Our ocean, particularly deep ocean, is one of the least explored places on earth. We know just a fraction of what plants and animals live under the waves, and barely understand the complexity of ocean ecosystems. One part of this is because we haven't spent as much time designing and building the sophisticated tools required for diving into the deepest parts of the sea as we have building space ships. That needs to change, and Sir Richard Branson wants to be a leading figure in that change. He has unveiled the Virgin Oceanic submarine, capable of diving into even the Mariana Trench. But this will be just one of five incredible trenches the submarine is set to explore.