Icy Volcanic Action on Comet 3I/ATLAS Has Produced an Unusual Combo of Chemicals
Speeding near the sun with an unusual aura of gas and dust, Comet 3I/ATLAS has captured the attention of astronomers and the general public for months now. This interstellar visitor to our Solar System — only the third ever observed — has raised eyebrows for a few reasons, including its carbon-rich composition and intense brightness as it approached the sun.
A paper recently published on the preprint server arXiv has introduced what could be another head-turning trait of 3I/ATLAS: ice volcanoes. The paper, which has not yet been peer reviewed, suggests that the comet is showing signs of cryovolcanism, a process often observed in trans-Neptunian objects — faint celestial bodies that orbit the sun beyond Neptune’s orbit.
Read More: New Images of Comet 3I/ATLAS Reveal “How Magical the Universe Could Be”
3I/ATLAS’ Cold Journey
Comet 3I/ATLAS came barreling into the Solar System at a remarkably high velocity of 130,000 miles per hour, but its exact origins in the Milky Way galaxy are still under debate. Previous research based on details of stars compiled in the Gaia DR3 catalog (collected by the European Space Agency’s Gaia mission) has indicated that the comet hasn’t passed close to any other stars over the past 10 million years.
The authors of the recent preprint paper note that Comet 3I/ATLAS may have a unique composition because it has spent such a long time crossing cold regions of the interstellar medium (the gas and dust that fills the space in between stars).
Before it entered the Solar System, it may have accumulated ices and organic compounds on its surface. This material may have then been processed by cosmic rays as the comet passed through the interstellar medium, creating a crust on its surface.
“Implantation of foreign materials, and their processing by cosmic rays during its long trip through our galaxy could have hidden the real nature of 3I,” the authors wrote in the paper.
Comparing with Chondrites
As Comet 3I/ATLAS got closer to the sun in late October 2025, the cloud of gas and dust that surrounded it — what’s known as its “coma” — became exceptionally bright. Most comets don’t get nearly as bright because of the dust mantle that they gain, which insulates subsurface ice and hinders abrupt brightening.
Comet 3I/ATLAS, in contrast, likely doesn’t have a dust mantle because it hasn’t passed by stars in 10 million years. Because of this, the comet is considered to be “pristine,” never thermally processed like other comets.
The preprint authors report that the pristine quality of Comet 3I/ATLAS is comparable to that of carbonaceous chondrites, a class of meteorites rich in carbon. To confirm the similarities, they used spectroscopic observations to compare how light would reflect off the comet and several carbonaceous chondrites collected from Antarctica.
One of the chondrites in the collection contains what may be a remnant from a trans-Neptunian object (TNO). Based on their comparisons, the authors hypothesize that Comet 3I/ATLAS is a TNO-like primordial object that contains metal grains and was launched from its ancient planetary system after a close encounter with a giant planet or a star.
Icy Eruptions on an Interstellar Visitor
TNOs experience cryovolcanism, a process characterized by the eruption of liquid or gaseous volatiles, such as water, ammonia, or methane.
According to the preprint authors, Comet 3I/ATLAS could be experiencing something similar; as it passed near the sun, water-ice sublimated, and its icy surface was heated enough to reveal a more porous subsurface. Warmed liquid water may have then breached the porous subsurface, coming into contact with metal grains akin to those found in certain groupings of carbonaceous chondrites.
These minerals would’ve been corroded by the water, producing reactions that result in cryovolcanic jets spewing out of the comet. This, the authors suggest, is what appears to be making the comet’s coma extremely rich in carbon monoxide (CO) and carbon dioxide (CO2).
While there’s still much to be explored about the composition and potential cryovolcanism of Comet 3I/ATLAS, it’s exciting to think that an interstellar visitor may share something in common with objects in our own Solar System.
Read More: Radio Signals Detected From Comet 3I/ATLAS — What Its Interstellar Origins Reveal
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