2060 Chiron

Template:Short description Template:Distinguish Template:Use dmy dates {{#invoke:infobox|infoboxTemplate | class = vcard | titleclass = fn org | title = 2060 Chiron
95P/Chiron | image = {{#invoke:InfoboxImage|InfoboxImage|image=2060_Chiron_Hubble.jpg|upright={{#if:||1.1}}|alt=}} | caption = Hubble Space Telescope image of 2060 Chiron, taken in 2015. | headerstyle = {{#if:#C7FF8F|background-color:#C7FF8F|background-color:#E0CCFF}} | labelstyle = max-width:{{#if:||11em}}; | autoheaders = y

| header1 = Discovery<ref name="MPC-Chiron" /><ref name="Kowal-1978" /><ref name="gsfc-Chiron" />

| header10 = {{#if:|Designations|Designations}}

| header20 = Orbital characteristics{{#ifeq:|yes| (barycentric)}}<ref name="jpldata" />

| data21 = | data22 = {{#if:2021-Jul-01 (JD 2459396.5) |Epoch 2021-Jul-01 (JD 2459396.5)}} | data23 = {{#if:0 | Uncertainty parameter 0}} | label24 = Observation arc | data24 = 126.29 yr | label25 = Earliest precovery date | data25 = 24 April 1895<ref name="MPC-Chiron"/>
(Harvard Observatory) | label26 = {{#switch:{{{apsis}}} |apsis|gee|barion|center|centre|(apsis)=Apo{{{apsis}}} |Ap{{#if:|{{{apsis}}}|helion}}}} | data26 = Template:Convert
(occurred May 2021)<ref name="Horizons2021"/> | label27 = Peri{{#if:|{{{apsis}}}|helion}} | data27 = Template:Convert | label28 = Peri{{#if:|{{{apsis}}}|apsis}} | data28 = | label29 = {{#switch:{{{apsis}}} |helion|astron=Ap{{{apsis}}} |Apo{{#if:|{{{apsis}}}|apsis}}}} | data29 = | label30 = Periastron | data30 = | label31 = Apoastron | data31 = | label32 = Template:Longitem | data32 = Template:Convert | label33 = Template:Longitem | data33 = | label34 = Eccentricity | data34 = 0.3772 | label35 = Template:Longitem | data35 = 50.71 yr (18,523 days) | label36 = Template:Longitem | data36 = | label37 = Template:Longitem | data37 = 7.75 km/s | label38 = Template:Longitem | data38 = 180.70° | label39 = Template:Longitem | data39 = Template:Deg2DMS / day | label40 = Inclination | data40 = 6.9299° | label41 = Template:Longitem | data41 = | label42 = Template:Longitem | data42 = 209.27° | label43 = Template:Longitem | data43 = | label44 = Template:Longitem | data44 = Template:Ublist | label45 = Template:Longitem | data45 = 339.71° | label46 = Template:Nowrap | data46 = | label47 = Satellite of | data47 = | label48 = Group | data48 = | label49 = {{#switch: |yes|true=Satellites |Known satellites}} | data49 = | label50 = Star | data50 = | label51 = Earth MOID | data51 = | label52 = Mercury MOID | data52 = | label53 = Venus MOID | data53 = | label54 = Mars MOID | data54 = | label55 = Jupiter MOID | data55 = Template:Convert | label56 = Saturn MOID | data56 = Template:Convert<ref name="MPC-Chiron"/> | label57 = Uranus MOID | data57 = Template:Convert<ref name="MPC-Chiron"/> | label58 = Neptune MOID | data58 = | label59 = T_Jupiter | data59 = 3.363

| header60 = Proper orbital elements

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({{#expr:365.25*360/1 round 3}} d) }} | label66 = Template:Longitem | data66 = {{#if:|{{{perihelion_rate}}} arcsec Template:\yr }} | label67 = Template:Longitem | data67 = {{#if:|{{{node_rate}}} arcsec Template:\yr}}

| header70 = Template:Anchor{{#if:yes| Physical characteristics|Physical characteristics}}

