2060 Chiron is a small Solar System body 22 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.[a]
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. Chiron is named after the centaur Chiron in Greek mythology.
Chiron was discovered on 1 November 1977 by Charles Kowal from images taken on 18 October at Palomar Observatory. It was given the temporary designation of 1977 UB. It was found near aphelion and at the time of discovery it was the most distant known minor planet.[b] Chiron was even claimed as the tenth planet by the press. Chiron was later found on several precovery images, going back to 1895, which allowed its orbit to be accurately determined. It had been at perihelion in 1945 but was not discovered then because there were few searches being made at that time, and these were not sensitive to slow-moving objects. The Lowell Observatory's survey for distant planets would not have gone down faint enough in the 1930s and did not cover the right region of the sky in the 1940s. The April 1895 precovery image was one month after the March 1895 perihelion.
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. The official naming citation was published by the Minor Planet Center on 1 April 1978 (M.P.C. 4359). It was suggested that the names of other centaurs be reserved for objects of the same type.
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.
Chiron's orbit was found to be highly eccentric (0.37), with perihelion just inside the orbit of Saturn and aphelion just outside the perihelion of Uranus (it does not reach the average distance of Uranus, however). According to the program Solex, Chiron's closest approach to Saturn in modern times was around May 720, when it came within 30.5±2.0 million km (0.204 ± 0.013 AU) of Saturn. During this passage Saturn's gravity caused Chiron's semi-major axis to decrease from 14.55±0.12 AU to 13.7 AU. Chiron's orbit does not intersect Uranus.
Chiron attracted considerable interest because it was the first object discovered in such an orbit, well outside the asteroid belt. Chiron is classified as a centaur, the first of a class of objects orbiting between the outer planets. Chiron is a Saturn–Uranus object because its perihelion lies in Saturn's zone of control and its aphelion lies in that of Uranus. Centaurs are not in stable orbits and will be removed by gravitational perturbation by the giant planets over a period of millions of years, moving to different orbits or leaving the Solar System altogether. Chiron is probably from the Kuiper belt and will probably become a short-period comet in about a million years. Chiron came to perihelion (closest point to the Sun) in 1996 and aphelion in May 2021.
The visible and near-infrared spectrum of Chiron is neutral, and is similar to that of C-type asteroids and the nucleus of Halley's Comet. The near-infrared spectrum of Chiron shows absence of water ice.
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=3/3/3).
|1984||180 km||Lebofsky (1984)|||
|1994||188 km||Campins (radius 94±6 km)|||
|1998||166 km||Dunham occultation list |
|2007||233 km||Spitzer Space Telescope|||
|2013||218 km||Herschel Space Observatory |
(PACS and SPIRE)
The assumed size of an object depends on its absolute magnitude (H) and the albedo (the amount of light it reflects). In 1984 Lebofsky estimated Chiron to be about 180 km in diameter. Estimates in the 1990s were closer to 150 km in diameter. Occultation data from 1993 suggests a diameter of about 180 km. Combined data from the Spitzer Space Telescope in 2007 and the Herschel Space Observatory in 2011 suggests that Chiron is 218±20 km in diameter. Therefore, Chiron may be as large as 10199 Chariklo. 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.
In February 1988, at 12 AU from the Sun, Chiron brightened by 75 percent. This is behavior typical of comets but not asteroids. Further observations in April 1989 showed that Chiron had developed a cometary coma, A tail was detected in 1993. Chiron differs from other comets in that water is not a major component of its coma, because it is too far from the Sun for water to sublimate. 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. Cyanide was also detected in the spectrum of Chiron in 1991. At the time of its discovery, Chiron was close to aphelion, whereas the observations showing a coma were done closer to perihelion, perhaps explaining why no cometary behavior had been seen earlier. The fact that Chiron is still active probably means it has not been in its current orbit very long.
Chiron is officially designated as both a comet—95P/Chiron—and a minor planet, an indication of the sometimes fuzzy dividing line between the two classes of object. The term proto-comet has also been used. Being 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). 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. Michael Brown lists it as possibly a dwarf planet with a measured diameter of 200 km (120 mi), which may be near the lower limit for an icy object to have been a dwarf planet at some point in its history.
