In a remarkable stroke of luck, Nasa’s Hubble Space Telescope has captured a comet in the act of breaking apart—an event scientists say is extraordinarily rare to witness in real time.
The observations, published Wednesday in the journal Icarus, detail how comet C/2025 K1 (ATLAS) fragmented into multiple pieces while being observed, offering an unprecedented glimpse into the internal structure of these ancient celestial bodies.
The discovery was entirely accidental. Researchers had originally planned to observe a different comet, but had to switch targets due to technical constraints. What followed surprised even seasoned astronomers.
“Sometimes the best science happens by accident,” said co-investigator John Noonan of Auburn University. “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.”
When Noonan first examined the images, he immediately realised something unusual. Instead of a single comet, the data revealed at least four distinct fragments, each surrounded by its own glowing coma, a cloud of gas and dust.
The breakup occurred shortly after the comet’s closest approach to the Sun, known as perihelion. At that point, K1 had travelled within Mercury’s orbit, exposing it to intense solar heating and stress, conditions known to trigger fragmentation in long-period comets.
Scientists estimate the comet, likely around 8 kilometres wide before breaking apart, began disintegrating about eight days before Hubble observed it in November 2025. The telescope captured the process in a series of images taken over three days, even recording a secondary breakup of one fragment.
The findings are particularly significant because Hubble observed the event just days after fragmentation, far earlier than typical observations, which often occur weeks later.
“This is telling us something very important about the physics of what’s happening at the comet’s surface,” Noonan explained.
The observations also raise new questions. Despite exposing fresh ice, the comet did not immediately brighten as expected. Scientists suggest that dust layers or internal pressure buildup may delay visible outbursts.
By catching this rare event in action, Hubble has opened a new window into understanding how comets evolve—and how the earliest materials of the solar system behave under extreme conditions.
