Theia

Theia (Greek: Θεία) is a hypothetical ancient planet that, according to the giant-impact hypothesis, collided with the early Earth around 4.5 billion years ago. This catastrophic event is believed to have resulted in the formation of the Moon from the debris ejected into Earth's orbit. The name "Theia" is derived from the Greek titaness Theia, the mother of Selene, the goddess of the Moon. In Hebrew, Theia is transliterated as תיאה. In Latin, it is Theia, and in French, it is Théia. The giant-impact hypothesis suggests that Theia was roughly the size of Mars and that its collision with Earth was a glancing blow, leading to the accretion of the Moon. This theory explains several observations, such as the Moon's relatively small iron core and its similar isotopic composition to Earth's mantle, indicating a shared origin.