NASA’s Hubble Space Telescope had a lucky break last year, capturing the rare disintegration of a comet—marking the first time the observatory has ever witnessed such an event in real time.
The observation came as a surprise. The comet, C/2025 K1 (ATLAS)—unrelated to 3I/ATLAS and commonly referred to as K1—was not the original target of the observation. Researchers detailed the unexpected findings in a recent letter published in Icarus, noting the comet’s highly unusual chemical makeup.
Accidental Science
“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.”
The Hubble Space Telescope captured the surprise images on November 8, 9, and 10, 2025, marking the first time that the telescope has ever viewed a comet break up. At the time, no one even realized the significance of what had occurred, and researchers only recognized it during an image review the next day.
Ironically, previous researchers had proposed using Hubble to intentionally observe a comet breakup. However, because such events are extremely difficult to predict, those efforts had never succeeded.
The Hubble Space Telescope Spies a Breakup
In the images, K1 appears fragmented into four distinct pieces, each surrounded by its own envelope of gas and dust, known as a coma. Ground-based observations had only revealed indistinct blobs, lacking the resolution needed to identify the separate fragments.
“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.”
The high-resolution imagery allowed researchers to reconstruct the breakup, working backward to determine the sequence of events. The team estimates that K1 was originally about five miles across, making it larger than a typical comet.
The comet’s disintegration occurred roughly one month after its closest approach to the Sun, known as perihelion. Breakups shortly after perihelion are not uncommon for long-period comets like K1. Researchers estimate that the fragmentation likely began about eight days before Hubble’s observations.
The Hubble Space Telescope Spots It First
The researchers were surprised to find a delay between when the comet broke apart and when bright bursts were detected by ground-based observatories. They suggest this discrepancy may be tied to the behavior of dust, which is responsible for much of a comet’s visible brightness through reflected sunlight.
Two leading explanations have emerged: either dust requires time to accumulate on newly exposed ice after the comet begins to fracture, or heat must build beneath the surface before ejecting dust in a visible burst.
“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.”
The team’s early research has demonstrated that K1 contains an unusual chemical makeup, being highly depleted in carbon. They plan to follow up with further analysis of the comet’s gases to learn about this strange visitor, thanks to the Hubble Space Telescope’s fortunate observation.
The letter, “Sequential fragmentation of C/2025 K1 (ATLAS) After its Near-Sun Passage,” appeared in Icarus on February 6, 2026.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.