2060 Chiron
Encyclopedia
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), 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 classified as an asteroid
, it was later found to exhibit behaviour 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 Pluto
nian moon Charon
, discovered the following year, in 1978.
. It was given the temporary designation of 1977UB.
It was found near aphelion and at the time of discovery it was the most distant known minor planet
. Chiron was 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 2060 Chiron in 1979. The proposed symbol is ⚷. Chiron was one of the centaur
s, and it was suggested that the names of other centaurs be reserved for other objects of the same type.
spectrum of Chiron is neutral, and is similar to that of C-type asteroid
s 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. Asteroid occultation data from 1993 suggests a diameter of about 180 km. The data from the Spitzer Space Telescope
in 2007 suggests that Chiron is closer to in diameter. Therefore Chiron may be as large as 10199 Chariklo
.
Its rotational period is 5.917813 hours, a value determined by observing its distinct light curve.
, and 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 this orbit that long.
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. 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 asteroids 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.
There are other non-centaurs that are classified as comets: 4015 Wilson–Harrington, 7968 Elst–Pizarro, and 118401 LINEAR
.
(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 in May 720, at just under 30 million kilometres. During this passage Saturn's gravity caused Chiron's semi-major axis
to decrease from 14.4AU to 13.7AU. It does not come nearly as close to Uranus; Chiron crosses Uranus' orbit where the latter is farther than average from the Sun. It 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 an SU object since its perihelion lies within Saturn's zone of control and its aphelion lies within Uranus' zone of control. Centaurs are not in stable orbits and over millions of years will eventually be removed by gravitational perturbation
by the giant planets, 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.
Chiron came to perihelion
(closest point to the Sun) in 1996.
Minor planet
An asteroid group or minor-planet group is a population of minor planets that have a share broadly similar orbits. Members are generally unrelated to each other, unlike in an asteroid family, which often results from the break-up of a single asteroid...
in the outer Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
. Discovered in 1977 by Charles T. Kowal
Charles T. Kowal
Charles Thomas Kowal was an American astronomer.He discovered two moons of Jupiter: Leda in 1974 and Themisto in 1975, although the latter was lost and not rediscovered until 2000....
(precovery
Precovery
Precovery is a term used in astronomy that describes the process of finding the image of an object in old archived images or photographic plates, for the purpose of calculating a more accurate orbit...
images have been found as far back as 1895), it was the first-known member of a new class of objects now known as centaurs, with an orbit
Orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
between Saturn
Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
and Uranus
Uranus
Uranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. It is named after the ancient Greek deity of the sky Uranus , the father of Cronus and grandfather of Zeus...
.
Although it was initially classified as an asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
, it was later found to exhibit behaviour typical of a comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the 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
Centaur
In Greek mythology, a centaur or hippocentaur is a member of a composite race of creatures, part human and part horse...
Chiron
Chiron
In Greek mythology, Chiron was held to be the superlative centaur among his brethren.-History:Like the satyrs, centaurs were notorious for being wild and lusty, overly indulgent drinkers and carousers, given to violence when intoxicated, and generally uncultured delinquents...
in Greek mythology
Greek mythology
Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...
. It should not be confused with the Pluto
Pluto
Pluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System and the tenth-most-massive body observed directly orbiting the Sun...
nian moon Charon
Charon (moon)
Charon is the largest satellite of the dwarf planet Pluto. It was discovered in 1978 at the United States Naval Observatory Flagstaff Station. Following the 2005 discovery of two other natural satellites of Pluto , Charon may also be referred to as Pluto I...
, discovered the following year, in 1978.
Discovery and naming
Chiron was discovered on 18 October 1977 by Charles Kowal from images taken two weeks earlier at Palomar ObservatoryPalomar Observatory
Palomar Observatory is a privately owned observatory located in San Diego County, California, southeast of Pasadena's Mount Wilson Observatory, in the Palomar Mountain Range. At approximately elevation, it is owned and operated by the California Institute of Technology...
