C/2017 K2 (PanSTARRS)

C/2017 K2 (PanSTARRS)
Time-lapse with an 8" Celestron telescope on July 14, 2022 - the night of its closest approach to Earth. Below the comet is the Globular Cluster Messier 10.
Discovery
Discovery date21 May 2017[1]
Orbital characteristics
Epoch2022-12-07 (2459920.5)
Observation arc9.46 years
Number of
observations		477
Orbit typeOort cloud
Aphelion~50000 AU (inbound)[2]
~1400 AU (outbound)[2]
Perihelion1.7969 AU[3]
Eccentricity~0.99992 (inbound)
~0.9975 (outbound)[2]
Orbital periodMillions of years inbound[2]
~19,000 years (outbound)[2]
Inclination87.563°
88.26730
Last perihelion19 December 2022[3][4][a]
Earth MOID1.10 AU (165 million km)
Jupiter MOID1.29 AU
Physical characteristics
DimensionsRn between 14 km (8.7 mi) and 80 km (50 mi)[5]
maximum Dn ~18 km (11 mi)[6]

C/2017 K2 (PanSTARRS) is an Oort cloud comet with an inbound hyperbolic orbit, discovered in May 2017 at a distance beyond the orbit of Saturn when it was 16 AU (2.4 billion km) from the Sun. Precovery images from 2013 were located by July.[7] It had been in the constellation of Draco from July 2007 until August 2020. As of June 2022, the 3-sigma uncertainty in the current distance of the comet from the Sun is ±6000 km.[8]

The comet is record breaking because it was already becoming active at such a distance. Only Comet Hale–Bopp produced such a show from that distance with a similar nucleus. However, this comet will not be as visible as Hale–Bopp was in 1997 in part because it does not come nearly as close to the Sun.[b] Astronomers had never seen an active inbound comet this far out, where sunlight is 1/225th its brightness as seen from Earth. Temperatures, correspondingly, are at -440 °F (-262 °C) in the Oort cloud. However, as it was approaching the Sun at a distance of 16 AU at discovery, a mix of ancient ices on the surface containing oxygen, nitrogen, carbon dioxide and carbon monoxide began to sublimate and shed the dust frozen into it. This material expands into a vast 130,000 km (81,000 mi) wide halo of dust, called a coma, enveloping the solid nucleus.[9] Outgasing of carbon monoxide was detected when the comet was 6.72 AU from the Sun.[10]

Research with the Canada–France–Hawaii Telescope (CFHT) infers the comet nucleus to have a radius between 14–80 km (9–50 mi), so there is a chance the nucleus could be as large as C/1995 O1 (Hale-Bopp).[5] However, research with the Hubble Space Telescope (HST) estimates the nucleus to have a circular equivalent diameter of less than 18 km (11 mi).[6] On 17 September 2020, morphological studies of the inner coma, observed on 12 September 2020, were reported, noting that two jet-streamed structure were emitted from the nucleus and, as well, that the length of the tail was about 800,000 km (500,000 mi) long.[11]

The comet was within 5 AU (750 million km) of Earth by 11 January 2022.[12] Around 6 July 2022, the comet crossed the celestial equator, and then on 14 July 2022, it passed 1.8 AU (270 million km) from Earth[13] and shone around 9.0 magnitude making it a decent binoculars object.[14][4] It reached perihelion on 19 December 2022, close to the orbit of Mars, and was not visible to naked eye at 8.0 magnitude.[3][4][a]

On 27 July 2021, further detailed observations of the comet were reported on The Astronomer's Telegram.[15][16]

JPL Horizons models that C/2017 K2 took millions of years to come from the Oort cloud at a distance of roughly 50,000 AU (0.8 ly).[2] The heliocentric orbital eccentricity drops below 1 in December 2023.[17] The outbound orbital period will be around 19000 years with aphelion being around 1400 AU.[2] There was a dispute whether that was the first time the comet entered the inner solar system, but its orbit suggests that the comet isn't dynamically new and there is a 29% chance that the comet is of interstellar origin and was captured by the solar system within the last 3 million years.[18]

  1. ^ Cite error: The named reference MPEC2017-K35 was invoked but never defined (see the help page).
  2. ^ a b c d e f g Cite error: The named reference barycenter was invoked but never defined (see the help page).
  3. ^ a b c Cite error: The named reference MPC was invoked but never defined (see the help page).
  4. ^ a b c Cite error: The named reference Yoshida was invoked but never defined (see the help page).
  5. ^ a b Cite error: The named reference Meech2017 was invoked but never defined (see the help page).
  6. ^ a b Cite error: The named reference Jewitt2017 was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference MPEC2017-N26 was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference current was invoked but never defined (see the help page).
  9. ^ Byrd, Deborah (2 October 2017). "Farthest active inbound comet yet". Earth & Sky. Retrieved 19 September 2020.
  10. ^ Yang, Bin; Jewitt, David; Zhao, Yuhui; Jiang, Xuejian; Ye, Quanzhi; Chen, Ying-Tung (10 June 2021). "Discovery of Carbon Monoxide in Distant Comet C/2017 K2 (PANSTARRS)". The Astrophysical Journal Letters. 914 (1): L17. arXiv:2105.10986. Bibcode:2021ApJ...914L..17Y. doi:10.3847/2041-8213/ac03b7. S2CID 235166808.
  11. ^ Manzini, Federico; et al. (17 September 2020). "ATel #14026: Morphological structures in the inner coma of comet C/2017 K2 (PanStarrs)". The Astronomer's Telegram. Retrieved 19 September 2020.
  12. ^ Cite error: The named reference Earth-5au was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference Earth-July was invoked but never defined (see the help page).
  14. ^ Hubble Spots Farthest-Ever Incoming Active Comet September 29, 2017
  15. ^ Manzini, Federico; et al. (27 July 2021). "ATel #14813: Comet C/2017 K2 (PanStarrs) shows jet-shaped dust emissions modulated by extremely slow rotation at greater-than-usual distance from the Sun". The Astronomer's Telegram. Retrieved 28 July 2021.
  16. ^ Manzini, Federico; et al. (27 July 2021). "ATel #14814: Erratum to ATEL #14813: Comet C/2017 K2 (PanStarrs) shows jet-shaped dust emissions modulated by extremely slow rotation at greater-than-usual distance from the Sun". The Astronomer's Telegram. Retrieved 28 July 2021.
  17. ^ Cite error: The named reference closed was invoked but never defined (see the help page).
  18. ^ Marcos, Raúl de la Fuente; Marcos, Carlos de la Fuente (24 April 2018). "Comet C/2017 K2 (PANSTARRS): Dynamically Old or New?". Research Notes of the AAS. 2 (2): 10. arXiv:1804.07292. Bibcode:2018RNAAS...2...10D. doi:10.3847/2515-5172/aabf8f. S2CID 118938922.


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