Season 2

The collisions that created Earth and the moon; the people who work to stave off the apocalypse; violent impacts deep in the cosmos.

Earth's weather is compared to that of other planets; cataclysmic space weather that could cripple life on Earth.

Are we alone? It's an age-old question that was relatively "taboo" in mainstream science until the mid-1990s, when astronomers found planets outside our solar system. Now, Known Universe joins the hunt for alien life as scientists search for planets with similar characteristics to Earth's. We'll take you on a journey to find planets that may support life and show you new space-based technologies that aid in the search for advanced alien civilizations.

Our ancestors' relationship with the heavens led to some of mankind's ancient discoveries and greatest creations. The ancient Greeks discovered Earth was round; the Polynesians used the sun and stars to navigate vast oceans in simple canoes; some think amazing structures like Stonehenge were designed to observe the sky. Now, Known Universe examines mankind's first observations of the cosmos to understand how they put us on the path to modern discovery. An alternate name of the episode: Star Gates

More than 70 percent of Earth is covered in water, but we've only explored roughly 5 percent of it. We've roamed even less of our solar system. Now, armed with some of the latest advances in technology, we join scientists on a voyage into the unknown - from the far reaches of space to the extreme depths of our oceans - where new discoveries have experts questioning everything we know about the universe, and ultimately ourselves. An alternate name of the episode: To the Extremes

Earthquakes and volcanoes pose an unpredictable and deadly threat here on Earth, but they also occur far out in the universe. What can we learn from these interplanetary phenomena that may help us predict when Mother Nature will next unleash her fury? Scientists are looking to Io, a moon of Jupiter that is jam-packed with volcanoes, for insights. Then we'll travel deep under the Earth's crust to see the physical source of these catastrophic events. An alternate name of the episode: Time Bombs