BYMICHAEL GRESHKO
PUBLISHED SEPTEMBER 29, 2021
12 MIN READ

More than 2.7 billion miles from the sun—29 times farther than Earth treads—a tiny sliver of sunlight reflected off something plummeting toward our home star(Earth). Something icy. Something unimaginably old. Something big.

About four hours later, in the predawn hours of October 20, 2014, a telescope in Chile’s Atacama Desert turned its gaze toward the heavens and snapped an enormous picture of the southern night sky, capturing hints of this reflected light.

However, it would take nearly seven years for researchers to identify that strange dot of light as a huge primordial comet—possibly the biggest ever studied with modern telescopes. [/b]Called Bernardinelli-Bernstein, the comet was announced in June, and researchers have now compiled everything they know about it in a discovery paper submitted to The Astrophysical Journal Letters.

“My phone didn’t stop ringing—I wasn’t expecting the reception the [scientific] community gave to the discovery,” says Pedro Bernardinelli, a postdoctoral researcher at the University of Washington. He co-discovered the comet during the final weeks of his Ph.D. research at the University of Pennsylvania with his then-adviser Gary Bernstein. “Overall, it’s been pretty overwhelming.”
[b]The latest estimates put the comet’s nucleus at about 93 miles (150 kilometers) wide. That’s by far the biggest size estimate for a comet in decades. By contrast, comet 67P/Churyumov–Gerasimenko, which the European Space Agency’s Rosetta spacecraft orbited from 2014 to 2016, was only about 2.5 miles wide. “We’re going from your city-size comets to your island-size comets,” says Michele Bannister, an astronomer at New Zealand’s University of Canterbury who was not involved in the discovery paper.
Comet Bernardinelli-Bernstein’s size may even rank alongside some historical “great comets,” including a very bright—and presumably huge—comet that journeyed into the inner solar system in 1729.

Over the next decade, Bernardinelli-Bernstein will continue to get brighter as it approaches the inner solar system, dive-bombing the plane of the planets’ orbits from below. It will make its closest approach on January 21, 2031, when the comet is expected to come within about a billion miles of the sun, slightly farther away than Saturn’s average distance. It will then begin its long retreat back into the solar system’s outer realms, remaining visible into at least the 2040s, if not decades longer.

Depending on how much gas the comet releases as its ices vaporize in the sun’s glare, Bernardinelli-Bernstein could get as bright in the night sky as Saturn’s largest moon Titan. If so, the comet should be visible in 2031 with a decent backyard telescope.

Astronomers calculate that this comet takes millions of years to circle the sun. Only three such “long-period” comets have ever been discovered on their way in from the Oort cloud, and Bernardinelli-Bernstein was found when it was still more than 2.7 billion miles away, a record for a comet. Because it was discovered so early, a generation of astronomers will have the opportunity to unravel its mysteries.

An illustration shows the distant Comet Bernardinelli-Bernstein as it might look in the outer Solar System.
The comet Bernardinelli-Bernstein, depicted in this illustration below, is estimated to be about 1,000 times more massive than a typical comet.
One of the largest comets ever seen is headed our way
Comet Bernardinelli-Bernstein offers a rare opportunity for a generation of astronomers to study an object from the extreme edges of the solar system.

More than 2.7 billion miles from the sun—29 times farther than Earth treads—a tiny sliver of sunlight reflected off something plummeting toward our home star. Something icy. Something unimaginably old. Something big.

About four hours later, in the predawn hours of October 20, 2014, a telescope in Chile’s Atacama Desert turned its gaze toward the heavens and snapped an enormous picture of the southern night sky, capturing hints of this reflected light.

However, it would take nearly seven years for researchers to identify that strange dot of light as a huge primordial comet—possibly the biggest ever studied with modern telescopes. Called Bernardinelli-Bernstein, the comet was announced in June, and researchers have now compiled everything they know about it in a discovery paper submitted to The Astrophysical Journal Letters.

“My phone didn’t stop ringing—I wasn’t expecting the reception the [scientific] community gave to the discovery,” says Pedro Bernardinelli, a postdoctoral researcher at the University of Washington. He co-discovered the comet during the final weeks of his Ph.D. research at the University of Pennsylvania with his then-adviser Gary Bernstein. “Overall, it’s been pretty overwhelming.”



An approaching giant

A large comet, named Bernardinelli-

Bernstein, was discovered earlier this year. It will take ten years to reach its closest approach to the sun, affording astronomers plenty of time to study this cosmic giant.

2036

The comet will swoop up between the orbits of Saturn and Uranus.



Bernardinelli-Bernstein is the largest comet ever observed, and dwarfs other well-known comets.

93 miles (150 km)

in diameter

Hale-Bopp

37 miles (60 km)

Halley’s comet

Manhattan

13.4 miles long

(21.5 km)

6.8 miles (11 km)

Jason Treat, NG Staff.

