2060 Chiron: Difference between revisions
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{{short description| | {{short description|Ringed centaur and comet}} | ||
{{distinguish|text=Pluto's moon [[Charon (moon)|Charon]]}} | {{distinguish|text=Pluto's moon [[Charon (moon)|Charon]]}} | ||
{{Use dmy dates|date=July 2021}} | {{Use dmy dates|date=July 2021}} | ||
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| background = #C7FF8F | | background = #C7FF8F | ||
| name = 2060 Chiron<br/>95P/Chiron | | name = 2060 Chiron<br/>95P/Chiron | ||
| symbol = [[File:Chiron symbol (bold).svg|24px|⚷]] (astrological) | | symbol = [[File:Chiron symbol (bold).svg|24px|class=skin-invert|⚷]] (astrological) | ||
| image = | | image = 2060 Chiron.jpg | ||
| image_scale = | | image_scale = | ||
| caption = [[Hubble Space Telescope]] image of | | caption = [[Hubble Space Telescope]] image of Chiron and its [[coma (cometary)|coma]], taken in 1996 | ||
| discovery_ref = <ref name="MPC-Chiron" /><ref name="Kowal-1978" /><ref name="gsfc-Chiron" /> | | discovery_ref = <ref name="MPC-Chiron"/><ref name="Kowal-1978"/><ref name="gsfc-Chiron"/> | ||
| discoverer = [[Charles Kowal]] | | discoverer = [[Charles Kowal]] | ||
| discovery_site = [[Palomar Observatory]] | | discovery_site = [[Palomar Observatory]] | ||
| discovered = 1 November 1977 | | discovered = 1 November 1977 | ||
| mpc_name = {{ublist|(2060) Chiron|95P/Chiron<ref name="dualstatus" />}} | | mpc_name = {{ublist|(2060) Chiron|95P/Chiron<ref name="dualstatus"/>}} | ||
| alt_names = 1977 UB | | alt_names = 1977 UB<br>OK (Object Kowal) | ||
| pronounced = {{IPAc-en|ˈ|k|aɪ|r|ɒ|n}} | | pronounced = {{IPAc-en|ˈ|k|aɪ|r|ɒ|n}} | ||
| adjectives = {{ubl|Chironian|Chironean|(both {{IPAc-en|k|aɪ|ˈ|r|oʊ|n|i|ən}})}} | | adjectives = {{ubl|Chironian|Chironean|(both {{IPAc-en|k|aɪ|ˈ|r|oʊ|n|i|ən}})}} | ||
| named_after = [[Chiron]] {{small|([[Greek mythology]])}}<ref name="springer" /> | | named_after = [[Chiron]] {{small|([[Greek mythology]])}}<ref name="springer"/> | ||
| mp_category = {{ublist|[[Centaur (minor planet)|centaur]]<ref name="jpldata" /><ref name="Centaurs" />|[[comet]]|[[Distant minor planet|distant]]<ref name="MPC-Chiron" />}} | | mp_category = {{ublist|[[Centaur (minor planet)|centaur]]<ref name="jpldata"/><ref name="Centaurs"/>|[[comet]]|[[Distant minor planet|distant]]<ref name="MPC-Chiron"/>}} | ||
| orbit_ref = <ref name="jpldata" /> | | orbit_ref = <ref name="jpldata"/> | ||
| epoch = 2021-Jul-01 ([[Julian day|JD]] | | epoch = 2021-Jul-01 ([[Julian day|JD]] 2,459,396.5) | ||
| uncertainty = 0 | | uncertainty = 0 | ||
| observation_arc = 126.29 yr | | observation_arc = 126.29 yr | ||
| Line 41: | Line 41: | ||
| uranus_moid = {{Convert|1.4|AU|e6km|abbr=unit}}<ref name="MPC-Chiron"/> | | uranus_moid = {{Convert|1.4|AU|e6km|abbr=unit}}<ref name="MPC-Chiron"/> | ||
| tisserand = 3.363 | | tisserand = 3.363 | ||
| | | dimensions = {{val|252|x|218|x|136}} km<ref name="Sickafoose2023"/><br/>± ({{val|44|x|38|x|24}} km)<ref name="Sickafoose2023"/> | ||
| | | mean_diameter = {{val|196|34|u=km}}<ref name="Sickafoose2023"/> | ||
| rotation = {{val|5.918}} [[Hour|h]]<ref name="lcdb" /><ref name="Bus-1989" /><ref name="Luu-1990b" /><ref name="Marcialis-1993" /><ref name="Lazzaro-1997" /> | | rotation = {{val|5.918}} [[Hour|h]]<ref name="lcdb"/><ref name="Bus-1989"/><ref name="Luu-1990b"/><ref name="Marcialis-1993"/><ref name="Lazzaro-1997"/> | ||
| albedo = {{ublist|0.057 {{small|(assumed)}}<ref name="lcdb" />|{{val|0.15|0.03}}<ref name="jpldata" />|{{val|0.160|0.030}}<ref name="Fornasier-2013" />}} | | albedo = {{ublist|0.057 {{small|(assumed)}}<ref name="lcdb"/>|{{val|0.15|0.03}}<ref name="jpldata"/>|{{val|0.160|0.030}}<ref name="Fornasier-2013"/>}} | ||
| spectral_type = {{ublist | |||
| spectral_type = {{ublist | |||
| [[B-type asteroid|B]] {{small|([[Tholen classification|Tholen]])}}, Cb {{small|([[SMASS classification|SMASS]])}}, Double-Dip type {{small|(DiSCo-Webb)}} | |||
| [[Asteroid color indices|B–V]] {{=}} 0.704<ref name="jpldata"/> | |||
| [[Asteroid color indices|U–B]] {{=}} 0.283<ref name="jpldata"/> | |||
| [[Trans-Neptunian object#Spectra|BB]]<ref name="Belskaya-2015"/> | |||
| [[C-type asteroid|C]]<ref name="lcdb"/> | |||
}} | }} | ||
| magnitude = 18.93<ref name="AstDys" /><br/>14. | | magnitude = 18.93<ref name="AstDys"/><br/>14.6 {{small|([[Apsis|Perihelic]] opposition)}}<ref name="apmag1996"/> | ||
| abs_magnitude = {{ublist|{{val|5.80|0.27}}<ref name="Veres-2015" />|{{val|5.82|0.07}}<ref name="Belskaya-2010b" />|5.83<ref name="jpldata"/>|{{val|5.92|0.20}}<ref name="Fornasier-2013" />|{{nowrap|{{val|6.287|0.022}} {{small|(R)}}<ref name="Peixinho-2012" />}}|6.56<ref name="lcdb" /><ref name="Davies-1998b" />|6.79<ref name="Lazzaro-1997" />}} | | abs_magnitude = {{ublist|{{val|5.80|0.27}}<ref name="Veres-2015"/>|{{val|5.82|0.07}}<ref name="Belskaya-2010b"/>|5.83<ref name="jpldata"/>|{{val|5.92|0.20}}<ref name="Fornasier-2013"/>|{{nowrap|{{val|6.287|0.022}} {{small|(R)}}<ref name="Peixinho-2012"/>}}|6.56<ref name="lcdb"/><ref name="Davies-1998b"/>|6.79<ref name="Lazzaro-1997"/>}} | ||
| angular_size = 0.035" (max)<ref name="arcsec" /> | | angular_size = 0.035" (max)<ref name="arcsec"/> | ||
}} | }} | ||
