Centaurs (minor planets)
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In planetary astronomy, a centaur is a small Solar System body with either a perihelion or a
semi-major axis In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The semi-major axis (major semiaxis) is the long ...
between those of the
outer planets The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
(between Jupiter and Neptune). Centaurs generally have unstable orbits because they cross or have crossed the orbits of one or more of the giant planets; almost all their orbits have dynamic lifetimes of only a few million years, but there is one known centaur,
514107 Kaʻepaokaʻawela 514107 Kaʻepaokaʻāwela (), provisionally designated and nicknamed Bee-Zed, is a small asteroid, approximately in diameter, in a resonant, co-orbital motion with Jupiter. It is an unusual minor planet in that its orbit is retrograde, which ...
, which may be in a stable (though retrograde) orbit. Centaurs typically exhibit the characteristics of both
asteroid An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...
s and comets. They are named after the mythological
centaur A centaur ( ; grc, κένταυρος, kéntauros; ), or occasionally hippocentaur, is a creature from Greek mythology with the upper body of a human and the lower body and legs of a horse. Centaurs are thought of in many Greek myths as being ...
s that were a mixture of horse and human. Observational bias toward large objects makes determination of the total centaur population difficult. Estimates for the number of centaurs in the Solar System more than 1 km in diameter range from as low as 44,000 to more than 10,000,000. The first centaur to be discovered, under the definition of the Jet Propulsion Laboratory and the one used here, was 944 Hidalgo in 1920. However, they were not recognized as a distinct population until the discovery of
2060 Chiron 2060 Chiron is a small Solar System body in the outer Solar System, orbiting the Sun between Saturn and Uranus. Discovered in 1977 by Charles Kowal, it was the first-identified member of a new class of objects now known as centaurs—bodies orb ...
in 1977. The largest confirmed centaur is
10199 Chariklo 10199 Chariklo is the largest confirmed centaur (small body of the outer Solar System). It orbits the Sun between Saturn and Uranus, grazing the orbit of Uranus. On 26 March 2014, astronomers announced the discovery of two rings (nicknamed ...
, which at 260 kilometers in diameter is as big as a mid-sized main-belt asteroid, and is known to have a system of rings. It was discovered in 1997. No centaur has been photographed up close, although there is evidence that
Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...
's moon Phoebe, imaged by the ''Cassini'' probe in 2004, may be a captured centaur that originated in the
Kuiper belt The Kuiper belt () is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune at 30 astronomical units (AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger—20 times ...
. In addition, the Hubble Space Telescope has gleaned some information about the surface features of 8405 Asbolus.
Ceres Ceres most commonly refers to: * Ceres (dwarf planet), the largest asteroid * Ceres (mythology), the Roman goddess of agriculture Ceres may also refer to: Places Brazil * Ceres, Goiás, Brazil * Ceres Microregion, in north-central Goiás st ...
may have originated in the region of the outer planets, and if so might be considered an ex-centaur, but the centaurs seen today all originated elsewhere. Of the objects known to occupy centaur-like orbits, approximately 30 have been found to display comet-like dust
coma A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to respond normally to painful stimuli, light, or sound, lacks a normal wake-sleep cycle and does not initiate voluntary actions. Coma patients exhi ...
s, with three,
2060 Chiron 2060 Chiron is a small Solar System body in the outer Solar System, orbiting the Sun between Saturn and Uranus. Discovered in 1977 by Charles Kowal, it was the first-identified member of a new class of objects now known as centaurs—bodies orb ...
,
60558 Echeclus 60558 Echeclus is a centaur, approximately in diameter, located in the outer Solar System. It was discovered by Spacewatch in 2000 and initially classified as a minor planet with provisional designation (also written 2000 EC98). Research in 20 ...
, and 29P/Schwassmann-Wachmann 1, having detectable levels of volatile production in orbits entirely beyond Jupiter. Chiron and Echeclus are therefore classified as both centaurs and comets, while Schwassmann-Wachmann 1 has always held a comet designation. Other centaurs, such as 52872 Okyrhoe, are suspected of having shown
comas A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to respond normally to painful stimuli, light, or sound, lacks a normal wake-sleep cycle and does not initiate voluntary actions. Coma patients exhi ...
. Any centaur that is perturbed close enough to the Sun is expected to become a comet.


