Physical characteristics
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. [10] Outgassing of carbon monoxide was detected when the comet was 6.72 AU (1,005 million km) from the Sun. [11]
Research with the Canada–France–Hawaii Telescope (CFHT) infers the comet 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 as C/1995 O1 (Hale–Bopp). [12] However, research with the Hubble 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 the James 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 on The Astronomer's Telegram . [16]
Orbit
The comet was within 5 AU (750 million km) of Earth by 11 January 2022. [17] 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 [18] and shone around 9.0 magnitude making it a decent binoculars object. [19] [20] It reached perihelion on 19 December 2022, close to the orbit of Mars, 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 heliocentric orbital 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 inner Solar System, but its orbit suggests that the comet is not 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. [22] [23]
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