'''2060 Chiron''' is a ringed [[small Solar System body]] in the [[Solar System#Outer Solar System|outer Solar System]], [[orbit]]ing 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 [[centaur (small Solar System body)|centaur]]s—bodies orbiting between the [[asteroid belt]] and the [[Kuiper belt]].<ref group=lower-alpha>[[944 Hidalgo]], discovered in 1920, also fits this definition, but was not identified as belonging to a distinct population.</ref> Chiron is named after the [[centaur]] [[Chiron]] in [[Greek mythology]]. | '''2060 Chiron''' is a ringed [[small Solar System body]] in the [[Solar System#Outer Solar System|outer Solar System]], [[orbit]]ing 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 [[centaur (small Solar System body)|centaur]]s—bodies orbiting between the [[asteroid belt]] and the [[Kuiper belt]].<ref group=lower-alpha>[[944 Hidalgo]], discovered in 1920, also fits this definition, but was not identified as belonging to a distinct population.</ref> Chiron is named after the [[centaur]] [[Chiron]] in [[Greek mythology]]. | ||
Although it was initially called an [[asteroid]] and classified only as a [[minor planet]] with the designation "2060 Chiron", in 1989 it was found to exhibit behavior typical of a [[comet]]. Today it is classified as both a minor planet and a comet, and is accordingly also known by the cometary designation '''95P/Chiron'''. More recently, a series of [[occultation]] events through the 2010s and early 2020s revealed that Chiron hosts [[ring system|rings]], making it one of four minor planets and the only known comet to | Although it was initially called an [[asteroid]] and classified only as a [[minor planet]] with the designation "2060 Chiron", in 1989 it was found to exhibit behavior typical of a [[comet]]. Today it is classified as both a minor planet and a comet, and is accordingly also known by the cometary designation '''95P/Chiron'''. More recently, a series of [[occultation]] events through the 2010s and early 2020s revealed that Chiron hosts [[ring system|rings]], making it one of [[Ring system#Rings systems of minor planets and moons|four minor planets known to have rings]] (the three others being [[10199 Chariklo]], [[Haumea]], and [[Quaoar]]) and the only known comet to do so. | ||
== History == | == History == | ||
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=== Discovery === | === Discovery === | ||
Chiron was discovered on 1 November 1977 by [[Charles Kowal]] from images taken on 18 October at [[Palomar Observatory]].<ref name="Kowal-1978" /><ref name="gsfc-Chiron" /> It was given the temporary designation of {{mp|1977 UB}}.<ref name="Campins-1994" /> It was found near [[aphelion]]<ref name="Kowal-1978" /> and at the time of discovery it was the most distant known minor planet.<ref group=lower-alpha>[[Pluto]], now considered to be a [[dwarf planet]] and hence a minor planet, was known at the time, but was considered a planet.</ref><ref name="Campins-1994" /> Chiron was even claimed as the tenth planet by the press.<ref name="Collander-Brown2000" /> Chiron was later found on several [[precovery]] images, going back to 1895,<ref name="Perihelion" /> which allowed its orbit to be accurately determined.<ref name="Kowal-1978" /> 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.<ref name="Kowal-1978" /> The April 1895 precovery image was one month after the March 1895 perihelion.<ref name="Horizons1895"/> | Chiron was discovered on 1 November 1977 by [[Charles Kowal]] from images taken on 18 October at [[Palomar Observatory]].<ref name="Kowal-1978"/><ref name="gsfc-Chiron"/> It was given the temporary designation of {{mp|1977 UB}}.<ref name="Campins-1994"/> It was found near [[aphelion]]<ref name="Kowal-1978"/> and at the time of discovery it was the most distant-known minor planet.<ref group=lower-alpha>[[Pluto]], now considered to be a [[dwarf planet]] and hence a minor planet, was known at the time, but was considered a planet.</ref><ref name="Campins-1994"/> Chiron was even claimed as the tenth planet by the press.<ref name="Collander-Brown2000"/> Chiron was later found on several [[precovery]] images, going back to 1895,<ref name="Perihelion"/> which allowed its orbit to be accurately determined.<ref name="Kowal-1978"/> 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.<ref name="Kowal-1978"/> The April 1895 precovery image was one month after the March 1895 perihelion.<ref name="Horizons1895"/> | ||
=== Naming === | === Naming === | ||
This [[minor planet]] was named after [[Chiron]], a half-human, half-horse [[centaur]] from [[Greek mythology]]. Son of the Titan [[Cronus]] and the nymph [[Philyra (Oceanid)|Philyra]], Chiron was the wisest and most just of all centaurs, serving as an instructor of the Greek heroes.<ref name="springer" /> The official {{MoMP|2060|naming citation}} was published by the [[Minor Planet Center]] on 1 April 1978 ({{small|[[Minor Planet Circulars|M.P.C.]] 4359}}).<ref name="springer" /><ref name="DoMP-Circular-dates" /> It was suggested that the names of other centaurs be reserved for objects of the same type.<ref name="Kowal-1978" /> | This [[minor planet]] was named after [[Chiron]], a half-human, half-horse [[centaur]] from [[Greek mythology]]. Son of the Titan [[Cronus]] and the nymph [[Philyra (Oceanid)|Philyra]], Chiron was the wisest and most just of all centaurs, serving as an instructor of the Greek heroes.<ref name="springer"/> The official {{MoMP|2060|naming citation}} was published by the [[Minor Planet Center]] on 1 April 1978 ({{small|[[Minor Planet Circulars|M.P.C.]] 4359}}).<ref name="springer"/><ref name="DoMP-Circular-dates"/> It was suggested that the names of other centaurs be reserved for objects of the same type.<ref name="Kowal-1978"/> | ||