Classification

The generic definition of a centaur is a small body that orbits the Sun between Jupiter and
Neptune Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...
and crosses the orbits of one or more of the giant planets. Due to the inherent long-term instability of orbits in this region, even centaurs such as and , which do not currently cross the orbit of any planet, are in gradually changing orbits that will be perturbed until they start to cross the orbit of one or more of the giant planets. Some astronomers count only bodies with semimajor axes in the region of the outer planets to be centaurs; others accept any body with a perihelion in the region, as their orbits are similarly unstable.


Discrepant criteria

However, different institutions have different criteria for classifying borderline objects, based on particular values of their
orbital elements Orbital elements are the parameters required to uniquely identify a specific orbit. In celestial mechanics these elements are considered in two-body systems using a Kepler orbit. There are many different ways to mathematically describe the same ...
: * The
Minor Planet Center The Minor Planet Center (MPC) is the official body for observing and reporting on minor planets under the auspices of the International Astronomical Union (IAU). Founded in 1947, it operates at the Smithsonian Astrophysical Observatory. Function ...
(MPC) defines centaurs as having a perihelion beyond the orbit of Jupiter () and a semi-major axis less than that of Neptune (). Though nowadays the MPC often lists centaurs and scattered disc objects together as a single group. * The Jet Propulsion Laboratory (JPL) similarly defines centaurs as having a semi-major axis, ''a'', between those of Jupiter and Neptune (). * In contrast, the
Deep Ecliptic Survey The Deep Ecliptic Survey (DES) is a project to find Kuiper belt objects (KBOs), using the facilities of the National Optical Astronomy Observatory (NOAO). The principal investigator is Robert L. Millis. Since 1998 through the end of 2003, the sur ...
(DES) defines centaurs using a dynamical classification scheme. These classifications are based on the simulated change in behavior of the present orbit when extended over 10 million years. The DES defines centaurs as non-resonant objects whose instantaneous ( osculating) perihelia are less than the osculating semi-major axis of Neptune at any time during the simulation. This definition is intended to be synonymous with planet-crossing orbits and to suggest comparatively short lifetimes in the current orbit. * The collection ''The Solar System Beyond Neptune'' (2008) defines objects with a semi-major axis between those of Jupiter and Neptune and a Jupiter-relative
Tisserand's parameter Tisserand's parameter (or Tisserand's invariant) is a value calculated from several orbital elements (semi-major axis, orbital eccentricity and inclination) of a relatively small object and a larger " perturbing body". It is used to distinguish dif ...
above 3.05 as centaurs, classifying the objects with a Jupiter-relative Tisserand's parameter below this and, to exclude
Kuiper belt The Kuiper belt () is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune at 30 astronomical units (AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger—20 times ...
objects, an arbitrary perihelion cut-off half-way to Saturn () as Jupiter-family comets, and classifying those objects on unstable orbits with a semi-major axis larger than Neptune's as members of the scattered disc. * Other astronomers prefer to define centaurs as objects that are non-resonant with a perihelion inside the orbit of Neptune that can be shown to likely cross the Hill sphere of a gas giant within the next 10 million years, so that centaurs can be thought of as objects scattered inwards and that interact more strongly and scatter more quickly than typical scattered-disc objects. * The JPL Small-Body Database lists 452 centaurs. There are an additional 116  trans-Neptunian objects (objects with a semi-major axis further than Neptune's, i.e. ) with a perihelion closer than the orbit of Uranus ().


