Mysterious comet breakup captured by telescope after lucky break

We happened to see the comet just days after it broke into four pieces. This could provide a crucial window into the history of the solar system.

John Noonan at Auburn University in Alabama and his colleagues had planned to observe another comet with the Hubble Space Telescope, but limitations in the spacecraft’s ability to spin quickly made that impossible, so they found a new target: a comet called C/2025 K1 (ATLAS). When they pointed HST at K1, they saw not a single comet, but four fragments.

“We’ve seen comets break up before—we’ve seen them break away from the ground all the time—but this one wasn’t known to break up when we looked at it,” Noonan says. “The amount of sheer happiness that went into taking these pictures cannot be overstated.”

We’ve never taken such clear images of a comet that has just broken up before, because it’s hard to predict when one will start to break up, and it’s even harder to point a space telescope at it just in time. Thanks to the high resolution of the images, scientists were able to calculate when K1 began to fragment, about a week before the images were taken.

Comets are made of pristine ice from the early days of the solar system’s formation, but their exteriors are eroded over time by sunlight and other cosmic radiation. To get to those pristine ices that could tell us about the environments that formed the planets, we have to look below the surface, which is exactly what a fragmenting comet allows.

When a comet breaks up, the ice inside it is expected to sublimate, turn into gas, and float away. “These really cold ices that are exposed to heat for the first time in billions of years, and they should start to sublimate really quickly,” Noonan says. But that doesn’t appear to be the case here – it took about two days after K1 disintegrated to brighten, which is usually seen as a sign of sunlight illuminating sublimated gas and dust.

The cause of this delay is a mystery for now, but Noonan and his colleagues are currently working on analyzing the rest of their data on K1, which should explain the delay and reveal the composition of the comet’s interior. “We’re about to get a really fascinating look at this comet and the early solar system,” he says.

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