Artist's impression of comet Bernardinelli-Bernstein. Credit: J. da Silva / NOIRLab / NSF / AURA

Massive Comet Heading Our Way Likely Larger Than Mars’ Moons

Researchers say that Comet Bernardinelli-Bernstein will be an impressive target for ground observations in 2031.


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 to date. It is assumed that its current activity is due to the sublimation of particles of ammonia and carbon dioxide ice. 

Scientists revealed new information about the largest comet in decades: Everything you need to know

Oort Cloud

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.


Comet Bernardinelli-Bernstein

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.

Latest observational data

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. This data was used to discover the comet and determine its properties and orbit.

Comet’s orbit

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.

Previous perihelion

Comet Bernardinelli-Bernstein passed the previous perihelion at a distance of about 18 astronomical units from the Sun 3.5 million years ago.

The current position and orbit of the object is 2014 UN271. Credit: JPL Small-Body Database
The current position and orbit of the object is 2014 UN271. Credit: JPL Small-Body Database


Comet Bernardinelli-Bernstein’s nucleus has been estimated at 150 kilometers in size, making it the largest cometary nucleus known (about ten times that of Hale-Bopp’s nucleus) and the largest known Oort cloud body.

Comet Bernardinelli-Bernstein is bigger than the moons of Mars

A common comparison has been made between the comet and Mars’ moons – Phobos and Deimos. For instance, Phobos is about 22.2 kilometers in diameter while Deimos is 12.6 km, making them significantly smaller than the comet.

Model of comet activity

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.

Ground observations

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.

How bright will it be?

Near the point of perihelion, comet Bernardinelli-Bernstein will be slightly fainter than Saturn’s moon Titan, and the rate of sublimation of carbon dioxide from the core will increase 200 times.

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Bernardinelli, P. H., Bernstein, G. M., Montet, B. T., Weryk, R., Wainscoat, R., Aguena, M., Allam, S., Andrade-Oliveira, F., Annis, J., Avila, S., Bertin, E., Brooks, D., Burke, D. L., Rosell, A. C., Kind, M. C., Carretero, J., Cawthon, R., Conselice, C., Costanzi, M., … Zhang, Y. (2021, September 22). C/2014 UN271 (BERNARDINELLI-BERNSTEIN): The nearly spherical cow of comets.
Ciaccia, C. (2021, September 23). Megacomet c/2014 UN271 is likely bigger than one of mars’ moons with a 93 mile-wide DIAMETER: STUDY. Daily Mail Online.
Hall, J. (2021, September 27). Our newest celestial visitor is a truly gigantic comet. ExtremeTech.
Mack, E. (2021, September 23). Monster comet falling toward the sun is bigger than a Martian moon. CNET.

Written by Vladislav Tchakarov

Hello, my name is Vladislav and I am glad to have you here on Curiosmos. As a history student, I have a strong passion for history and science, and the opportunity to research and write in this field on a daily basis is a dream come true.

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