Imagine a hidden planet within Earth, buried hundreds of kilometers beneath our feet. This discovery is not science fiction, ...

The hypothesis posits that a budding planet (referred to as Theia) crashed into proto-Earth billions of years ago, throwing large amounts of material into space and giving rise to our Moon.

Thus, the fragments of Theia now found in Earth close a many-centuries-long puzzle over the origin of our moon and give voice to our unique geological history.

Relics of an ancient planet might be hiding under our feet, according to new research. Some scientists believe that a “protoplanet” named Theia collided with Earth some 4.5 billion years ago.

It’s generally thought that Earth did live through an apocalypse of planetary proportions about 4.5 billion years ago, when a Mars-sized planet named Theia slammed into it.

A planet called Theia collided with Earth, creating the Moon. Large, dense remnants of Theia exist deep within Earth's mantle. Computer models support the idea that these remnants are from Theia ...

Theia, an ancient planet, collided with Earth to form the moon, scientists believe. A new study suggests Theia could have also formed mysterious blobs called large low-velocity provinces, or LLVPs.

Scientists think a planet may have crashed into Earth 4.5 billion years ago, creating the moon. This alien planet, Theia, was thought to have completely disappeared in the collision.

Editor's Note: This story was updated at 1:50 p.m. ET to properly credit Edward Belbruno and Richard Gott with the idea that a planet like Theia might have impacted Earth to form the moon.