Ambiguous objects

The Gladman & Marsden (2008) criteria would make some objects Jupiter-family comets: Both Echeclus (, ) and Okyrhoe (; ) have traditionally been classified as centaurs. Traditionally considered an asteroid, but classified as a centaur by JPL, Hidalgo (; ) would also change category to a Jupiter-family comet. Schwassmann-Wachmann 1 (; ) has been categorized as both a centaur and a Jupiter-family comet depending on the definition used. Other objects caught between these differences in classification methods include , which has a semi-major axis of 32 AU but crosses the orbits of both Uranus and Neptune. It is listed as an outer centaur by the ''Deep Ecliptic Survey'' (DES). Among the inner centaurs,
(434620) 2005 VD (434620) 2005 VD, provisional designation , is a Centaur (minor planet), centaur and damocloid on a retrograde orbit from the outer Solar System, known for having the second most highly inclined orbit of any small Solar System body, behind . It wa ...
, with a perihelion distance very near Jupiter, is listed as a centaur by both JPL and DES. A recent orbital simulation of the evolution of Kuiper Belt Objects through the centaur region has identified a short-lived "''orbital gateway''" between 5.4 and 7.8 AU through which 21% of all centaurs pass, including 72% of the centaurs that become Jupiter-family comets. Four objects are known to occupy this region, including 29P/Schwassmann-Wachmann, P/2010 TO20 LINEAR-Grauer, P/2008 CL94 Lemmon, and 2016 LN8, but the simulations indicate that there may of order 1000 more objects >1 km in radius that have yet to be detected. Objects in this gateway region can display significant activity and are in an important evolutionary transition state that further blurs the distinction between the centaur and Jupiter-family comet populations. The Committee on Small Body Nomenclature of the International Astronomical Union has not formally weighed in on any side of the debate. Instead, it has adopted the following naming convention for such objects: Befitting their centaur-like transitional orbits between TNOs and comets, "objects on unstable, non-resonant, giant-planet-crossing orbits with semimajor axes greater than Neptune's" are to be named for other hybrid and shape-shifting mythical creatures. Thus far, only the binary objects Ceto and Phorcys and Typhon and Echidna have been named according to the new policy. Centaurs with measured diameters listed as possible dwarf planets according to Mike Brown's website include
10199 Chariklo 10199 Chariklo is the largest confirmed centaur (small body of the outer Solar System). It orbits the Sun between Saturn and Uranus, grazing the orbit of Uranus. On 26 March 2014, astronomers announced the discovery of two rings (nicknamed ...
, and
2060 Chiron 2060 Chiron is a small Solar System body in the outer Solar System, orbiting the Sun between Saturn and Uranus. Discovered in 1977 by Charles Kowal, it was the first-identified member of a new class of objects now known as centaurs—bodies orb ...
.


Orbits


Distribution

The diagram illustrates the orbits of known centaurs in relation to the orbits of the planets. For selected objects, the eccentricity of the orbits is represented by red segments (extending from perihelion to aphelion). The orbits of centaurs show a wide range of eccentricity, from highly eccentric ( Pholus, Asbolus, Amycus, Nessus) to more circular ( Chariklo and the Saturn-crossers
Thereus __NOTOC__ ''Thereus'' is a genus of gossamer-winged butterflies (family Lycaenidae). Among these, it belongs belong to the tribe Eumaeini of the subfamily Theclinae. These small butterflies occur essentially all over the Neotropics.See referenc ...
and Okyrhoe). To illustrate the range of the orbits' parameters, the diagram shows a few objects with very unusual orbits, plotted in yellow : * ( Apollo asteroid) follows an extremely eccentric orbit (), leading it from inside Earth's orbit (0.94 AU) to well beyond Neptune () * follows a quasi-circular orbit () * has the lowest inclination (). * is one of a small proportion of centaurs with an extreme prograde inclination (). It follows such a highly inclined orbit (79°) that, while it crosses from the distance of the asteroid belt from the Sun to past the distance of Saturn, if its orbit is projected onto the plane of Jupiter's orbit, it does not even go out as far as Jupiter. Over a dozen known centaurs follow retrograde orbits. Their inclinations range from modest (''e.g''., 160° for Dioretsa) to extreme (; ''e.g''. 105° for ). Seventeen of these high-inclination, retrograde centaurs were controversially claimed to have an interstellar origin.


Changing orbits

Because the centaurs are not protected by orbital resonances, their orbits are unstable within a timescale of 106–107 years. For example,
55576 Amycus 55576 Amycus is a centaur discovered on 8 April 2002 by the NEAT at Palomar. The minor planet was named for Amycus, a male centaur in Greek mythology. It came to perihelion in February 2003. Data from the Spitzer Space Telescope gave a diamete ...
is in an unstable orbit near the 3:4 resonance of Uranus. Dynamical studies of their orbits indicate that being a centaur is probably an intermediate orbital state of objects transitioning from the
Kuiper belt The Kuiper belt () is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune at 30 astronomical units (AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger—20 times ...
to the Jupiter family of short-period comets. Objects may be perturbed from the Kuiper belt, whereupon they become
Neptune Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...
-crossing and interact gravitationally with that planet (see theories of origin). They then become classed as centaurs, but their orbits are chaotic, evolving relatively rapidly as the centaur makes repeated close approaches to one or more of the outer planets. Some centaurs will evolve into Jupiter-crossing orbits whereupon their perihelia may become reduced into the inner Solar System and they may be reclassified as active comets in the Jupiter family if they display cometary activity. Centaurs will thus ultimately collide with the Sun or a planet or else they may be ejected into interstellar space after a close approach to one of the planets, particularly Jupiter.


