Astronomers have confirmed the discovery of 3I/ATLAS, an interstellar comet now racing through the solar system. The object, first detected on 1 July by the NASA-funded Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope in Rio Hurtado, Chile, was formally designated C/2025 N1 (ATLAS) and assigned the interstellar label 3I by the International Astronomical Union’s Minor Planet Center after independent observations by observatories worldwide and verification from the European Space Agency. Rough analyses indicate the comet spans roughly 10 to 30 kilometres and is travelling at about 60 kilometres per second—far too fast to be captured by the Sun’s gravity. At discovery it lay just beyond Jupiter’s orbit, some 420 million miles from Earth, and early imaging already shows faint signs of a coma and tail, confirming cometary activity. Trajectory calculations show 3I/ATLAS will swing inside the orbit of Mars on 30 October, passing within 1.4 astronomical units of the Sun, before reaching its nearest point to Earth in mid-December at more than 1.6 AU—well outside any impact zone. The comet should remain observable with ground-based telescopes until September, disappear behind the Sun, and reappear for renewed study in December. 3I/ATLAS is only the third confirmed interstellar object, following ʻOumuamua in 2017 and comet Borisov in 2019. Preliminary modelling by University of Oxford researchers suggests it may have originated in the Milky Way’s ancient thick disk around a star at least eight billion years old, potentially making it the oldest comet ever observed. Large facilities, including the forthcoming Vera C. Rubin Observatory, are preparing intensive campaigns to analyse the visitor’s composition and glean fresh insights into planet-forming processes beyond our solar system.