Isotopes Trace Interstellar Visitor 3I/ATLAS to Ancient, Metal-Poor Disk

Astronomers using ESO's Very Large Telescope measured carbon and nitrogen isotope ratios in the interstellar comet 3I/ATLAS, finding carbon-12/carbon-13 ~151 and nitrogen-14/nitrogen-15 ~363. These values are higher than typical solar-system comets, suggesting formation in the cold outer disk around an older, metal-poor star, consistent with isotope-selective chemistry in such environments. The results, published online July 6, 2026 in Nature Astronomy, provide a rare glimpse into material from another planetary system and the efficiency of planetesimal formation around ancient stars.