NASA's Unexplained Files - Episode Guide

Astronaut Leroy Chao's spacewalk is interrupted by bright lights flying past. A flying saucer photographed from the Apollo capsule, dark shapes caught on camera shadowing the shuttle...the ideas are science fiction, but the incidents are science fact.

The Viking Lander may have found life on Mars, so why don't we know about it? What is the most destructive force in the universe? How could a Starship be spotted in the Aurora Borealis? And what are NASA's mysterious Moon Pigeons?

A chunk of the sun appears to have vanished. An ominous dark craft beneath the Shuttle Endeavour. And Hubble spots thousands of unidentified objects travelling faster than light. Are we being watched? Or could we ourselves be aliens from another world?

A distant planet shows evidence of an Earth-like atmosphere, while a mysterious glowing light suggests the impossible - an atmosphere on the Moon. Have we found evidence of a crashed alien ship on the asteroid belt, and why are there blueberries on Mars?

Could spaceships be powered by atomic bombs? Can artificial rings encircle an entire star? why was Neil Armstrong's transmission feed cut off when he spotted strange lights on the Moon? And how can lightning talk to itself?

What could make a NASA astronaut report seeing a flying saucer in the skies above a US Air Force test range? How have the swirling gases of Saturn formed a perfect Hexagon that has hovered above the planet's pole for 30 years?

A UFO crashes in Pennsylvania. Was it a secret Soviet satellite -- or something far more dangerous? On Mercury, NASA finds the impossible: frozen water. A strange object causes a skyscraper-sized shadow on the surface of Mars's largest moon. What is it?

Was the Moon landing faked? Images of Mercury reveal massive spider-like formations on its surface. Is it an odd geological formation -- or something much more ominous? A classifed space shuttle mission ends in near-disaster. What was its secret mission?

Are burning lights in the skies above Nevada and Utah signs of a secret space weapons project? What are the mysterious trails on the lunar surface near the Apollo landing sites? Does a strange space object spell disaster for the crew of the space shuttle?

An astronaut on a spacewalk begins to drown. How could this terrifying event happen? Have NASA scientists discovered an asteroid that's been converted into a spacecraft? What are the strange objects spotted when NASA sends a top-secret payload into space?

Could NASA really be responsible for a nuclear explosion on Jupiter? Could new evidence finally reveal the truth behind the mystery of the iconic face on Mars? What unknown force crashed a spacecraft from the Apollo program into the lunar surface?

A Russian probe discovers something has disturbed the lunar soil before the US or the USSR got there. Did Nazis get there first? Have scientists detected a laser signal from a planet capable of supporting life? Is there really a Bermuda Triangle of Space?

How did pictures from the Hubble telescope make the comet of the century look like an alien spacecraft? Has earth already been invaded by alien organisms? What mysterious force is smashing a near-earth asteroid to pieces?

Something in space is attacking the brains of our astronauts. What is it? Should NASA be worried about the sudden appearance of so-called space fireflies? Who could be responsible for the bizarre glowing spiral in the skies over Norway?

Lost tapes reveal that Apollo astronauts heard unexplained transmissions on the far side of the moon, an amateur astronomer spots a strange disturbance in Martian atmosphere and an unidentified object in Earth orbit starts stalking Russian spacecraft.

Apollo 12 astronauts bring back something alive from the moon and NASA track an asteroid heading towards Earth but make a shocking discovery: it's not an asteroid, but an object that's artificial in nature.

Neil Armstrong goes into an unexplained spin. He needs to figure out what's causing it, or he faces certain death. An Apollo 17 photo seems to show a US military outpost on the Moon... and could there be alien life swimming in the oceans of Jupiter's moons.

When a Chinese moon rover breaks down, a NASA scientist points to a mysterious material that seemed to sabotage the Apollo missions, decades earlier. The Rosetta spacecraft finds a comet that appears to be singing.

Recently discovered documents reveal NASA's secret plan B for failure of the first moon landing, a Soyuz capsule carrying NASA astronaut Peggy Whitson back to Earth vanishes without explanation and NASA's Cassini mission unravels a mystery.

Three cosmonauts die mysteriously as they re-enter Earth's atmosphere and NASA needs to know why, a declassified document reveals a CIA plan to use a space disaster as a cover to start World War 3 and a NASA rover discovers clues that help solve a murder.

