Astronomers utilizing the Atacama Large Millimeter/Submillimeter Array (ALMA) have made a groundbreaking discovery of hydrogen cyanide, a nitrogen-rich organic molecule commonly associated with comets, and remarkably elevated levels of methanol, an organic compound linked to prebiotic chemistry, in the interstellar comet 3I/ATLAS.
Artist’s impression as 3I/ATLAS approaches the Sun. Methanol gas appears in blue, and hydrogen cyanide in orange. Image credit: NSF / AUI / NRAO / M.Weiss.
“Observing 3I/ATLAS is like capturing a fingerprint from an entirely different solar system,” said Nathan Ross, a professor at American University.
“A detailed analysis reveals its composition, showing methanol emissions that are atypical for comets in our own solar system.”
Professor Ross and his team employed ALMA’s Atacama Compact Array in Chile to monitor 3I/ATLAS as it neared the Sun.
As sunlight warmed its icy exterior, this interstellar visitor released gas and dust, forming a surrounding coma.
By studying the coma, astronomers unveiled chemical signatures indicative of its materials.
They concentrated on the subtle submillimeter signatures of two molecules: methanol and hydrogen cyanide.
ALMA’s findings indicated that 3I/ATLAS is extraordinarily high in methanol compared to hydrogen cyanide, significantly surpassing levels typically observed in comets from our solar system.
On the two observation days, researchers recorded methanol to hydrogen cyanide ratios of approximately 70 and 120, positioning this object as one of the most methanol-rich comets ever examined.
These observations imply that the icy components of 3I/ATLAS were formed under conditions markedly different from those that motivate the formation of most comets within our solar system.
ALMA’s precision also allowed the team to analyze the movement of different molecules as they emanated from the comet, revealing unexpected disparities between methanol and hydrogen cyanide.
Notably, most hydrogen cyanide appears to originate from the comet’s core, which is an unusual characteristic for comets from our solar system.
Conversely, methanol is believed to originate from both the core and the comatose ice particles.
These minuscule ice particles behave like tiny comets; as the object approaches the Sun, the ice sublimates, releasing methanol gas.
While this behavior has been observed in various solar system comets, this is the first time the dynamics of outgassing have been documented with such detail in an interstellar object.
“The methanol to hydrogen cyanide ratio measured for 3I/ATLAS is among the highest observed in any comet, exceeded only by the anomalous Solar System comet C/2016 R2 (Pan-STARRS),” the authors noted.
Further findings will be published in the Astrophysical Journal.
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Nathan X. Ross et al. 2026. CH3OH and HCN of interstellar comet 3I/ATLAS mapped with the ALMA Atacama Compact Array: unique outgassing behavior and significantly elevated CH3OH/HCN production rate ratio. APJL 999, L32; doi: 10.3847/2041-8213/ae433b
Source: www.sci.news
