- Astronomers took a chemical fingerprint of interstellar comet 3I/ATLAS. They discovered it’s loaded with methanol – a type of alcohol – far more than most comets in our solar system.
- The comet’s coma revealed record-high methanol-to-hydrogen-cyanide ratios. This makes 3I/ATLAS one of the most methanol-rich comets ever observed.
- The observations also revealed different outgassing behaviors. Hydrogen cyanide mainly comes from the comet’s nucleus, while methanol comes from both from the nucleus and icy grains in the coma. This info provides clues about how materials formed in another planetary system.
The National Radio Astronomy Observatory published this original story on March 6, 2026. Edits by EarthSky.
Interstellar comet 3I/ATLAS has a high alcohol content
Comet 3I/ATLAS is making headlines again, thanks to new findings from astronomers using the ALMA telescope in Chile. This research reveals that the comet is packed with an unusually large amount of methanol, the organic molecule that’s basically alcohol. In fact, 3I/ATLAS contains more methanol than almost any comet in our solar system, making it a true cosmic cocktail.
Nathan Roth, lead author and professor at American University, explained:
Observing 3I/ATLAS is like taking a fingerprint from another solar system. 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.
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Observing our interstellar visitor
Using ALMA – the Atacama Large Millimeter/submillimeter Array – on multiple dates in late 2025, the team observed 3I/ATLAS as it approached our sun. As sunlight warmed its icy surface, 3I/ATLAS released gas and dust. This material formed a glowing halo (or coma) around its core. Astronomers analyzed this coma, revealing the chemical fingerprints of the material that composes it. And this allowed them to study how objects might be made in another planetary system, without leaving our own.
The team focused on the faint submillimeter fingerprints of two molecules: methanol (CH3OH), a type of alcohol, and hydrogen cyanide (HCN), a nitrogen-bearing organic molecule commonly seen in comets. The ALMA data reveal that 3I/ATLAS is heavily enriched in methanol compared to hydrogen cyanide. In fact, it’s far beyond what we typically see in comets born in our own solar system. On two observing dates, the team measured methanol-HCN ratios of about 70 and 120, placing 3I/ATLAS among the most methanol-rich solar system comets ever studied.
A comet unlike any in our solar system
These measurements imply that the icy material from 3I/ATLAS formed in (or experienced) very different conditions than those that shape most comets in our own solar system. Previous work with the James Webb Space Telescope shoed that 3I/ATLAS had a coma dominated by carbon dioxide when it was far from the sun. And these new ALMA results add methanol as another unusual detail in its chemical inventory.
ALMA’s high resolution for imaging also allowed the team to see how different molecules move away from the comet. And this revealed surprising differences between methanol and hydrogen cyanide. Hydrogen cyanide appears to come, for the most part, directly from the comet’s core, or nucleus. That’s typical for comets in our solar system.
Methanol, on the other hand, appears to come from both the nucleus and from ice particles in the coma. These tiny, icy grains act like mini-comets. As the object moves closer to the sun, where ice turns into gas, they also release methanol. Scientists have seen similar behavior in some solar system comets. But this is the first time scientists have traced the physics of such detailed outgassing in an interstellar object.
3rd confirmed interstellar visitor
Comet 3I/ATLAS is only the third confirmed object ever seen passing through our solar system from interstellar space, after 1I/‘Oumuamua and 2I/Borisov. Observations of these objects also revealed unusual properties. As astronomers continue to discover and study more interstellar objects, our understanding of planet formation in other planetary systems continues to grow more interesting.
Bottom line: Astronomers took a detailed look at the chemical fingerprint of interstellar comet 3I/ATLAS. They found it has a high alcohol content. Specifically, it has an abundance of methanol.
Via NRAO