Interstellar Comet 3I/ATLAS may be 12 billion years old

Spotted in 2025, interstellar comet 3I/ATLAS is the third such object found crossing our solar system. A new study using JWST and ALMA data suggests the comet could be as old as 12 billion years—nearly as ancient as the universe itself—and likely formed in a m

When 3I/ATLAS came into view in 2025. it looked like just another icy visitor—until astronomers started teasing out the chemistry hidden in its gas. As the sun heated the comet and burned away its insides. researchers tracked the isotopes in the outflow. using those molecular fingerprints to reach back across cosmic time.

The result is now sharpening into something almost unnerving: the new study’s authors believe 3I/ATLAS may be as old as 12 billion years. If that holds. the comet’s history stretches far beyond our solar system’s 4.5 billion years. landing just less than two billion years younger than the universe itself.

3I/ATLAS is the third interstellar comet astronomers have identified flying through our solar system. following 1I/ʻOumuamua and 2I/Borisov. Since its discovery. scientists have used the space-based James Webb Space Telescope and the ground-based Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to study the gas spouting from the comet as solar heat accelerated what was frozen within.

Isotopes in that gas do more than confirm an origin story—they offer a way to date it. By using carbon isotopes to estimate its age, the authors conclude 3I/ATLAS could be even more ancient than earlier estimates suggested.

The same measurements are also pointing to where it likely formed. The study shows 3I/ATLAS came from a much colder region of its own solar system than any of the comets astronomers typically see here. The clue is heavy hydrogen, present as deuterium—hydrogen with one neutron and one proton. 3I/ATLAS contains far more deuterium than any local space rock. In comet chemistry, that kind of surplus tends to be linked to colder environments, where particular isotopic signatures are preserved.

Taken together. the findings sit in line with other recent research. and they feed into a growing unease about what we’ve assumed. Astronomers have been increasingly speculating that our solar system might be the oddball—that the comets we’ve studied for centuries may not represent the norm elsewhere in the cosmos.

That speculation is now running on better fuel than ever. and it’s tied to instruments that can see what earlier generations couldn’t. The interstellar visitors themselves—these first three—were spotted thanks to cutting-edge telescopes like ALMA and JWST. And with the Vera C. Rubin Observatory in Chile beginning a decade-long sky survey, more such discoveries are likely to follow.

“We hope they will be as exciting as 3I/ATLAS. ” said Cyrielle Opitom of the University of Edinburgh in Scotland. a co-author of the new study. For astronomers, the payoff isn’t just a new object added to a growing list. These vagrant rocks could reveal what the universe’s outer reaches look like. and—just as importantly—how strange or familiar the building blocks of other planetary systems really are.

3I/ATLAS interstellar comet James Webb Space Telescope JWST ALMA Vera C. Rubin Observatory deuterium carbon isotopes astronomy Nature study solar system formation