Comet 3I/ATLAS, an object from another star that was found speeding through our solar system last summer, is now fading from telescopic view as it retreats back to interstellar space. But it continues to offer lessons about its faraway origins—and, consequently, to demonstrate how special our solar system may be.
Astronomers caught a glimpse of 3I/ATLAS just days after the icy comet made its closest approach to the sun in late October 2025. With the telescopes of the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, they used radio waves of light to study the starlight-warmed material the comet was venting into space. The spectroscopic results showed way more exotic, “heavy” water than would be expected for a comet from our own solar system, according to research
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