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Astronomers spot first activity on giant megacomet beyond Saturn

Comet C/2014 UN271 (Bernardinelli-Bernstein), as seen in a synthetic color composite image made with the Las Cumbres Observatory 1-meter telescope at Sutherland, South Africa, on 22 June 2021. The diffuse cloud is the comet’s coma.
Comet C/2014 UN271 (Bernardinelli-Bernstein), as seen in a synthetic color composite image made with the Las Cumbres Observatory 1-meter telescope at Sutherland, South Africa, on 22 June 2021. The diffuse cloud is the comet’s coma. (Image credit: LOOK/LCO)

Spotting the first signs of activity on a record-setting comet of gargantuan size came down to a time-zone advantage.

Astronomers in New Zealand were the first to spot a coma, or zone of gas and dust, spreading around the megacomet C/2014 UN271, also known as Bernardinelli-Bernstein, which may be 1,000 times more massive than a typical comet. It could be the most massive comet ever found in all of recorded history.

The team that monitors images captured by the Las Cumbres Observatory (LCO) is spread around the world, and images from one of LCO's 1-meter telescopes hosted at the South African Astronomical Observatory were available on June 23 at midnight EDT (0400 GMT). That happens to be afternoon in New Zealand.

Related: The 9 most brilliant comets ever seen

"The other folks were asleep," recalled LCO team member Michele Bannister, of New Zealand's University of Canterbury, in a statementreleased Wednesday (July 14). 

At first glance, however, she thought the new imagery was a bust, thanks to the ever-present problem of satellites going through the field of view of telescopes.

"The first image had the comet obscured by a satellite streak, and my heart sank," she continued. "But then the others were clear enough, and gosh: there it was, definitely a beautiful little fuzzy dot, not at all crisp like its neighboring stars." 

What caught Bannister's attention was a foamy coma emerging at an incredible distance from the sun. When the image was taken, Bernardinelli-Bernstein was about 19 astronomical units (AU) from the sun. (One AU is the average Earth-sun distance — about 93 million miles, or 150 million kilometers). That's roughly double the orbital distance of Saturn from the sun. Solar energy at that juncture is a fraction of what we enjoy here on Earth.

That said, the comet has a lot of mass available to heat up. Bernardinelli-Bernstein's huge core (or nucleus) is estimated to be more than 62 miles (100 km) in diameter, which is three times as large as the next-known largest comet nucleus — that of Comet Hale-Bopp, a famous naked-eye comet that passed by Earth in 1998. Unfortunately for eager astronomers, however, Bernardinelli-Bernstein won't get very close to our planet for observations.

Bernardinelli-Bernstein's closest approach to the sun will still be beyond Saturn in January 2031, but astronomers have a decade to plan for that approach. If history is any guide, telescopes around the world and in space, along with any spacecraft that happen to be nearby, will peer at the comet to learn as much as possible about its composition and history.

This artist's illustration shows the distant Comet Bernardinelli-Bernstein as it might look in the outer Solar System. Comet Bernardinelli-Bernstein is estimated to be about 1000 times more massive than a typical comet, making it arguably the largest comet discovered in modern times. It has an extremely elongated orbit, journeying inward from the distant Oort Cloud over millions of years. It is the most distant comet to be discovered on its incoming path. (Image credit: NOIRLab/NSF/AURA/J. da Silva)

LCO's LOOK Project, which already observes several comets, will continue to watch Bernardinelli-Bernstein; you can see its anticipated viewing schedule here. It is expected to be of help since its network of telescopes allows for a "rapid response" within 15 minutes whenever any outbursts occur, the statement said. But LCO scopes won't be the only ones watching.

"There are now a large number of surveys, such as the Zwicky Transient Facility and the upcoming Vera C. Rubin Observatory, that are monitoring parts of the sky every night," LOOK member Tim Lister, an LCO staff scientist, said in the same statement. 

"These surveys can provide alerts if one of the comets changes brightness suddenly," he added. "Then we can trigger the robotic telescopes of LCO to get us more detailed data, and a longer look at the changing comet while the survey moves onto other areas of the sky."

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Elizabeth Howell

Elizabeth Howell is a contributing writer for who is one of the few Canadian journalists to report regularly on space exploration. She is the author or co-author of several books on space exploration. Elizabeth holds a Ph.D. from the University of North Dakota in Space Studies, and an M.Sc. from the same department. She also holds a bachelor of journalism degree from Carleton University in Canada, where she began her space-writing career in 2004. Besides writing, Elizabeth teaches communications at the university and community college level, and for government training schools. To see her latest projects, follow Elizabeth on Twitter at @howellspace.