There’s quite a bit of activity on the largest comet we’ve ever spotted

Despite its great distance from the sun – more than double the distance between Saturn and our parent star – the massive comet already possesses a distinctive coma.

A few weeks ago, astronomers made an interesting discovery. A huge comet – possibly from the still hypothetical Oort cloud – is currently heading towards the inner reaches of our solar system. Since then, researchers have been keeping a close eye on the object. And now this story is – literally – getting a tail.

C/2014 UN271 Bernardinelli-Bernstein
The object has been given the name C/2014 UN271 Bernardinelli-Bernstein, named after its two discoverers. What makes this comet so special, among other things, is its bizarre size. For example, C/2014 UN271 turns out to be the largest known comet ever. Judging by the brightness, its size is currently estimated at about 100 kilometers, which is more than three times the size of the number two; Comet Hale-Bopp, which was discovered in 1995.

More about his discovery
The comet was discovered as part of the Dark Energy Survey (DES), a research project in which scientists are trying to get a better grip on the accelerated expansion of the universe and the driving force behind it (dark energy). Many photos of the night sky were taken between 2013 and 2019. But those images aren’t just being used to learn more about dark energy. For example, these images are also used to search for as yet unknown objects in our own solar system. And that’s how researchers Bernardinelli and Bernstein tracked down C/2014 UN271.

At first glance, it did not appear that C/2014 UN271 Bernardinelli-Bernstein was a very active comet yet. And that makes sense, given its immense distance from the sun. It is currently more than double the distance between Saturn and our parent star, about 2.9 billion kilometers from the sun. Then, as a comet gets closer and closer to a star, some of the matter that makes up it sublimates to form a so-called coma and/or comet tail. So expectations were high. Because when would this large, newly discovered object begin to exhibit such a coma?

What is a comet?
Comets are relatively small celestial bodies that whiz through our solar system. They are made up of ice, dust and tiny rocky particles and can sometimes have very crazy orbits around the sun. Comets often have a tail. When the ice ball comes close to the sun or another star, it heats up. The ice in the comet sublimes (evaporates) and rushes away from the surface. In doing so, it carries light dust and debris particles with it. This creates a dust tail and coma (dusty atmosphere) so characteristic of comets. It also means that comets get brighter as they get closer to the sun. The more dust is released, the brighter the comet—or more accurately, the coma, or nebulous cloud around the comet’s nucleus—appears.

Using follow-up observations with telescopes at Las Cumbres Observatory, astronomers then made the surprising discovery that C/2014 UN271 Bernardinelli-Bernstein had already been activated by the sun’s heat. Observations indicate that the comet has a faint cloud of gas and dust, which means that it is indeed active.

New images
Now, newly released images provide more insight into the comet’s activity. The image below shows C/2014 UN271 Bernardinelli-Bernstein.

Photo of comet C/2014 UN271 Bernardinelli-Bernstein, taken by the Las Cumbres Observatory located in South Africa. The diffuse cloud is the comet’s coma. Image: LOOK/LCO

The images confirm that there is quite a bit of activity on this comet. You see a beautiful small, blurry dot, which indicates a bright comet tail. And that while C/2014 UN271 is still so far from the sun.

It means that this comet could have quite a bit in store for us. As the comet approaches the sun and brightens, the coma will become more and more extensive. Will the comet be visible to the naked eye at some point? Probably not, so the researchers must disappoint us. It will presumably remain a telescopic object. When the comet reaches perihelion in 2031 — the point in its (highly eccentric) orbit where the distance between the comet and the sun is smallest — it will still be between the orbits of Uranus and Saturn.

The traced path of comet C/2014 UN271 Bernardinelli-Bernstein. Image: NASA

The fact that astronomers discovered C/2014 UN271 Bernardinelli-Bernstein so early means we could witness C/2014 UN271 rushing toward the interior of our solar system for years to come. It means there is plenty of time to study the comet using powerful telescopes. For example, astronomers will continue to monitor the comet’s behavior and analyze how its activity evolves as it moves closer to the sun.

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