An interstellar comet that blazed past the sun and swung by Earth last year could be nearly three times older than our solar system and is unlike anything ever before seen in our cosmic backyard, astronomers said Monday.The comet 3I/ATLAS is just the third visitor from beyond our solar system that humanity has ever observed, its unusual brightness offering scientists an unprecedented opportunity to study something that came from elsewhere in the galaxy.After being spotted in July last year, the space rock prompted excitement online, with one prominent Harvard researcher speculating it could be an alien spacecraft — a theory that NASA shot down.AdvertisementAdvertisementNow, observations by the world’s most powerful telescopes are revealing more about the unique comet.According to a new study published Monday in the journal Nature, 3I/ATLAS could be up to 12 million years old. Our solar system is believed to have formed around 4.5 billion years ago.Lead study author Martin Cordiner of NASA’s Goddard Space Flight Center told AFP that “maybe it’s the oldest object to have been observed in our solar system.”This image, provided by NASA, shows the interstellar comet 3I/Atlas captured by the Hubble Space Telescope on Nov. 30, 2025, about 178 million miles from Earth. / Credit: NASA, ESA, STScI, D. Jewitt (UCLA), M.-T. Hui (Shanghai Astronomical Observatory), J. DePasquale (STScI) via APHowever, there could be “edge-case scenarios” that offer other explanations for the comet’s unusual chemical composition, he added.AdvertisementAdvertisementThe new research is based on the comet’s ratio of chemical elements, called isotopes, detected by the James Webb space telescope and the ALMA observatory in Chile.These measurements “reveal an elemental composition unlike any solar system body,” the study said.Possible relic from “cosmic noon”Compared to comets in our solar system, 3I/ATLAS has 10 times more deuterium, a type of hydrogen commonly seen in heavy water, according to the study.”That high abundance of heavy water can only really happen, according to our understanding of astrochemistry, in a very cold environment,” Cordiner explained.AdvertisementAdvertisementThis means the comet is also likely among the coldest objects ever seen in our solar system, the isotopic evidence suggesting it formed in an environment that was minus 243 degrees Celsius.Exactly where this comet came from within the Milky Way remains a mystery.But these interstellar objects are thought to form in a similar way to the comets in our Solar System — being flung out during the violent formation of a new planet.Untethered to any star, 3I/ATLAS likely spent billions of years on “vast unimaginable trajectories around our galaxy,” Cordiner said.The scientists also detected a strange lack of chemical enrichment on the comet, which suggests it formed relatively close to stars being born.AdvertisementAdvertisementIt could even be a “relic” from an era called “cosmic noon” when many stars were forming around 10 billion years ago, Cordiner said.The previous interstellar objects — 1I/’Oumuamua, which was spotted in 2017, followed by 2I/Borisov in 2019 — were not bright enough to gather …
