NASA's Unexplained Files — Season 4

Astronomers find evidence for incredible alien technology around a distant star. The first pictures of Pluto may show something moving across its surface. Apollo astronauts see something they can't explain as they approach the Moon.

A probe captures an image of a strange structure on Mars. Files from the first Apollo mission record an eerie sighting on the dark side of the Moon. A planet-eating star gives scientists a glimpse of Earth's terrible demise.

Geysers are discovered on a frozen moon, and NASA redirects a probe on a daring mission to detect evidence of life. An unidentified object is spotted approaching a near-earth asteroid. A future president is an eyewitness to a UFO.

Astronomers detect a potentially habitable planet tantalizingly close to Earth. A chance discovery at NASA reveals a top secret military space program. The Apollo missions bring back evidence that the moon may be rich in the building blocks for life.

Two cosmonauts fight for their lives while trapped inside a capsule in a frozen lake. A NASA scientist investigates the deadly Nazi secret that doomed the Hindenburg. NASA astronomers are spooked when the full moon starts affecting their experiments.

A discovery suggests the hellish clouds of Venus may be the origin of life on Earth. A bizarre sighting 2,000 years ago raises the possibility that Earth once had two moons. A scientist helps the FBI crack the 1996 Olympic bombing.

A probe carrying a message to aliens malfunctions as it enters deep space. A NASA mission goes disastrously wrong when an imposter breaches Mission Control. Astronomers may have found an invisible planet around a distant star.

British astronomers working for the CIA intercept Soviet photos of the moon. A malfunction on the ISS could poison its crew with ammonia gas. A startling image taken by a NASA probe points to evidence that life could exist on Mars.