After Neil Armstrong's moonwalk, he leads an expedition into 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 quest.

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.

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 find a rocket crash-landed in a crater on the Moon.

Neil Armstrong enters an unexplained spin; an Apollo 17 photo seems to show a US military outpost on the Moon; possible alien life swimming in the oceans of Jupiter's moons.

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.

A Russian probe uncovers something has disturbed the lunar soil before the US or the USSR got there; scientists may have detected a laser signal from a planet capable of supporting life.

What was thought to be a secret Soviet satellite could have been a UFO crashing in Pennsylvania; NASA makes an unbelievable discovery, frozen water on Mercury.

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

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.

"The Unexplained Files" investigates actual, inexplicable occurrences that have confounded scientists and inspired legends, from mysterious disappearances and UFO encounters, to unidentified fanged predators and reported curses. Besides never-before-seen footage, the series features scientists, government officials, journalists and eyewitnesses sharing vivid accounts of truly bewildering experiences. Episodes include investigations of bizarre creatures that prey on livestock in Texas, a centuries-old tome -- the Voynich Manuscript -- written in an unknown language, and Frederick Valentich, a pilot on a training flight who reported a strange craft hovering above him just minutes before he disappeared.

A new breed of explorer has taken space travel beyond the moon to unlock and reveal first-ever views of alien worlds and cosmic bodies far beyond anyone's imagination. "Space's Deepest Secrets" shares stories of the men and women who pushed their ingenuity and curiosity to uncover some of the most groundbreaking findings in the history of space exploration. Hourlong episodes cover NASA's New Horizons mission to Pluto, the Hubble Telescope, the twin Voyager explorations, and other past, current and future missions and projects.

Discovery Channel chronicles the first 50 years of space travel -- from the first Mercury flights through the Gemini program to the Apollo moon landings, the Space Shuttle, and the construction of the International Space Station -- with this dazzling six-hour documentary. The series incorporates interviews with eyewitnesses (astronauts John Glenn and Neil Armstrong among them) and original NASA mission footage that has been transferred to high-definition clarity. Actor Gary Sinise, who portrayed astronaut Ken Mattingly in "Apollo 13," narrates.

When people think of American space travel, the first names that come to their minds are usually the likes of Buzz Aldrin, Neil Armstrong and Sally Ride. Like with most massive projects like NASA's, there are a number of people behind the scenes who work tirelessly to get to the point where astronauts can go into space. Those people, however, aren't household names like the folks who blast off on the space shuttles. This series profiles the secret heroes, engineers who helped build the spacecraft and other instruments that have allowed astronauts to launch into space to explore the world beyond what's visible from Earth. The show reveals the stories behind how they created such machines as the Saturn V moon rocket and the Hubble Space Telescope.

Oscar winners Ron Howard and Brian Grazer put their storytelling acumen to work as executive producers of "Breakthrough," a series of hourlong documentaries highlighting the stories, people, and technology behind the world's most cutting-edge scientific innovations. After considering more than 100 scientific topics for the series, the pair -- helped by National Geographic archives and research, along with the scientific resources of partner GE -- selected biotechnology, neuroscience, anti-aging technology, alternative energy, water conservation, and global pandemics. Each episode is directed by a prominent Hollywood star -- Howard himself helms "The Age of Aging," joining actors Angela Bassett ("Water Apocalypse") and Paul Giamatti ("More Than Human"), directors Peter Berg ("Fighting Pandemics") and Brett Ratner ("Decoding the Brain"), and screenwriter Akiva Goldsman ("Energy From the Edge").

"Naked Science" strips away the layers of a scientific investigation into one of the big mysteries of our time, revealing through expert analysis realistic scenarios that either confirm or deny long-held assumptions and misconceptions.

A look behind the scenes at how everyday things are manufactured. Typically each episode includes three to four products featured, with a mix consisting of common items such as jeans, aluminum foil and cereal, and less predictable ones like wax figurines, braille typewriters and pinball machines.