In a rare glimpse into the formation of planetary systems beyond our own, scientists have observed evidence of cryovolcanic activity-eruptions of ice and gas-on the interstellar comet 3I/ATLAS. The findings, published as a preprint on arXiv November 24th, suggest the comet, traveling from another star system, possesses a surprising compositional similarity to objects found within our solar system’s distant Kuiper Belt. This marks only the third time an interstellar object has been detected within our solar system, offering a unique possibility to study the building blocks of planets around other stars.Researchers are racing to gather data as 3I/ATLAS is expected to leave our solar system in 2026.
Scientists have detected what appears to be cryovolcanic activity on the interstellar comet 3I/ATLAS, observing material erupting as the comet approached the Sun. The findings, currently awaiting peer review, were published as a preprint on arXiv November 24th. Understanding the composition of comets like 3I/ATLAS can offer insights into the building blocks of planetary systems and the potential for life beyond Earth.
The study reveals that comet 3I/ATLAS shares characteristics with trans-Neptunian objects – icy bodies located beyond the orbit of Neptune, including dwarf planets. This similarity is particularly surprising given that the comet is believed to originate from another star system.
“We were all surprised,” said Josep Trigo-Rodríguez, a researcher at the Institute of Space Sciences (CSIC/IEEC) in Spain, according to a report from Live Science on December 2nd, 2025.
“For a comet that formed in a distant planetary system, it’s remarkable that the mixture of materials making up this object’s surface resembles those of trans-Neptunian objects, which formed far from the Sun but within our own planetary system,” he added.
Comet 3I/ATLAS is only the third interstellar object ever recorded, providing a rare opportunity for scientists to study conditions around other stars and the early formation of planetary systems. Estimated to be billions of years older than our solar system, the comet is expected to leave our region of space next year.
Researchers monitored the comet using the Joan Oró Telescope at the Montsec Observatory in Spain, combining their observations with data from other observatories. The monitoring occurred as the comet reached perihelion – its closest approach to the Sun – on October 29th, when solar heating caused surface ice to sublimate into gas.
The team observed increased sublimation activity when the comet was approximately 235 million miles from the Sun. High-resolution images captured by the Joan Oró Telescope revealed plumes of gas and dust, considered strong evidence of cryovolcanism. This process, similar to traditional volcanism but involving icy materials, suggests a dynamic internal environment within the comet.
According to the research team, the cryovolcanism is likely triggered by reactions within the comet’s interior as solid carbon dioxide begins to sublimate with the increasing heat. This process may allow oxidizing fluids to penetrate the comet’s interior and react with iron-nickel metal grains and sulfides.
To analyze the comet’s composition, researchers compared spectroscopic data with samples of carbonaceous chondrites – ancient meteorites – collected by NASA from Antarctica. One sample contained fragments believed to originate from a trans-Neptunian object, and the analysis revealed compositional similarities with 3I/ATLAS.
Despite its behavioral similarities to trans-Neptunian objects, comet 3I/ATLAS is confirmed to not originate from our solar system due to its hyperbolic trajectory. NASA first detected the object traveling at approximately 138,000 miles per hour – too fast to be gravitationally bound to the Sun.
Trigo-Rodríguez emphasized the importance of studying interstellar comets, both in terms of potential collision risks and their scientific value. He described the comet as an “extraordinary object,” adding that “it is a space capsule, containing valuable information about the chemistry that takes place in other locations in our galaxy.”
