Mega comet Bernardinelli-Bernstein heading sunward, now belching jets

Comet Bernardinelli-Bernstein is about 80 miles wide! That’s 10 times wider than a typical comet core. Astronomers just announced they now see jets erupting from the comet’s core as it barrels sunward. We’ll be talking about this comet with Nathan Roth, an astronomer who studies it. The video drops at 12:15 p.m. CDT (17:15 UTC) on Monday, June 30. EarthSky’s Deborah Byrd will host. Watch in the player above or on YouTube.

Mega comet Bernardinelli-Bernstein is erupting with jets

An enormous comet, named Bernardinelli-Bernstein, is headed toward the sun. Don’t worry! It’s not coming anywhere near Earth. On January 29, 2031, Comet Bernardinelli-Bernstein will reach its closest point to the sun – slightly farther than Saturn’s orbit – a comfortable 1 billion miles away (1.6 billion km). But, as it barrels inward, there’s news about the comet. On June 16, 2025, the U.S. National Radio Astronomy Observatory – with headquarters in Charlottesville, Virginia – said it has now detected jets erupting from the comet’s nucleus, or core. Scientists called the jets “explosive.”

Comet Bernardinelli-Bernstein, affectionately known as Comet BB, is 85 miles wide (140 km wide). It’s about 10 times the size of a typical comet. At the moment, the comet is still at a distance about halfway to Neptune’s orbit around our sun. It’s 16.6 astronomical units (AU) away, or more than 16 times Earth’s distance from the sun.

Jets of gas and dust are a common occurrence for comets as they approach the sun and their icy surfaces heat up. Comets are icy bodies. The jets happen when ice sublimates (changes directly from a solid to a vapor). This process is known as outgassing.

Though the giant comet is still far away, astronomers were able to use the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to get a look at it.

Latest observations of Comet Bernardinelli-Bernstein

Bernardinelli-Bernstein has been known since 2014. We and many others first told you about it in 2021, when its large size was recognized.

Now the new observations confirm that Bernardinelli-Bernstein is the largest Oort Cloud comet ever found … by far. And they show carbon monoxide gas erupting in complex and evolving jets from the comet’s nucleus or core. Lead author Nathan Roth of American University and NASA Goddard Space Flight Center said:

These measurements give us a look at how this enormous, icy world works. We’re seeing explosive outgassing patterns that raise new questions about how this comet will evolve as it continues its journey toward the inner solar system.

The astronomers published their peer-reviewed research in The Astrophysical Journal Letters on June 12, 2025.

Why scientists are excited about the jets

Astronomers expect more outgassing and increased jet activity as Comet Bernardinelli-Bernstein draws closer to the sun. In the meantime, as they continue to observe the comet, they expect observations of the outgassing will shed light on the comet’s composition. And that new knowledge, in turn, will provide insight into conditions in the early solar system. The scientists said in a statement:

Such discoveries help answer fundamental questions about where Earth and its water came from, and how life-friendly environments might form elsewhere.

How was the comet discovered?

University of Pennsylvania astronomers Pedro Bernardinelli and Gary Bernstein discovered the comet. They were reviewing images from 2014 to 2018 from the Dark Energy Survey as part of their computer-aided search for trans-Neptunian objects.

While the discovery of Comet BB came in 2014, its first appearance on image data was in 2010.

Other big comets

The previous record holder for the largest comet nucleus was C/2002 VQ94 (LINEAR). It measures about 60 miles (100 km) at its widest.

The new big kid on the cosmic block is far from alone, said David Jewitt. Jewitt is a professor of planetary science and astronomy at UCLA and co-author of the study that refined the comet’s measurements. Jewitt said:

This comet is literally the tip of the iceberg for many thousands of comets that are too faint to see in the more distant parts of the solar system. 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.

2022 images images of Comet BB

The Hubble Space Telescope’s Wide Field Camera 3 captured five photos of the comet on January 8, 2022.

NASA described the process team members used to discern the size of the nucleus against the backdrop of the glare of the comet’s coma and tails:

The comet is currently too far away for its nucleus to be visually resolved by Hubble. Instead, the Hubble data show a bright spike of light at the nucleus’ location. Hui and his team next made a computer model of the surrounding coma and adjusted it to fit the Hubble images. Then, the glow of the coma was subtracted to leave behind the starlike nucleus.

By combining the Hubble data set with radio observations made by the Atacama Large Millimeter/Submillimeter Array (ALMA) in Chile, the team was able to assign upper and lower limits to the size of C/2014 UN271.

The team also found the comet is less reflective than they originally thought. According to Jewitt:

It’s big and it’s blacker than coal.

Bottom line: Astronomers have made new observations of the mega comet Bernardinelli-Bernstein. They’ve found the comet is erupting with jets as it barrels toward the sun.

Source (2025): The First Detection of Molecular Activity in the Largest Known Oort Cloud Comet: ALMA Imaging of C/2014 UN271 (Bernardinelli–Bernstein) at 16.6 au from the Sun

Source (2022): Hubble Space Telescope Detection of the Nucleus of Comet C/2014 UN271 (Bernardinelli–Bernstein)

Via NRAO

Via NASA