NASA's Hubble confirms largest comet ever seen

It looks like a pinprick of light in snapshots, but scientists have confirmed this recently discovered space snowball is the largest comet ever observed, spanning the length of over three marathons.

A team of scientists used the Hubble Space Telescope, an Earth-orbiting observatory shared by NASA and the European Space Agency, to determine that Comet Bernardinelli-Bernstein has a nucleus about 50 times larger than the average known comet. This bright ball of ice, dust, and rock stretches some 85 miles across — more than double the width of Rhode Island — and weighs 500 trillion tons. By comparison, it's more than 40 percent larger than the runner-up.

Researchers say the scale of this comet is significant because it provides a clue about the size range of comets orbiting in the distant outskirts of our solar system. The so-called Oort Cloud is a sphere of ancient, icy objects surrounding the system. NASA says the cloud remains a theory because the comets there have been too faint and distant to be directly observed.

There could be trillions of icy comets in the Oort Cloud. That means Comet Bernardinelli-Bernstein may be just "the tip of the iceberg," David Jewitt, a UCLA astronomer and co-author on the new research, said in a statement. (We hope the pun was intended.)

A giant Chilean desert-based telescope detected the comet in 2014. But it took years of intensive computing to sift through loads of observations and identify the remote object, previously known as C/2014 UN271.

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Scientists knew then it was enormous but hadn't confirmed measurements. A team used Hubble to take five photos of the comet on Jan. 8. The new findings were published in The Astrophysical Journal Letters on April 12.

Given how active the comet appears to be despite its great distance from the sun (which heats up and boils particles off closer comets), it's "an amazing object," the study's lead author, Man-To Hui, said in a statement.

"We guessed the comet might be pretty big," said Hui, an astronomer from the Macau University of Science and Technology, "but we needed the best data to confirm this."

Comets, known for their millions-of-miles-long streaks, are among the oldest objects in the solar system. These icy bodies are leftover from the early days of neighboring planets' formation.

The previous record-holder for largest comet was C/2002 VQ94, with a nucleus estimated to be 60 miles across. Astronomers discovered it in 2002 with the Lincoln Near-Earth Asteroid Research (LINEAR) project.

On left, Hubble's image of Bernardinelli-Bernstein; at center, a computer model of the comet's coma; on right, the nucleus with the modeled coma removed. Credit: NASA / ESAm / Man-To Hui (Macau University of Science and Technology) / David Jewitt (UCLA) / Image processing: Alyssa Pagan (STScI)

Hale-Bopp is no competition for Comet Bernardinelli-Bernstein. Credit: NASA / ESA / Zena Levy (STScI)

Comet Bernardinelli-Bernstein, named after the astronomers Pedro Bernardinelli and Gary Bernstein who discovered it, is approaching the sun from the edge of the solar system at 22,000 mph. Though the imposing boulder has often been described as "headed this way," space is a big place. It will never get closer than a billion miles from the sun, a little farther out than Saturn's orbit. Astronomers say it'll reach that point in 2031.

In short: It's not coming anywhere close to Earth.

The comet is now less than 2 billion miles from the sun, and, in a few million years, will loop back to where it came from in the far-off Oort Cloud.