Mysterious interstellar object 3I/ATLAS reached its perihelion, or its closest point to the Sun, earlier this year, shedding copious amounts of ice and dust in the process.
The material has formed enormous jets that reach out like a tail behind the visitor, which is widely believed to be a comet — and even an “anti-tail” that faces the Sun.
It’s such a violent process, astronomers have found that the surface of 3I/ATLAS’ nucleus could be dotted with erupting “ice volcanoes,” as Live Science reports. They posit that could make the visitor surprisingly similar to trans-Neptunian objects, faint chunks of rock and ice that form in the Kuiper Belt beyond Neptune’s orbit.
“We were all surprised,” Josep Trigo-Rodríguez, lead author of a yet-to-be-peer-reviewed paper and staff researcher at the Institute of Space Sciences in Spain, told Live Science. “Being a comet formed in a remote planetary system, it is remarkable that the mixture of materials forming the surface of the body has resemblance with trans-Neptunian objects, bodies formed at [a] large distance from the Sun but belonging to our planetary system.”
Trigo-Rodríguez and his colleagues used the Joan Oró Telescope at the Montsec Observatory in Spain to carefully study 3I/ATLAS’ perihelion in late October, a point at which solar system comets usually release the largest amount of material as they’re heated up by the Sun.
The team observed detailed images of jets of gas and dust particles being released, concluding that 3I/ATLAS was showing signs of cryovolcanism. Other planetary bodies, like trans-Neptunian objects, also frequently feature cryovolcanoes, caused by an internal heat source that causes ice to sublimate and spew vapor into space.
Trigo-Rodríguez and his colleagues suggest in their paper that sublimating carbon dioxide ice inside 3I/ATLAS may be reacting with metals, like nickel and iron sulfides, in its core, causing them to oxidize and thereby powering the object’s cryovolcanism.
Yet plenty of questions remain. For one, we don’t even know the exact mass of 3I/ATLAS; scientists have estimated that it could measure anywhere from 1,400 feet to 3.5 miles across.
Studying interstellar objects traveling through the solar system is an exceedingly rare opportunity that we shouldn’t take for granted. 3I/ATLAS is expected to reach its closest point to Earth later this month and Jupiter in March 2026.
“Interstellar visitors like 3I/ATLAS continue to challenge and refine our understanding of planetary-system formation and the chemical evolution of small bodies,” Trigo-Rodríguez and his fellow team members concluded in their paper. “Each newly discovered object reveals unexpected properties that test and expand current models.”
“Future intercept missions will be essential for visiting, and directly sampling these rare messengers and unlocking the record they carry from distant planetary systems,” they added.
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