Season 4 - Episode Guide

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

A mission to Mars captures an image of a strange structure on the Red Planet. 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 US 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 could 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 startling discovery suggests that the hellish clouds of Venus may be the origin of life on Earth. A bizarre sighting 2,000 years ago raises the possibility that the Earth once had two moons. A NASA scientist helps the FBI crack the 1996 Olympic bombing.

A probe carrying a message to aliens mysteriously malfunctions as it enters deep space. A NASA mission goes disastrously wrong when an imposter breaches Mission Control. Astronomers find evidence of an invisible planet in a distant solar system.

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

Mars is the home of some of the strangest and most mysterious phenomena in the universe; counting down the Red Planet's greatest mysteries.

Our moon has been the home of some of the strangest and most mysterious phenomena in the universe; counting down the moon's most perplexing mysteries.