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NASA’s Hubble Unexpectedly Catches Comet Breaking Up

In a happy twist of fate, NASA’s Hubble Space Telescope just witnessed a comet in the act of breaking apart. The chance of that happening while Hubble watched is extraordinarily minuscule. The findings published Wednesday in the journal Icarus. The comet K1, whose full name is C/2025 K1 (ATLAS)—not to be confused with interstellar comet […]

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Mar 18, 2026 - 22:00

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NASA’s Hubble Unexpectedly Catches Comet Breaking Up

A time sequence of three panels side by side. From left to right, the panels are labeled November 8, 2025; November 9, 2025; and November 10, 2025. This series of images from NASA’s Hubble Space Telescope of the fragmenting comet C/2025 K1 (ATLAS), or K1 for short, was taken over the course of three consecutive days. The sequence shows the progressive disintegration of the comet over this brief period.

Each panel features several bright, fuzzy, blue, streaking lights in a diagonal line from the upper left to the lower right of a black background. In the first panel, four comet-like objects appear. The largest is the second from the upper left. In the second panel, the largest object has broken into two pieces. In the third panel, the pieces appear to be moving away from each other along the invisible diagonal line.

A series of images from NASA’s Hubble Space Telescope of the fragmenting comet C/2025 K1 (ATLAS).

Credits:
Image: NASA, ESA, Dennis Bodewits (AU); Image Processing: Joseph DePasquale (STScI)

In a happy twist of fate, NASA’s Hubble Space Telescope just witnessed a comet in the act of breaking apart. The chance of that happening while Hubble watched is extraordinarily minuscule. The findings published Wednesday in the journal Icarus.

The comet K1, whose full name is C/2025 K1 (ATLAS)—not to be confused with interstellar comet 3I/ATLAS—was not the original target of the Hubble study.

“Sometimes the best science happens by accident,” said co-investigator John Noonan, a research professor in the Department of Physics at Auburn University in Alabama. “This comet got observed because our original comet was not viewable due to some new technical constraints after we won our proposal. We had to find a new target—and right when we observed it, it happened to break apart, which is the slimmest of slim chances.”

This series of images from NASA’s Hubble Space Telescope of the fragmenting comet C/2025 K1 (ATLAS) was taken over the course of three consecutive days: Nov. 8, 9, and 10, 2025. This is the first time Hubble has witnessed a comet so early in the process of breaking up.

Image: NASA, ESA, Dennis Bodewits (AU); Image Processing: Joseph DePasquale (STScI)

Noonan didn’t know K1 was fragmenting until he viewed the images the day after Hubble took them. “While I was taking an initial look at the data, I saw that there were four comets in those images when we only proposed to look at one,” said Noonan. “So we knew this was something really, really special.”

This is an experiment the researchers always wanted to do with Hubble. They had proposed many Hubble observations to catch a comet breaking up. Unfortunately, these are very difficult to schedule, and they were never successful.

“The irony is now we’re just studying a regular comet and it crumbles in front of our eyes,” said principal investigator Dennis Bodewits, also a professor in Auburn University’s Department of Physics.

“Comets are leftovers of the era of solar system formation, so they’re made of ‘old stuff’—the primordial materials that made our solar system,” said Bodewits. “But they are not pristine—they’ve been heated; they’ve been irradiated by the Sun and by cosmic rays. So, when looking at a comet’s composition, the question we always have is, ‘Is this a primitive property or is this due to evolution?’ By cracking open a comet, you can see the ancient material that has not been processed.”

Hubble caught K1 fragmenting into at least four pieces, each with a distinct coma, the fuzzy envelope of gas and dust that surrounds a comet’s icy nucleus. Hubble cleanly resolved the fragments, but to ground-based telescopes, at the time they only appeared as barely distinguishable, bright blobs.

Hubble’s images were taken just a month after K1’s closest approach to the Sun, called perihelion. The comet’s perihelion was inside Mercury’s orbit, about one-third the distance of the Earth from the Sun. During perihelion, a comet experiences its most intense heating and maximum stress. Just past perihelion is when some long-period comets like K1 tend to fall apart.

Diagram shows K1’s path. With Sun at center, nearly circular orbits of Mercury, Venus, Earth, and Mars appear against black background. In sharp contrast is K1’s tight parabolic curve, marked by solid, light blue curving line illustrating how K1 swooped toward the Sun from above. It curved around the Sun, coming closest inside Mercury’s orbit, and continued its outbound journey. After passing the Sun, as K1 approached Mercury’s orbit, NASA’s Hubble Space Telescope captured the inset image of comet. Five, bright, fuzzy, blue, comet-like objects streak diagonally from upper left to lower right of a black box outlined in white. At outside top of box is label C/2025 K1 (ATLAS). Outside the right side of box is a white, horizontal line labeled November 10, 2025. To right of this line is a perpendicular, vertical line pointing to a white glow just inside Mercury’s orbit that illustrates K1. To left of this glow, the comet’s outbound path is marked by a dashed gray line that continues off the image.

This diagram shows the path Comet C/2025 K1 (ATLAS), or K1, took as it swung past the Sun and began its journey out of the solar system. NASA’s Hubble Space Telescope captured the inset image of the fragmenting comet just a month after K1’s closest approach to the Sun.