Chiron, along with most major and minor planetary bodies, is not generally given a symbol in astronomy. A symbol [[File:Chiron symbol (fixed width).svg|24px|⚷]] was devised for it by Al H. Morrison and is mostly used among astrologers: it resembles a key as well as an OK monogram for '''O'''bject '''K'''owal.<ref> | Chiron, along with most major and minor planetary bodies, is not generally given a symbol in astronomy. A symbol, [[File:Chiron symbol (fixed width).svg|24px|class=skin-invert|⚷]], was devised for it by Al H. Morrison and is mostly used among astrologers: it resembles a key as well as an OK monogram for '''O'''bject '''K'''owal.<ref> | ||
{{cite journal | {{cite journal | ||
| last = Morrison | | last = Morrison | ||
| Line 84: | Line 86: | ||
== Orbit == | == Orbit == | ||
[[File:Chiron orbit.PNG|thumb|left|200px|Orbital diagram of Chiron]] | [[File:Chiron orbit.PNG|thumb|left|200px|Orbital diagram of Chiron]] | ||
Chiron's orbit was found to be highly [[Orbital eccentricity|eccentric]] (0.37), with [[Apsis|perihelion]] just inside the orbit of [[Saturn]] and [[Apsis|aphelion]] just outside the perihelion of [[Uranus]] (it does not reach the average distance of Uranus, however). According to the program [https://web.archive.org/web/20081220235836/http://chemistry.unina.it/~alvitagl/solex/ Solex], Chiron's closest approach to Saturn in modern times was around May 720, when it came within {{val|30.5|2.0}} million km ({{cvt|30.5|±|2.0|e6km|AU|disp=out}}) of the planet. During this passage Saturn's gravity caused Chiron's [[semi-major axis]] to decrease from {{val|14.55|0.12}} AU<ref name="Chiron700AD" /> to 13.7 AU.<ref name="jpldata" /> Chiron's orbit does not intersect Uranus' orbit. | Chiron's orbit was found to be highly [[Orbital eccentricity|eccentric]] (0.37), with [[Apsis|perihelion]] just inside the orbit of [[Saturn]] and [[Apsis|aphelion]] just outside the perihelion of [[Uranus]] (it does not reach the average distance of Uranus, however). According to the program [https://web.archive.org/web/20081220235836/http://chemistry.unina.it/~alvitagl/solex/ Solex], Chiron's closest approach to Saturn in modern times was around May 720, when it came within {{val|30.5|2.0}} million km ({{cvt|30.5|±|2.0|e6km|AU|disp=out}}) of the planet. During this passage Saturn's gravity caused Chiron's [[semi-major axis]] to decrease from {{val|14.55|0.12}} AU<ref name="Chiron700AD"/> to 13.7 AU.<ref name="jpldata"/> Chiron's orbit does not intersect Uranus' orbit. | ||
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 planet]]s. Chiron is a Saturn–Uranus object because its perihelion lies in Saturn's zone of control and its aphelion lies in that of Uranus.<ref name="Horner2004" /> Centaurs are not in stable orbits and will be removed by gravitational [[Perturbation (astronomy)|perturbation]] by the giant planets over a period of millions of years, moving to different orbits or leaving the Solar System altogether.<ref name="Jewitt2006" /> Chiron likely comes from the [[Kuiper belt]] and will probably become a [[short-period comet]] in about a million years.<ref name="Horner2004" /> Chiron came to [[Apsis|perihelion]] (closest point to the Sun) in 1996 and aphelion in May 2021.<ref name="Horizons2021"/> | 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 planet]]s. Chiron is a Saturn–Uranus object because its perihelion lies in Saturn's zone of control and its aphelion lies in that of Uranus.<ref name="Horner2004"/> Centaurs are not in stable orbits and will be removed by gravitational [[Perturbation (astronomy)|perturbation]] by the giant planets over a period of millions of years, moving to different orbits or leaving the Solar System altogether.<ref name="Jewitt2006"/> Chiron likely comes from the [[Kuiper belt]] and will probably become a [[short-period comet]] in about a million years.<ref name="Horner2004"/> Chiron came to [[Apsis|perihelion]] (closest point to the Sun) in 1996 and aphelion in May 2021.<ref name="Horizons2021"/> | ||
== Physical characteristics == | == Physical characteristics == | ||
| Line 92: | Line 94: | ||
=== Spectral type === | === Spectral type === | ||
The visible and near-[[infrared]] spectrum of Chiron is neutral,<ref name="Campins-1994" /> and is similar to that of [[C-type asteroid]]s and the nucleus of [[Halley's Comet]].<ref name="Luu-1990b" /> The near-infrared spectrum of Chiron shows absence of water ice.<ref name="Luu-2000" /> | The visible and near-[[infrared]] spectrum of Chiron is neutral,<ref name="Campins-1994"/> and is similar to that of [[C-type asteroid]]s and the nucleus of [[Halley's Comet]].<ref name="Luu-1990b"/> The near-infrared spectrum of Chiron shows absence of water ice.<ref name="Luu-2000"/> The infrared spectrum, however, from 0.97 to 5.27 μm, as revealed by the James Webb Space Telescope<ref name="Pinilla-2024"/> reveals the presence of gas in the coma and a diverse inventory of ices, on the surface or in the coma. Absorption bands of [[carbon dioxide]], [[carbon monoxide]], [[ethane]], [[propane]], and [[acetylene]] were detected, together with water ice in its amorphous state. In addition, irradiation byproducts of methane, carbon dioxide, and carbon monoxide were detected under both reducing (e.g., ethane) and oxidizing (e.g., CO<sub>3</sub>) conditions; however, complex carbon-bearing molecules resulting from the combined irradiation of –CH– and –CO– groups (such as H<sub>2</sub>CO, CH<sub>3</sub>CHO, or CH<sub>3</sub>COOH) were not observed, which may indicate a physical or temporal segregation of the methane and carbon dioxide reservoirs. A key finding was the detection of fluorescent methane emissions,<ref name="Pinilla-2024"/> providing the first evidence of a gas coma rich in this compound. Gaseous carbon dioxide emission was also identified in the fundamental stretching band at 4.27 μm. The authors argue that the presence of methane emission is the first proof of the desorption of methane due to a density phase transition of amorphous water ice at low temperature (61 K) previously studied in the laboratory.<ref name="Tamai-2023"/> | ||
