Theia (/'θeɪ.a/) is a hypothetical planet that is theorized to have collided with Earth over four billion years ago and formed the Moon. This is referred to as the giant impact hypothesis.

The name derives from Greek mythology, as Theia was the Titan who gave birth to the Moon goddess Selene.

Hypothetical Solar System planets | MoonEarth | Historical geology

Theia (planet) | Theia (Planet) | Theia (planeet) | テイア (惑星) | Theia (planeta) | Theia (hành tinh)