> FILE INDEX_

Despite having craters that span hundreds of miles wide, no crater on the Moon is deeper than about 2.5 to 3 miles. It behaves as if an unbreakable, armored inner layer prevents meteors from penetrating deeper.

Two prominent Soviet scientists published a formal paper arguing that the Moon is not a natural satellite, but a hollowed-out, armored artificial space station parked in Earth's orbit by an ancient, advanced intelligence.

Theory that an advanced ancient civilization left ruins and technologies scattered throughout the solar system billions of years ago.

Theories about advanced lost civilizations that existed in prehistoric times and were destroyed by cataclysms.