Astronomers using one of the world's most powerful radio telescope arrays have discovered that the interstellar comet 3I/ATLAS contains extraordinary levels of methanol compared with hydrogen cyanide, a chemical fingerprint unlike nearly anything observed in comets born in our own solar system. The findings, announced by the ALMA Observatory on March 8, suggest the comet formed under conditions vastly different from those that shaped familiar solar system objects.
The research team, led by Nathan Roth, a professor at American University, used ALMA's Atacama Compact Array in Chile to observe 3I/ATLAS multiple times in late 2025 as it drew closer to the Sun. On two separate observation dates, they measured methanol-to-hydrogen cyanide ratios of roughly 70 and 120, placing the comet among the most methanol-rich ever studied.
"Observing 3I/ATLAS is like taking a fingerprint from another solar system," Roth said. "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."
A Chemical Profile From Another Star System
3I/ATLAS, discovered in July 2025, is only the third confirmed interstellar object detected passing through our solar system, following 1I/'Oumuamua and 2I/Borisov. As sunlight heated the comet's icy surface, frozen material vaporized and formed a coma — a glowing halo of gas and dust — that allowed scientists to read its chemical composition through faint submillimeter signals.
The ALMA data revealed a striking contrast in how the two molecules escape the comet. Hydrogen cyanide appears to originate mainly from the nucleus, behavior typical of solar system comets. Methanol, however, is released both from the nucleus and from tiny icy grains drifting within the coma, which act as miniature comets themselves, releasing methanol gas as sunlight warms them.
Martin Cordiner, an astronomer at the Catholic University of America who also participated in observing the comet, told New Scientist that "molecules like cyanide and methanol present in trace amounts and are not the primary components of our own comets. Here, we observe that, in this foreign comet, they are quite abundant."
Building on Earlier Surprises:
The methanol findings add to an already unusual chemical portrait. Earlier observations with the James Webb Space Telescope had revealed that 3I/ATLAS possesses one of the highest ratios of carbon dioxide to water ever seen in a comet, hinting that it may have formed near the carbon dioxide ice line in its parent star's protoplanetary disk or been exposed to unusually high levels of radiation.
The measurements suggest that the icy material composing 3I/ATLAS was formed or processed under conditions fundamentally different from those in our solar system. For scientists, the comet represents a rare opportunity to study planetary chemistry from a distant and likely ancient star system — one potentially two to three times older than our own.
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