Interstellar Comet 3I/ATLAS Is Packed With Alcohol — Indicating That It Formed Beyond Our Solar System
Comet 3I/ATLAS is making headlines again, this time for its chemistry. New observations show that the interstellar visitor contains an unusually large amount of methanol, a molecule that rarely appears in comets in our solar system in such high concentrations.
Using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, astronomers measured methanol in the comet’s expanding cloud of gas and dust. The observations revealed far more methanol than hydrogen cyanide, compared to what astronomers usually measure.
“Observing 3I/ATLAS is like taking the fingerprint of another solar system,” said Nathan Roth, lead author of this research, in a press release. “The details reveal what it’s made of, and it’s packed with methanol in a way we don’t usually see in comets in our own solar system.”
Learn more: Comet 3I/ATLAS displays bright halo and tail in new image taken by Jupiter-bound spacecraft
3I/ATLAS: a comet rich in methanol
The team observed 3I/ATLAS several times in late 2025 as the comet approached the sun. As sunlight warmed the comet’s frozen surface, its ices began to turn directly into gas. The escaping material formed a luminous cloud called a coma around the comet’s nucleus.
In this cloud, molecules emit weak signals at specific radio wavelengths. By measuring these signals (sometimes called chemical fingerprints), astronomers can identify substances escaping from the comet.
The observations focused on two molecules commonly found in cometary gases: methanol, a simple alcohol, and hydrogen cyanide, an organic nitrogen compound.
Comparison of comet chemical signals
Measurements taken on two observation dates in late 2025 revealed methanol/hydrogen cyanide ratios of approximately 70 and 120. These levels place 3I/ATLAS among the most methanol-rich cometary objects ever measured.
This unusually high ratio suggests that the comet’s ice formed under different chemical conditions than those that shaped most comets in our solar system.
The observations also revealed differences in the way gas escapes from the comet. The hydrogen cyanide appears to come primarily from the comet’s icy core. Methanol, on the other hand, comes from the core and tiny icy grains drifting in a coma.
Tiny “mini-comets” in a coma
These drifting grains act almost like miniature comets. As sunlight warms them, their ice turns to gas, releasing additional methanol into the surrounding cloud.
Similar behavior has been observed in certain comets in our solar system. But this is the first time that astronomers have traced such detailed outgassing in an interstellar object.
Previous observations with the James Webb Space Telescope had already shown that the comet’s comet contains large amounts of carbon dioxide. With the new measurements, the results suggest that the ice within 3I/ATLAS formed in a very different environment than that which produced most comets around the sun.
So far, only a handful of interstellar objects have been observed passing through our solar system, including ‘Oumuamua in 2017 and comet Borisov in 2019. Each of these offers a rare chance to study matter that formed around another star, without ever leaving our own solar system.
Learn more: Another ATLAS comet appears fragmented after close encounter with the Sun
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