Hubble Telescope Captures Comet C/2025 K1 (ATLAS) Fragmenting in Real Time

In a rare astronomical event, NASA's Hubble Space Telescope observed comet C/2025 K1 (ATLAS) disintegrating into multiple fragments. The comet, discovered in May 2025 by the ATLAS survey, was not the original target of Hubble's observations. However, due to unforeseen technical constraints, researchers shifted focus to K1, coincidentally capturing its fragmentation in real time.

"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."

Hubble's images, taken from November 8 to 10, 2025, revealed the comet splitting into at least four pieces, each surrounded by its own coma. One of the smaller fragments further divided during the observation period. The breakup likely began around eight days prior to these observations, shortly after the comet's closest approach to the Sun, known as perihelion. At that time, K1 had traveled inside Mercury's orbit, experiencing intense heat and gravitational stress.

Before disintegration, K1 was estimated to be slightly larger than a typical comet, measuring about 5 miles across. The event provided scientists with a unique opportunity to study the internal composition of a comet. By analyzing the exposed material from the breakup, researchers aim to distinguish between primitive properties and those resulting from evolutionary processes.

"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 principal investigator Dennis Bodewits, also a professor in Auburn University's Department of Physics. "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."

An unexpected aspect of the observation was a delay between the comet's fragmentation and the bright outbursts later seen from Earth. Scientists propose several explanations, including the formation of a dust layer over the exposed ice or the buildup of heat beneath the surface leading to a delayed release 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 ... ," said Noonan. "This is telling us something very important ... ."

Further analysis of gases released by the comet is planned, as early observations suggest an unusual chemical composition with significantly lower levels of carbon compared to most comets. Additional data from Hubble's instruments are expected to provide deeper insight into K1's composition and its implications for understanding the origins of the solar system.

Currently, K1's fragments are located about 250 million miles from Earth in the constellation Pisces, moving away from the Sun and unlikely to return to the inner solar system. The Hubble Space Telescope, a joint project between NASA and the European Space Agency, continues to deliver significant discoveries, enhancing our understanding of the universe.