Source: NASA Jet Propulsion Labratory.

The latest estimates put the comet’s nucleus at about 93 miles (150 kilometers) wide. That’s by far the biggest size estimate for a comet in decades. By contrast, comet 67P/Churyumov–Gerasimenko, which the European Space Agency’s Rosetta spacecraft orbited from 2014 to 2016, was only about 2.5 miles wide.


“We’re going from your city-size comets to your island-size comets,” says Michele Bannister, an astronomer at New Zealand’s University of Canterbury who was not involved in the discovery paper. Comet Bernardinelli-Bernstein’s size may even rank alongside some historical “great comets,” including a very bright—and presumably huge—comet that journeyed into the inner solar system in 1729.

Over the next decade, Bernardinelli-Bernstein will continue to get brighter as it approaches the inner solar system, dive-bombing the plane of the planets’ orbits from below. It will make its closest approach on January 21, 2031, when the comet is expected to come within about a billion miles of the sun, slightly farther away than Saturn’s average distance. It will then begin its long retreat back into the solar system’s outer realms, remaining visible into at least the 2040s, if not decades longer.

Depending on how much gas the comet releases as its ices vaporize in the sun’s glare, Bernardinelli-Bernstein could get as bright in the night sky as Saturn’s largest moon Titan. If so, the comet should be visible in 2031 with a decent backyard telescope.


But Bernardinelli-Bernstein is also notable for how far it was from the sun when it was first spotted. The icy object hails from the Oort cloud, an enormous spherical haze of objects that surrounds the sun thousands of times farther out than Earth.

Astronomers calculate that this comet takes millions of years to circle the sun. Only three such “long-period” comets have ever been discovered on their way in from the Oort cloud, and Bernardinelli-Bernstein was found when it was still more than 2.7 billion miles away, a record for a comet. Because it was discovered so early, a generation of astronomers will have the opportunity to unravel its mysteries.

A DOT OF LIGHT IN THE DARK
Bernardinell-Bernstein came to humankind’s attention thanks to an exquisitely sensitive digital camera installed at the 13-foot-wide Blanco Telescope, part of the Cerro Tololo Inter-American Observatory in Chile’s Atacama Desert.

This camera wasn’t specifically looking for far-flung solar system objects; rather, it was the key source of data for the Dark Energy Survey, an effort that collected 80,000 exposures of wide swaths of the southern night sky from 2013 to 2019. This dataset has transformed scientists’ quest to understand dark energy, a mysterious force that drives the universe’s accelerating expansion. But images taken to study dark energy and other cosmic phenomena can also be used to discover objects much closer to home.
For his Ph.D. research, Bernardinelli’s goal was to use the Dark Energy Survey images to find previously undiscovered objects that orbit the sun beyond Neptune. He faced a tall order. Each image was so massive, displaying just one at full resolution would require a grid of 275 HD televisions. Bernardinelli scoured tens of thousands of these images for dots of light a few pixels wide.
To pull off this hunt, Bernardinelli wrote computer code that searched the Dark Energy Survey’s images for dots that moved against the backdrop of distant stars. Six months of grueling calculations, run on a cluster of some 200 computers at Illinois’s Fermi National Accelerator Laboratory, whittled down this massive dataset to a final list of 817 newfound objects whose orbits didn’t match any known body in the solar system. As a final step, Bernardinelli and Bernstein checked this list by hand to make sure the code did its job correctly.

That’s when they noticed it: an object as bright as some of the 100-mile-wide worlds beyond Neptune, but with an extreme orbit that means it must have originated trillions of miles from the sun, just like a long-period comet.

Finding the comet was “a very big needle-in-the-haystack problem,” Bernstein says. “But we managed to figure that out, and we got this little cherry on top of the sundae!”
A BRIGHT FUTURE!
Scientists are already brainstorming what it would take to visit Bernardinelli-Bernstein with a spacecraft. For now, there’s no official mission in the works, but if the world’s space agencies move quickly, a mission could intercept the comet in 2033 if it launches no later than 2029.

Researchers are also hard at work deciphering the comet’s past voyages through the solar system to determine how much it has been changed by the sun. Bernardinelli and Bernstein’s team calculate that in 2031, the comet will be the closest it’s come to the sun in at least three million years.
The good news is that Bernardinelli-Bernstein gives the world’s astronomers a rare luxury: time. The Vera C. Rubin Observatory in Chile, set to come online in 2023, will be able to track the object for at least the next decade, if not longer. Along the way, the state-of-the-art telescope will transform our view of the solar system—and likely uncover many more comets like Bernardinelli-Bernstein.
In the meantime, as the newfound comet makes its way toward us, scientists and people all over the world will be able to turn their telescopes to the night sky and see an extraordinary visitor: a massive iceball dragging a huge, hazy tail behind it. “It should look spectacular,” Montet says.