The interstellar comet 3I/ATLAS could be covered in erupting “ice volcanoes,” new observations suggest.
The study’s findings, which have yet to be peer-reviewed, suggest that comet 3I/ATLAS is similar to icy trans-Neptunian objects — dwarf planets and other objects that orbit the sun beyond Neptune. If this is confirmed, it means that despite coming from another solar system, comet 3I/ATLAS has a surprising amount in common with objects in our own cosmic neighborhood.
“We were all surprised,” study lead author Josep Trigo-Rodríguez, a staff leading researcher at the Institute of Space Sciences (CSIC/IEEC) 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.”
There has been endless speculation about the origins of comet 3I/ATLAS since astronomers first spotted it in July. Much of the online speculation has centered around whether this interstellar visitor could be an alien spacecraft. However, most astronomers are confident that 3I/ATLAS is a comet from an unknown star system.
Comet 3I/ATLAS is only the third interstellar object ever recorded, and offers researchers a rare opportunity to learn more about conditions around other stars and in the deep past (comet 3I/ATLAS could be billions of years older than our system). This means that scientists are scrambling to study the object before it departs our solar system forever next year.
For the new study, Trigo-Rodríguez and his colleagues studied the comet using the Joan Oró Telescope at the Montsec Observatory in the northeastern Catalonia region of Spain, pairing its observations with those made by other observatories in the region. The astronomers watched the comet carefully as it approached its closest point to our star, known as perihelion, on Oct. 29. Comets heat up as they fly closer to stars, causing ice on their surface to sublimate into gas, which researchers can then detect and study.
The researchers found that the comet entered a more intense sublimation stage when it got within about 235,000,000 miles (378 million kilometers) of the sun, while also brightening rapidly. Using the Joan Oró Telescope, they snapped the highest-resolution images yet of jets of gas and dust particles coming off the comet, which they interpreted as clear signs of cryovolcanism.
Cryovolcanoes are typically found in planetary bodies that are rich in ice, like trans-Neptunian objects. Trigo-Rodríguez noted that these planetary bodies have internal heat that melts the ice and produces the cryovolcanoes, which release vapor and dust into space.
PRE-PERIHELION STUDY OF #COMET #3IATLAS with our findings about its spectroscopic similitude with CR carbonaceous chondrites. Manuscript submitted for publication in which we propose it is a #TNO-like body experiencing #cryovolcanism
Now in Cornell Univ. @arxiv repository:
➡️ arxiv.org/abs/2511.19112— @joseptrigo.bsky.social (@joseptrigo.bsky.social.bsky.social) 2025-12-01T19:02:15.194Z
In the case of comet 3I/ATLAS, the researchers believe that the cryovolcanism is driven by the corrosion of pristine material locked inside the comet. As the sun heated the comet, the threshold at which solid carbon dioxide (dry ice) sublimated into gas was breached. This then enabled an oxidizing liquid to flow into the comet’s interior and react with reactive metallic grains like nickel and iron sulfides.
To test their theories about the comet’s composition, the researchers ran a spectroscopic comparison (analyzing how matter interacts with light) using primitive and pristine rocky meteorites called carbonaceous chondrites that NASA collected from Antarctica.
One of these Antarctic samples contained what the researchers believe is a piece of a trans-Neptunian object. The analysis revealed that comet 3I/ATLAS was similar to these remnants from the earliest days of our solar system, and is likely rich in natural metal.
Carbonaceous chondrites are believed to have played a role in life’s origins on Earth, bringing volatile materials that helped establish our atmosphere and other conditions necessary for life, according to the Natural History Museum in London.
Comet 3I/ATLAS origins
While 3I/ATLAS’s exact size is still uncertain, Hubble Space Telescope observations suggest that it’s somewhere between 1,400 feet (440 meters) and 3.5 miles (5.6 kilometers) wide. Rodriguez and his colleagues calculated that if the comet is 0.6 miles (1 km) wide and has the rocky composition they suspect it has, then its mass would be more than 660 million tons (600 million metric tons).
However, even if 3I/ATLAS has a similar composition to carbonaceous chondrites and behaves like trans-Neptunian objects approaching the sun, it’s still without a doubt not from our solar system. That’s because of its hyperbolic trajectory, along which scientists first noticed it zooming at around 137,000 miles per hour (221,000 kilometers per hour) — too fast to be bound to our sun’s gravity, according to NASA.
Researchers don’t know which star system comet 3I/ATLAS originated from, but it has certainly travelled a long way. The comet is likely billions of years old and potentially more than 3 billion years older than our own solar system. In fact, the comet has spent so much time in space that it could be extremely irradiated, which would make deciphering its origins even more difficult.
Trigo-Rodríguez noted that it’s important to study and track interstellar comets because they are a potential collision hazard for Earth. However, he also described them as “extraordinary objects” in their own right and worthy of consideration.
They “are space capsules, containing valuable information about the chemistry ongoing in another location of our galaxy,” Trigo-Rodríguez said.
