The visitor did not announce itself with a streak across the sky. It appeared as a faint moving point in four survey images, the kind of evidence that looks insignificant until its positions are fitted to an orbit. ATLAS recorded those images from Río Hurtado in Chile on 1 July 2025. The NASA-funded Asteroid Terrestrial-impact Last Alert System exists to search wide areas of sky for objects that could threaten Earth. This object was safely remote, but its path was far stranger than that of an ordinary asteroid. Within hours, the preliminary orbit was clearly hyperbolic. The object was moving too fast for the Sun to hold it. By the following day it had a formal identity: 3I/ATLAS, only the third confirmed interstellar object after 1I/ʻOumuamua and 2I/Borisov. The story then seemed to accelerate with the comet. It passed the Sun, disappeared into solar glare, re-emerged on the outbound leg and swept past Jupiter’s neighbourhood. Around 20 March 2026, less than nine months after discovery, its distance from the Sun again exceeded Jupiter’s average orbital radius. That crossing was not the end of the Solar System. It was, however, a clean marker in a one-way journey. 3I/ATLAS is not beginning a long ellipse that will bring it back in a century or a millennium. Its orbit is open. Four dots became an orbit The discovery sequence contained four exposures of a crowded field toward the Galactic centre. Between frames, one tiny point changed position. Astronomers measured those coordinates and sent the astrometry to the Minor Planet Center, the international clearing house for small-body observations. One photograph cannot establish an interstellar origin. An orbit must be fitted to positions measured at different times. Follow-up observatories quickly lengthened the arc, while searches through existing survey data found the comet in images taken