3I/ATLAS, only the third comet confirmed to come from beyond our solar system, carries water with a heavy-hydrogen ratio 40 times higher than Earth's oceans, evidence it formed somewhere far colder than our own star system ever was

3I/ATLAS, only the third comet confirmed to come from beyond our solar system, carries water with a heavy-hydrogen ratio 40 times higher than Earth's oceans, evidence it formed somewhere far colder than our own star system ever was

On 1 July 2025, a robotic sky survey in Rio Hurtado, Chile, called ATLAS flagged a faint point of light moving in a way nothing native to our solar system moves. Archived images later traced it back to 14 June 2025. Follow-up observations confirmed what the discovery team suspected: the object, since named 3I/ATLAS, was only the third comet ever confirmed to have arrived here from outside our solar system, after ‘Oumuamua in 2017 and Borisov in …