Interstellar object
An object passing through the Solar System that came from outside it, from the space between the stars.
Almost everything in the Solar System is bound to the Sun. An interstellar object is not: it arrives on a hyperbolic orbit, moving too fast for the Sun's gravity to hold it, and leaves again for good. Astronomers recognise one from its orbit, not its appearance; an eccentricity well above 1 and a high speed far from the Sun are the giveaway.
The first confirmed example, 1I/ʻOumuamua, was discovered in October 2017. It appeared elongated or flattened, showed no visible coma, yet accelerated slightly as if pushed by escaping gas. The second, 2I/Borisov, found in 2019, looked like an ordinary comet. A third, 3I/ATLAS, was discovered in July 2025 and was also comet-like. Such objects are thought to have been ejected from planetary systems around other stars, so they offer the only close look we can get at material from those systems.
No meteorite has been shown to be interstellar. A small fireball over the Pacific in 2014 has been claimed as interstellar, but the evidence is disputed. Laboratory researchers find tiny presolar grains, older than the Sun, inside chondrites such as Murchison, but those arrived as dust in the solar nebula, not as interstellar objects.
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