Astronomers confirm record size of a comet from the Oort cloud


@willgater / Twitter, ESA, NASA, NOIRLab

Astronomers have determined that the diameter of the nucleus of C / 2014 UN271 (Bernardinelli-Bernstein) from the Oort cloud is about 150 kilometers, making it the largest comet and the largest body from the Oort cloud known. It is assumed that its current activity is due to the sublimation of particles of ammonia and carbon dioxide ice. A preprint of the work is available at

Scientists’ current understanding of the population of the Oort cloud is based on a small sample of bodies in orbits with perihelions of less than 10 astronomical units. At the same time, only a part of them showed cometary activity, which facilitates the search for such objects and makes it possible to assess the composition of their surface layer. The recent discovery of C / 2014 UN271 (Bernardinelli-Bernstein), which was originally thought to be a dwarf planet from the Oort cloud now moving towards the Sun, allows astronomers to learn more about the properties of bodies from the outskirts of the solar system, which enter as objects captured from the interstellar medium and bodies born at the dawn of the solar system.

A group of astronomers led by the discoverers of the comet Pedro Bernardinelli and Gary Bernstein of the University of Pennsylvania published a paper in which they presented the results of an analysis of all observational data up to June 2021, which were used to discover the comet and determine its properties and orbit. such as DES (Dark Energy Survey) and PanSTARRS1 sky surveys and data from the VISTA, CFHT and Gaia telescopes.

Scientists have determined that the inclination of the comet’s orbit is 95 degrees to the plane of the ecliptic, the previous aphelion of its orbit is at a distance of 40.4 thousand astronomical units, and the next perihelion it will pass in early 2031, being at a distance of 10.97 astronomical units from the Sun. The comet passed the previous perihelion at a distance of about 18 astronomical units from the Sun 3.5 million years ago.

The comet’s nucleus has been estimated at 150 kilometers in size, making C / 2014 UN271 the largest cometary nucleus known (about ten times that of Hale-Bopp’s nucleus) and the largest known Oort cloud body. So far, scientists have not been able to determine the rotation period of the nucleus, but the dynamics of the brightness of the nucleus as it approaches the Sun fits into a simple model of comet activity due to the sublimation of particles of frozen carbon dioxide or ammonia from the surface of the nucleus. More volatile substances such as molecular nitrogen, methane or carbon monoxide can also be present in a coma.

The researchers believe that despite the fact that the rate of sublimation of water ice on the comet will be extremely low, it will be an impressive target for ground observations – near the point of perihelion, it will be slightly fainter than Saturn’s moon Titan, and the rate of sublimation of carbon dioxide from the core will increase 200 times.

Earlier we talked about the discovery of the most distant object in the solar system to date 2018 AG37, a year which lasts about 10 earthly centuries.

Alexander Voytyuk


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