Science editor Anoushka Sinha discusses the discovery of interstellar comet 3I/ATLAS. In July 2025, the ATLAS telescope discovered a comet had entered our Solar System; the third interstellar object to ever be detected. The former two interstellar objects to enter our Solar System were 1I/’Oumuamua in 2017 and 2I/Borisov in 2019. It is therefore likely that the comet came from a stellar system which has more carbon dioxide than our own Solar System. The velocity of the comet also indicates that it is over seven billion years older than both the other interstellar comets and the Sun.