The oceans define the earth. They are crucial to life and we used to think that they were unique to our blue planet. But we were wrong. It has recently been discovered that there are oceans all over our solar system, and they are very similar to our own. And now scientists are going on an epic journey in search of new life in places that never seemed possible. Nasa is even planning to dive to the depths of a strange, distant ocean in a remarkable submarine. Horizon discovers that the hunt for oceans in space is marking the dawn of a new era in the search for alien life.