A US government report on UFOs has said there was no clear explanation for the unidentified aircraft, but did not rule out extra-terrestrial origin. Hundreds of millions of dollars have been invested into searching for signs of alien intelligence. Ed Butler speaks to Lisa Kaltenegger, an astronomer at Cornell University, who has analysed the closest, most likely planets to support alien life. If, or when, we do make contact what could we trade with our new neighbours? David Brin, a science fiction writer and astro-physicist says our culture would be the most easily exchanged aspect of our civilisation. And what about making money on Earth from the continued interest in aliens? Juanita Jennings is the public affairs director for the town of Roswell, New Mexico. The site of the most famous UFO sighting. (Picture: a UFO over the Mojave desert, USA. Credit: Getty Images.)