Season 2 focuses on places on Earth where aliens may have landed, tales of monsters and giants in different cultures, legendary ruins in Peru and underground extraterrestrial lairs.
In Season 3, experts visit a cemetery said to contain the body of an alien, examine an ancient Hindi scripture about a giant flying creature and look at evidence of aliens at holy sites.
Season 4 focuses on evidence suggesting that the Ancient Maya conspired with aliens, creatures rumoured to be alien life forms and links between geniuses and extraterrestrial activity.
Season 5 looks at the similarities in burial tombs from distant cultures, mysterious phenomena of the Nazca Lines and the story of a man who claims to have been taken aboard an alien ship.
Season 6 considers whether remote outposts could be the earthly homes of aliens, hilltop spirits could have been extraterrestrials and alleged stargates have brought ancient aliens to Earth.
Season 7 focuses on an ancient monolith said to have represented an alien being, people who claim they met aliens while on the brink of death and secret conduits to other worlds.
Season 8 investigates ancient accounts of robots, people throughout history who have tapped into dark powers, accounts of modern-day alien abductees and the emergence of crop circles.
Season 9 shines a light on a theory that aliens may have colonised a pre-Ice Age Antarctica, the creation myth of the Cosmic Egg and evidence to suggest human life was first seeded on Mars.