Interstellar comet 3I/ATLAS has surprised astronomers again. New observations with the ALMA radio telescope have shown that the object contains an unusually high amount of methanol - an organic compound that is also found in comets from the Solar System, but in 3I/ATLAS it is in a significantly higher concentration.
In two observations, the ratio between methanol and hydrogen cyanide in the gas envelope around the comet was approximately 70 and 120. According to the research team, these values place 3I/ATLAS among the most methanol-rich comets studied so far.
„Observing 3I/ATLAS is like taking a fingerprint from another planetary system. "Its composition suggests that it contains methanol in amounts that we don't typically see in comets from our solar system," said Nathan Roth of American University, the study's lead author.The radio observations were made in late 2025, when solar heat activated the object's icy surface. In addition to gases from the nucleus, scientists have also detected small ice grains in the coma - the glowing shell around the comet - which also emit methanol. This behavior makes it possible to study not only the nucleus itself, but also the material that is released from it as it approaches the Sun.
Comet with a chemical composition different from the known
ALMA is not the only instrument to detect unusual features of 3I/ATLAS. Observations with the Institute of Radio Astronomy's 30-meter telescope in the millimetre range showed a lower content of hydrogen cyanide and an unusually low rate of gas escape from the coma.
This could mean that the gas flow is driven primarily by heavier molecules such as carbon dioxide, rather than water vapour. Another possibility is that the water is released by evaporation of ice particles around the nucleus, rather than directly from its surface.
Studies with the William Herschel telescope add another feature. A large amount of molecular nitrogen has been found in the object's plasma tail. According to the team, this points to formation at extremely low temperatures, far from the star around which the comet originally formed.
The data fit in with earlier results from the James Webb Space Telescope. The telescope's spectrograph detected about 30 times more deuterium - a heavy isotope of hydrogen - than typical comets from the Solar System. The isotopic ratios point to an old, heavy-element-poor star system, on the outskirts of which 3I/ATLAS likely formed.
No confirmation of artificial origin
3I/ATLAS was discovered on July 1, 2025, and is only the third confirmed interstellar object after 1I/Oumuamua and 2I/Borisov. It passed through the Solar System on a hyperbolic trajectory and is now moving away from the Sun.
Its unusual chemical composition and behavior have led to speculation of artificial origin. However, scientific observations have so far found no evidence of a motor, a controlled trajectory, or a technological signal. The search for radio signals that could be linked to extraterrestrial technology has yielded no results.
The most supported explanation from observations remains that 3I/ATLAS is a natural comet from another planetary system. It is the differences in its composition - high levels of methanol, nitrogen and deuterium - that make the object valuable to astronomers: it allows for the first time to study in detail material that formed around another star.
Source: ScienceDaily