Astronomers studying the interstellar visitor 3I/ATLAS have discovered the comet is unusually rich in alcohol — a chemical clue that could reveal how planets and icy bodies form around other stars.
Using the powerful radio antennas of the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, researchers detected extremely strong signals of methanol (CH3OH), a simple alcohol molecule, in the comet‘s expanding cloud of gas.
As 3I/ATLAS approached the sun and sunlight warmed its icy surface, it released gas and dust, forming a glowing halo — or coma — around its core, which allowed ALMA to analyze the comet’s chemical composition in detail.
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The measurements show that methanol is far more abundant, relative to hydrogen cyanide, than astronomers typically see in comets from our own solar system. That chemical imbalance suggests 3I/ATLAS likely formed in a planetary system with very different physical conditions — such as colder temperatures and/or a different chemical inventory — than the one that produced our own comets, according to a statement from the National Radio Astronomy Observatory (NRAO).
“Observing 3I/ATLAS is like taking a fingerprint from another solar system,” Nathan Roth, lead author of the study and a professor at American University, said in the statement. “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.”
Methanol — which is used for industrial purposes here on Earth, in contrast to the drinkable ethanol — isn’t rare in space. It forms on the surfaces of icy dust grains in interstellar clouds and is commonly incorporated into comets during planet formation. But the amount detected in 3I/ATLAS appears unusually high compared with the ratios seen in solar system comets, making the object a valuable chemical “fingerprint” from another planetary system.
Discovered in July 2025 by the Asteroid Terrestrial-impact Last Alert System, 3I/ATLAS is only the third known object confirmed to have entered the solar system from interstellar space. The first was ‘Oumuamua, spotted in 2017, followed in 2019 by 2I/Borisov, which displayed a more traditional comet-like appearance.
Since 3I/ATLAS’ discovery, telescopes around the world — including the Hubble Space Telescope and the James Webb Space Telescope — have been monitoring the comet as it travels through the inner solar system. Images show a diffuse coma and faint dust tail created as sunlight heats the comet’s ices, releasing gas and dust into space.
Those outflows also help explain another phenomenon observed around the comet: a vast cloud of gas glowing in X-rays as charged particles from the solar wind slam into material escaping from the nucleus. The ALMA observations further revealed that hydrogen cyanide mostly streams directly from the comet’s nucleus, while methanol is released both from the nucleus and from icy grains in the coma acting like miniature comets — the first time such detailed outgassing behavior has been mapped in an interstellar object, according to the statement.
The arrival of a new interstellar object has also fueled speculation online, including suggestions that 3I/ATLAS could be artificial in origin. But the growing body of evidence — including its comet-like tail, gas jets and molecular composition — strongly indicates that the object is a natural icy body.
For astronomers, that’s the real excitement. Objects like 3I/ATLAS act as messengers from other planetary systems, preserving the chemical conditions present where they formed billions of years ago — and offering rare opportunities to study the building blocks of distant worlds without ever leaving our own solar system.
The new study has been submitted for publication and is currently available as a preprint on arXiv.