=== Rotation period === | === Rotation period === | ||
Four rotational [[light curve]]s of | Four rotational [[light curve]]s of Chiron were taken from [[Photometry (astronomy)|photometric]] observations between 1989 and 1997. Lightcurve analysis gave a concurring, well-defined [[rotational period]] of 5.918 hours with a small brightness variation of 0.05 to 0.09 [[Magnitude (astronomy)|magnitude]], which indicates that the body has a rather spheroidal shape ({{small|[[LCDB quality code|U=3/3/3]]}}).<ref name="lcdb"/><ref name="Bus-1989"/><ref name="Luu-1990b"/><ref name="Marcialis-1993"/><ref name="Lazzaro-1997"/> | ||
=== Diameter === | === Diameter === | ||
[[File:Centaur size color comparison.svg|thumb|upright=1.5|Comparison of sizes, albedos, and colors of various large centaurs with measured diameters. Chiron is at the center in the top row.|alt=Infographic showing a comparison of sizes, albedo, and colors of various large centaurs]] | |||
{| class="wikitable" style="text-align:center; font-size: 0.9em; margin-left: 0.7em;" align=right | {| class="wikitable" style="text-align:center; font-size: 0.9em; margin-left: 0.7em;" align=right | ||
| Line 104: | Line 107: | ||
!Year !! Diameter !! Notes !! Refs | !Year !! Diameter !! Notes !! Refs | ||
|- | |- | ||
| 1984 || 180 km || align=left | Lebofsky (1984) || <ref name="Groussin-2004" /> | | 1984 || 180 km || align=left | Lebofsky (1984) || <ref name="Groussin-2004"/> | ||
|- | |- | ||
| 1991 || 186 km || align=left | [[IRAS]] || <ref name="Groussin-2004" /> | | 1991 || 186 km || align=left | [[IRAS]] || <ref name="Groussin-2004"/> | ||
|- | |- | ||
| 1994 || 188 km || align=left | Campins (radius {{val|94|6}} km)|| <ref name="Campins-1994" /> | | 1994 || 188 km || align=left | Campins (radius {{val|94|6}} km)|| <ref name="Campins-1994"/> | ||
|- | |- | ||
| 1996 || 180 km || align=left | [[Occultation#Occultations by asteroids|occultation]] || <ref name="Groussin-2004" /> | | 1996 || 180 km || align=left | [[Occultation#Occultations by asteroids|occultation]] || <ref name="Groussin-2004"/> | ||
|- | |- | ||
| 1998 || 166 km || align=left | Dunham occultation list<br />(Dunham 1998) || <ref name="jpldata" /> | | 1998 || 166 km || align=left | Dunham occultation list<br/>(Dunham 1998) || <ref name="jpldata"/> | ||
|- | |- | ||
| 2007 || 233 km || align=left | [[Spitzer Space Telescope]] || <ref name="Stansberry-2007" /> | | 2007 || 233 km || align=left | [[Spitzer Space Telescope]] || <ref name="Stansberry-2007"/> | ||
|- | |- | ||
| 2013 || 218 km || align=left | [[Herschel Space Observatory]]<br />{{small|(PACS and SPIRE)}} || <ref name="Fornasier-2013" /> | | 2013 || 218 km || align=left | [[Herschel Space Observatory]]<br/>{{small|(PACS and SPIRE)}} || <ref name="Fornasier-2013"/> | ||
|- | |- | ||
| 2017 || 271 km || align=left | LCDB || <ref name="lcdb" /> | | 2017 || 271 km || align=left | LCDB || <ref name="lcdb"/> | ||
|- | |- | ||
| 2023 || 196 km || align=left | Sickafoose || <ref name="Sickafoose2023"/> | | 2023 || 196 km || align=left | Sickafoose || <ref name="Sickafoose2023"/> | ||
|} | |} | ||
The assumed size of an object depends on its [[Absolute magnitude#Solar System bodies (H)|absolute magnitude]] (H) and the [[albedo]] (the amount of light it reflects). In 1984 Lebofsky estimated Chiron to be about 180 km in diameter.<ref name="Groussin-2004" /> Estimates in the 1990s were closer to 150 km in diameter.<ref name="jpldata" /><ref name="Groussin-2004"/> [[Occultation#Occultations by asteroids|Occultation]] data from 1993 suggests a diameter of about 180 km.<ref name="Groussin-2004" /> Combined data from the [[Spitzer Space Telescope]] in 2007 and the Herschel Space Observatory in 2011 suggests that Chiron is {{nowrap|{{val|218|20}} km}} in diameter.<ref name="Fornasier-2013" /> Therefore, Chiron may be as large as [[10199 Chariklo]].<ref name="Stansberry-2007" /> The diameter of Chiron is difficult to estimate in part because the true absolute magnitude of its nucleus is uncertain due to its highly variable cometary activity.<ref name="Fornasier-2013" /> | The assumed size of an object depends on its [[Absolute magnitude#Solar System bodies (H)|absolute magnitude]] (H) and the [[albedo]] (the amount of light it reflects). In 1984 Lebofsky estimated Chiron to be about 180 km in diameter.<ref name="Groussin-2004"/> Estimates in the 1990s were closer to 150 km in diameter.<ref name="jpldata"/><ref name="Groussin-2004"/> [[Occultation#Occultations by asteroids|Occultation]] data from 1993 suggests a diameter of about 180 km.<ref name="Groussin-2004"/> Combined data from the [[Spitzer Space Telescope]] in 2007 and the Herschel Space Observatory in 2011 suggests that Chiron is {{nowrap|{{val|218|20}} km}} in diameter.<ref name="Fornasier-2013"/> Therefore, Chiron may be as large as [[10199 Chariklo]].<ref name="Stansberry-2007"/> The diameter of Chiron is difficult to estimate in part because the true absolute magnitude of its nucleus is uncertain due to its highly variable cometary activity.<ref name="Fornasier-2013"/> | ||
=== Cometary behavior === | === Cometary behavior === | ||
