- Hubble has captured a rare view of a comet breaking apart. It captured these images about a month after the comet made its closest pass by the sun.
- The discovery was a happy accident. The scientist’s original target was a different comet. But this is the first time Hubble has caught a fragmenting comet so close to when it actually fell apart.
- The breakup offers scientists a glimpse of pristine material, helping them study the early solar system’s building blocks.
NASA published this original story on March 18, 2026. Edits by EarthSky.
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Comet breaks apart, and Hubble sees it happen
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 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.
Co-investigator John Noonan, a research professor in the Department of Physics at Auburn University in Alabama, said:
Sometimes the best science happens by accident. 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.
The peer-reviewed journal Icarus published the findings on March 18, 2026.
Hubble sees the comet fragment
Noonan didn’t know K1 was fragmenting until he viewed the images the day after Hubble took them. Noonan said:
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. 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. Principal investigator Dennis Bodewits, also a professor in Auburn University’s Department of Physics, said:
The irony is now we’re just studying a regular comet and it crumbles in front of our eyes.
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. 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.
A closer look at a solar system breakup
Hubble caught K1 fragmenting into at least four pieces. Each had a distinct coma, which is 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 took its images 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.
Before it fragmented, K1 was likely a bit larger than an average comet, probably around 5 miles (8 km) 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 November 8 through 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?
Exploring the mysteries of comet K1 ATLAS
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. Noonan said:
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. 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.
Video via NASA’s Goddard Space Flight Center; Lead Producer: Paul Morris.
What’s next?
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.
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.
Bottom line: Hubble captures a rare moment as a comet breaks apart after passing close to our sun. The images revealing ancient material from the early solar system.
Source: Sequential fragmentation of C/2025 K1 (ATLAS) after its near-sun passage
Via NASA