Illustration: NASA, ESA, Ralf Crawford (STScI)

Before it fragmented, K1 was likely a bit larger than an average comet, probably around 5 miles across. The team estimates the comet began to disintegrate eight days before Hubble viewed it. Hubble took three 20-second images, one on each day from Nov. 8 through Nov. 10, 2025. As it watched the comet, one of K1’s smaller pieces also broke up.

Because Hubble’s sharp vision can distinguish extremely fine details, the team could trace the history of the fragments back to when they were one piece. That allowed them to reconstruct the timeline. But in doing so, they uncovered a mystery: Why was there a delay between when the comet broke up and when bright outbursts were seen from the ground? When the comet fragmented and exposed fresh ice, why didn’t it brighten almost instantaneously?

The team has some theories. Most of a comet’s brightness is sunlight reflected off of dust grains. But when a comet cracks open, it reveals pure ice. Maybe a layer of dry dust needs to form over the pure ice and then blow off. Or maybe heat needs to get below the surface, build up pressure, and then eject an expanding shell of dust.

“Never before has Hubble caught a fragmenting comet this close to when it actually fell apart. Most of the time, it’s a few weeks to a month later. And in this case, we were able to see it just days after,” said Noonan. “This is telling us something very important about the physics of what’s happening at the comet’s surface. We may be seeing the timescale it takes to form a substantial dust layer that can then be ejected by the gas.”

NASA’s Goddard Space Flight Center; Lead Producer: Paul Morris

The research team is looking forward to finishing the analysis of the gases to come from the comet. Already, ground-based analysis shows that K1 is chemically very strange—it is significantly depleted in carbon, compared with other comets. Spectroscopic analysis from Hubble’s STIS (Space Telescope Imaging Spectrograph) and COS (Cosmic Origins Spectrograph) instruments is likely to reveal much more about the composition of K1 and the very origins of our solar system, as NASA’s space telescopes continue to contribute to our understanding of planetary science.

The comet K1 is now a collection of fragments about 250 million miles from Earth. Located in the constellation Pisces, it is heading out of the solar system, not likely to ever return.

The Hubble Space Telescope has been operating for over three decades and continues to make ground-breaking discoveries that shape our fundamental understanding of the universe. Hubble is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope and mission operations. Lockheed Martin Space, based in Denver, also supports mission operations at Goddard. The Space Telescope Science Institute in Baltimore, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.

Related Images & Videos

Fragmentation of Comet C/2025 K1

Diagram shows K1u2019s path. With Sun near middle right of image, truncated nearly circular orbits of Mercury, Venus, Earth, and Mars appear against black background. K1u2019s tight parabolic curve, marked by solid, light blue curving line, illustrates how K1 swooped toward the Sun from above. It curved around the Sun, coming closest inside Mercuryu2019s orbit, and continued its outbound journey.nAfter passing the Sun, as K1 approached Venusu2019 orbit, NASAu2019s Hubble Space Telescope captured the inset image of comet. Five, bright, fuzzy, blue, comet-like objects streak diagonally from upper left to lower right of a black box outlined in white. At outside top of box is label C/2025 K1 (ATLAS). Outside the right side of box is a white, horizontal line labeled November 10, 2025. To right of this line is a perpendicular, vertical line pointing to a white glow just inside Mercuryu2019s orbit that illustrates K1. To left of this glow, the cometu2019s outbound path is marked by a dashed gray line that continues off the image.

Comet C/2025 K1 Orbit Illustration

Three annotated panels side by side show K1 fragmenting over three consecutive days. Arrows show the orientation of object on sky.u00a0At top left of first panel, label on first line reads Fragmentation of Comet C/2025 K1 (ATLAS). Second line reads HST STIS MIRVIS. From left to right, panels are labeled November 8, 2025; November 9, 2025; and November 10, 2025.nnEach panel shows several bright, fuzzy, blue objects streaking diagonally from upper left to lower right of black background. In first panel, four comet-like objects are numbered 1 thru 4. In second panel, the largest object has broken into two pieces, 2a and 2b. In third panel, pieces appear to be moving away from each other diagonally.nnu00a0nnArrows on last panel show orientation of image on sky. Arrow labeled N points to 8:30. Arrow labeled E points to 5:30. Relationship between north and east on the sky as seen from below is flipped relative to direction arrows on a map of the ground as seen from above.

Comet C/2025 K1 Compass Image

This annotated series of images from NASA’s Hubble Space Telescope of the fragmenting comet C/2025 K1 (ATLAS), or K1 for short, was taken over the course of three consecutive days: Nov. 8, 9, and 10, 2025. Arrows show the orientation of the image on the sky.

Fragmenting Comet C/2025 K1

This animation steps through the three images from NASA’s Hubble Space Telescope of the fragmenting comet C/2025 K1 (ATLAS), or K1 for short, taken consecutively on Nov. 8, 9, and 10, 2025. Captured by Hubble’s STIS (Space Telescope Imaging Spectrograph) instrument, t…

Video: Hubble Accidentally Catches Comet Breaking Up

In a happy twist of fate, NASA’s Hubble Space Telescope just witnessed a comet in the act of breaking apart. The chance of that happening while Hubble watched is extraordinarily miniscule.