Mars Curiosity rover: Nasa mission's search for life clues
John Grotzinger is Nasa's chief scientist for the Curiosity mission which will seek to land a rover vehicle in the bottom of an enormous crater on Mars.
The Gale crater is more than three billion years old and Nasa hope that tests on the ancient rock strata in this depression will reveal if Mars was ever capable of supporting life.
Curiosity is due to land on Mars at about 06:31 BST (05:31 GMT) on Monday 6 August.
Horizon: Mission to Mars was broadcast on BBC Two Monday 30 July. Watch online via iPlayer (UK only) or browse more Horizon clips at the above link.