Comet C/2025 K1 (ATLAS) reached perihelion at 0.33 au on October 8, 2025, and observers then tracked a sharp increase in activity between November 2 and 4, including rapid changes in coma structure.
Hubble captured the breakup sequence on November 10, 2025, showing the comet had split into at least four fragments. The nucleus size before fragmentation is described as an estimate of roughly 5 miles (about 8 kilometers) across.
This observation is notable because it gives researchers a rare look at an active fragmentation event while it is unfolding, improving how scientists model structural failure and evolution in volatile comet nuclei.
Original source: https://science.nasa.gov/missions/hubble/nasas-hubble-unexpectedly-catches-comet-breaking-up/