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.
Chiron possibly has rings, similar to the better-established rings of 10199 Chariklo.[c] Based on unexpected occultation events observed in stellar-occultation data obtained on 7 November 1993, 9 March 1994, and 29 November 2011, which were initially interpreted as resulting from jets associated with Chiron's comet-like activity, Chiron's rings are proposed to be 324±10 km in radius and sharply defined. Their changing appearance at different viewing angles can largely explain the long-term variation in Chiron's brightness and hence estimates of Chiron's albedo and size. Moreover, it can, by assuming that the water ice is in Chiron's rings, explain the changing intensity of the infrared water-ice absorption bands in Chiron's spectrum, including their disappearance in 2001 (when the rings were edge-on). Also, the geometric albedo of Chiron's rings as determined by spectroscopy is consistent with that used to explain Chiron's long-term brightness variations.
The preferred pole of Chiron's rings is, in ecliptic coordinates, λ = 144°±10°, β = 24°±10°. The rings' width, separation, and optical depths are nearly identical to those of Chariklo's rings, indicating that the same type of structure is responsible for both. Moreover, both their rings are within their respective Roche limits.
The Chiron Orbiter Mission is a mission proposed for NASA's New Frontiers program or Flagship program. It was published in May 2010 and proposes an orbiter mission to Chiron. Its launch date could vary from as early as 2023, but as late as 2025 depending on budget and propulsion type.
There is another mission proposed apart of the Discovery Program known as Centaurus; if approved it would launch between 2026 to 2029 and make a flyby of 2060 Chiron and one other Centaur sometime in the 2030s.
Hubble Space Telescope image of the centaur 2060 Chiron, taken on 14 September 2015
Chaotic, unstable motion of Chiron with Saturn (stationary, white dot at 10 o'clock) and Jupiter (blue)
Animated orbital diagram with Chiron
- List of centaurs (small Solar System bodies) § 2060
- List of Solar System objects by size
- Lists of small Solar System bodies
- ^ 944 Hidalgo, discovered in 1920, also fits this definition, but was not identified as belonging to a distinct population.
- ^ Pluto, now considered to be a dwarf planet and hence a minor planet, was known at the time, but was considered a planet.
- ^ A stellar occultation in 2017 of another minor planet, Haumea (a trans-Neptunian object), indicated the presence of a ring.
- ^ a b c d e f "2060 Chiron (1977 UB)". Minor Planet Center. Retrieved 8 August 2017.
- ^ a b c d e f Kowal, Charles T.; Liller, William; Marsden, Brian G. (December 1978). "The discovery and orbit of /2060/ Chiron". In: Dynamics of the Solar System; Proceedings of the Symposium, Tokyo, Japan, May 23–26, 1978. 81: 245–250. Bibcode:1979IAUS...81..245K.
- ^ a b "Chiron Fact Sheet". NASA Goddard Space Flight Center. 20 August 2014.
- ^ a b c "Dual-Status Objects". Minor Planet Center.
- ^ a b c Schmadel, Lutz D. (2007). "(2060) Chiron". Dictionary of Minor Planet Names – (2060) Chiron. Springer Berlin Heidelberg. p. 167. doi:10.1007/978-3-540-29925-7_2061. ISBN 978-3-540-00238-3.
- ^ a b c d e f g h i j "JPL Small-Body Database Browser: 2060 Chiron (1977 UB)" (2017-06-22 last obs.). Jet Propulsion Laboratory. Retrieved 8 August 2017.
- ^ "List of Centaurs and Scattered-Disk Objects". Minor Planet Center. Retrieved 13 November 2014.
- ^ a b "Horizons Batch for 2060 Chiron (1977 UB) on 2021-May-27" (Aphelion occurs when rdot flips from positive to negative). JPL Horizons. Retrieved 3 October 2021.
- ^ "Horizons Batch for 2060 Chiron (1977 UB) on 2046-Aug-03" (Perihelion occurs when rdot flips from negative to positive). JPL Horizons. Retrieved 1 October 2021.
