Is there another Earth? Adam Hart-Davis is on the summit of La Palma in the Canary Islands, searching for planets around other suns. He discovers how it is possible to find planets too small to see, and tells the story of how the first ever planet outside our solar system was found - an event that rocked the world of astronomy. Janet Sumner visits the Virtual Planetary Laboratory, where they invent inhabited planets so that astronomers know what to look for.
