The Freedom of Information Act: In 1969, the US government officially announced it would stop investigating UFOs, but declassified documents seem to tell another story. (S4, ep 3)
Astronaut Encounters: To this day, NASA denies all UFO accounts and has taken measures to prevent its astronauts from telling their stories. But what are they hiding? (S2, ep 3)
The 1952 Wave: In Spring 1952, reports of UFO sightings shot through the roof. Can former US Air Officials shed any light on this? (S4, ep 2)
Human Harvest: A look at frightening reports of alleged alien abduction, including cases in which abductees claim to have been subjected to torturous medical experiments. (S2, ep 2)
Second Skin: To enter space, humans require a space suit. Are the aliens that are said to have visited earth any different? Or are they more akin to artificial drones? (S4, ep 1)
Alien Origins: The compelling series returns to examine more eerie reports of UFOs. Can it determine where in the universe such strange flying crafts could be coming from? (S2, ep 1)
Alien Gods of Egypt. Experts scrutinise the engineering behind the Egyptians' Sphinx and pyramids. Could this advanced civilisation have received extra-terrestrial help? (S1, ep 14)
Aliens and Presidents: Could history's most powerful men know more about extra-terrestrials than us? Experts explore the complex relationship between presidents and aliens. (S1, ep 13)
The Solway Firth Spaceman: Experts investigate the mystery of the Solway Firth Spaceman - a spacesuit-clad figure who strangely appeared in a photograph taken in Cumbria . (S1, ep 12)
Experts unseal the truth about the potential aliens living and working among us. Who has come in peace? And who has a more sinister motive in mind? (S1, ep 11)