 Time-lapse of C/2017 K2 (PanSTARRS) above the globular cluster,Messier 10, on 14 July 2022 | |
| Discovery[1] | |
|---|---|
| Discovery site | Pan-STARRS |
| Discovery date | 21 May 2017 |
| Designations | |
| CK17K020 | |
| Orbital characteristics[2][3][4] | |
| Epoch | 7 December 2022 (JD 2459920.5) |
| Observation arc | 12.56 years |
| Earliestprecovery date | 12 May 2013 |
| Number of observations | 3211 (used in fit) |
| Orbit type | Oort cloud |
| Aphelion | ~51,200 AU (inbound) ~1,750 AU (outbound) |
| Perihelion | 1.797 AU |
| Semi-major axis | ~25,600 AU (inbound) ~870 AU (outbound) |
| Eccentricity | ~0.99993 (inbound) ~0.99795 (outbound) |
| Orbital period | ~4.1 million years (inbound) ~25,800 years (outbound) |
| Inclination | 87.555° |
| 88.241° | |
| Argument of periapsis | 236.19° |
| Mean anomaly | –0.003° |
| Last perihelion | 19 December 2022[a] |
| TJupiter | 0.170 |
| EarthMOID | 1.092 AU |
| JupiterMOID | 1.254 AU |
| Physical characteristics | |
Mean radius | < 4.2 km (2.6 mi)[5] |
| 14.24 hours[6] | |
| Comet total magnitude (M1) | 8.5[3] |
| 7.2[7] (2022 apparition) | |
C/2017 K2 (PanSTARRS) is anOort cloudcomet with an inbound hyperbolic orbit, discovered in May 2017 at a distance beyond the orbit ofSaturn when it was 16 AU (2.4 billion km) from theSun.
Precovery images taken from 2013 were located by July 2017.[8] It had been in the constellation ofDraco from July 2007 until August 2020. As of June 2022[update], the3-sigma uncertainty in the current distance of the comet from the Sun is±6000 km.[9]
The comet is record breaking because it was already becoming active at such a distance. OnlyComet 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 −262.2 °C (−440 °F) 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 containingoxygen,nitrogen,carbon dioxide andcarbon 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 acoma, enveloping the solid nucleus.[10] Outgassing of carbon monoxide was detected when the comet was 6.72 AU (1,005 million km) from the Sun.[11]
Research with theCanada–France–Hawaii Telescope (CFHT) infers thecomet nucleus to have a radius between 14–80 km (8.7–49.7 mi), so there is a chance the nucleus could be as large asC/1995 O1 (Hale–Bopp).[12] However, research with theHubble Space Telescope (HST) estimates the nucleus to have a circular equivalent diameter of less than 18 km (11 mi).[13] Near-infrared observations conducted by theJames Webb Space Telescope in 2023 revealed a much smaller nucleus, estimated to be less than 8.4 km (5.2 mi) in diameter.[5][14] 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.[15]
On 27 July 2021, further detailed observations of the comet about its jet-shaped dust emissions were reported onThe Astronomer's Telegram.[16]
The comet was within 5 AU (750 million km) of Earth by 11 January 2022.[17] Around 6 July 2022, the comet crossed thecelestial equator, and then on 14 July 2022, it passed 1.8 AU (270 million km) from Earth[18] and shone around 9.0 magnitude making it a decentbinoculars object.[19][20] It reachedperihelion on 19 December 2022, close to the orbit ofMars, and was not visible to naked eye at 8.0 magnitude.[4][20][a]
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 (0.79 ly).[2] The heliocentricorbital eccentricity drops below 1 in December 2023.[21] The outbound orbital period will be around 25,800 years with aphelion being around 1,750 AU (262 billion km).[2] There was a dispute whether that was the first time the comet entered the innerSolar System, but its orbit suggests that the comet is not dynamically new and there is a 29% chance that the comet is ofinterstellar origin and was captured by the Solar System within the last 3 million years.[22][23]
![June 2017 by Hubble's Wide Field Camera 3[24]](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aDistant_active_comet_C_2017_K2.jpg)
_with_M10.jpg)
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