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, relative to what astronomers typically measure.
“Observing 3I/ATLAS is like taking a fingerprint from another Solar System,” said Nathan Roth, lead author on this research, in a news release. “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.”
Read More: Comet 3I/ATLAS Flaunts Bright Halo and Tail in New Image Taken by Jupiter-Bound Spacecraft
3I/ATLAS: A Methanol-Rich Comet
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 turning directly into gas. The escaping material formed a glowing cloud called a coma around the comet’s nucleus.
Within that cloud, molecules emit faint signals at specific radio wavelengths. By measuring those signals (sometimes called chemical fingerprints), astronomers can identify the substances escaping from the comet.
The observations focused on two molecules commonly found in cometary gases: methanol, a simple alcohol, and hydrogen cyanide, a nitrogen-bearing organic compound.
Comparing the Comet’s Chemical Signals
Measurements taken on two observing dates in late 2025 revealed methanol-to-hydrogen-cyanide ratios of about 70 and 120. Those levels place 3I/ATLAS among the most methanol-rich cometary objects ever measured.
The unusually high ratio suggests the comet’s ice formed under chemical conditions different from those that shaped most comets in our Solar System.
The observations also revealed differences in how the gases escape from the comet. Hydrogen cyanide appears to stream mainly from the comet’s nucleus, the icy core. Methanol, however, comes from the nucleus and tiny icy grains drifting through the coma.
Tiny “Mini-Comets” in the Coma
Those drifting grains act almost like miniature comets themselves. As sunlight warms them, their ice turns into gas, releasing additional methanol into the surrounding cloud.
Similar behavior has been seen in some comets from our Solar System. But this is the first time astronomers have traced such detailed outgassing in an interstellar object.
Earlier observations with the James Webb Space Telescope had already shown that the comet’s coma contains large amounts of carbon dioxide. Together with the new measurements, the findings suggest that the ice within 3I/ATLAS formed in an environment quite different from 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 one offers a rare chance to study material that formed around another star — without ever leaving our own Solar System.
Read More: Other ATLAS Comet Appears Fragmented After Close Encounter with The Sun
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