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. — 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)

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.”

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.