. It was given the temporary designation of 1977UB.
It was found near aphelion and at the time of discovery it was the most distant known minor planet
Minor planet
An asteroid group or minor-planet group is a population of minor planets that have a share broadly similar orbits. Members are generally unrelated to each other, unlike in an asteroid family, which often results from the break-up of a single asteroid...
. Chiron was even claimed as the tenth planet by the press. Chiron was later found on several precovery
Precovery
Precovery is a term used in astronomy that describes the process of finding the image of an object in old archived images or photographic plates, for the purpose of calculating a more accurate orbit...
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 2060 Chiron in 1979. The proposed symbol is ⚷. Chiron was one of the centaur
Centaur
In Greek mythology, a centaur or hippocentaur is a member of a composite race of creatures, part human and part horse...
s, and it was suggested that the names of other centaurs be reserved for other objects of the same type.
Physical characteristics
The visible and near-infraredInfrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
spectrum of Chiron is neutral, and is similar to that of C-type asteroid
C-type asteroid
C-type asteroids are carbonaceous asteroids. They are the most common variety, forming around 75% of known asteroids, and an even higher percentage in the outer part of the asteroid belt beyond 2.7 AU, which is dominated by this asteroid type...
s and the nucleus of Halley's Comet.
The assumed size of an object depends on its absolute magnitude (H) and the albedo
Albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...
(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. Asteroid occultation data from 1993 suggests a diameter of about 180 km. The data from the Spitzer Space Telescope
Spitzer Space Telescope
The Spitzer Space Telescope , formerly the Space Infrared Telescope Facility is an infrared space observatory launched in 2003...
in 2007 suggests that Chiron is closer to in diameter. Therefore Chiron may be as large as 10199 Chariklo
10199 Chariklo
10199 Chariklo is the largest known centaur. It orbits the Sun between Saturn and Uranus, grazing Uranus.Chariklo was discovered by James V. Scotti of the Spacewatch program on February 15, 1997. Chariklo is named after the nymph Chariclo , the wife of Chiron and the daughter of Apollo.A...
.
Its rotational period is 5.917813 hours, a value determined by observing its distinct light curve.
Cometary behaviour
In February 1988, at 12 AU from the Sun, Chiron brightened by 75 percent. This is behaviour typical of comets but not asteroids. Further observations in April 1989 showed that Chiron had developed a cometary comaComa (cometary)
frame|right|The [[153P/Ikeya-Zhang|comet Ikeya-Zhang]] exhibiting a bright, condensed coma In astronomy, a coma is the nebulous envelope around the nucleus of a comet. It is formed when the comet passes close to the Sun on its highly elliptical orbit; as the comet warms, parts of it sublimate...
, and a tail was detected in 1993. Chiron differs from other comets in that water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
is not a major component of its coma, because it is too far from the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
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 this orbit that long.
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. Being at least 130 km in diameter, it is unusually large for a comet nucleus
Comet nucleus
The nucleus is the solid, central part of a comet, popularly termed a dirty snowball. A cometary nucleus is composed of rock, dust, and frozen gases. When heated by the Sun, the gases sublimate and produce an atmosphere surrounding the nucleus known as the coma...
.
Since the discovery of Chiron, other centaurs have been discovered, and nearly all are currently classified as asteroids but are being observed for possible cometary behavior. 60558 Echeclus
60558 Echeclus
60558 Echeclus is a centaur in the outer Solar System. It was discovered by Spacewatch in 2000 and initially classified as an asteroid with provisional designation . Research in 2001 by Rousselot and Petit at the Besançon observatory in France showed no evidence of cometary activity, but in late...
has displayed a cometary coma and now also has the cometary designation 174P/Echeclus. After passing perihelion in early 2008, centaur 52872 Okyrhoe
52872 Okyrhoe
52872 Okyrhoe is a centaur orbiting in the outer Solar System between Jupiter and Neptune. It was discovered on September 19, 1998, by Spacewatch.-Orbit:Centaurs have short dynamical lives due to strong interactions with the giant planets...
significantly brightened.