Two astronauts trapped in the vacuum of space face an agonizing death; the first close up images of Pluto reveal an alien landscape, and residents of Houston struggle to explain videos of unidentified flying lights captured above their city at night.

Astronauts are evacuated when a mystery object is discovered hurtling towards the ISS, a NASA secret agent goes undercover to recover missing moon rocks and scientists struggle to find answers when they find a huge void at the edge of the solar system.

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.

A declassified letter written by President Kennedy demands that the CIA share its UFO data with NASA. A bizarre pattern on the surface of Mars could be a coded alien message. Investigators are shocked to find a rocket crash-landed in a crater on the Moon.

Jupiter is far hotter than it should be, and scientists don't understand why. The Curiosity Rover finds something strange on Mars. Could it be a lost spacecraft, or something far more sinister? Detectives turn to NASA for help with a murder cold case.

Two suns are photographed in the sky over Indonesia. Is it a trick of the light or the first sighting of our Sun's evil twin? Scientists are baffled by ghostly white swirls on the Moon's surface. An astronaut disappears during his return to Earth.

An astronomer records an unusual radio signal from beyond our solar system. FBI agents find classified documents at the home of a NASA scientist. When scientists discover strange DNA in the octopus, they examine if their origins could be alien.

When NASA spots a something on Mars that resembles Stonehenge, they investigate what could have made this strange structure. Scientists discover a mysterious hole in Saturn's rings. An ancient tribe claims contact with alien visitors.

When the Soviet Union unveils its own space shuttle, the CIA hatches a secret revenge plot. Recent discoveries shed new light on the destruction of Sodom and Gomorrah. A missing nuclear weapon could threaten a NASA base in the Arctic.

The last humans to walk on the Moon discover something strange on the surface. A NASA scientist investigates a strange phenomenon responsible for horrific mass deaths. A landmark NASA mission threatens to destroy the reputation of an American hero.

A mysterious object is orbiting Saturn, and it looks just like the Death Star. New evidence might shed new light on the mysterious death of Yuri Gagarin, the first man in space. When a cuting-edge satellite vanishes, fears of a space war escalate.

When NASA discovers something strange on Saturn's biggest moon, experts investigate if aliens feeding on the electric atmosphere could be the culprit. The disturbing evidence points to a grisly apocalypse if these monsters ever make it to Earth.

When a former Area 51 insider alleges that the Roswell UFO incident was a nefarious Soviet conspiracy masterminded by Stalin, experts investigate if it was indeed an enemy plot against America -- or if the confession is just another cover-up.

When astronomers discover a rogue black hole speeding through the Milky Way, they investigate how much danger this cosmic monster poses to Earth, and what would happen if it ever entered our solar system.

After NASA's New Horizons spacecraft flies by Pluto, it encounters a strange alien world that shuts down the probe's computers, and experts investigate if this mysterious object is an alien spacecraft hiding at the edge of our solar system.

After Neil Armstrong's moonwalk, he led an expedition to the Amazon to find a legendary library that holds all knowledge of an advanced alien civilization. Experts ask if a close encounter on the moon's surface inspired Armstrong's mysterious quest.

When NASA begins a strange experiment to communicate with dolphins, experts investigate if it's a prelude to making alien contact. But some fear that such a discovery could have apocalyptic consequences.

Experts investigate if a nearby exoplanet could be the home to a alien civilization of strange, metallic monsters, after a new discovery confirms that life can thrive on such a strange world.

A strange discovery by NASA's Mars Curiosity rover suggests the Red Planet was home to an alien nuclear war 300 million years ago, and experts investigate if an extraterrestrial Armageddon transformed an earth-like world into the wasteland we know today.

Strange flying objects have been caught on NASA's cameras and astronauts have reported seeing UFOs. Some of the odd shapes and lights can be identified; others remain a mystery. We'll reveal NASA footage and interview the astronauts and scientists.

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.

Strange sightings on Mars, including possible pillars of fire and signs of life.

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.

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

Counting down the most narrow escapes, and the strange, unexplainable and almost deadly phenomena astronauts face.

The cosmos are home to some of the strangest and most mysterious phenomena. In this special episode, we countdown some of the most terrifying moments in the history of space exploration.