3I/ATLAS comet is bursting with alcohol, surprising astronomers
Comet 3I/ATLAS is well on its way back into deep space, but the famous cosmic visitor continues to fascinate astronomers. Since its discovery in July 2025, researchers have spent months observing and analyzing the icy rock to better understand its composition and behavior. 3I/ATLAS is only the third known interstellar object to pass through our neighborhood, meaning it contains a wealth of information about other regions of the galaxy.
âObserving 3I/ATLAS is like taking the fingerprint of another solar system,â said Nathan Roth, an astronomer at American University.
After reviewing readings collected in late 2025 with the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, Roth and his colleagues have new information to share about the comet. Everyone’s favorite interstellar space rock is full of alcohol and cyanide. Specifically, 3I/ATLAS contains a surprising combination of methanol and hydrogen cyanide (HCN). While the latter nitrogen-containing molecule is often seen in comets, methanol has surprised astronomers. During two observing sessions, Roth’s team measured methanol/HCN ratios of around 70 and 120, making 3I/ATLAS one of the most methanol-rich comets ever observed.
“It’s packed with methanol in a way that we don’t usually see in comets in our own solar system,” Roth said.
The data suggests that the icy rock originated in a very different environment than standard comet models. Before it approached our sun, the bright halo of dust and debris surrounding 3I/ATLAS, called a coma, was mostly carbon dioxide. As our sun began to heat it, 3I/ATLAS began releasing large amounts of methanol and HCN. Based on the way the molecules move away from the comet, the astronomers determined that although the HCN comes largely from the nucleus, the methanol disperses from the nucleus along with the ice particles in the coma. Although some comets in the Solar System have shown similar behavior, this is the first time scientists have observed the reactions in such detail in an interstellar visitor.
Although the exact birthplace of 3I/ATLAS will likely never be known, each new piece of information from the comet fills the void of a distant area of ââspace we may have never seen.
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