What if aliens landed on Earth? Much of science fiction explores the moment of first contact – what will people do when the aliens land? From H. G. Wells’ pioneering The War of the Worlds to Independence Day, Men in Black, and District 9, Invasion deals with our fears of alien invasions of earth. David Tennant explains the appeal of Doctor Who’s Daleks and Cybermen while John Carpenter and Chris Carter explore the rich appeal of the paranoia fuelled by hidden aliens with The Thing and The X-Files. It also asks, what if the monsters were our own creation? With the aid of rarely seen animation tests, Phil Tippett takes us behind the scenes in the creation of the dinosaurs of Jurassic Park. But not all invasions are hostile. Peter Coyote and Richard Dreyfuss discuss the creation of Spielberg’s spellbinding classics E.T. the Extra-Terrestrial and Close Encounters of the Third Kind. There is more than one kind of invasion.

The episode, devoted to the planet Mars, begins with scientific and fictional speculation about the Red Planet during the late nineteenth and early twentieth centuries (H. G. Wells' The War of the Worlds, Edgar Rice Burroughs' science fiction books, and Percival Lowell's false vision of canals on Mars). It then moves to Robert Goddard's early experiments in rocket-building, inspired by reading science fiction, and the work by Mars probes, including the Viking, searching for life on Mars. The episode ends with the possibility of the terraforming and colonization of Mars and a Cosmos Update on the relevance of Mars' environment to Earth's and the possibility of a manned mission to Mars.

What if we could travel not just through space, but through time itself? If you could travel through time, would you change the past or the future? What if you found it couldn’t be changed? What price does the time traveller -- and the people they are closest to -- pay? This is a journey from H. G. Wells' The Time Machine through ideas like The Grandfather Paradox and The Butterfly Effect to the professional time traveller that is the ever popular Doctor Who. Steven Moffat, David Tennant, Karen Gillan, and Neil Gaiman offer a unique perspective on the Doctor. Edward James Olmos reveals the hidden meaning of the language he created for the vision of the future that is Blade Runner. Bob Gale and Christopher Lloyd take us behind the scenes of Back to the Future, while Ed Solomon describes the joy of solving a time travel conundrum for Bill & Ted’s Excellent Adventure. But what would be the physical and emotional cost to the time traveller? Audrey Niffenegger explains what inspired her novel The Time Traveller’s Wife. And what if someone from the future tried to travel back in time to warn us? Would we believe them? From the apocalyptic tones of 12 Monkeys to the drama of Quantum Leap and the comedy of Groundhog Day, time travel is a subject that has been irresistible to the creators of every type of science fiction.