On the final night of their astronomical adventure, Brian and Dara discuss meteors, comets and asteroids and reveal how studying them reveals information about the origins of life on Earth. Meanwhile, Liz Bonnin meets the NASA team tasked with tracki... (more)ng any space objects on a collision course with Earth. The results of the experiment carried out by the Stargazing viewers - to explore an uncharted area on the surface of Mars - are also revealed.