The largest comet that’s ever been found in modern times has been discovered by Pedro Bernardinelli (a graduate student at the University of Pennsylvania) and astronomer Gary Bernstein. It was discovered in images taken by the Dark Energy Survey in 2014.
Named Comet C/2014 UN271 (or Bernardinelli-Bernstein after the two men who discovered it), it could be up to a thousand times larger than a typical comet. Its diameter has been estimated as being between 62 and 124 miles (between 100 and 200 kilometers) which is about ten times wider than a typical comet. Astronomers made this estimation based on how much sunlight reflects off the icy body.
In a statement, Bernstein discussed their discovery, “We have the privilege of having discovered perhaps the largest comet ever seen — or at least larger than any well-studied one — and caught it early enough for people to watch it evolve as it approaches and warms up.”
After Comet C/2014 UN271 was detected, it didn’t show any evidence of a tail between the years 2014 and 2018; however, recent observations conducted this year by an independent observation from the Las Cumbres Observatory network found that the comet now has a distinct coma of gas and dust that is surrounding it.
It is currently at a distance of about 20 astronomical units (AU) from the sun – basically, the equivalent of where Uranus is located. It is extremely difficult to see as it has a current magnitude of 20. To put this into better perspective, with the naked eye, people can see stars with a magnitude of 5 or 6. It will make its closest approach to the sun in the year 2031 but it will still be quite far from us with a magnitude of 11 so it won’t be any easier to spot (this is a bit further out than Saturn’s orbit around our sun). (An image from the Dark Energy Survey of the comet located at a distance of 25 AU in 2017 can be seen here.)
What’s even more interesting is that the comet hasn’t traveled through the inner part of our Solar System in approximately 3 million years. It comes from a very long distance away – about 40,000 AU in the Oort Cloud where scientists have estimated trillions of comets are located.
The National Science Foundation (NSF) noted, “Astronomers suspect that there may be many more undiscovered comets of this size waiting in the Oort Cloud far beyond Pluto and the Kuiper Belt,” adding, “These giant comets are thought to have been scattered to the far reaches of the solar system by the migration of Jupiter, Saturn, Uranus and Neptune early in their history.”
An artist’s illustration of what Comet C/2014 UN271 would look like can be seen here.