ALMA measured high methanol-to-hydrogen-cyanide ratios in interstellar comet 3I/ATLAS, according to observations made with the Atacama Large Millimeter/submillimeter Array. The National Radio Astronomy Observatory (NRAO) reports ratios of about 70 and 120 on two observing dates in late 2025.

The observations also indicate that methanol was released from two locations: directly from the comet’s nucleus and from icy particles in the surrounding coma. Hydrogen cyanide, by contrast, appeared to come primarily from the nucleus.

NRAO describes the measured ratios as placing 3I/ATLAS among the most methanol-rich comets studied in the Solar System. The release does not provide the full comparison sample or absolute production rates, so the reported result is specifically a comparison of methanol with HCN rather than a measurement of the total amount of methanol in the comet.

That combination gives astronomers more than a detection of methanol. It provides a view of how different molecules were distributed and released as the comet approached the Sun.

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What ALMA measured

3I/ATLAS is described by NRAO as the third confirmed object observed passing through the Solar System from interstellar space, after 1I/’Oumuamua and 2I/Borisov. Unlike comets formed around the Sun, it provides an opportunity to study material that originated in another planetary system.

Astronomers used ALMA’s Atacama Compact Array in Chile to observe the object on multiple dates in late 2025, while solar heating was causing it to release gas and dust. This activity produced a coma: the cloud of gas and dust surrounding a comet’s nucleus when volatile material is released as the object warms.

The observations focused on molecular signatures from methanol, written chemically as CH₃OH, and hydrogen cyanide, or HCN. Molecules emit or absorb radiation at characteristic frequencies. Radio and submillimeter telescopes can use those spectral fingerprints to identify molecules and estimate how their emission is distributed around an object.

The key result was the methanol-to-HCN ratio. The measured values were about 70 and 120 on two observing dates. A molecular ratio compares the relative amount of one detected molecule with another; it is not the same as an absolute measurement of how much methanol the entire comet contains.

NRAO says these values place 3I/ATLAS among the most methanol-rich comets studied in the Solar System. The release does not provide the measurement uncertainties, absolute production rates or the complete comparison sample behind that comparison.

Methanol is an alcohol in the chemical sense. In this astronomical context, however, its detection describes the comet’s molecular composition and outgassing; it is not evidence that the object contains drinkable or biologically relevant alcohol.

Two sources of methanol

ALMA’s usefulness here was not limited to detecting molecular emission. As an interferometric observatory operating at millimetre and submillimetre wavelengths, it can also help map where emission is concentrated and examine how gas moves away from an astronomical object.

The spatial and motion analysis described by NRAO suggests that methanol came from both the nucleus and icy grains suspended in the coma. As these grains moved closer to the Sun, sunlight warmed them. Ice in the grains then turned into gas, releasing methanol into the surrounding coma.

The release compares these icy grains with small comets. That comparison reflects the observation that the grains warm and release methanol as they approach the Sun.

HCN showed a different pattern. NRAO says it appeared to originate primarily from the nucleus. The contrast between the two molecules indicates that the coma was not chemically uniform and that different compounds were being supplied through different physical processes.

Earlier James Webb Space Telescope observations found that 3I/ATLAS had a coma dominated by carbon dioxide when it was farther from the Sun. The ALMA observations therefore add a later, more detailed view of molecular activity as solar heating changed the comet’s coma.

Why this matters for comet formation

The measurements provide an indirect chemical comparison between an object from outside the Solar System and comets formed around the Sun. The unusually high methanol-to-HCN ratios may indicate that the icy material in 3I/ATLAS formed under, or later experienced, conditions different from those associated with many Solar System comets.

The observations do not identify which conditions were responsible. The supplied release also does not establish whether the measured ratios reflect the comet’s original formation environment, later changes during its journey, or both.

The different source regions may help astronomers assess how active outgassing affects the molecules detected around the comet. However, the observations do not by themselves separate the present coma activity from the untouched bulk composition of the nucleus.

With only three confirmed interstellar objects observed so far, every comparison is necessarily limited. A single object can show that a chemical composition is possible among interstellar visitors, but it cannot establish what is typical of that population.

Limits and what to watch

The result is based on one interstellar comet observed on multiple dates during its approach to the Sun. The measured composition therefore describes its active outgassing state at those times, not necessarily the untouched composition of the entire nucleus.

The NRAO material is an institutional research news release rather than the underlying research paper. It does not provide the study’s calibration details, statistical uncertainties, detailed modelling methods, authorship or publication status. It also summarises the comparison with Solar System comets without listing the comparison objects or defining the full dataset.

The source describes the different origins of methanol and HCN as an interpretation of the spatial and motion data, but the supplied information does not include the underlying model details. The specific formation conditions that produced the high methanol-to-HCN ratios remain unknown.

Further observations of 3I/ATLAS and future interstellar objects could show whether methanol-rich chemistry is unusual for interstellar comets generally or whether it reflects a broader population. Additional analysis may also clarify how the comet’s formation environment and its warming history produced the observed molecular ratios and icy-grain outgassing.

Sources