Space

Largest known comet sprouts tail on its inward journey

Largest known comet sprouts ta...
An artist's illustration of comet C/2014 UN271 Bernardinelli-Bernstein
An artist's illustration of comet C/2014 UN271 Bernardinelli-Bernstein
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An artist's illustration of comet C/2014 UN271 Bernardinelli-Bernstein
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An artist's illustration of comet C/2014 UN271 Bernardinelli-Bernstein
Comet C/2014 UN271 Bernardinelli-Bernstein (center), with the coma visible as a fuzzy cloud around the bright spot, in contrast with stars such as the one at the top, which have a crisp outline
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Comet C/2014 UN271 Bernardinelli-Bernstein (center), with the coma visible as a fuzzy cloud around the bright spot, in contrast with stars such as the one at the top, which have a crisp outline

A huge comet making its journey towards the solar system has begun to show a tail. A newly released image shows the fuzzy coma, confirming that it is indeed a comet and may be one of the largest ever discovered.

With confirmation that the object is a comet, it’s now been officially designated C/2014 UN271 Bernardinelli-Bernstein, in reference to its discoverers Pedro Bernardinelli and Gary Bernstein. Although it was unknowingly photographed in 2014, astronomers only identified it in old data in June 2021.

At the time the original image was captured, the comet was about 29 Astronomical Units (AU) from the Sun, putting it slightly closer than the orbit of Neptune, although it is approaching from above the plane of the solar system. That makes it the most distant comet ever discovered – although it’s quickly shrinking that distance.

At 29 AU, it wasn’t showing signs of activity associated with comets, such as a tail or coma which arise as the heat of the Sun vaporizes material off the surface. But things could have changed in the years since, so immediately after it was identified astronomers rushed to image the object anew.

Within a few days, astronomers at the Las Cumbres Observatory in South Africa snapped new shots of UN271, at its current distance of about 19 AU away. Sure enough, the bright spot had a fuzzy border, indicating comet activity. In contrast, stars have a far more crisp outline, with the difference stark in the image.

Comet C/2014 UN271 Bernardinelli-Bernstein (center), with the coma visible as a fuzzy cloud around the bright spot, in contrast with stars such as the one at the top, which have a crisp outline
Comet C/2014 UN271 Bernardinelli-Bernstein (center), with the coma visible as a fuzzy cloud around the bright spot, in contrast with stars such as the one at the top, which have a crisp outline

Further research over the past month has also helped astronomers pin down its orbit more precisely. It’s now known that C/2014 UN271 is on its way in from its most distant point of 40,000 AU, about 1.5 million years ago. At its closest point in 2031, it will reach just 10.9 AU – which is a distance slightly further than the orbit of Saturn.

It’s estimated that the comet is more than 100 km (62 miles) wide, which would make it one of the largest ever discovered. Sadly though, we shouldn’t expect a big show from here on the ground – C/2014 UN271 will not get close enough to be visible with the naked eye. However, we can look forward to some amazing images taken with telescopes.

After the comet swings through the solar system, its outward journey will be even longer, taking it to a distance of around 54,000 AU in about 4.5 million years’ time.

Source: Las Cumbres Observatory

1 comment
1 comment
piperTom
It's odd that there is so much asymmetry in the orbit. The infall from aphelion takes 1.5 megayears (from 40 KAU) but the other side of the ellipse (?) takes 4.5 megayears (up to 54 KAU). What's the reason for the asymmetry?