Physical characteristics

The relatively small size of centaurs precludes remote observation of surfaces, but
colour indices In astronomy, the color index is a simple numerical expression that determines the color of an object, which in the case of a star gives its temperature. The lower the color index, the more blue (or hotter) the object is. Conversely, the large ...
and spectra can provide clues about surface composition and insight into the origin of the bodies.
Preprint version (pdf)


Colours

The colours of centaurs are very diverse, which challenges any simple model of surface composition. In the side-diagram, the
colour indices In astronomy, the color index is a simple numerical expression that determines the color of an object, which in the case of a star gives its temperature. The lower the color index, the more blue (or hotter) the object is. Conversely, the large ...
are measures of apparent magnitude of an object through blue (B), visible (V) (i.e. green-yellow) and red (R) filters. The diagram illustrates these differences (in exaggerated colours) for all centaurs with known colour indices. For reference, two moons:
Triton Triton commonly refers to: * Triton (mythology), a Greek god * Triton (moon), a satellite of Neptune Triton may also refer to: Biology * Triton cockatoo, a parrot * Triton (gastropod), a group of sea snails * ''Triton'', a synonym of ''Triturus' ...
and Phoebe, and planet Mars are plotted (yellow labels, size not to scale). Centaurs appear to be grouped into two classes: * very red – for example
5145 Pholus 5145 Pholus is an eccentric centaur in the outer Solar System, approximately in diameter, that crosses the orbit of both Saturn and Neptune. It was discovered on 9 January 1992 by American astronomer David Rabinowitz (uncredited) of UA's Space ...
* blue (or blue-grey, according to some authors) – for example
2060 Chiron 2060 Chiron is a small Solar System body in the outer Solar System, orbiting the Sun between Saturn and Uranus. Discovered in 1977 by Charles Kowal, it was the first-identified member of a new class of objects now known as centaurs—bodies orb ...
or There are numerous theories to explain this colour difference, but they can be divided broadly into two categories: *The colour difference results from a difference in the origin and/or composition of the centaur (see origin below) * The colour difference reflects a different level of space-weathering from
radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: * ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...
and/or cometary activity. As examples of the second category, the reddish colour of Pholus has been explained as a possible mantle of irradiated red organics, whereas Chiron has instead had its ice exposed due to its periodic cometary activity, giving it a blue/grey index. The correlation with activity and color is not certain, however, as the active centaurs span the range of colors from blue (Chiron) to red (166P/NEAT). Bauer, J. M., Fernández, Y. R., & Meech, K. J. 2003.
An Optical Survey of the Active Centaur C/NEAT (2001 T4)
, Publication of the Astronomical Society of the Pacific", 115, 981
Alternatively, Pholus may have been only recently expelled from the Kuiper belt, so that surface transformation processes have not yet taken place. Delsanti et al. suggest multiple competing processes: reddening by the radiation, and blushing by collisions. Hainaut & Delsanti (2002) ''Color of Minor Bodies in the Outer Solar System'' Astronomy & Astrophysics, 389, 64
datasource


