Interstellar Comet 3I/Atlas Has Another Surprise: It’s Full of Alcohol

Comet 3I/Atlas is now heading out of the solar system and into interstellar space, but scientists are still analyzing the data it left behind as it passed through our cosmic neighborhood. A new study, still under review, reveals a surprising detail: The comet is laden with alcohol.

Observations from the ALMA telescope in Chile's Atacama Desert show that the coma of this celestial object is heavily enriched in methanol, a type of alcohol common in fuels and solvents. Although methanol is commonly found in comets in the solar system, 3I/Atlas contained up to four times the typical amount.

According to the study, available at arXiv, 3I/Atlas is the second most methanol-rich comet ever measured, behind only the unusual C/2016 R2, discovered 10 years ago. Parallel investigations have also detected high abundances of other organic compounds, such as carbon dioxide, iron, and nitrogen, reinforcing the idea that this object has an out-of-the-ordinary composition.

The combination of excess methanol, a carbon dioxide-dominated coma, and other atypical chemical ratios supports the hypothesis that 3I/Atlas formed in an environment that is colder, more irradiated, or chemically distinct from any region where comets in the solar system formed.

The paper also suggests that 3I/Atlas may belong to the category of hyperactive comets, bodies that produce more water vapor than their surface can justify. In these comets, some of the gas comes not from the nucleus but from ice grains that float in the coma and sublimate. The researchers propose that 3I/Atlas released methanol, water, and carbon dioxide from both the nucleus and these icy grains.

In this case, a significant fraction of methanol came from detached ices that sublimated during the comet's approach to the sun. This behavior fits with that of hyperactive comets and reinforces the idea that 3I/Atlas is a natural, extremely cold, and chemically complex object, further ruling out any speculation about an artificial origin.

Today, the comet is moving away from the solar system at 60 kilometers per second. It is only the third confirmed interstellar object in history, but astronomers expect that future searches with new, more advanced instruments will reveal many more.