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)

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)

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.

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)

Summer of Saucers: In 1947, there was an unprecedented wave of UFO sightings that propelled the UFO phenomenon to the world stage. What were the US Air Force's findings? (S4, ep 13)

UFOs from Earth: For years many have argued that UFOs are as terrestrial as you or I. They may be correct, but not in the way they thought they were. (S4, ep 12)

UFO Photos: As the world continues to evolve into the digital age, more and more people are capturing images in the sky that they are unable to explain. (S4, ep 11)

Finding Aliens: Advances in technology have given us unprecedented access to distant galaxies that may harbour life. However, alien life may be found closer to home. (S4, ep 10)

Alien Journeys: Alien encounters have offered a possible glimpse into the secrets of interstellar navigation. Could this one day ensure mankind's survival? (S4, ep 9)

Fast Eddie: While the guys pick the back roads of Minnesota, they challenge Danielle to sell a 10-foot fiberglass cowboy boot that's been gathering dust for more than a year. (S4, ep 11)