There are other non-centaurs that are classified as comets: 4015 Wilson–Harrington, 7968 Elst–Pizarro, and 118401 LINEAR
118401 LINEAR
118401 LINEAR is an asteroid and main-belt comet which was discovered by the Lincoln Near-Earth Asteroid Research 1-metre telescopes in Socorro, New Mexico on September 7, 1999. LINEAR was discovered to be cometary on November 26, 2005, by Henry H. Hsieh and David C...
.
Orbit
Chiron's orbit was found to be highly eccentricOrbital eccentricity
The orbital eccentricity of an astronomical body is the amount by which its orbit deviates from a perfect circle, where 0 is perfectly circular, and 1.0 is a parabola, and no longer a closed orbit...
(0.37), with perihelion
Apsis
An apsis , plural apsides , is the point of greatest or least distance of a body from one of the foci of its elliptical orbit. In modern celestial mechanics this focus is also the center of attraction, which is usually the center of mass of the system...
just inside the orbit of Saturn
Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
and aphelion
Apsis
An apsis , plural apsides , is the point of greatest or least distance of a body from one of the foci of its elliptical orbit. In modern celestial mechanics this focus is also the center of attraction, which is usually the center of mass of the system...
just outside the perihelion of Uranus
Uranus
Uranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. It is named after the ancient Greek deity of the sky Uranus , the father of Cronus and grandfather of Zeus...
(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 in May 720, at just under 30 million kilometres. During this passage Saturn's gravity caused Chiron's semi-major axis
Semi-major axis
The major axis of an ellipse is its longest diameter, a line that runs through the centre and both foci, its ends being at the widest points of the shape...
to decrease from 14.4AU to 13.7AU. It does not come nearly as close to Uranus; Chiron crosses Uranus' orbit where the latter is farther than average from the Sun. It attracted considerable interest because it was the first object discovered in such an orbit, well outside the asteroid belt
Asteroid belt
The asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets...
. Chiron is classified as a centaur, the first of a class of objects orbiting between the outer planets. Chiron is an SU object since its perihelion lies within Saturn's zone of control and its aphelion lies within Uranus' zone of control. Centaurs are not in stable orbits and over millions of years will eventually be removed by gravitational perturbation
Perturbation (astronomy)
Perturbation is a term used in astronomy in connection with descriptions of the complex motion of a massive body which is subject to appreciable gravitational effects from more than one other massive body....
by the giant planets, moving to different orbits or leaving the Solar System altogether. Chiron is probably a refugee from the Kuiper belt
Kuiper belt
The Kuiper belt , sometimes called the Edgeworth–Kuiper belt, is a region of the Solar System beyond the planets extending from the orbit of Neptune to approximately 50 AU from the Sun. It is similar to the asteroid belt, although it is far larger—20 times as wide and 20 to 200 times as massive...
and will probably become a short-period comet in about a million years.
Chiron came to perihelion
Apsis
An apsis , plural apsides , is the point of greatest or least distance of a body from one of the foci of its elliptical orbit. In modern celestial mechanics this focus is also the center of attraction, which is usually the center of mass of the system...
(closest point to the Sun) in 1996.
The orbit of 2060 Chiron compared with the orbits of Jupiter Jupiter Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,... , Saturn Saturn Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,... , Uranus Uranus Uranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. It is named after the ancient Greek deity of the sky Uranus , the father of Cronus and grandfather of Zeus... and Neptune Neptune Neptune is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times... . |
The chaotic unstable motion of Chiron as simulated by Gravity Simulator. It is possible that Chiron will evolve into a 2:1 near resonance with Saturn over the next 10,000+ years. |
External links
- Orbital simulation from JPL (Java) / Ephemeris
- 95P/Chiron at Cometography
- A single clone run of centaur 2060 Chiron showing how Chiron may someday become an active comet (Solex 10)