Astronomers have detected high levels of methanol and hydrogen cyanide in the interstellar comet 3I/ATLAS, marking the first such finding in an object from beyond our solar system. These carbon-rich compounds, essential for prebiotic chemistry, appear in greater quantities than in typical solar system comets. The discovery highlights differences in this third interstellar visitor's composition.
The comet 3I/ATLAS, only the third confirmed interstellar object to enter our solar system, has revealed unusual chemical activity as it approaches the sun. Unlike comets from our galactic neighborhood, it produces carbon-rich compounds at elevated rates. Observations show an envelope of water vapor and gas forming rapidly around it, with notably higher carbon dioxide levels than standard solar system comets. Its light spectrum is redder, suggesting distinct surface chemistry, and gas release began at a greater distance from the sun—possibly indicating it has not neared a star closely for hundreds of millions of years.
Using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, Martin Cordiner at NASA's Goddard Space Flight Center and his team identified significant hydrogen cyanide near the comet's rocky core, at rates of 0.25 to 0.5 kilograms per second. Methanol, however, dominates, emanating from both the core and the coma—the dusty tail extending kilometers away—at about 40 kilograms per second. This constitutes roughly 8 percent of the comet's total vapor, compared to 2 percent in typical comets.
"Molecules like hydrogen cyanide and methanol are at trace abundances and not the dominant constituents of our own comets," Cordiner noted. "Here we see that, actually, in this alien comet they’re very abundant."
These variations imply a non-uniform nucleus, offering clues to the comet's formation. Methanol serves as a crucial precursor for complex life-essential molecules. As Cordiner explained, "It seems really chemically implausible that you could go on a path to very high chemical complexity without producing methanol."
Josep Trigo-Rodríguez at Spain's Institute of Space Sciences suggests the methanol in the coma may signal a metal-rich composition, where solar heat mobilizes liquid water to react with iron compounds, generating the molecule. This could reveal more about interstellar chemistry and life's building blocks.