Interstellar comet 3I/ATLAS is bursting with methanol
New CapabilitiesALMA finds the third interstellar visitor is packed with methanol, a chemical signature unlike most solar system comets
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Overview
Updated 1 hour ago3I/ATLAS is only the third object ever confirmed to pass through our solar system from another star system. New ALMA observations show it is one of the most methanol-rich comets ever measured, with alcohol-to-hydrogen-cyanide ratios of roughly 70 and 120.
The methanol is a chemical fingerprint of how another planetary system made its icy bodies. The data also show the alcohol outgasses from tiny grains in the coma, not just the comet's core — the first time such behavior has been traced in an interstellar object.
Why it matters
Every interstellar comet is a direct sample of another star system. 3I/ATLAS shows they can be chemically unlike anything in ours.
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A 66-antenna radio array in Chile's Atacama Desert that detected methanol and hydrogen cyanide in 3I/ATLAS.
The U.S. partner in ALMA whose researchers led the methanol analysis of 3I/ATLAS.
Timeline
August 2025 September 2026
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Methanol-rich chemistry reported
Today Research publicationResearchers publish methanol-to-HCN ratios of about 70 and 120, ranking 3I/ATLAS among the most methanol-rich comets ever measured.
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Observation campaign closes
ObservationThe final methanol run places 3I/ATLAS at 1.7 astronomical units from the Sun, with methanol production rising sharply toward perihelion.
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Hydrogen cyanide detected in the coma
ObservationALMA measures HCN, whose production traces direct sublimation from the comet's nucleus.
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ALMA begins methanol observations of 3I/ATLAS
ObservationThe Atacama Compact Array first detects methanol in 3I/ATLAS while the comet sits 2.6 astronomical units from the Sun.
Historical Context
3 moments from history that rhyme with this story — and how they unfolded.
Comet C/2016 R2 (Pan-STARRS)
C/2016 R2 is a solar system comet from the Oort Cloud distinguished by extraordinary carbon monoxide and ion-driven chemistry. It held the highest methanol-to-HCN ratio measured in any comet until 3I/ATLAS.
It became a test case for how comet chemistry varies with formation conditions.
It remains the sole local reference point for extreme methanol enrichment.
The only comet with a higher methanol-to-HCN ratio than 3I/ATLAS is this local oddball, sharpening the view that 3I/ATLAS formed under unusual conditions.
1I/'Oumuamua (2017)
The Pan-STARRS telescope spotted a fast-moving object on October 19, 2017, later named 1I/'Oumuamua — Hawaiian for "scout." It was the first object confirmed to come from beyond our solar system, with an elongated shape and no visible coma.
Its odd acceleration and absence of outgassing sparked years of debate over whether it was an asteroid, a comet, or something stranger.
It broke the assumption that comets must look like comets and established a naming system for interstellar objects.
1I/'Oumuamua showed interstellar objects can defy easy classification; 3I/ATLAS now shows they can also be chemically extreme.
2I/Borisov (2019)
Amateur astronomer Gennady Borisov found the second interstellar object, 2I/Borisov, on August 30, 2019. Unlike 'Oumuamua, it developed a proper coma, and telescopes detected hydrogen cyanide and carbon monoxide.
Its chemistry resembled typical solar system comets, easing fears that interstellar objects were fundamentally strange.
It set a baseline expectation that interstellar comets behave like local ones — a baseline 3I/ATLAS now challenges.
The extreme methanol enrichment in 3I/ATLAS breaks the pattern Borisov established.
