Interstellar comet 3I/ATLAS is bursting with methanol

Space scientists analyzing the third confirmed interstellar object to visit our solar system have uncovered chemical characteristics that set the distant wanderer apart from local comets. The interstellar object originated in a distant corner of the Galaxy and zipped through our Solar System on its journey through space. While it was in our neck of the woods, humanity threw all its best observing power at the comet to find out as much about it as we could, while we had the chance, as it moved closer to the Sun and then on its onward passage to the edge of the Solar System.

ALMA Observations Reveal Exceptional Methanol Abundance

New observations captured by the Atacama Large Millimeter/submillimeter Array (ALMA), of which the U.S. National Science Foundation National Radio Astronomy Observatory (NSF NRAO) is a partner, show that the interstellar visitor contains an unusually large amount of methanol. In fact, its methanol abundance exceeds that seen in almost all known comets from our own solar system.

“Observing 3I/ATLAS is like taking a fingerprint from another solar system,” shares Nathan Roth, lead author on this research, “The details reveal what it’s made of, and it’s bursting with methanol in a way we just don’t usually see in comets in our own solar system.”

The research team used ALMA’s Atacama Compact Array in Chile to observe 3I/ATLAS on several dates in late 2025 as it moved closer to the Sun. As sunlight heated the comet’s icy surface, gas and dust escaped and created a bright cloud or coma around its core. By studying the molecules in this coma, astronomers could identify the chemical makeup of material carried by the comet. Because 3I/ATLAS originated outside our solar system, those measurements provide a rare opportunity to investigate how small icy bodies may form in another planetary system without traveling beyond our own.

The scientists concentrated on the faint submillimeter signatures of two molecules: methanol, a type of alcohol, and hydrogen cyanide, a nitrogen-bearing organic molecule commonly seen in comets. ALMA revealed that 3I/ATLAS contains an unusually high amount of methanol relative to hydrogen cyanide. On two observation dates, researchers measured methanol-to-HCN ratios of roughly 70 and 120, placing 3I/ATLAS among the most methanol-rich solar system comets ever studied.

Spectrograph Data Points to Extremely Cold Origins

While ALMA focused on submillimeter signatures, independent research led from the Canary Islands utilized a next-generation spectrograph to analyze the stream of charged particles leaving the comet as it moved away from the Sun. Dr. Lea Ferellec, a Research Fellow based in Northumbria’s School of Engineering, Physics and Mathematics, led a study looking at the charged particles streaming off 3I/ATLAS. The research was carried out with colleagues at the University of Edinburgh, and a paper entitled Ion abundances in the plasma tail of 3I/ATLAS show that it is N2-rich has been published in the leading astronomy research journal Monthly Notices of the Royal Astronomical Society.

Using WEAVE (the William Herschel Telescope Enhanced Area Velocity Explorer), a new-generation spectrograph on a powerful telescope in the Canary Islands, the team was able to identify five different charged molecules in this stream at once, something rarely achieved for a comet, let alone an object like this. By measuring how much dinitrogen gas was present compared to carbon monoxide, the researchers worked out that 3I/ATLAS formed somewhere extremely cold, likely colder than -240°C. This suggests it formed a long way from its home star, in the outer, icier edges of wherever its solar system took shape.

Speaking about the findings Dr. Ferellec said: “This object gives us a rare chance to study material that formed somewhere completely different to our own Solar System. Finding that it’s so rich in nitrogen tells us it likely formed in extremely cold conditions, far from its home star. Every one of these objects we study helps us understand a little more about how planets form around other stars.”

The team also looked at how the charged gases changed the further they travelled along 3I/ATLAS’s tail, which forms when plasma streaming from the Sun sweeps the object’s charged particles out behind it. This is the first time this level of detail has been captured for an object of this kind. Earlier observations with the James Webb Space Telescope had already found that 3I/ATLAS had a coma dominated by carbon dioxide while it was still far from the Sun, and the new measurements add abundant methanol and nitrogen to the growing list of unusual features in its chemical makeup.

Comparing the Three Interstellar Visitors

Astronomers place 3I/ATLAS in an exclusive category as the third interstellar object ever discovered. The first interstellar object ever discovered, ‘Oumuamua, was found by the same type of telescope, but the second, 2I/Borisov, was found by an amateur astronomer. 3I/ATLAS in particular was discovered by the ATLAS survey, which in summer 2025 alerted astronomers that there was an unknown object moving across the sky. After a few follow-up observations, researchers realized it was actually a moving object that originated beyond our own Solar System by looking at its orbit.

Some of our most powerful observatories—like the Hubble and James Webb space telescopes—caught a glimpse of 3I/ATLAS. Scientists were even able to point robotic spacecraft at Mars and Jupiter at the interstellar visitor, giving them a unique view of the strange body while it was too close to the Sun to observe from Earth. An ultraviolet image showing the coma around comet 3I/ATLAS was also captured on 9 October 2025 by NASA’s MAVEN spacecraft.

Cyrielle Opitom, an astronomer at the University of Edinburgh in the UK, co-led a study of comet 3I/ATLAS using the Very Large Telescope, one of the world’s finest observatories located under the dark skies of Chile’s Atacama Desert. Opitom explained that discoveries of Solar System comets and interstellar comets generally come from surveys, which are observatories that look at the whole sky on a regular basis to detect objects moving or changing.

Mini-Comets Within the Coma

ALMA’s high resolution for imaging also allowed astronomers to track how different molecules are released and travel away from the comet. The observations revealed a striking contrast between methanol and hydrogen cyanide. Hydrogen cyanide appears to originate mostly from the comet’s central body, or nucleus, while the high-resolution imaging helped uncover the broader spatial distribution of methanol throughout the coma as sunlight heated the icy surface.