A rare interstellar comet from another star system is “bursting with alcohol”, according to astronomers who say the discovery offers an unprecedented glimpse of the chemistry of a distant region of the cosmos.
3I/Atlas, as it is known, is only the third confirmed visitor from another solar system ever detected in our own.
First spotted in late 2024, it is a cosmic nomad thought to have been ejected from its home system billions of years ago. It was seen hurtling through our neighbourhood at 100,000mph, far too fast for the sun’s gravity to ever capture it, and on a trajectory that showed it must have formed around another star.
The comet, the bright dot with a tail, passing through a field of stars in JanuaryNASA/Daniel Muthukrishna/MIT
Its solid core is estimated to be about 5km wide. However, the glowing cloud of gas, or coma, that surrounds it swelled to 100,000km (over 62,000 miles) across as it neared the sun and became warmer.
Trailing behind it was a massive tail of dust and ionised gas, stretching for more than one million kilometres through space.
Now scientists say this ancient traveller carries an unusual chemical signature.
New research from the Atacama Large Millimeter/submillimeter Array (Alma) observatory in Chile has revealed that 3I/Atlas contains exceptionally high levels of methanol, a simple alcohol molecule.
“Observing 3I/Atlas is like taking a fingerprint from another solar system,” said Nathan Roth, the study’s lead author and a professor of astronomy at American University in Washington DC.
“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 observed the comet on multiple dates in 2025 as it approached the sun. As sunlight warmed its icy surface, frozen material vaporised and streamed into space, expanding the glowing coma.
The comet 178 million miles away in NovemberAP
By studying the dim patterns of light coming from the gas cloud, astronomers were able to identify the specific chemicals leaking out of the comet.
They focused on two in particular: methanol and hydrogen cyanide. While both are seen in typical comets, the balance between them in 3I/Atlas was unusual. Methanol molecules outnumbered hydrogen cyanide by up to 120 to one, a far higher ratio than usually observed.
This suggests the comet formed in conditions quite different from those that shaped the solar system.
Earlier observations with the James Webb Space Telescope had already hinted that the object was unusual. When it was still far from the sun, Webb detected a coma dominated by carbon dioxide, another feature rarely seen so strongly in comets formed around our star.
Alma’s high-resolution data also revealed how the comet releases its gases. Hydrogen cyanide appears to stream directly from the solid nucleus, as is typical for comets. Methanol, however, is released both from the nucleus and from tiny icy grains drifting through the coma.
These particles act like miniature comets: as they are warmed by sunlight, their ice vaporises, releasing additional methanol into the surrounding cloud.
Astronomers have detected only two other confirmed interstellar wanderers: 1I/‘Oumuamua, discovered in 2017, and 2I/Borisov, spotted in 2019.