Spectra

The interpretation of spectra is often ambiguous, related to particle sizes and other factors, but the spectra offer an insight into surface composition. As with the colours, the observed spectra can fit a number of models of the surface. Water ice signatures have been confirmed on a number of centaurs (including
2060 Chiron 2060 Chiron is a small Solar System body in the outer Solar System, orbiting the Sun between Saturn and Uranus. Discovered in 1977 by Charles Kowal, it was the first-identified member of a new class of objects now known as centaurs—bodies orb ...
,
10199 Chariklo 10199 Chariklo is the largest confirmed centaur (small body of the outer Solar System). It orbits the Sun between Saturn and Uranus, grazing the orbit of Uranus. On 26 March 2014, astronomers announced the discovery of two rings (nicknamed ...
and
5145 Pholus 5145 Pholus is an eccentric centaur in the outer Solar System, approximately in diameter, that crosses the orbit of both Saturn and Neptune. It was discovered on 9 January 1992 by American astronomer David Rabinowitz (uncredited) of UA's Space ...
). In addition to the water ice signature, a number of other models have been put forward: *Chariklo's surface has been suggested to be a mixture of
tholin Tholins (after the Greek (') "hazy" or "muddy"; from the ancient Greek word meaning "sepia ink") are a wide variety of organic compounds formed by solar ultraviolet or cosmic ray irradiation of simple carbon-containing compounds such as carbon ...
s (like those detected on
Titan Titan most often refers to: * Titan (moon), the largest moon of Saturn * Titans, a race of deities in Greek mythology Titan or Titans may also refer to: Arts and entertainment Fictional entities Fictional locations * Titan in fiction, fictiona ...
and
Triton Triton commonly refers to: * Triton (mythology), a Greek god * Triton (moon), a satellite of Neptune Triton may also refer to: Biology * Triton cockatoo, a parrot * Triton (gastropod), a group of sea snails * ''Triton'', a synonym of ''Triturus' ...
) with
amorphous In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid, glassy solid) is a solid that lacks the long-range order that is characteristic of a crystal. Etymology The term comes from the Greek ''a'' ("wi ...
carbon. *Pholus has been suggested to be covered by a mixture of Titan-like
tholin Tholins (after the Greek (') "hazy" or "muddy"; from the ancient Greek word meaning "sepia ink") are a wide variety of organic compounds formed by solar ultraviolet or cosmic ray irradiation of simple carbon-containing compounds such as carbon ...
s, carbon black, olivine and
methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is a ...
ice. *The surface of
52872 Okyrhoe 52872 Okyrhoe is a centaur orbiting in the outer Solar System between Jupiter and Saturn. It was discovered on 19 September 1998, by the Spacewatch survey at Kitt Peak Observatory in Arizona, United States, and named after Ocyrhoe from Greek myt ...
has been suggested to be a mixture of kerogens, olivines and a small percentage of water ice. * 8405 Asbolus has been suggested to be a mixture of 15% Triton-like
tholin Tholins (after the Greek (') "hazy" or "muddy"; from the ancient Greek word meaning "sepia ink") are a wide variety of organic compounds formed by solar ultraviolet or cosmic ray irradiation of simple carbon-containing compounds such as carbon ...
s, 8% Titan-like tholin, 37% amorphous carbon and 40% ice tholin. Chiron appears to be the most complex. The spectra observed vary depending on the period of the observation. Water ice signature was detected during a period of low activity and disappeared during high activity.


Similarities to comets

Observations of Chiron in 1988 and 1989 near its perihelion found it to display a
coma A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to respond normally to painful stimuli, light, or sound, lacks a normal wake-sleep cycle and does not initiate voluntary actions. Coma patients exhi ...
(a cloud of gas and dust evaporating from its surface). It is thus now officially classified as both a minor planet and a comet, although it is far larger than a typical comet and there is some lingering controversy. Other centaurs are being monitored for comet-like activity: so far two,
60558 Echeclus 60558 Echeclus is a centaur, approximately in diameter, located in the outer Solar System. It was discovered by Spacewatch in 2000 and initially classified as a minor planet with provisional designation (also written 2000 EC98). Research in 20 ...
, and 166P/NEAT have shown such behavior. 166P/NEAT was discovered while it exhibited a coma, and so is classified as a comet, though its orbit is that of a centaur.
60558 Echeclus 60558 Echeclus is a centaur, approximately in diameter, located in the outer Solar System. It was discovered by Spacewatch in 2000 and initially classified as a minor planet with provisional designation (also written 2000 EC98). Research in 20 ...
was discovered without a coma but recently became active, and so it too is now classified as both a comet and an asteroid. Overall, there are ~30 centaurs for which activity has been detected, with the active population biased toward objects with smaller perihelion distances. Carbon monoxide has been detected in
60558 Echeclus 60558 Echeclus is a centaur, approximately in diameter, located in the outer Solar System. It was discovered by Spacewatch in 2000 and initially classified as a minor planet with provisional designation (also written 2000 EC98). Research in 20 ...
and Chiron in very small amounts, and the derived CO production rate was calculated to be sufficient to account for the observed coma. The calculated CO production rate from both
60558 Echeclus 60558 Echeclus is a centaur, approximately in diameter, located in the outer Solar System. It was discovered by Spacewatch in 2000 and initially classified as a minor planet with provisional designation (also written 2000 EC98). Research in 20 ...
and Chiron is substantially lower than what is typically observed for
29P/Schwassmann–Wachmann Comet 29P/Schwassmann–Wachmann, also known as Schwassmann–Wachmann 1, was discovered on November 15, 1927, by Arnold Schwassmann and Arno Arthur Wachmann at the Hamburg Observatory in Bergedorf, Germany. It was discovered photographically, w ...
, another distantly active comet often classified as a centaur. There is no clear orbital distinction between centaurs and comets. Both 29P/Schwassmann-Wachmann and
39P/Oterma 39P/Oterma is a currently inactive List of periodic comets, periodic comet with an orbital period of nearly 20 years that stays outside the orbit of Jupiter. The comet nucleus, nucleus has a diameter around 4–5 km. It was last observed in Augu ...
have been referred to as centaurs since they have typical centaur orbits. The comet 39P/Oterma is currently inactive and was seen to be active only before it was perturbed into a centaur orbit by Jupiter in 1963. The faint comet 38P/Stephan–Oterma would probably not show a coma if it had a perihelion distance beyond Jupiter's orbit at 5 AU. By the year 2200, comet 78P/Gehrels will probably migrate outwards into a centaur-like orbit.


