Only 1 of 5: Comet discovered 2 billion kilometres from Sun is acting in a bizarre way

NASA has spotted an object 2.1 billion kilometres from the Sun which defies all principles of how the universe works. Only a handful of such events have been recorded ever since humans started keeping track of the many occurrences in space. This object in question is a comet orbiting between the orbits of Saturn and Uranus that has left scientists baffled because of the way it is behaving despite being so far away from the Sun.

Named C/2025 D1 (Gröller), it was discovered by Hannes Gröller, an astronomer at the University of Arizona, using the Catalina Sky Survey. It is a historic discovery because it is acting in the opposite way a comet ideally does. Comets are made of water ice and develop a tail only when they reach a certain distance from the Sun.

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This is the point at which comets become active and the heat from the Sun starts to vapourise the water ice, leading to a visible tail and a coma. This occurrence happens when comets pass at a distance of between 3 and 5 AU. But Comet C/2025 D1 (Gröller), is nowhere near this point. The comet is zooming at a distance of 14.1 AU from the Sun, the farthest for any active comet. This is 14 times further than Earth is from the Sun. It also has extremely high temperatures, making it an absolute anomaly.

Comet Gröller contains elements from ancient solar system

Experts are puzzled by this comet. Some of them think that the comet might be composed of some different chemical compounds normally not seen in comets. Ingredients more volatile than water, such as carbon monoxide or carbon dioxide, could be present in Comet Gröller.

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They could also contain extremely rare supervolatiles, materials that do not exist in any celestial body whose orbits bring them towards the inner solar system. Scientists think that this comet can offer clues about the early solar system, when the Sun was born 4.6 billion years ago. It could also explain how the universe shaped up after the Big Bang 13.8 billion years ago.

Comet Gröller is not the first such comet seen in the solar system. Only five ultradistant comets have been identified to date acting in a similar fashion beyond 20 AU. These comets are dynamically new, roaming in orbits which never bring them closer to the Sun. Their distance means that they are potentially frozen and belong to the early days of the Solar System.