Advanced technology that lets us see previously unseen parts of the solar system, combined with the frequent discovery of “Earth-like” planets, has strengthened our longstanding cultural belief that aliens could exist (not to mention the fact that extraterrestrials continue to capture our imagination at the box office). And now, there’s even more to the idea that there is life beyond our planet. Some of the latest scientific theories supporting the existence of alien life are collected in an anthology of essays called “Aliens,” edited by theoretical physicist Jim Al-Khalili. Al-Khalili joins Joshua Johnson to weigh in on why scientists are more optimistic than ever before that we’re not alone in the universe. Additional guests include Adam Rutherford, a geneticist and host of “Inside Science” on BBC Radio 4 and Nathalie Cabrol, senior research scientist at the SETI Institute and director of the Carl Sagan Center.