Rotational periods

A periodogram analysis of the light-curves of these Chiron and Chariklo gives respectively the following rotational periods: 5.5±0.4~h and 7.0± 0.6~h.


Size, density, reflectivity

Centaurs can reach diameters up to hundreds of kilometers. The largest centaurs have diameters in excess of 300 km, and primarily reside beyond 20 AU.


Hypotheses of origin

The study of centaurs’ origins is rich in recent developments, but any conclusions are still hampered by limited physical data. Different models have been put forward for possible origin of centaurs. Simulations indicate that the orbit of some
Kuiper belt The Kuiper belt () is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune at 30 astronomical units (AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger—20 times ...
objects can be perturbed, resulting in the object's expulsion so that it becomes a centaur. Scattered disc objects would be dynamically the best candidates (For instance, the centaurs could be part of an "inner" scattered disc of objects perturbed inwards from the Kuiper belt.) for such expulsions, but their colours do not fit the bicoloured nature of the centaurs. Plutinos are a class of Kuiper belt object that display a similar bicoloured nature, and there are suggestions that not all plutinos' orbits are as stable as initially thought, due to
perturbation Perturbation or perturb may refer to: * Perturbation theory, mathematical methods that give approximate solutions to problems that cannot be solved exactly * Perturbation (geology), changes in the nature of alluvial deposits over time * Perturbatio ...
by Pluto. Further developments are expected with more physical data on Kuiper belt objects. Some centaurs may have their origin in fragmentation episodes, perhaps triggered during close encounters with Jupiter. The orbits of centaurs
2020 MK4 (PanSTARRS) is a Chiron-type comet or active centaur orbiting in the outer Solar System between Jupiter and Saturn. It was discovered on 24 June 2020, by the Pan-STARRS survey at Haleakala Observatory in Hawaii, United States. Size A lower ...
, P/2008 CL94 (Lemmon), and P/2010 TO20 (LINEAR-Grauer) pass close to that of comet
29P/Schwassmann–Wachmann Comet 29P/Schwassmann–Wachmann, also known as Schwassmann–Wachmann 1, was discovered on November 15, 1927, by Arnold Schwassmann and Arno Arthur Wachmann at the Hamburg Observatory in Bergedorf, Germany. It was discovered photographically, w ...
, the first discovered centaur and close encounters are possible in which one of the objects traverses the coma of 29P when active. At least one centaur, 2013 VZ70, might have an origin among Saturn's irregular moon population via impact, fragmentation, or tidal disruption.


Notable centaurs


See also

*
Asteroid An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...
* Dwarf planet


Notes


References


External links


List of centaurs and scattered-disk objects
* Centaurs fro

*
NASA's WISE Finds Mysterious Centaurs May Be Comets (2013)
{{DEFAULTSORT:Centaur (Minor Planet) Distant minor planets