Astronomers employed the Atacama Large Millimeter/submillimeter Array (ALMA), installed in the Atacama desert at The spectral analysis identified significant amounts of methanol, a type of organic alcohol (CH₃OH), released by the object’s coma. Data collected between August and October 2025 show that 3I/ATLAS exhibits ratios of methanol to hydrogen cyanide (HCN) much higher than those found in most native Sistema Solar comets.
Comet 3I/ATLAS, the third object confirmed to originate from another star system, was discovered in July 2025 by the ATLAS surveillance system. Complementary Observações carried out with telescopes such as Hubble, Subaru and James Webb had already indicated chemical peculiarities, including the high presence of carbon dioxide in phases more distant from Sol. ALMA measurements have provided additional evidence about the unique composition of this interstellar visitor.
High proportions of alcohol methanol
The observations focused on the spectral lines of methanol and hydrocyanic hydrogen in the comet’s temporary atmosphere. In September 2025, methanol/HCN ratios reached values of approximately 124 on one date and 79 on another, numbers that place 3I/ATLAS among the most alcohol-enriched celestial objects ever characterized.
Comets from Sistema Solar have, on average, methanol about 26 times more abundant than HCN. The previous record belongs to comet C/2016 R2 (Pan-STARRS), with a proportion close to 280. 3I/ATLAS is positioned as the second richest in this organic compound.
Multiple sources of alcohol release
ALMA’s angular resolution made it possible to map the exact origin of molecular emissions. Hydrocyanic hydrogen emerges predominantly from the comet’s solid nucleus, a common pattern in solar comets.
Methanol, on the other hand, presents significant contributions from ice grains in the coma, located hundreds of kilometers from the core. Esses grains heated by solar radiation release alcohol in a similar way to small secondary comets.
Asymmetry in alcohol distribution
Methanol exhibits greater concentration on the illuminated side of the comet facing Sol. Já hydrocyanic hydrogen appears less abundant in this same region, suggesting differences in surface composition or selective sublimation effects.
Methanol production increased sharply as the object approached Sol. Esse behavior reinforces the thermal dependence on the release of volatile compounds such as alcohol.
Evidence of origin in a different environment
The high abundance of methanol alcohol suggests that the constituent material of 3I/ATLAS formed under chemical conditions different from those of primordial Sistema Solar. Dados previous James Webb had already detected excess carbon dioxide, completing the profile of differentiated organic composition.
Directly studying the chemistry of interstellar objects provides valuable information about comet and planet formation processes in other stellar systems. Methanol, a molecule associated with prebiotic pathways, expands the understanding of cosmic chemical diversity.
Continuous monitoring and intense activity
Several terrestrial and space observatories accompanied 3I/ATLAS during its passage through the Sistema Solar interior. Medições of other volatiles, including water, corroborate the progressive increase in activity as the comet received more solar energy.
The combination of these data sets confirms that 3I/ATLAS presents unusual gas release mechanisms, highlighting the abundant emission of alcohol at scales never before mapped in such detail.
Results published in a specialized journal
The team coordinated by Nathan Roth, from American University, detailed the findings in the publication The Astrophysical Journal Letters. The work emphasizes ALMA’s ability to capture molecular signatures of distant and active objects.
The authors compare the analysis to obtaining a unique chemical signature from another planetary system. The detection reinforces the importance of submillimeter instruments in studying interstellar visitors.