Hubble Captures Comet C/2025 K1 (ATLAS) in Dramatic Breakup

In a rare cosmic event, NASA’s Hubble Space Telescope has observed comet C/2025 K1 (ATLAS) – often referred to as K1 – actively fragmenting, providing scientists with a unique opportunity to study the breakup of a comet in real-time. The findings, published on March 18, 2026, in the journal Icarus, detail the comet’s disintegration into at least five distinct pieces.

A Serendipitous Discovery

The observation wasn’t originally planned. According to co-investigator John Noonan, a research professor in the Department of Physics at Auburn University, the team had to switch targets due to technical constraints with their initial observation plan. “Sometimes the best science happens by accident,” Noonan stated. “This comet got observed because our original comet was not viewable… We had to find a recent target—and right when we observed it, it happened to break apart, which is the slimmest of slim chances.”

Witnessing the Fragmentation

Noonan first noticed the fragmentation while reviewing images captured by Hubble. “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,” he explained. The images, taken between November 8 and November 10, 2025, show the comet splitting apart, each fragment surrounded by its own coma – the cloud of gas and dust enveloping the comet’s nucleus.

Unveiling the Comet’s Interior

Principal investigator Dennis Bodewits, also a professor at Auburn University’s Department of Physics, emphasized the significance of observing a comet during its breakup. “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,” Bodewits said. “But they are not pristine… By cracking open a comet, you can witness the ancient material that has not been processed.”

Timing and the Perihelion Passage

The breakup occurred approximately a month after K1’s closest approach to the Sun, known as perihelion. At this point, the comet had ventured inside Mercury’s orbit. This proximity to the sun subjects comets to intense heat and stress, often triggering fragmentation, particularly in long-period comets like K1. Researchers estimate the breakup began around eight days before Hubble captured the images.

A Puzzle of Brightness

Scientists are currently investigating a puzzling aspect of the breakup: a delay between the fragmentation and observed increases in brightness from Earth. The team hypothesizes that a layer of dust must form and then be ejected before significant brightening occurs, or that heat penetrates beneath the surface, building pressure and releasing dust. “Never before has Hubble caught a fragmenting comet this close to when it actually fell apart,” Noonan noted. “This is telling us something extremely important about the physics of what’s happening at the comet’s surface.”

Chemical Composition and Future Research

Initial observations suggest K1 has an unusual chemical composition, with lower levels of carbon compared to most comets. Further analysis using Hubble’s Space Telescope Imaging Spectrograph (STIS) and Cosmic Origins Spectrograph (COS) is planned to gain deeper insights into the comet’s composition and its origins.

A One-Time Visitor

Currently located about 250 million miles from Earth in the constellation Pisces, comet K1 is now a cluster of fragments moving away from the Sun and is not expected to return to the inner solar system.

Hubble’s Continued Legacy

This observation highlights the ongoing value of the Hubble Space Telescope, a joint project between NASA and the European Space Agency (ESA). NASA’s Goddard Space Flight Center manages the mission, with support from Lockheed Martin Space. The Space Telescope Science Institute conducts scientific operations.