We think of comets as beautiful glowing balls of light streaking across our skies with their long sweeping tails, yet comets are so much more than just a cosmic firework display. Comets have a uniquely important place in modern science. As time machines from the early universe, they could hold the key to unlock the secrets of the cosmos. Comets could even be the origin of life itself. We follow the incredible odyssey of a comet as it sails through the solar system, watching it's every move as it evolves from a dormant chunk of ice and rock into a tumbling, violently active nucleus engulfed in a gaseous haze. What we learn is a revelation; comets are even more mysterious and fascinating than we had ever imagined.

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.

The idea of intelligence is explored in the concepts of computers (using bits as their basic units of information), whales (in their songs and their disruptions by human activities), DNA, the human brain (the evolution of the brain stem, frontal lobes, neurons, cerebral hemispheres, and corpus callosum under the Triune Brain Model), and man-made structures for collective intelligence (cities, libraries, books, computers, and satellites). The episode ends with speculation on alien intelligence and the information conveyed on the Voyager Golden Record.

Brian asks how, from a lifeless cosmos, it is possible that a planet can produce the more than eight million species we know of.

The Universe as we know it is condemned to death. Space, matter and even time will one day cease to exist and there's nothing we can do about it. Harsh realities are revealed about the future of our Universe; it may collapse and burn or it might be gripped by a galactic ice age. Either of these scenarios might be a long way off. However, our Universe could suddenly be destroyed by a "random quantum fluctuation", a bubble of destruction that can obliterate the entire cosmos in the blink of an eye. No matter how it ends, life in our Universe is doomed.

Today, we know black holes exist, and now scientists are trying to confirm that other holes lurk in hyperspace. Our infinite cosmos could contain a variety of "holes" such as black, white, "mini" and wormholes. White holes are the reverse of black holes; instead of matter being sucked into it, matter is ejected out. Wormholes are gateways in the fabric of space and time. They are included in Einstein's field equations as possibilities for their existence. Neither white holes nor wormholes have ever been found. Learn about new discoveries including, colliding binary black holes, intermediate black holes and manufacturing mini black holes.