A comet is sweeping across the solar system carrying a strange chemical recipe that could allow astronomers to scrutinize the worlds that might have formed around distant stars.
Astronomers studying interstellar comet 3I/ATLAS have detected two gases flowing from its icy surface: methanol (an alcohol molecule) and hydrogen cyanide (a compound made of hydrogen, carbon and nitrogen). They discovered them using a powerful network of radio telescopes in Chile called the Atacama Large Millimeter/submillimeter Array.
Comets release gases into space when sunlight warms the comet’s frozen surface. The ice turns directly into vapor and forms a hazy cloud called the coma around the comet’s head. By measuring the gas in this cloud, astronomers can figure out what ingredients are locked away in the comet’s ancient ice.
It wasn’t just the gases that caught the researchers’ attention, but also the balance between them. The comet is unusually rich in methanol compared to hydrogen cyanide—one of the highest ratios astronomers have measured in any comet.
This is important because comets retain the ingredients that were present when they formed, in the same gas and dust disks that make up planetary systems. Because 3I/ATLAS formed elsewhere entirely, its chemical composition gives us a rare glimpse into how another planetary system differs from our own.
Around the Sun, most comets form where water ice dominates. But chemical reactions in 3I/ATLAS suggest that its birth environment may have been favorable for the creation or preservation of methanol-rich ice. This could mean that its origin is colder or filled with stronger radiation.
Whatever the exact cause, the comet’s bizarre chemistry suggests that planet-forming disks can produce icy bodies very different from those in our solar system. If these compositions differ in different star systems, the starting chemistry of planets (and therefore the starting chemistry of life) could vary greatly across the galaxy.
“Observing 3I/ATLAS is like picking up a fingerprint from another solar system,” American University professor Nathan Ross said in a statement. “The details reveal its composition, which is filled with methanol, something we don’t typically see in comets in our solar system.”
The new study, led by Ross, is published in Astrophysical Journal Communications March 6th.
Comet 3I/ATLAS came from another part of the galaxy and was later ejected, possibly by gravitational jolts from a planet or a passing star, and then drifted through interstellar space for hundreds of millions of years. Scientists know of only two other interstellar visitors that have passed through our cosmic neighbor: ‘Oumuamua in 2017, which turned out not to be a comet, and Comet 2I/Borisov in 2019.
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The latest findings reinforce the idea that alien planetary systems may produce comets with different chemical fingerprints. Early observations from NASA’s James Webb Space Telescope showed that 3I/ATLAS’s halo contains unusually large amounts of carbon dioxide compared to water – another strange feature.
Astronomers tracked the interstellar comet for several months in 2025 as it moved toward the sun, just past the orbit of Mars before beginning its long journey away from the solar system. Because it was traveling at about 137,000 mph when it arrived, it was too fast for the sun’s gravity to catch it.
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