- ^ a b "Horizons Batch for 2060 Chiron (1977 UB) on 1895-Mar-16" (Perihelion occurs when rdot flips from negative to positive). JPL Horizons. Retrieved 3 October 2021.
- ^ a b c d e f g Fornasier, Sonia; Lellouch, Emmanuel; Müller, Thomas; Santos-Sanz, Pablo; Panuzzo, Pasquale; Kiss, Csaba; et al. (July 2013). "TNOs are Cool: A survey of the trans-Neptunian region. VIII. Combined Herschel PACS and SPIRE observations of nine bright targets at 70-500 mum". Astronomy and Astrophysics. 555: 22. arXiv:1305.0449. Bibcode:2013A&A...555A..15F. doi:10.1051/0004-6361/201321329. S2CID 119261700.
- ^ a b c Stansberry, John; Grundy, Will; Brown, Michael E.; Cruikshank, Dale P.; Spencer, John; Trilling, David; Margot, Jean-Luc (November 2007). "Physical Properties of Kuiper Belt and Centaur Objects: Constraints from Spitzer Space Telescope". arXiv:astro-ph/0702538.
- ^ a b c d e f g "LCDB Data for (2060) Chiron". Asteroid Lightcurve Database (LCDB). Retrieved 8 August 2017.
- ^ a b Bus, Schelte J.; Bowell, Edward L. G.; Harris, Alan W.; Hewitt, Anthony V. (February 1989). "2060 Chiron - CCD and electronographic photometry". Icarus. 77 (2): 223–238. Bibcode:1989Icar...77..223B. doi:10.1016/0019-1035(89)90087-0. ISSN 0019-1035.
- ^ a b c Luu, Jane X.; Jewitt, David C. (September 1990). "Cometary activity in 2060 Chiron". Astronomical Journal. 100: 913–932. Bibcode:1990AJ....100..913L. doi:10.1086/115571. ISSN 0004-6256.
- ^ a b Marcialis, Robert L.; Buratti, Bonnie J. (August 1993). "CCD photometry of 2060 Chiron in 1985 and 1991". Icarus. 104 (2): 234–243. Bibcode:1993Icar..104..234M. doi:10.1006/icar.1993.1098. ISSN 0019-1035.
- ^ a b c Lazzaro, Daniela; Florczak, Marcos A.; Angeli, Cláudia A.; Carvano, Jorge Márcio F.; Betzler, Alberto S.; Casati, A. A.; et al. (December 1997). "Photometric monitoring of 2060 Chiron's brightness at perihelion". Planetary and Space Science. 45 (12): 1607–1614. Bibcode:1997P&SS...45.1607L. doi:10.1016/S0032-0633(97)00124-4.
- ^ a b c d Brown, Michael E. "How many dwarf planets are there in the outer solar system?". California Institute of Technology. Retrieved 8 August 2017.
- ^ Belskaya, Irina N.; Barucci, Maria Antonietta; Fulchignoni, Marcello; Dovgopol, Anatolij N. (April 2015). "Updated taxonomy of trans-Neptunian objects and centaurs: Influence of albedo". Icarus. 250: 482–491. Bibcode:2015Icar..250..482B. doi:10.1016/j.icarus.2014.12.004.
- ^ "AstDys (2060) Chiron Ephemerides". Department of Mathematics, University of Pisa, Italy. Retrieved 8 August 2017.
- ^ "Chiron Apmag March-April 1996" (Perihelion year). JPL Horizons. Retrieved 6 July 2021.
- ^ Veres, Peter; Jedicke, Robert; Fitzsimmons, Alan; Denneau, Larry; Granvik, Mikael; Bolin, Bryce; et al. (November 2015). "Absolute magnitudes and slope parameters for 250,000 asteroids observed by Pan-STARRS PS1 - Preliminary results". Icarus. 261: 34–47. arXiv:1506.00762. Bibcode:2015Icar..261...34V. doi:10.1016/j.icarus.2015.08.007. S2CID 53493339.
