2060 Chiron

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Not to be confused with Pluto's moon Charon.

2060 Chiron
95P/Chiron
U–B = 0.283[6]
  • BB[19]
  • C[13]
    • 18.93[20]
    14.9 (Perihelic opposition)[21]
    0.035" (max)[26]

    2060 Chiron is a

    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.[1]

    History

    Discovery

    Chiron was discovered on 1 November 1977 by

    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.[2] The April 1895 precovery image was one month after the March 1895 perihelion.[10]

    Naming

    This

    M.P.C. 4359).[5][30] It was suggested that the names of other centaurs be reserved for objects of the same type.[2]

    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.[31][32]

    Orbit

    Orbital diagram of Chiron

    Chiron's orbit was found to be highly

    semi-major axis to decrease from 14.55±0.12 AU[33] to 13.7 AU.[6]
    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

    short-period comet in about a million years.[34] Chiron came to perihelion (closest point to the Sun) in 1996 and aphelion in May 2021.[8]

    Physical characteristics

    Spectral type

    The visible and near-infrared spectrum of Chiron is neutral,[27] and is similar to that of C-type asteroids and the nucleus of Halley's Comet.[15] The near-infrared spectrum of Chiron shows absence of water ice.[36]

    Rotation period

    Four rotational

    U=3/3/3).[13][14][15][16][17]

    Diameter

    Summary – size estimates for Chiron:
    Year Diameter Notes Refs
    1984 180 km Lebofsky (1984) [37]
    1991 186 km IRAS [37]
    1994 188 km Campins (radius 94±6 km) [27]
    1996 180 km occultation [37]
    1998 166 km Dunham occultation list
    (Dunham 1998)    		 [6]
    2007 233 km Spitzer Space Telescope [12]
    2013 218 km Herschel Space Observatory
    (PACS and SPIRE)    		 [11]
    2017 271 km LCDB [13]
    2017 206 km Brown [18]

    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.[37] Estimates in the 1990s were closer to 150 km in diameter.[6][37] Occultation data from 1993 suggests a diameter of about 180 km.[37] 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.[11] Therefore, Chiron may be as large as 10199 Chariklo.[12] 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.[11]

    Cometary behavior

    In February 1988, at 12 AU from the Sun, Chiron brightened by 75 percent.

    coma,[39] A tail was detected in 1993.[27] 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.[40] 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.[41] Cyanide was also detected in the spectrum of Chiron in 1991.[42] 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.[29]

    Chiron is officially designated as both a comet—95P/Chiron—and a minor planet,

    a > aJupiter).[6] 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.[4] Michael Brown lists it as possibly a dwarf planet with a measured diameter of 200 km (120 mi),[18]
    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.[43]

    Rings

    Depiction of Chiron and its rings

    Chiron has

    rings, similar to the better-established rings of 10199 Chariklo.[44][45][46][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 were proposed to be 324±10 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.[44]

    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.[47] 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 fully developed.[48] 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.[47] However, Sickafoose saw no connection.[clarification needed]

    The preferred pole of Chiron's rings is, in ecliptic coordinates, λ = 151°±8°, β = 18°±11°. 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.[44][47]

    Exploration

    The Chiron Orbiter Mission was a mission proposed for NASA's

    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.[49]

    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

    Wikimedia Commons has media related to 2060 Chiron.
    • Hubble Space Telescope image of the centaur 2060 Chiron, taken on 14 September 2015
      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)
      Chaotic, unstable motion of Chiron with Saturn (stationary, white dot at 10 o'clock) and Jupiter (blue)
    • Animated orbital diagram with Chiron (violet) not showing perturbation
      Animated orbital diagram with Chiron (violet) not showing perturbation

    See also

    Notes

    1. ^ 944 Hidalgo, discovered in 1920, also fits this definition, but was not identified as belonging to a distinct population.
    2. ^ Pluto, now considered to be a dwarf planet and hence a minor planet, was known at the time, but was considered a planet.
    3. ^ A stellar occultation in 2017 of another minor planet, Haumea (a trans-Neptunian object), indicated the presence of a ring.

    References

    1. ^ a b c d e f "2060 Chiron (1977 UB)". Minor Planet Center. Retrieved 8 August 2017.
    2. ^
      Bibcode:1979IAUS...81..245K
      .
    3. ^ a b "Chiron Fact Sheet". NASA Goddard Space Flight Center. 20 August 2014.
    4. ^ a b c "Dual-Status Objects". Minor Planet Center.
    5. ^
      ISBN 978-3-540-00238-3
      .
    6. ^ 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.
    7. ^ "List of Centaurs and Scattered-Disk Objects". Minor Planet Center. Retrieved 13 November 2014.
    8. ^ 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.
    9. ^ "Horizons Batch for 2060 Chiron (1977 UB) on 2046-Aug-03" (Perihelion occurs when rdot flips from negative to positive). JPL Horizons. Archived from the original on 1 October 2021. Retrieved 1 October 2021.
    10. ^ 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.
    11. ^
      S2CID 119261700
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    12. ^
      arXiv:astro-ph/0702538
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    13. ^ a b c d e f g "LCDB Data for (2060) Chiron". Asteroid Lightcurve Database (LCDB). Retrieved 8 August 2017.
    14. ^
      ISSN 0019-1035
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    15. ^
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    16. ^
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    17. ^
      doi:10.1016/S0032-0633(97)00124-4
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    18. ^ 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.
    19. doi:10.1016/j.icarus.2014.12.004
      .
    20. ^ "AstDys (2060) Chiron Ephemerides". Department of Mathematics, University of Pisa, Italy. Retrieved 8 August 2017.
    21. ^ "Chiron Apmag March-April 1996" (Perihelion year). JPL Horizons. Retrieved 6 July 2021.
    22. S2CID 53493339
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    23. doi:10.1016/j.icarus.2010.06.005
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    25. doi:10.1006/icar.1998.5931
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    26. ^ 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.
    27. ^
      ISSN 0004-6256
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    28. doi:10.1046/j.1365-8711.2000.t01-1-03640.x
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    29. ^ 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.
    30. ISBN 978-3-642-01964-7
      .
    31. ^ Morrison, Al H. (1977). "Chiron". CAO Times. 3: 57.
    32. ^ Miller & Stein (2021) Comment on U+26B7 CHIRON L2/21-225, UTC Document Registry
    33. ^ "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.
    34. ^
      S2CID 2994935
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    35. ISBN 978-3-540-26056-1
      . "Preprint version" (PDF). Archived from the original (PDF) on 25 May 2006.)
    36. S2CID 9946112
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    37. ^
      doi:10.1051/0004-6361:20031564
      . Retrieved 8 August 2017.
    38. doi:10.1016/0019-1035(90)90002-Q
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    39. Bibcode:1989IAUC.4770....1M
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    40. doi:10.1086/115600
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    41. ^ 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.
    42. S2CID 32230927
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    43. ^ 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.
    44. ^
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    45. Planetary Society
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    46. ^ "A second minor planet may possess Saturn-like rings". Space Daily. 17 March 2015.
    47. ^
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    48. doi:10.3847/PSJ/ad0632
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    49. ^ "Chiron Orbiter Mission Concept Study".

    Further reading

    External links


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