The birth of our Solar System was both violent and chaotic. As planets formed around our Sun, gravity and luck determined their fate: some are tossed into the Sun, others thrown into interstellar space, never to return. It is survival of the fittest, on an interplanetary scale.
Carl Sagan opens the program with a description of the cosmos and a "Spaceship of the Imagination" (shaped like a dandelion seed). The ship journeys through the universe's hundred billion galaxies, the Local Group, the Andromeda Galaxy, the Milky Way, the Orion Nebula, our Solar System, and finally the planet Earth. Eratosthenes' successful calculation of the circumference of Earth leads to a description of the ancient Library of Alexandria. Finally, the "Ages of Science" are described, before pulling back to the full span of the Cosmic Calendar. Note: This revised version of the series adds an introduction by Ann Druyan, in which she discusses some of the changes that occurred in the years after its broadcast.
If we faced a countdown to destruction, could we build a spacecraft to take us to new and habitable worlds? Can we Evacuate Earth? This documentary special examines this terrifying but scientifically plausible scenario by exploring how we could unite to ensure the survival of the human race.
Scientists are only now starting to unravel the secrets of comets. Often referred to as dirty snowballs, they contain ice and elements from the very start of the universe. Some theorize that a comet, crashing into our planet, brought with it the organic material that started life on Earth. Spacecraft continues to offer new information on their makeup, from bringing back samples from a comet's tail to direct contact when a NASA-launched craft slammed into the comet Tempel-1.