What can we learn from Nasa's Dawn probe?

After a seven and a half year journey, and with a price tag just shy of half a billion Dollars, NASA's Dawn spacecraft finally has the asteroid Ceres in its sights. Ceres is a massive asteroid which sits among a clutch of much smaller boulders, pebbles and dust out beyond the orbit of Mars. This field of debris is the rocky rubble left over from the time when the inner planets, including the Earth, were first forming, about 4 and a half billion years ago. This means asteroids like Ceres can help to uncover the origins of Earth and the minerals and materials, including the water, that we have here. Professor Andrew Coates is the head of Planetary Science at the Mullard Space Science Laboratory, and he spoke to Chris Smith about the mission...