In February 1988, at 12 AU from the Sun, Chiron brightened by 75 percent.<ref name="hartmann1990" /> This is behavior typical of comets but not asteroids. Further observations in April 1989 showed that Chiron had developed a cometary [[ | In February 1988, at 12 AU from the Sun, Chiron brightened by 75 percent.<ref name="hartmann1990"/> This is behavior typical of comets but not asteroids. Further observations in April 1989 showed that Chiron had developed a cometary [[Coma (comet)|coma]],<ref name="meech1989"/> A tail was detected in 1993.<ref name="Campins-1994"/> 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.<ref name="Meech90"/> In 1995 [[carbon monoxide]] was detected in Chiron in very small amounts, and the derived CO production rate was calculated to be sufficient to account for the observed coma.<ref name="womack1999"/> [[Cyanide]] was also detected in the spectrum of Chiron in 1991.<ref name="Bus91"/> 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.<ref name="Perihelion"/> | ||
Chiron is officially designated as both a comet—95P/Chiron—and a minor planet,<ref name=" | Chiron is officially designated as both a comet—95P/Chiron—and a minor planet,<ref name="Fornasier-2013" /><ref name="dualstatus"/> an indication of the sometimes fuzzy dividing line between the two classes of object. The term proto-comet has also been used. Being about 220 km in diameter, it is unusually large for a [[comet nucleus]]. Chiron was the first member of a new family of [[Chiron-type comet]]s (CTC) with ([[Tisserand's parameter|T<sub>Jupiter</sub>]] > 3; [[Semi-major axis|a]] > a<sub>Jupiter</sub>).<ref name="jpldata"/> Other CTCs include: [[39P/Oterma]], [[165P/LINEAR]], [[166P/NEAT]], and [[167P/CINEOS]]. There are also non-centaur asteroids that are simultaneously classified as comets, such as [[4015 Wilson–Harrington]], [[7968 Elst–Pizarro]], and [[118401 LINEAR]].<ref name="dualstatus"/> | ||
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.<ref name="cometary" /> | 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.<ref name="cometary"/> | ||
== Rings == | == Rings == | ||
[[File:Chiron_in_Celestia.jpg|thumb|upright=1.5|Depiction of Chiron and its rings]] | [[File:Chiron_in_Celestia.jpg|thumb|upright=1.5|Depiction of Chiron and its rings]] | ||
Chiron has [[planetary ring|rings]], similar to the better-established [[Rings of Chariklo|rings of]] [[10199 Chariklo]].<ref name="Ortiz2015" /><ref name="Lakdawalla2015" /><ref name="spacedaily" /><ref group=lower-alpha name=Haumea/> 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 were proposed to be {{val|324|10|u=km}} in radius and sharply defined. The rings' 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.<ref name="Ortiz2015" /> | Chiron has [[planetary ring|rings]], similar to the better-established [[Rings of Chariklo|rings of]] [[10199 Chariklo]].<ref name="Ortiz2015"/><ref name="Lakdawalla2015"/><ref name="spacedaily"/><ref group=lower-alpha name=Haumea/> 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 were proposed to be {{val|324|10|u=km}} in radius and sharply defined. The rings' 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.<ref name="Ortiz2015"/> | ||
Further evidence of the rings was provided by two independent observations of occultations on 28 November 2018 and 15 December 2022, which suggests that their structure is constantly evolving.<ref name="Ortiz2023"/> In the 2018 event Chiron's rings were observed to have less material than in 2011, but seemed to be developing a partial third ring; by the 2022 event there was more material than either of the previous observations, and the third ring had become fully developed.<ref name="Sickafoose2023">{{cite journal |last1=Sickafoose |first1=Amanda A. |last2=Levine |first2=Stephen E. |last3=Bosh |first3=Amanda S. |last4=Person |first4=Michael J. |last5=Zuluaga |first5=Carlos A. |last6=Knieling |first6=Bastian |last7=Lewis |first7=Mark C. |last8=Schindler |first8=Karsten |title=Material around the Centaur (2060) Chiron from the 2018 November 28 UT Stellar Occultation |journal=The Planetary Science Journal |date=1 November 2023 |volume=4 |issue=11 |pages=221 |doi=10.3847/PSJ/ad0632 |arxiv=2310.16205 |bibcode=2023PSJ.....4..221S |doi-access=free }}</ref> J.L. Ortiz speculated that the extra material in the 2022 event could be from an outburst observed in 2021, which left more material in orbit and thus bolstered the generation of the third | Further evidence of the rings was provided by two independent observations of occultations on 28 November 2018 and 15 December 2022, which suggests that their structure is constantly evolving.<ref name="Ortiz2023"/> In the 2018 event Chiron's rings were observed to have less material than in 2011, but seemed to be developing a partial third ring; by the 2022 event there was more material than either of the previous observations, and the third ring had become fully developed.<ref name="Sickafoose2023">{{cite journal |last1=Sickafoose |first1=Amanda A. |last2=Levine |first2=Stephen E. |last3=Bosh |first3=Amanda S. |last4=Person |first4=Michael J. |last5=Zuluaga |first5=Carlos A. |last6=Knieling |first6=Bastian |last7=Lewis |first7=Mark C. |last8=Schindler |first8=Karsten |title=Material around the Centaur (2060) Chiron from the 2018 November 28 UT Stellar Occultation |journal=The Planetary Science Journal |date=1 November 2023 |volume=4 |issue=11 |pages=221 |doi=10.3847/PSJ/ad0632 |arxiv=2310.16205 |bibcode=2023PSJ.....4..221S |doi-access=free }}</ref> J.L. Ortiz speculated that the extra material in the 2022 event could be from an outburst observed in 2021, which left more material in orbit and thus bolstered the generation of the third ring—this is also expected to be cyclical, maintaining the rings.<ref name="Ortiz2023"/> | ||
