Thanks to two coincidences: Hubble unexpectedly photographs breaking comet
Solely because the intended observation target could not be captured, Hubble photographed another comet – with spectacular results.
The three images of the breaking comet
(Image: NASA, ESA, D. Bodewits (Auburn). Image processing: J. DePasquale (STScI))
By a double stroke of luck, the Hubble Space Telescope has completely unexpectedly observed the breakup of comet C/2025 K1 (ATLAS) almost in real-time. The European Space Agency ESA has now made public and published several images showing the individual fragments drifting apart. Hubble was actually supposed to photograph a different comet, but that wasn't possible for technical reasons, explains John Noonan from Auburn University in the US state of Alabama. Therefore, the instrument was pointed at C/2025 K1 (ATLAS) instead. When the first image was available, it showed not one but four comets. That was “something really, really special.”
The first of many images of the fragments
Comet C/2025 K1 (ATLAS), nicknamed K1 and not to be confused with the interstellar comet 3I/ATLAS. It was only visible far south of the Northern Hemisphere and in the Southern Hemisphere. It reached its closest point to the sun (perihelion) within Mercury's orbit on October 8, and it was considered likely that it could break apart afterward. That this actually happened was already known. The fragments were recorded with the Gemini North Observatory from Mauna Kea in Hawaii, among others. When Hubble was pointed at the celestial body on November 8, 2025, it was not yet known that it had broken up. Hubble then also photographed the fragments on the following two days.
The ESA now explains that researchers have long been trying to study a comet during or shortly after its breakup with Hubble. However, this has never been successful. Until now, such an event has only been observed weeks or months later and at a much greater distance. The research group suspects that K1 broke apart slowly eight days before the first Hubble image, having had a diameter of about 8 km until then. Thanks to Hubble's high resolution, the group was also able to calculate from the three images how the remnants drifted apart.
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The images have now already raised a question, the ESA writes. It is unclear why bright outbursts were only visible on the celestial body after a delay, after it had broken up. One would have expected the exposed ice to directly cause an increase in brightness. The research group now speculates that a new dust layer must first form over the exposed ice, which is then blown away. This dust reflects sunlight and is therefore bright to us. Perhaps heat also needs to reach beneath the surface and build up pressure there before an expanding dust envelope is ejected. A scientific paper on the images was published in the journal Icarus.
(mho)
