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Interstellar comet 3I/ATLAS is unusually rich in methanol. New data gathered by the Atacama Large Millimeter/submillimeter Array (ALMA) show that this visitor from beyond our solar system contains far more methanol than nearly any comet native to our own system — a discovery that offers fresh insight into how icy bodies take shape around other stars.
The U.S. National Science Foundation National Radio Astronomy Observatory (NSF NRAO) shared these findings on September 9, 2026.
“Observing 3I/ATLAS is like taking a fingerprint from another solar system,” said Nathan Roth, lead author of the study and a professor at American University. “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 Chemical Fingerprint of 3I/ATLAS
Using ALMA’s Atacama Compact Array in Chile, researchers observed 3I/ATLAS on multiple occasions in late 2025 as it drew nearer to the Sun. Solar heating caused gas and dust to stream off the comet’s icy surface, forming a glowing envelope, or coma, around its nucleus.
By analyzing the molecular content of that coma, scientists were able to determine what materials the comet is made of. Since 3I/ATLAS originated outside our solar system, these measurements give a rare glimpse into how icy bodies might form in other planetary systems.
Methanol and Hydrogen Cyanide
The team concentrated on faint submillimeter signals from two specific molecules:
- Methanol (CH3OH), a type of alcohol
- Hydrogen cyanide (HCN), a nitrogen-bearing organic molecule common in comets
ALMA detected an unusually large proportion of methanol relative to hydrogen cyanide in 3I/ATLAS. Measurements taken on two separate dates yielded methanol-to-HCN ratios of about 70 and 120 — figures that rank the comet among the most methanol-heavy ever recorded when measured against known solar system comets.
Unusual Chemistry Points to Different Origins
Such findings imply that the ice within 3I/ATLAS either formed under, or was later altered by, conditions markedly different from those that shaped the majority of comets native to our solar system.
Previous observations using the James Webb Space Telescope had already shown that 3I/ATLAS possessed a coma rich in carbon dioxide even while still distant from the Sun. The new methanol data from ALMA add yet another unusual trait to the comet’s already distinctive chemical profile.
Tracking the Molecules
Thanks to ALMA’s fine resolution, scientists could also follow how various molecules were emitted and dispersed from the comet, uncovering a clear difference in behavior between methanol and hydrogen cyanide.
Hydrogen cyanide appeared to be released primarily from the comet’s nucleus — a pattern typical of comets within our own solar system. Methanol, by contrast, seemed to emerge from both the nucleus itself and from small ice particles suspended in the coma.
Tiny Ice Grains Act Like Mini-Comets
These minute icy grains essentially function as miniature comets of their own. As 3I/ATLAS nears the Sun and warms, the ice inside these grains vaporizes, releasing extra methanol into the surrounding cloud.
Similar activity has been observed in some solar system comets before, but this marks the first time scientists have mapped out this outgassing process in such detail for an object originating from interstellar space.
A Rare Interstellar Visitor
3I/ATLAS is just the third confirmed object detected entering our solar system from beyond it, and like the interstellar visitors before it, it has proven to have its own set of peculiarities.
Chemistry Adds to the Broader Picture
Every interstellar object provides another opportunity to compare our own solar system with planetary systems elsewhere in the galaxy. The unusual composition of 3I/ATLAS contributes yet another data point to scientists’ evolving understanding of how planets, comets, and other small bodies come together around distant stars.
The Published Study
The research appears in The Astrophysical Journal Letters. The paper is titled “CH3OH and HCN in Interstellar Comet 3I/ATLAS Mapped with the ALMA Atacama Compact Array: Distinct Outgassing Behaviors and a Remarkably High CH3OH/HCN Production Rate Ratio.”
It offers a rare and detailed look at an object hailing from another star system entirely.
Source: sciencedaily.com
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