17.8
0.2
07-Nov-15
17.94
0.02
17.8
0.2
16-Nov-15
17.88
0.03
15.1
0.2
03-Dec-15
18.13
0.05
18.0
0.2
11-Dec-15
18.06
0.06
17.9
0.2
09-Jun-16
18.21
0.04
17.7
0.2
26-Aug-16
18.10
0.10
n/a
n/a
01-Sep-16
17.92
0.03
17.6
0.2
08-Sep-16
17.82
0.03
17.8
0.2
22-Sep-16
17.86
0.08
17.6
0.2
30-Sep-16
17.96
0.04
17.8
0.2
08-Oct-16
18.00
0.05
17.9
0.2
29-Oct-16
18.09
0.03
17.7
0.2
05-Nov-16
18.12
0.03
18.0
0.2
24-Nov-16
18.14
0.04
18.1
0.2
27-Dec-16
18.01
0.09
17.9
0.2
26-May-17
18.11
0.10
17.9
0.2
06-Jun-17
18.22
0.07
17.7
0.2
22-Jun-17
18.12
0.05
17.8
0.2
06-Jul-17
18.12
0.06
17.8
0.2
21-Jul-17
18.17
0.09
17.9
0.2
30-Jul-17
18.06
0.07
18.0
0.2
25-Aug-17
17.97
0.04
17.9
0.2
28-Aug-17
18.00
0.04
17.8
0.2
04-Sep-17
17.93
0.06
17.6
0.2
15-Sep-17
17.83
0.04
17.7
0.2
26-Sep-17
17.87
0.05
17.6
0.2
01-Oct-17
17.97
0.12
17.5
0.2
11-Oct-17
18.00
0.03
17.9
0.1
18-Oct-17
18.10
0.04
18.0
0.2
20-Nov-17
18.00
0.04
17.9
0.2
05-Jan-18
18.20
0.08
17.8
0.2
14-Jul-18
18.27
0.04
18.2
0.2
22-Jul-18
18.24
0.05
18.0
0.2
06-Aug-18
18.14
0.03
17.3
0.2
04-Sep-18
18.03
0.18
18.0
0.2
12-Oct-18
17.93
0.02
17.8
0.2
30-Oct-18
18.15
0.06
18.0
0.2
29-Nov-18
18.27
0.02
17.9
0.2
08-Dec-18
18.30
0.05
18.1
0.2
28-Dec-18
18.32
0.05
18.3
0.2
13-Aug-19
18.21
0.05
17.9
0.2
26-Aug-19
18.17
0.04
18.0
0.2
02-Sep-19
18.08
0.04
16.9
0.2
10-Sep-19
17.96
0.02
18.0
0.2
26-Sep-19
17.80
0.04
17.5
0.2
02-Oct-19
17.92
0.04
17.9
0.2
21-Oct-19
18.03
0.01
17.8
0.2
28-Oct-19
18.04
0.02
18.0
0.2
20-Nov-19
18.09
0.04
18.0
0.2
26-Dec-19
18.21
0.05
18.1
0.2
15-Jan-20
18.22
0.05
18.1
0.2
14-Sep-20
18.34
0.08
17.7
0.4
21-Sep-20
18.20
0.08
17.9
0.4
09-Oct-20
18.15
0.13
17.3
0.4
07-Nov-20
18.32
0.15
18.0
0.4
16-Nov-20
18.26
0.07
17.8
0.4
08-Dec-20
17.7
0.4
16-Dec-20
17.8
0.4
01-Jan-21
17.7
0.4
31-Aug-21
17.7
0.4
05-Aug-22
18.4
0.4
25-Aug-22
18.2
0.4
06-Sep-22
18.0
0.4
21-Sep-22
18.1
0.4
02-Oct-22
17.7
0.4
19-Oct-22
18.2
0.4
26-Oct-22
18.1
0.4
01-Nov-22
18.3
0.4
13-Nov-22
18.1
0.4
22-Nov-22
17.8
0.4
19-Aug-23
18.1
0.4
09-Sep-23
18.2
0.4
21-Sep-23
18.2
0.4
11-Aug-24
18.5
0.4
30-Aug-24
18.6
0.4
06-Sep-24
18.3
0.4
05-Oct-24
18.2
0.4
03-Dec-24
18.8
0.4