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Auburn physicists document a cosmic fragmentation event as it unfolds, offering an unprecedented close-up view of a comet cracking apart.
When John Noonan opened his laptop at his brother and sister in-law’s kitchen table in Colorado, it was supposed to be a routine data check.
Instead, he found a comet had split.
"I opened up the data to make sure everything went well, and where I was expecting to see a picture of just one comet, there was a picture of four," said Noonan, an assistant research professor in the College of Sciences and Mathematics’ Department of Physics.
The images, taken by the Hubble Space Telescope, captured something astronomers almost never see: a comet in the act of breaking apart.
"There was no way to plan it like this," Noonan said. "It all had to be by chance."
For Dennis Bodewits, who leads Auburn’s Comet Research Group, the sequence amounted to an unusually close look at a cosmic breakup.
"We were at the crash scene," Bodewits said.
This Hubble Space Telescope image shows comet C/2025 K1 (ATLAS) during a rare fragmentation event, with several bright pieces separating and surrounded by a diffuse cloud of dust and gas. The sequence allowed Auburn physicists to capture the breakup in progress and track how the fragments drifted apart over time.
This Hubble Space Telescope image shows comet C/2025 K1 (ATLAS) during a rare fragmentation event, with several bright pieces separating and surrounded by a diffuse cloud of dust and gas. The sequence allowed Auburn physicists to capture the breakup in progress and track how the fragments drifted apart over time.
This Hubble Space Telescope image shows comet C/2025 K1 (ATLAS) during a rare fragmentation event, with several bright pieces separating and surrounded by a diffuse cloud of dust and gas. The sequence allowed Auburn physicists to capture the breakup in progress and track how the fragments drifted apart over time.
A backup plan becomes a breakthrough
The team had originally proposed to observe a different comet. But new safety restrictions on Hubble, which is operating with only one functioning gyroscope, meant the target was no longer viable. The Space Telescope Science Institute invited the Auburn researchers to select a replacement that would still meet their scientific goals.
They chose comet C/2025 K1, also known as ATLAS. It was meant to be a straightforward study. Then the comet began to behave strangely.
Ground-based observers reported that it had brightened suddenly, an event known as an outburst. Rumors followed that it might be fragmenting. Because Hubble observations must be scheduled weeks in advance, astronomers rarely capture the actual moment of breakup. By the time telescopes can be redirected, the fragments are already far apart.
In this case, the Auburn team already had three consecutive days of Hubble observations on the calendar.
"We were already planning on observing it," Noonan said. "And it happens to fall apart right before your eyes."
The nature of Auburn’s physics department means we’re able to connect a lot of different aspects of physics in a way that strengthens our work
John Noonan, assistant research professor in the College of Sciences and Mathematics’ Department of Physics
Seeing the breakup up close
The context images taken to inform spectroscopic measurements were only 20 seconds long, but they revealed a remarkable sequence. In the first frame, four distinct fragments were visible. One piece displayed faint structures that comet scientists call winglets, features long associated with fragmentation in ground-based observations.
"This is the first time we can see it close up where it’s happening," Bodewits said.
Over three days, the team watched the pieces drift apart. One fragment moved away rapidly, suggesting it was smaller and more easily accelerated. Another appeared to fade and disperse into a cloud. A third began to brighten days after the initial breakup.
By tracking the fragments’ motions backward in time, the researchers reconstructed when the comet had been intact. The pieces had separated several days before any outburst was reported from Earth.
That delay challenges a long-standing assumption: that fresh ice exposed by fragmentation immediately drives the brightening seen from the ground.
"What’s weird about that is this appears to show that there’s actually a delay," Noonan said.
The team proposes two leading explanations. Freshly exposed ice may initially release mostly gas, which does not reflect sunlight efficiently. Only after a layer of dust accumulates and is lifted away does the comet brighten visibly. Alternatively, the interior may require time to warm enough to drive major activity.
Whatever the mechanism, the breakup offers a rare scientific opportunity.
John Noonan (left), assistant research professor, and Dennis Bodewits (right), professor of physics and leader of Auburn’s Comet Research Group, collaborated on the Hubble observations that captured a rare comet breakup in progress.
Cracking open the early solar system
Fragmenting comets are scientifically valuable because they expose material that has been shielded from sunlight and radiation for billions of years.
"We say that comets are the old building blocks of the solar system," Bodewits said. "But they’ve been processed ever since by heat, by light, by radiation. The outside is not necessarily representative of that old material."
When a comet cracks open, its interior is briefly revealed.
The Auburn team also collected ultraviolet light measurements, capturing wavelengths humans cannot see. Those data can help measure water, carbon monoxide and sulfur-bearing species, building a chemical fingerprint of the comet. From ground-based observations, the comet already appeared chemically unusual, showing high levels of nitrogen-related compounds and far fewer carbon-chain molecules than astronomers typically see.
"There’s something really interesting about this," Noonan said. "It either came from a very unique place in the protoplanetary disk chemically, or it comes from a population that’s very poor at surviving to this point in the solar system."
Positioned for discovery
Comet science draws on expertise ranging from molecular spectroscopy to radiation pressure and plasma physics. That interdisciplinary foundation helps Auburn compete for time on major observatories.
"The nature of Auburn’s physics department means we’re able to connect a lot of different aspects of physics in a way that strengthens our work," Noonan said.
The result in this case is extraordinary. The images represent an unusually high-resolution view of a comet fragmentation event captured close in time to the breakup. One fragment even disappeared during the three-day sequence, dissolving before it would have been detectable from the ground.
Comets, Bodewits explained, are fragile mixtures of ice and dust with half the density of water ice.
"They’re like freshly fallen snow," Noonan said.
As of two weeks ago, two fragments remained. The comet is now headed permanently out of the solar system.
Because the team had already secured time on Hubble, they were able to capture the breakup as it unfolded and analyze it in detail.
“We can really reconstruct what happened,” Bodewits said.
