Interstellar Comet 3I/ATLAS Carries Frozen Clues From Ultra-Cold Star-Forming Realms

Astronomers using ALMA detected an exceptionally high abundance of deuterated water (HDO) in interstellar comet 3I/ATLAS—more than 30 times what’s typical in solar-system comets and over 40 times Earth's ocean water—indicating the comet formed in environments colder than about 30 Kelvin, far colder than the region that formed our solar system. The finding suggests interstellar comets carry preserved birth-region chemistry and underscores that planetary formation varies with local temperature and radiation across the galaxy.