| label71 = Dimensions | data71 = Template:Val x Template:Val x Template:Val<ref name="Sickafoose2023"/> | label72 = Template:Longitem | data72 = | label73 = Template:Longitem | data73 = Template:Ublist | label74 = Template:Longitem | data74 = | label75 = Template:Longitem | data75 = | label76 = Flattening | data76 = | label77 = Circumference | data77 = | label78 = Template:Longitem | data78 = | label79 = Volume | data79 = | label80 = Mass | data80 = | label81 = Template:Longitem | data81 = | label82 = Template:Longitem | data82 = | label83 = Template:Longitem | data83 = | label84 = Template:Longitem | data84 = | label85 = Template:Longitem | data85 = Template:Val h<ref name="lcdb" /><ref name="Bus-1989" /><ref name="Luu-1990b" /><ref name="Marcialis-1993" /><ref name="Lazzaro-1997" /> | label86 = Template:Longitem | data86 = | label87 = Template:Longitem | data87 = | label88 = Template:Longitem | data88 = | label89 = Template:Longitem | data89 = | label90 = Template:Longitem | data90 = | label91 = Template:Longitem | data91 = | label92 = Template:Longitem | data92 = | label93 = {{#if:yes |Template:Longitem |Albedo}} | data93 = Template:Ublist | label94 = Temperature | data94 =

| data100 = {{#if:|

Surface temp.	min	mean	max
{{{temp_name1}}}
{{{temp_name2}}}
{{{temp_name3}}}
{{{temp_name4}}}

}}

| header110 = Atmosphere

| below = {{#if:||Template:Reflist }}

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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.<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 rings, making it one of four minor planets and the only known comet to host a ring system.

HistoryEdit

DiscoveryEdit

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 Template:Mp.<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"/>

NamingEdit

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.<ref name="springer" /> The official Template:MoMP was published by the Minor Planet Center on 1 April 1978 (Template:Small).<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 ⚷ 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.<ref> Template:Cite journal</ref><ref>Miller & Stein (2021) Comment on U+26B7 CHIRON L2/21-225, UTC Document Registry</ref>

OrbitEdit

File:Chiron orbit.PNG

Orbital diagram of Chiron

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 Template:Val million km (Template:Cvt) of the planet. During this passage Saturn's gravity caused Chiron's semi-major axis to decrease from Template:Val 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 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.<ref name="Horner2004" /> 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.<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 perihelion (closest point to the Sun) in 1996 and aphelion in May 2021.<ref name="Horizons2021"/>

Physical characteristicsEdit

Spectral typeEdit

The visible and near-infrared spectrum of Chiron is neutral,<ref name="Campins-1994" /> and is similar to that of C-type asteroids 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" />

Rotation periodEdit

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 (Template:Small).<ref name="lcdb" /><ref name="Bus-1989"/><ref name="Luu-1990b" /><ref name="Marcialis-1993" /><ref name="Lazzaro-1997" />

DiameterEdit

Summary – size estimates for Chiron:
Year	Diameter	Notes	Refs
1984	180 km	Lebofsky (1984)	<ref name="Groussin-2004" />
1991	186 km	IRAS	<ref name="Groussin-2004" />
1994	188 km	Campins (radius Template:Val km)	<ref name="Campins-1994" />
1996	180 km	occultation	<ref name="Groussin-2004" />
1998	166 km	Dunham occultation list (Dunham 1998)	<ref name="jpldata" />
2007	233 km	Spitzer Space Telescope	<ref name="Stansberry-2007" />
2013	218 km	Herschel Space Observatory Template:Small	<ref name="Fornasier-2013" />
2017	271 km	LCDB	<ref name="lcdb" />
2023	196 km	Sickafoose	<ref name="Sickafoose2023"/>

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.<ref name="Groussin-2004" /> Estimates in the 1990s were closer to 150 km in diameter.<ref name="jpldata" /><ref name="Groussin-2004"/> 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 Template:Nowrap 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 behaviorEdit

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,<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="dualstatus" /><ref name="Fornasier-2013" /> 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 (T_Jupiter > 3; a > a_Jupiter).<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" />

RingsEdit

File:Chiron in Celestia.jpg

Depiction of Chiron and its rings

Chiron has rings, similar to the better-established 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 Template: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.<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">Template:Cite journal</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 coordinates, λ = Template:Val, β = Template: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.<ref name="Ortiz2015"/><ref name="Ortiz2023"/>

ExplorationEdit

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>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

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.

GalleryEdit

Template:Sister project

2060 Chiron.jpg

Hubble Space Telescope image of the centaur 2060 Chiron and its coma, taken in 1996.
ChironAnimation.gif

Chaotic, unstable motion of Chiron with Saturn (stationary, white dot at 10 o'clock) and Jupiter (blue)
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

NotesEdit

Template:Notelist

ReferencesEdit

Template:Reflist

External linksEdit

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)

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