Top Civilian Encounters: From mass sightings in the sky to reports of alien probes found in human bodies, explore the ten most disturbing extraterrestrial encounters ever. (S2, ep 19)

Alien Communications: With light from distant stars taking millions of years to reach us, how long might it take for alien life to answer any communication sent into space? (S4, ep 18)

Countdown To Disclosure: Evidence suggests the world's governments could be on the verge of announcing everything they know about UFOs. What will this mean for our society? (S2, ep 18)

Mars: The New Frontier: With science closer than ever to proving that life once lived on Mars, is there a chance that something still exists there? (S4, ep 17)

UFO Zones: Journey to the world's hottest UFO zones, where physical and paranormal phenomenons and unidentified objects and aliens are reported with alarming frequency. (S2, ep 17)

Mass Sightings: While many UFO sightings occur in rural locations with only a single eyewitness, there have been sightings over cities witnessed by hundreds. (S4, ep 16)

Alien Bodies: Uncover the shocking truth about alien remains as experts investigate unsettling reports of extraterrestrial bodies recovered from crashed UFOs. (S2, ep 16)

Space Shuttle Encounters: Between 1981 and 2011, cameras on NASA space shuttles have picked up many images of UFOs that experts still struggle to explain.

Nazi UFOs: Could alien technology have helped the Nazis' rise to power? Experts question whether Hitler had extraterrestrial help in his quest for world domination. (S2, ep 15)

Police Sightings: For many people, the most credible UFO reports are those raised by law enforcement. We investigate the most significant reports from police records. (S4, ep 14)