- ^ Belskaya, Irina N.; Bagnulo, Stefano; Barucci, Maria Antonietta; Muǐnonen, Karri O.; Tozzi, Gian Paolo; Fornasier, Sonia; et al. (November 2010). "Polarimetry of Centaurs (2060) Chiron, (5145) Pholus and (10199) Chariklo". Icarus. 210 (1): 472–479. Bibcode:2010Icar..210..472B. doi:10.1016/j.icarus.2010.06.005.
- ^ Peixinho, Nuno; Delsanti, Audrey C.; Guilbert-Lepoutre, Aurélie; Gafeira, Ricardo; Lacerda, Pedro (October 2012). "The bimodal colors of Centaurs and small Kuiper belt objects". Astronomy and Astrophysics. 546: 12. arXiv:1206.3153. Bibcode:2012A&A...546A..86P. doi:10.1051/0004-6361/201219057. S2CID 55876118.
- ^ Davies, John K.; McBride, Neil; Ellison, Sara L.; Green, Simon F.; Ballantyne, David R. (August 1998). "Visible and Infrared Photometry of Six Centaurs". Icarus. 134 (2): 213–227. Bibcode:1998Icar..134..213D. doi:10.1006/icar.1998.5931.
- ^ Meech, Karen J. (19 February 1994). "The Structure of the Inner Coma of Comet Chiron: Imaging The Exopause". Institute for Astronomy, University of Hawaii. Retrieved 19 October 2007.
- ^ a b c d e Campins, Humberto; Telesco, Charles M.; Osip, David J.; Rieke, George H.; Rieke, Marcia J.; Schulz, Bernhard (December 1994). "The color temperature of (2060) Chiron: A warm and small nucleus". Astronomical Journal. 108: 2318–2322. Bibcode:1994AJ....108.2318C. doi:10.1086/117244. ISSN 0004-6256.
- ^ Collander-Brown, Simon J.; Maran, Michael D.; Williams, Iwan P. (2000). "The effect on the Edgeworth-Kuiper Belt of a large distant tenth planet". Monthly Notices of the Royal Astronomical Society. 318 (1): 101–108. Bibcode:2000MNRAS.318..101C. doi:10.1046/j.1365-8711.2000.t01-1-03640.x.
- ^ a b "The Chiron Perihelion Campaign". NASA Goddard Space Flight Center. 11 December 2003. Archived from the original on 11 October 2007. Retrieved 18 October 2007.
- ^ Schmadel, Lutz D. (2009). "Appendix – Publication Dates of the MPCs". Dictionary of Minor Planet Names – Addendum to Fifth Edition (2006–2008). Springer Berlin Heidelberg. p. 221. Bibcode:2009dmpn.book.....S. doi:10.1007/978-3-642-01965-4. ISBN 978-3-642-01964-7.
- ^ Morrison, Al H. (1977). "Chiron". CAO Times. 3: 57.
- ^ Miller & Stein (2021) Comment on U+26B7 CHIRON L2/21-225, UTC Document Registry
- ^ "Chiron's Osculating Elements 700AD generated with Solex 11, and data of close approach in 720". Retrieved 12 July 2015. "Solex 10 results". Archived from the original on 3 February 2012.
- ^ a b Horner, Jonathan M.; Evans, Norman W.; Bailey, Mark E. S. (2004). "Simulations of the Population of Centaurs II: Individual Objects". Monthly Notices of the Royal Astronomical Society. 355 (2): 321–329. arXiv:astro-ph/0408576. Bibcode:2004MNRAS.355..321H. doi:10.1111/j.1365-2966.2004.08342.x. S2CID 2994935.
- ^ Jewitt, David C.; Delsanti, Audrey C. (2006). "The Solar System Beyond The Planets". Solar System Update: Topical and Timely Reviews in Solar System Sciences. Springer-Praxis Ed. ISBN 978-3-540-26056-1. "Preprint version" (PDF). Archived from the original (PDF) on 25 May 2006.)
- ^ Luu, Jane X.; Jewitt, David C.; Trujillo, Chad (March 2000). "Water Ice in 2060 Chiron and Its Implications for Centaurs and Kuiper Belt Objects". The Astrophysical Journal. 531 (2): L151–L154. arXiv:astro-ph/0002094. Bibcode:2000ApJ...531L.151L. doi:10.1086/312536. PMID 10688775. S2CID 9946112.
