Interstellar Comet 3I/ATLAS Found Bursting With Unusual Amounts of Methanol

New observations from the Atacama Large Millimeter/submillimeter Array (ALMA) show that interstellar comet 3I/ATLAS contains an unusually large amount of methanol, exceeding that seen in almost all known comets from our own solar system, researchers reported.

"Observing 3I/ATLAS is like taking a fingerprint from another solar system," said Nathan Roth, the lead author of the research and a professor at American University. "The details reveal what it's made of, and it's bursting with methanol in a way we just don't usually see in comets in our own solar system."

The research team used ALMA's Atacama Compact Array in Chile to observe 3I/ATLAS on several dates in late 2025 as it moved closer to the sun, heating its icy surface and releasing gas and dust into a bright cloud, or coma, around its core. Studying two molecules in that coma — methanol and hydrogen cyanide, a nitrogen-bearing organic compound common in comets — the team measured methanol-to-hydrogen-cyanide ratios of roughly 70 and 120 on two observation dates, placing 3I/ATLAS among the most methanol-rich comets ever studied.

Earlier observations with the James Webb Space Telescope had found the comet's coma dominated by carbon dioxide while it was still far from the sun. The new ALMA data also revealed that hydrogen cyanide comes mostly from the comet's nucleus, as is common in solar system comets, while methanol escapes from both the nucleus and tiny ice grains floating in the coma, which behave like miniature comets as they warm and release their own gas.

3I/ATLAS is only the third confirmed object ever observed entering the solar system from interstellar space, following 1I/'Oumuamua and 2I/Borisov, and studies of those two earlier visitors also turned up unusual characteristics.