The team explores the threat of an asteroid impact on earth and meet space scientists who are developing methods of planetary defence that sound like the stuff of science fiction. Maggie meets Professor Alan Fitzsimmons, expert in asteroid observation, to learn how the latest technology monitors near-Earth asteroids. He explains which ones are a current concern, and why we missed the dangerous Chelyabinsk meteor - a 9,000-ton fireball that exploded in the sky above Russia
