Astronomers using the Hubble Space Telescope observed comet C/2025 K1 (ATLAS) shortly after it split into four fragments, thanks to a lucky scheduling change. The high-resolution images provide unprecedented detail on the event. Researchers noted an unexpected delay in the comet's brightening after the breakup.
John Noonan of Auburn University in Alabama and his team had intended to observe another comet with the Hubble Space Telescope but switched targets due to the spacecraft's limited turning speed. They pointed Hubble at C/2025 K1 (ATLAS) and discovered it had fragmented into four pieces, an event not previously known at the time of observation. Fragmentation occurred about one week before the images were captured, according to calculations from the high-resolution data—the clearest ever of a newly broken comet. Comets consist of pristine ices from the solar system's early formation, typically covered by eroded exteriors from sunlight and radiation. Breakups expose these interior ices, offering insights into planetary formation environments. Noonan remarked, “We have seen comets break up before – we’ve seen them break up from the ground all the time – but this one wasn’t known to have broken up when we looked at it. The amount of sheer luck that came into acquiring these images cannot be overstated.” Normally, exposed cold ices should rapidly sublimate into gas upon heating, but C/2025 K1 took about two days to brighten, a sign of sublimated gas and dust illuminated by sunlight. “These really cold ices that are being exposed to heat for the first time in billions of years, and they should start sublimating really fast,” Noonan said. The team is analyzing additional data to explain the delay and determine the comet's composition. Noonan added, “We’re about to get a really fascinating look into this comet and the early solar system.” The findings appear in Icarus (DOI: 10.1016/j.icarus.2026.116996).