NASA Spots Biggest Comet Ever—500 Trillion Ton Ice Ball Headed This Way

The biggest comet ever recorded has been spotted by the Hubble Space Telescope, NASA said Tuesday—and it is truly massive.

The comet's nucleus—the icy object at the heart of the comet that doesn't include its tail—is thought to be 80 miles across and may weigh about 500 trillion tons.

The cold behemoth is called C/2014 UN271 or comet Bernardinelli-Bernstein. It was discovered in 2010 by astronomers Pedro Bernardinelli and Gary Bernstein.

C/2014 UN271 (Bernardinelli-Bernstein)
NASA says C/2014 UN271 has the largest comet nucleus ever seen. The comet was spotted with the Hubble Space Telescope. NASA, ESA, Man-To Hui Macau University of Science and Technology), David Jewitt UCLA; Image processing: Alyssa Pagan (STScI

However, only now have researchers been able to determine exactly how big it is. That's partly because the comet is about 2 billion miles away—further than the planet Uranus. It's also partly because comets are surrounded by a shell of gas and dust forming their characteristic tails and shrouding their center.

By combining computer models with Hubble's observations, astronomers led by Man-To Hui of the Macau University of Science and Technology were able to separate the comet's core from its shell and reveal the size of its main body.

Comet C/2014 UN271
A sequence of photos shows how the nucleus of comet C/2014 UN271 was separated from its surrounding cloud. The comet's nucleus is estimated to weigh up to 500 trillion tons. NASA/ESA/Man-To Hui Macau University of Science and Technology/David Jewitt (UCLA

"It's big and it's blacker than coal," said David Jewitt, co-author of a study describing the finding, in a NASA press release. "We've always suspected this comet had to be big because it is so bright at such a large distance. Now we confirm it is."

C/2014 UN271 is slowly heading towards the sun and has been for over 1 million years, but it won't pose any danger to Earth. In fact, it's not predicted to get any closer than the planet Saturn in 2031. Given its size, that's perhaps close enough.

One day, the comet will begin heading away from the sun again and won't start its return journey until it's about half a light-year away. In total, its orbit around the sun takes 3 million years.

The comet's size measurements were outlined in a study published in the journal The Astrophysical Letters on April 12.

Comets are large objects made of ice and dust that orbit the sun, and are best known for their long, streaming trails that they leave behind when they pass near to our star. Sometimes these tails can be visible from Earth, providing a treat for night sky enthusiasts.

Long-distance comets, in particular, are of interest to astronomers since they are considered to be some of the most pristine leftovers from the early solar system that we know about. For most of their lives, they are preserved in the low-temperature environment of the outer solar system.

Despite receiving little in the way of heat from the sun, some comets this far out remain 'active'—they release clouds of gas or other material that increases their brightness. Scientists still aren't sure why, and comets like C/2014 UN271 present a key opportunity to find out more about these distant, icy objects.

"Although comets have been thought to be the most pristine objects in the solar system, we don't really understand how they evolve with time," Hui told Newsweek. "Apparently at least some of them can be quite active even at great distances from the sun.

"Discovering distant comets like UN271 definitely raises a series of new scientifically important questions as to the evolution of our solar system, like how pristine is pristine? Understanding the distant activity in comets like UN271 will really help in terms of constraining the early physical and chemical conditions of our solar system."

Update, 4/12/22, 11:18 a.m. ET: This article has been updated to include more information on comet C/2014 UN271.

Update, 4/14/22, 11:41 a.m. ET: This article has been updated to include a comment from Man-To Hui.

Comet size comparison
An illustration of the size of various comets compared. Some of these icy objects can take millions of years to orbit the sun. NASA/ESA/Zena Levy STScl