The preferred pole of Chiron's rings is, in [[Ecliptic coordinate system|ecliptic coordinates]], ''λ'' = {{val|151|8|u=deg}}, ''β'' = {{val|18|11|u=deg}}. The rings' width, separation, and optical depths were observed to be nearly identical to those of Chariklo's rings until the 2018 observation, indicating that the same type of structure had been responsible for both. Moreover, both their rings are within their respective [[Roche limit]]s, though Chiron's newly developed third ring may be outside of it depending on its density.<ref name="Ortiz2015"/><ref name="Ortiz2023"/> | The preferred pole of Chiron's rings is, in [[Ecliptic coordinate system|ecliptic coordinates]], ''λ'' = {{val|151|8|u=deg}}, ''β'' = {{val|18|11|u=deg}}. The rings' width, separation, and optical depths were observed to be nearly identical to those of Chariklo's rings until the 2018 observation, indicating that the same type of structure had been responsible for both. Moreover, both their rings are within their respective [[Roche limit]]s, though Chiron's newly developed third ring may be outside of it depending on its density.<ref name="Ortiz2015"/><ref name="Ortiz2023"/> | ||
| Line 144: | Line 147: | ||
The ''Chiron Orbiter Mission'' was a mission proposed for NASA's [[New Frontiers program]] or [[Flagship program]]. It was published in May 2010 and proposed an orbiter mission to Chiron. Its launch date could have varied from as early as 2023 to as late as 2025, depending on budget and propulsion type.<ref>{{Cite web|url=https://archive.org/details/ChironOrbiterMissionConceptStudy|title=Chiron Orbiter Mission Concept Study}}</ref> | The ''Chiron Orbiter Mission'' was a mission proposed for NASA's [[New Frontiers program]] or [[Flagship program]]. It was published in May 2010 and proposed an orbiter mission to Chiron. Its launch date could have varied from as early as 2023 to as late as 2025, depending on budget and propulsion type.<ref>{{Cite web|url=https://archive.org/details/ChironOrbiterMissionConceptStudy|title=Chiron Orbiter Mission Concept Study}}</ref> | ||
There was another mission proposed, part of the [[Discovery Program]] known as [[Centaurus (spacecraft mission)|''Centaurus'']]; if approved, it would have launched between 2026 and 2029 and made a flyby of 2060 Chiron and one other | There was another mission proposed, part of the [[Discovery Program]] known as [[Centaurus (spacecraft mission)|''Centaurus'']]; if approved, it would have launched between 2026 and 2029 and made a flyby of 2060 Chiron and one other centaur sometime in the 2030s. | ||
== Gallery == | == Gallery == | ||
{{Commons}} | {{Commons}} | ||
<gallery class="left" heights="150px"> | <gallery class="left" heights="150px"> | ||
File: | File:2060 Chiron Hubble.jpg|Hubble Space Telescope image of the centaur 2060 Chiron, taken on 14 September 2015 | ||
File:ChironAnimation.gif|Chaotic, unstable motion of Chiron with | File:ChironAnimation.gif|Chaotic, unstable motion of Chiron with Saturn (stationary, white dot at 10 o'clock) and Jupiter (blue) | ||
File:Animation of Chiron orbit.gif|Animated orbital diagram with Chiron (violet), alongside the giant planets Jupiter (red), Saturn (yellow), and | File:Animation of Chiron orbit.gif|Animated orbital diagram with Chiron (violet), alongside the giant planets Jupiter (red), Saturn (yellow), and Uranus (green). Perturbations of Chiron's orbit are not shown | ||
</gallery> | </gallery> | ||
| Line 170: | Line 173: | ||
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<ref name="apmag1996">{{cite web | <ref name="apmag1996">{{cite web | ||
| Line 676: | Line 691: | ||
|publisher=[[JPL Horizons On-Line Ephemeris System|JPL Horizons]] | |publisher=[[JPL Horizons On-Line Ephemeris System|JPL Horizons]] | ||
|type=Perihelion year | |type=Perihelion year | ||
|url= https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%27Chiron%27&START_TIME=%271996-03-20%27&STOP_TIME=%271996-04-10%27&STEP_SIZE=% | |url= https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%27Chiron%27&START_TIME=%271996-03-20%27&STOP_TIME=%271996-04-10%27&STEP_SIZE=%2712%20hours%27&QUANTITIES=%279,19%27 | ||
|accessdate= | |accessdate=2025-09-05}}</ref> | ||
<ref name="Horizons1895">{{cite web | <ref name="Horizons1895">{{cite web | ||
|title=Horizons Batch for 2060 Chiron (1977 UB) on 1895-Mar-16 | |||
|publisher=[[JPL Horizons On-Line Ephemeris System|JPL Horizons]] | |||
|type=Perihelion occurs when rdot flips from negative to positive | |||
|url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%272060%27&START_TIME=%271895-03-12%27&STOP_TIME=%271895-03-20%27&STEP_SIZE=%271%20hours%27&QUANTITIES=%2719%27 | |||
|accessdate=2021-10-03}}</ref> | |||
<ref name="Horizons2021">{{cite web | <ref name="Horizons2021">{{cite web | ||
|title=Horizons Batch for 2060 Chiron (1977 UB) on 2021-May-27 | |||
|publisher=[[JPL Horizons On-Line Ephemeris System|JPL Horizons]] | |||
|type=Aphelion occurs when rdot flips from positive to negative | |||
|url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%272060%27&START_TIME=%272021-05-25%27&STOP_TIME=%272021-05-29%27&STEP_SIZE=%271%20hours%27&QUANTITIES=%2719%27 | |||
|accessdate=2021-10-03}}</ref> | |||
<ref name="Horizons2046">{{cite web | <ref name="Horizons2046">{{cite web | ||
|title=Horizons Batch for 2060 Chiron (1977 UB) on 2046-Aug-03 | |||
|publisher=[[JPL Horizons On-Line Ephemeris System|JPL Horizons]] | |||
|type=Perihelion occurs when rdot flips from negative to positive | |||
