To accompany Space Odyssey: Voyage To The Planets, BBC FOUR broadcasts a documentary that looks at the history of space exploration to reveal the science behind the series. It tells the story of the human ingenuity that has dispatched robotic missions to all the planets except, as yet, Pluto. Voyager 2 - which accomplished the original grand tour of the planets in the Seventies and Eighties - is a prime example. Incredibly, more than 25 years since its launch and now over seven billion miles from Earth, we can still hear its whispers from deep space. It carries the spirit of human exploration like a metal Christopher Columbus as its sensors probe the edge of our planetary system.