Astronomers have confirmed that a fast-moving object spotted on 1 July has come from outside our planetary neighbourhood. The Minor Planet Center has formally designated the body comet 3I/ATLAS (C/2025 N1), making it only the third interstellar object ever recorded, after ‘Oumuamua in 2017 and comet 2I/Borisov in 2019. The object was first picked up by NASA’s Asteroid Terrestrial-impact Last Alert System telescope in Rio Hurtado, Chile, and quickly verified through observations coordinated by the European Space Agency. Travelling at about 60 kilometres per second, 3I/ATLAS is estimated to be 10 to 25 kilometres across. It is currently near Jupiter, roughly 670 million kilometres from the Sun, and is expected to reach perihelion on 30 October at 1.4 astronomical units—just inside Mars’s orbit—while never approaching Earth more closely than 1.6 AU. Its strongly hyperbolic trajectory shows the Sun’s gravity cannot capture it, confirming its origin in another star system. Pre-discovery images from instruments such as the Vera C. Rubin Observatory illustrate how newer telescopes are improving the chances of detecting transient interstellar visitors. Early spectroscopy points to abundant water ice and organic material. Using Gaia spacecraft data, an Oxford-led team argues the comet probably emerged from the Milky Way’s thick disk and could be more than 7 billion years old, potentially the oldest comet ever observed. Researchers worldwide plan intensive monitoring until the comet disappears behind the Sun in September and again after it re-emerges in December, hoping to glean insights into the composition of planetary systems beyond our own.