Earlier this year, astronomers announced the discovery of a massive object from the Oort Cloud that appeared to be the largest to date. Fast-forward a few weeks and we already know that the object is a gargantuan-sized comet – C/2014 UN271. the largest comet ever discovered. Astronomers observed the “awakening” of the object and spotted its coma.
Object 2014 UN271 was discovered in June 2021 on images from the DES (Dark Energy Survey) survey instrument. Analysis of archived data showed that it first appeared on astronomical images back in 2014. The object’s orbit is highly inclined and elongated, and the aphelion – the point of the trajectory farthest from the Sun – is located in the inner part of the Oort cloud.
Initially, it was assumed that the object may be a dwarf planet, but then a gas shell – a coma was found in it, after which 2014 UN271 was reclassified into a giant comet C / 2014 UN271 (Bernardinelli-Bernstein). The diameter of its core is estimated at more than 100 kilometers, which is larger than that of Hale-Bopp, which had the largest nucleus among the known comets (40-80 kilometers) for which such measurements were made.
Initially, it was assumed that the object may be a dwarf planet, but then a gas shell – a coma was found in it, after which 2014 UN271 was reclassified into a giant comet C / 2014 UN271 (Bernardinelli-Bernstein). The diameter of its core is estimated at more than 100 kilometers, which is larger than that of Hale-Bopp, which had the largest nucleus among the known comets (40-80 kilometers) for which such measurements have been made successfully.
The coma was discovered by a member of the team that monitors images from the Las Cumbres Observatory (LCO) – Michele Bannister. She analyzed several images before she was able to confirm the comet.
In addition, other astronomers from around the world have shared their own observations of the largest comet. Tony Farnham of the University of Maryland has published the results of an analysis of images taken by the TESS space telescope from September 21 to October 18, 2018, which show an extended and asymmetric bright region around the nucleus, indicating the presence of a coma.
At this time, the comet was at a distance of 23.8 astronomical units (AU) from the Sun, which is more than in the case of observations from other telescopes. In turn, the images analyzed by Michele Bannister were captured when the largest comet was about 19 astronomical units (AU) from the sun.
In addition, the constancy of the brightness of C / 2014 UN271 between 2014 and 2018 means that the comet may have become active even before it was detected at around 29.3 astronomical units from the Sun, which will further lead to an overestimation of the size of the core.
The comet is expected to pass its perihelion at a distance of approximately 10.5 astronomical units from the Sun (between the orbits of Uranus and Saturn) in early 2031.
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• Clarke, A. (2021, July 16). Comet Bernardinelli-Bernstein Will Make a Near-Earth Approach in 10 Years, Looks Like a Beautiful Dot in Image. Science Times.
• Farnham, T. (n.d.). Comet C/2014 UN271 (Bernardinelli-Bernstein) exhibited activity at 23.8 au. ATel.
• Howell, E. (2021, July 15). Astronomers spot first activity on giant megacomet beyond Saturn. Space.com.
• Las Cumbres Observatory. (n.d.). LCO Discovers Activity on Largest Comet Ever Found.