- ^ a b c d e f Groussin, Olivier; Lamy, Philippe; Jorda, Laurent (January 2004). "Properties of the nuclei of Centaurs Chiron and Chariklo" (PDF). Astronomy and Astrophysics. 413 (3): 1163–1175. Bibcode:2004A&A...413.1163G. doi:10.1051/0004-6361:20031564. Retrieved 8 August 2017.
- ^ Hartmann, William K.; Tholen, David J.; Meech, Karen J.; Cruikshank, Dale P. (January 1990). "2060 Chiron - Colorimetry and cometary behavior". Icarus. 83 (1): 1–15. Bibcode:1990Icar...83....1H. doi:10.1016/0019-1035(90)90002-Q.
- ^ Meech, Karen J.; Belton, Michael J. S. (April 1989). "(2060) Chiron". IAU Circular. 4770: 1. Bibcode:1989IAUC.4770....1M.
- ^ Meech, Karen J.; Belton, Michael J. S. (October 1990). "The Atmosphere of 2060 Chiron". The Astronomical Journal. 100: 1323–1338. Bibcode:1990AJ....100.1323M. doi:10.1086/115600.
- ^ Womack, Maria; Stern, Alan (1999). "Observations of Carbon Monoxide in (2060) Chiron" (PDF). Conference Proceedings, Lunar and Planetary Science XXVIII. 28th Lunar and Planetary Science Conference, Houston, TX, Mar. 17-21, 1997. Retrieved 11 July 2017.
- ^ Bus, Schelte J.; A'Hearn, Michael F.; Schleicher, David G.; Bowell, Edward L. G. (15 February 1991). "Detection of CN Emission from (2060) Chiron". Science. 251 (4995): 774–777. Bibcode:1991Sci...251..774B. doi:10.1126/science.251.4995.774. hdl:2060/19920003642. PMID 17775455. S2CID 32230927.
- ^ Trigo-Rodríguez, Josep M.; García Melendo, Enrique; García-Hernández, Domingo Aníbal; Davidsson, Björn J. R.; Sánchez, Albert; Rodriguez, Diego (2008). A continuous follow-up of Centaurs, and dormant comets: looking for cometary activity (PDF). 3rd European Planetary Science Congress 2008. Retrieved 12 October 2008.
- ^ a b c Ortiz Moreno, José Luis; Duffard, René Damián; Pinilla-Alonso, Noemi; Alvarez-Candal, Alvaro; Santos-Sanz, Pablo; Morales Palomino, Nicolás Francisco; Fernández-Valenzuela, Estela del Mar; Licandro, Javier; Campo Bagatin, Adriano; Thirouin, Audrey (2015). "Possible ring material around centaur (2060) Chiron". Astronomy & Astrophysics. 576: A18. arXiv:1501.05911. Bibcode:2015A&A...576A..18O. doi:10.1051/0004-6361/201424461. S2CID 38950384.
- ^ Lakdawalla, Emily (27 January 2015). "A second ringed centaur? Centaurs with rings could be common". Planetary Society. Retrieved 31 January 2015.
- ^ "A second minor planet may possess Saturn-like rings". Space Daily. 17 March 2015.
- ^ "Chiron Orbiter Mission Concept Study".
- Fernández, Yanga R.; Jewitt, David C.; Sheppard, Scott S. (2002). "Thermal Properties of Centaurs Asbolus and Chiron". Astronomical Journal. 123 (2): 1050–1055. arXiv:astro-ph/0111395. Bibcode:2002AJ....123.1050F. doi:10.1086/338436. S2CID 11266670.
- Moore, Patrick; Guinness book of Astronomy, ISBN 0-85112-375-9
- SOLEX 9.1
- 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)
- 2060 Chiron at AstDyS-2, Asteroids—Dynamic Site
- Ephemeris · Observation prediction · Orbital info · Proper elements · Observational info
- 2060 Chiron at the JPL Small-Body Database
- Close approach · Discovery · Ephemeris · Orbit diagram · Orbital elements · Physical parameters