Interstellar Comet 3I/ATLAS Shows Signs of Cryovolcanism, Challenging Planetary Formation Theories
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A newly observed interstellar comet, 3I/ATLAS, is exhibiting unexpected behavior, including potential cryovolcanism – eruptions of ice and gas – and a surprising compositional similarity to objects within our own solar system. The findings, published as a preprint paper on arXiv on November 24, 2025, and currently undergoing peer review, offer a rare glimpse into the building blocks of planetary systems beyond our own.
Scientists detected bursts of material emanating from the comet as it approached the Sun, leading to the hypothesis of active cryovolcanic processes. This discovery is particularly intriguing given that 3I/ATLAS is believed to have originated from another star system, making its resemblance to trans-Neptunian objects – icy bodies beyond Neptune’s orbit – a significant puzzle.
A Visitor From Another Star
Comet 3I/ATLAS is only the third interstellar object ever detected within our solar system, providing an unprecedented opportunity to study the conditions surrounding other stars and the early stages of planet formation. Researchers estimate the comet to be billions of years older than our solar system and predict it will exit our region of space next year.
“We were all surprised,” said the study’s lead author, Josep Trigo-Rodríguez, a researcher at the Institute of Space Sciences (CSIC/IEEC) in Spain. “As a comet that formed in a remote planetary system, it is remarkable that the mixture of materials that make up the surface of this object bears similarities to trans-Neptunian objects, objects that form at great distances from the Sun but belong to our planetary system.”
Evidence of Ice Volcanoes
The research team monitored 3I/ATLAS using the Joan Oró Telescope at the Montsec Observatory in Spain, supplementing their observations with data from other facilities. Observations focused on the comet’s approach to perihelion – its closest point to the Sun – on October 29, when increased solar heating caused surface ice to sublimate into gas.
At approximately 378 million kilometers from the Sun, researchers observed a significant increase in sublimation activity, accompanied by bursts of gas and dust captured in high-resolution images. These bursts are considered strong indicators of cryovolcanism. The team theorizes that this activity is triggered by a reaction within the comet’s interior, initiated when solid carbon dioxide begins to sublimate due to the Sun’s heat. This process could allow oxidizing fluids to interact with iron-nickel metal grains and sulfides within the comet.
Compositional Clues From Ancient Meteorites
To further investigate the comet’s composition, the researchers conducted spectroscopic comparisons using samples of carbonaceous chondrites – ancient meteorites collected by NASA from Antarctica. Notably, one sample contained fragments believed to originate from a trans-Neptunian object, and analysis revealed striking compositional similarities to 3I/ATLAS.
Despite these similarities, 3I/ATLAS is definitively an interstellar visitor. NASA data confirms its hyperbolic trajectory and exceptionally high speed – approximately 221,000 kilometers per hour – far exceeding the velocity required to remain gravitationally bound to our Sun.
A ‘Space Capsule’ From Another System
Trigo-Rodríguez emphasized the importance of studying interstellar comets, citing both their potential collision threat and their immense scientific value. He described the comet as a “remarkable object” and a “space capsule, containing valuable information about the chemistry taking place in other locations in our galaxy.”
The study of 3I/ATLAS promises to reshape our understanding of planetary formation and the diversity of materials present in star systems beyond our own, offering a unique window into the universe’s broader cosmic landscape.
