An interstellar object is a non-stellar astronomical object not in closed orbit around a stellar object. Interstellar refers to the space between stars. Such objects are so far away, that they are not locked to a star (or stellar object) through gravitation.

Interstellar objects usually travel through space on a more or less straight line. When near a star, they travel too fast to remain nearby. They pass near a given star only once, not in a repeating orbit. Typical interstellar objects are similar to asteroids and comets.

Spacecraft (e.g. Voyager 1) that escape our star system are usually not called interstellar objects because they are not natural.

Interstellar objects seen in our solar system

As of 2026, three interstellar objects have been observed transitioning our solar system.

1I/'Oumuamua transitioned in 2017
2I/Borisov transitioned in 2019
3I/Atlas transitioned in 2025