3I/ATLAS shows methanol production increasing with proximity to Sun

Observations of the interstellar object 3I/ATLAS by the Atacama Large Millimeter/Submillimeter Array (ALMA) in 2025 revealed measurable production of methanol (CH3OH) and hydrogen cyanide (HCN) as the object approached the Sun.

Methanol was detected on August 28, September 18 and 22, and October 1, while hydrogen cyanide was detected on September 12 and 15.

Pre-perihelion distances ranged between 2.6 and 1.7 astronomical units. Methanol production was enhanced in the sunward direction and also originated from the gas plume, while hydrogen cyanide came primarily from the nucleus.

Production rates of methanol increased with decreasing heliocentric distance, showing a power-law dependence of -5.2 ± 0.6.

Harvard professor Avi Loeb reported that 3I/ATLAS exhibits one of the highest methanol-to-hydrogen-cyanide ratios observed in any comet, second only to C/2016 R2 discovered by PanSTARRS.

Methanol and Hydrogen Cyanide production in 3I/ATLAS increases near the Sun

Methanol detection in 3I/ATLAS

Previous observations have detected methanol in various astronomical environments, including a large cloud near a newly formed star detected by the MERLIN array of radio telescopes at the Jodrell Bank Observatory in 2006, and in a planet-forming disk around the young star TW Hydrae detected by ALMA in 2016.

In 3I/ATLAS, ALMA identified methanol emissions that increased as the object moved closer to the Sun.

The production of methanol from the gas plume, in addition to the nucleus, suggests multiple sources of release for this molecule in interstellar objects.

The power-law relationship indicates that methanol production is strongly dependent on the heliocentric distance, according to Avi Loeb.

Hydrogen Cyanide observations

Hydrogen cyanide was also detected in 3I/ATLAS but showed a different distribution pattern compared with methanol.

Observations indicated that hydrogen cyanide production originated primarily from the nucleus and was depleted in the sunward direction.

Hydrogen cyanide has been previously measured in Titan’s atmosphere by instruments on the Cassini and Voyager missions, as well as through Earth-based observations.

In chemical terms, hydrogen cyanide can serve as a precursor for the formation of amino acids and nucleic acid bases, although its concentrations vary in biological and environmental contexts.

In 3I/ATLAS, hydrogen cyanide was consistently lower relative to methanol, resulting in an unusually high methanol-to-hydrogen-cyanide ratio.

Significance of Methanol and Hydrogen Cyanide

Methanol‍‌‍‍‌‍‌‍‍‌ is essential to create molecules such as amino acids and sugars, which are very important in the chemistry of life.

Some microorganisms, for instance, methylotrophic bacteria, and certain yeasts are capable of using methanol as their only source of energy, and they achieve this by means of an enzyme such as methanol dehydrogenase.

Besides that, methanol is generated in a similar way in nature in plants by the cell wall parts which are being broken and it also can be a signaling molecule.

Hydrogen cyanide, while very poisonous if it is in high concentrations, can still be a signaling compound in plants, animals, and microorganisms.

Being involved in the formation of complex organic molecules, it is released by bacteria and plants as a part of their metabolism.

Besides that, hydrogen cyanide has been utilized as a chemical weapon in the ‍‌‍‍‌‍‌‍‍‌past.

Production trends in 3I/ATLAS

The ALMA observations show that methanol production in 3I/ATLAS increased consistently as the object approached the Sun, while hydrogen cyanide remained primarily associated with the nucleus, as per Avi Loeb.

The large methanol-to-hydrogen-cyanide ratio observed in this interstellar object is comparable to the anomalous comet C/2016 R2.

These measurements provide data on the chemical composition of interstellar objects and the behavior of volatile molecules under varying heliocentric distances.