|url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%272060%27&START_TIME=%272046-07-25%27&STOP_TIME=%272046-08-12%27&STEP_SIZE=%273%20hours%27&QUANTITIES=%2719,22%27 | |||
|archive-url=https://web.archive.org/web/20211001125942/https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%272060%27&START_TIME=%272046-07-25%27&STOP_TIME=%272046-08-12%27&STEP_SIZE=%273%20hours%27&QUANTITIES=%2719%27 | |||
|archive-date=2021-10-01 | |||
|url-status=live | |||
|accessdate=2021-10-01}}</ref> | |||
}} <!-- end of reflist --> | }} <!-- end of reflist --> | ||
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== Further reading == | == Further reading == | ||
{{Refbegin}} | {{Refbegin}} | ||
* {{cite journal |last1=Fernández |first1=Yanga R. |author-link=Yanga R. Fernández |last2=Jewitt |first2=David C. |author-link2=David Jewitt |last3=Sheppard |first3=Scott S. |author-link3=Scott S. Sheppard |title=Thermal Properties of Centaurs Asbolus and Chiron |journal=[[Astronomical Journal]] |volume=123 |issue=2 |date=2002 |pages=1050–1055 |doi=10.1086/338436 |arxiv=astro-ph/0111395 |bibcode=2002AJ....123.1050F |s2cid=11266670 }} | * {{cite journal |last1=Fernández |first1=Yanga R. |author-link=Yanga R. Fernández |last2=Jewitt |first2=David C. |author-link2=David C. Jewitt |last3=Sheppard |first3=Scott S. |author-link3=Scott S. Sheppard |title=Thermal Properties of Centaurs Asbolus and Chiron |journal=[[Astronomical Journal]] |volume=123 |issue=2 |date=2002 |pages=1050–1055 |doi=10.1086/338436 |arxiv=astro-ph/0111395 |bibcode=2002AJ....123.1050F |s2cid=11266670 }} | ||
* | * {{cite journal|vauthors=Pereira CL, Braga-Ribas F, Sicardy B, Leiva R, Assafin M, Morgado BE, Ortiz JL, Santos-Sanz P, Camargo JI, Margoti G|title=The Rings of (2060) Chiron: Evidence of an Evolving System|journal=The Astrophysical Journal Letters|volume=992|issue=2|page=L19|doi=10.3847/2041-8213/ae0b6d|date=14 October 2025 |doi-access=free |arxiv=2510.12388}} | ||
{{Refend}} | {{Refend}} | ||
| Line 716: | Line 730: | ||
* [http://cometography.com/pcomets/095p.html 95P/Chiron] at [http://cometography.com/ Cometography] | * [http://cometography.com/pcomets/095p.html 95P/Chiron] at [http://cometography.com/ Cometography] | ||
* [https://web.archive.org/web/20130514124652/http://home.surewest.net/kheider/astro/Chiron100kd1.txt A single clone run of centaur 2060 Chiron showing how Chiron may someday become an active comet] (Solex 10) | * [https://web.archive.org/web/20130514124652/http://home.surewest.net/kheider/astro/Chiron100kd1.txt A single clone run of centaur 2060 Chiron showing how Chiron may someday become an active comet] (Solex 10) | ||
* {{JPL small body}} | |||
{{PeriodicComets Navigator|94P/Russell|96P/Machholz|PageName=95P/Chiron}} | {{PeriodicComets Navigator|94P/Russell|96P/Machholz|PageName=95P/Chiron}} | ||
Latest revision as of 19:33, 2 July 2026
Template:Short description Script error: No such module "Distinguish". Script error: No such module "Unsubst". Script error: No such module "infobox".Script error: No such module "Check for unknown parameters".
2060 Chiron is a ringed 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 orbiting between the asteroid belt and the Kuiper belt.[lower-alpha 1] Chiron is named after the centaur Chiron in Greek mythology.
Although it was initially called an asteroid and classified only as a minor planet with the designation "2060 Chiron", in 1989 it was found to exhibit behavior typical of a comet. Today it is classified as both a minor planet and a comet, and is accordingly also known by the cometary designation 95P/Chiron. More recently, a series of occultation events through the 2010s and early 2020s revealed that Chiron hosts rings, making it one of four minor planets known to have rings (the three others being 10199 Chariklo, Haumea, and Quaoar) and the only known comet to do so.
History
Discovery
Chiron was discovered on 1 November 1977 by Charles Kowal from images taken on 18 October at Palomar Observatory.[1][2] It was given the temporary designation of Template:Mp.[3] It was found near aphelion[1] and at the time of discovery it was the most distant-known minor planet.[lower-alpha 2][3] Chiron was even claimed as the tenth planet by the press.[4] Chiron was later found on several precovery images, going back to 1895,[5] which allowed its orbit to be accurately determined.[1] 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.[1] The April 1895 precovery image was one month after the March 1895 perihelion.[6]
Naming
This minor planet was named after Chiron, a half-human, half-horse centaur from Greek mythology. Son of the Titan Cronus and the nymph Philyra, Chiron was the wisest and most just of all centaurs, serving as an instructor of the Greek heroes.[7] The official Template:MoMP was published by the Minor Planet Center on 1 April 1978 (M.P.C. 4359Script error: No such module "Check for unknown parameters".).[7][8] It was suggested that the names of other centaurs be reserved for objects of the same type.[1]
Chiron, along with most major and minor planetary bodies, is not generally given a symbol in astronomy. A symbol, ⚷, was devised for it by Al H. Morrison and is mostly used among astrologers: it resembles a key as well as an OK monogram for Object Kowal.[9][10]
.svg){kind=link}
Orbit
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 Script error: No such module "val". million km (Template:Cvt) of the planet. During this passage Saturn's gravity caused Chiron's semi-major axis to decrease from Script error: No such module "val". AU[11] to 13.7 AU.[12] Chiron's orbit does not intersect Uranus' orbit.
