If a tree fell on another planet, would we be able to detect it? Not quite yet – but we might be able to tell if the planet was habitable. A living-planet is the promise of newly-discovered Gliese 581g. But does the planet exist at all?Discover how we learn a planet’s geology and chemistry from afar. Also, what we learn about a civilization from what it discards, beginning with our own sloppy habits.Plus, the hunt for derelict alien spaceships… and a man who sketches alien creatures for a living - based on real science.Guests: Lisa Kaltenegger - Astronomer, Harvard-Smithsonian Center for Astrophysics Brad Bebout - Biologist, NASA Ames Research Center Robin Nagle - Anthropologist, New York University Robin Hanson - Economist, George Mason University Joel Hagen - Computer graphics instructor, Modesto Junior College Descripción en español Learn more about your ad choices. Visit megaphone.fm/adchoices