Horizon goes behind the scenes at Nasa as they count down to the landing of a 2.5 billion-dollar rover on the surface of Mars. The nuclear-powered vehicle, the size of a car, will be winched down onto the surface of the red planet from a rocket-powered crane. That's if things go according to plan; Mars has become known as the Bermuda Triangle of space because so many missions there have ended in failure. The Curiosity mission is the most audacious, and expensive, attempt to answer the question of whether there is life on Mars.