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.[13] 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.[14] Chiron likely comes from the Kuiper belt and will probably become a short-period comet in about a million years.[13] Chiron came to perihelion (closest point to the Sun) in 1996 and aphelion in May 2021.[15]
Physical characteristics
Spectral type
The visible and near-infrared spectrum of Chiron is neutral,[3] and is similar to that of C-type asteroids and the nucleus of Halley's Comet.[16] The near-infrared spectrum of Chiron shows absence of water ice.[17] The infrared spectrum, however, from 0.97 to 5.27 μm, as revealed by the James Webb Space Telescope[18] reveals the presence of gas in the coma and a diverse inventory of ices, on the surface or in the coma. Absorption bands of carbon dioxide, carbon monoxide, ethane, propane, and acetylene were detected, together with water ice in its amorphous state. In addition, irradiation byproducts of methane, carbon dioxide, and carbon monoxide were detected under both reducing (e.g., ethane) and oxidizing (e.g., CO3) conditions; however, complex carbon-bearing molecules resulting from the combined irradiation of –CH– and –CO– groups (such as H2CO, CH3CHO, or CH3COOH) were not observed, which may indicate a physical or temporal segregation of the methane and carbon dioxide reservoirs. A key finding was the detection of fluorescent methane emissions,[18] providing the first evidence of a gas coma rich in this compound. Gaseous carbon dioxide emission was also identified in the fundamental stretching band at 4.27 μm. The authors argue that the presence of methane emission is the first proof of the desorption of methane due to a density phase transition of amorphous water ice at low temperature (61 K) previously studied in the laboratory.[19]
Rotation period
Four rotational light curves of Chiron were taken from photometric observations between 1989 and 1997. Lightcurve analysis gave a concurring, well-defined rotational period of 5.918 hours with a small brightness variation of 0.05 to 0.09 magnitude, which indicates that the body has a rather spheroidal shape (U=3/3/3Script error: No such module "Check for unknown parameters".).[20][21][16][22][23]
Diameter
| Year | Diameter | Notes | Refs |
|---|---|---|---|
| 1984 | 180 km | Lebofsky (1984) | [24] |
| 1991 | 186 km | IRAS | [24] |
| 1994 | 188 km | Campins (radius Script error: No such module "val". km) | [3] |
| 1996 | 180 km | occultation | [24] |
| 1998 | 166 km | Dunham occultation list (Dunham 1998) |
[12] |
| 2007 | 233 km | Spitzer Space Telescope | [25] |
| 2013 | 218 km | Herschel Space Observatory (PACS and SPIRE)Script error: No such module "Check for unknown parameters". |
[26] |
| 2017 | 271 km | LCDB | [20] |
| 2023 | 196 km | Sickafoose | [27] |
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.[24] Estimates in the 1990s were closer to 150 km in diameter.[12][24] Occultation data from 1993 suggests a diameter of about 180 km.[24] Combined data from the Spitzer Space Telescope in 2007 and the Herschel Space Observatory in 2011 suggests that Chiron is Script error: No such module "val". km in diameter.[26] Therefore, Chiron may be as large as 10199 Chariklo.[25] The diameter of Chiron is difficult to estimate in part because the true absolute magnitude of its nucleus is uncertain due to its highly variable cometary activity.[26]
Cometary behavior
In February 1988, at 12 AU from the Sun, Chiron brightened by 75 percent.[28] This is behavior typical of comets but not asteroids. Further observations in April 1989 showed that Chiron had developed a cometary coma,[29] A tail was detected in 1993.[3] 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.[30] In 1995 carbon monoxide was detected in Chiron in very small amounts, and the derived CO production rate was calculated to be sufficient to account for the observed coma.[31] Cyanide was also detected in the spectrum of Chiron in 1991.[32] 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.[5]
Chiron is officially designated as both a comet—95P/Chiron—and a minor planet,[26][33] an indication of the sometimes fuzzy dividing line between the two classes of object. The term proto-comet has also been used. Being about 220 km in diameter, it is unusually large for a comet nucleus. Chiron was the first member of a new family of Chiron-type comets (CTC) with (TJupiter > 3; a > aJupiter).[12] Other CTCs include: 39P/Oterma, 165P/LINEAR, 166P/NEAT, and 167P/CINEOS. There are also non-centaur asteroids that are simultaneously classified as comets, such as 4015 Wilson–Harrington, 7968 Elst–Pizarro, and 118401 LINEAR.[33]
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.[34]
Rings
Chiron has rings, similar to the better-established rings of 10199 Chariklo.[35][36][37][lower-alpha 3] 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 were proposed to be Script error: No such module "val". in radius and sharply defined. The rings' 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.[35]
Further evidence of the rings was provided by two independent observations of occultations on 28 November 2018 and 15 December 2022, which suggests that their structure is constantly evolving.[38] In the 2018 event Chiron's rings were observed to have less material than in 2011, but seemed to be developing a partial third ring; by the 2022 event there was more material than either of the previous observations, and the third ring had become fully developed.[27] J.L. Ortiz speculated that the extra material in the 2022 event could be from an outburst observed in 2021, which left more material in orbit and thus bolstered the generation of the third ring—this is also expected to be cyclical, maintaining the rings.[38]
The preferred pole of Chiron's rings is, in ecliptic coordinates, λ = Script error: No such module "val"., β = Script error: No such module "val".. The rings' width, separation, and optical depths were observed to be nearly identical to those of Chariklo's rings until the 2018 observation, indicating that the same type of structure had been responsible for both. Moreover, both their rings are within their respective Roche limits, though Chiron's newly developed third ring may be outside of it depending on its density.[35][38]
Exploration
The Chiron Orbiter Mission was a mission proposed for NASA's New Frontiers program or Flagship program. It was published in May 2010 and proposed an orbiter mission to Chiron. Its launch date could have varied from as early as 2023 to as late as 2025, depending on budget and propulsion type.[39]
There was another mission proposed, part of the Discovery Program known as Centaurus; if approved, it would have launched between 2026 and 2029 and made a flyby of 2060 Chiron and one other centaur sometime in the 2030s.
Gallery
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Hubble Space Telescope image of the centaur 2060 Chiron, taken on 14 September 2015
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Chaotic, unstable motion of Chiron with Saturn (stationary, white dot at 10 o'clock) and Jupiter (blue)
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Animated orbital diagram with Chiron (violet), alongside the giant planets Jupiter (red), Saturn (yellow), and Uranus (green). Perturbations of Chiron's orbit are not shown
See also
- Template:Section link
- List of Solar System objects by size
- Lists of small Solar System bodies
- 10199 Chariklo
Notes
References
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- ↑ Miller & Stein (2021) Comment on U+26B7 CHIRON L2/21-225, UTC Document Registry
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Further reading
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External links
- Orbit Fit and Astrometric record for (2060) Chiron, Marc W. Buie, SwRI – Space Science Department (2007)
- 95P/Chiron at Cometography
- A single clone run of centaur 2060 Chiron showing how Chiron may someday become an active comet (Solex 10)
- Template:PAGENAMEBASE at the JPL Small-Body DatabaseTemplate:EditAtWikidata
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Categories:
- Pages with script errors
- Pages with broken file links
- Pages with reference errors
- Centaurs (small Solar System bodies)
- Chiron-type comets
- Periodic comets
- Numbered comets
- Discoveries by Charles T. Kowal
- Named minor planets
- B-type asteroids (Tholen)
- Cb-type asteroids (SMASS)
- Astronomical objects discovered in 1977