The interstellar comet 3I/ATLAS releases carbon-rich compounds at a higher rate than most comets in the solar system, including methanol. This compound plays a crucial role in prebiotic chemistry and is not commonly found in other interstellar objects.

Having made only three known visits to our solar system, 3I/ATLAS stands apart from comets found in our galactic neighborhood. While approaching the Sun, it developed a crust of water vapor and gas, containing significantly more carbon dioxide than typically found in Solar System comets. Additionally, the comet’s light appeared unusually red, hinting at atypical surface chemistry, and it began emitting gas well before reaching the Sun. This could indicate that it has not approached another star in hundreds of millions of years, or possibly since leaving its home system.

Recently, Martin Cordiner and a team using the Atacama Large Millimeter/Submillimeter Array (ALMA) in Chile discovered that 3I/ATLAS generates significant amounts of hydrogen cyanide gas, as well as even larger quantities of gaseous methanol. “Hydrogen cyanide and methanol are usually found in trace amounts and aren’t dominant components in our comets,” explained Cordiner. “However, they appear to be notably abundant in this alien comet.”

Cordiner’s research team observed that the hydrogen cyanide comes from near the comet’s core, producing around a quarter to half a kilogram per second. Methanol was also found in the core, indicating large quantities are produced even within the comet’s coma, which is the extensive trail of dust and gas extending miles away from the comet itself.

Methanol is emitted at approximately 40 kilograms per second, significantly more than hydrogen cyanide, which represents about 8 percent of the total vapor released (compared to roughly 2 percent from typical solar system comets). The different locations of these two molecules suggest that the comet’s core may not be uniform, which could provide insights into how comets are formed, according to Cordiner.

Cordiner noted that, while methanol is a relatively straightforward carbon-based compound, it plays an essential role in forming more complex molecules critical for life. Its production appears to be high when chemical reactions producing these larger molecules occur. “Chemically, it seems unlikely that we can progress toward highly complex substances without generating methanol,” Cordiner said.

Josep Trigo-Rodriguez and colleagues from Spain’s Institute of Space Sciences suggested that comets with substantial iron and metals are likely to produce considerable methanol as well. The presence of liquid water heated by the Sun could permeate the comet’s core and engage in chemical reactions with its iron, resulting in methanol production. Thus, discovering methanol in the coma might indicate a metal-rich composition of the comet, he adds.