The Best Episodes of NASA's Unexplained Files Season 4

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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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