The observation of an object disintegrating in space offers a spectacle as rare as it is instructive. Astronomers were able to follow the fragmentation of C/2025 K1 (ATLAS) in real time, an event that reveals the extreme forces these icy bodies are subjected to when they approach the Sun.
Comet C/2025 K1 (ATLAS) was discovered in May 2025 and had gradually brightened as it approached our star. Under the effect of solar heat, the frozen gases contained in its nucleus turned into vapor, forming a luminous cloud called a coma. The solar wind then blew this material backward, creating the characteristic tail we associate with visible comets. Unfortunately for Earth observers, it never became bright enough to be seen with the naked eye.
Fragmentation of comet C/2025 K1 (ATLAS) captured by the 1.82-meter Copernicus telescope at the Asiago Observatory in Italy.
Credit: F. Ferrigno/INAF/Univ. Parthenope The close approach to the Sun on October 8th profoundly affected the comet's internal structure, setting the stage for its spectacular disintegration. On the nights of November 11th and 12th, astronomers using the Copernicus telescope in Italy witnessed the nucleus separating into several pieces. Astronomer Mazzotta Epifani confirmed in a statement published on the Italian National Institute for Astrophysics website that two main fragments of similar size had formed, about 1,200 miles (approximately 2,000 kilometers) apart, with a third smaller and fainter piece suspected.
Gianluca Masi of the Virtual Telescope Project also recorded remarkable views of this event on November 12th and 13th, showing a large section of the nucleus detaching from the main part. He explained that the animation showed how the fragments evolved over 24 hours after the breakup, thanks to exceptional observing conditions and the high resolution of his instrument. These valuable details document the process of comet destruction.
This comet is believed to originate from the Kuiper Belt, a distant region of the Solar System beyond Neptune, filled with icy bodies. Its probable first journey to the inner regions of the Solar System, certainly following a gravitational disturbance, ended in its disintegration, making it a time capsule preserved since the formation of the Solar System. Analysis of its composition could provide information about the primitive nebula that gave birth to the current planets.
Image of C/2025 K1 (ATLAS) captured by Gianluca Masi of the Virtual Telescope Project showing the evolution of the fragments.
Credit: Gianluca Masi, Virtual Telescope Project
It's important to clarify that C/2025 K1 (ATLAS) has no connection with the interstellar comet 3I/ATLAS that has recently been in the news. Their common name simply comes from the ATLAS program (Asteroid Terrestrial-Impact Last Alert System) that detected them. While one intrigues with its origin outside the Solar System, the other offers us a lesson about the fate of local comets subjected to the rigors of their orbital journey.
The fragile structure of comets
Comets are composed of a mixture of ices (water, carbon monoxide, carbon dioxide) and dust, forming a solid nucleus often compared to a dirty snowball. When they approach the Sun, solar radiation vaporizes the surface ices, creating a temporary atmosphere called a coma.
This gaseous envelope can extend for tens of thousands of kilometers, while radiation pressure and solar wind push particles to form the characteristic tails. The dust tail, white and curved, follows the comet's orbit, while the ion tail, bluish and straight, always points away from the Sun.
The structure of the cometary nucleus is often fragile and heterogeneous, with internal faults that make it vulnerable to tidal forces and thermal stresses. These structural weaknesses explain why some comets break apart spontaneously during their close approaches to the Sun, as demonstrated by C/2025 K1 (ATLAS).
The study of these fragmentations allows astronomers to better understand the internal composition of comets and the processes that presided over the formation of the Solar System 4.6 billion years ago.
The Kuiper Belt, reservoir of comets
The Kuiper Belt is a vast disk-shaped region located beyond Neptune's orbit, between 30 and 50 astronomical units from the Sun. It contains thousands of small icy bodies, remnants from the formation of the Solar System, some of which are gradually deflected inward under the gravitational influence of the giant planets.
Kuiper Belt objects are primarily composed of volatile ices (methane, ammonia, water) mixed with silicate rocks. Their size ranges from a few kilometers to over 1,200 miles (2,000 km) for the largest like Pluto and Eris. These bodies preserve the primitive composition of the solar nebula.
When gravitationally disturbed, some of these objects become long-period comets that then follow a highly elliptical orbit bringing them close to the Sun. C/2025 K1 (ATLAS) would belong to this category, making its first journey to the inner regions of the Solar System.
The study of these comets originating from the Kuiper Belt provides valuable information about the conditions that prevailed in the Solar System during its formation, long before the appearance of the current planets.