3I/ATLAS was found in the ring on 1 July 2025 by the ATLAS survey telescope in Chile: a dot of magnitude 17, far too faint for the eye. Within a day its path showed something new. It was not going round the Sun. It was passing through.
Here it is on its best night from where you are, about as bright as it ever got: a fuzzy spot in a small telescope. It is a comet, ice turning to gas off a core a few kilometres across at most — and, like Borisov in 2019, one made round another star.
The line is four weeks of its path, a night at a time. It barely bends. 3I swung past the Sun at 68 km/s, far too fast to be caught, and the Sun's pull turned its course by only 19°.
From outside, to scale. The rings are the orbits of Mercury, Venus, Earth and Mars; the long line is 3I's path. It is open: in once, past the Sun the opposite way round to every planet, bent just 19°, and out for good.
Edge-on, the rings flatten into the plane of the planets, and 3I's path is tilted 5° to it. It came in from above, crossed down through the plane on 9 Dec 2025, 6 weeks after its closest pass of the Sun, and leaves below.
Run four months. 3I passes close by Mars, sweeps past the Sun on its far side from us, hidden in the glare, then climbs out. The line from the Earth through it lands where the map showed it among the stars.
The dashed curve is escape speed: any faster, that far from the Sun, and nothing brings you back. Halley runs just under it, so it returns. 3I is far over it, still doing 61 km/s at Jupiter's distance. It came in at 58, and it leaves at 58.
The ring is where it came from: its path traced back, near the Milky Way's centre. ʻOumuamua in 2017 and Borisov in 2019 came in at 26 and 32 km/s. 3I's 58 hints at a long life among the stars — it may be older than the Sun.
And the ring is where it is going, in Gemini. It is already past Saturn's distance, too faint for all but the largest telescopes, and the Sun will never call it back. Three visitors in eight years means many more pass unseen; newer, deeper surveys should find them.