This week, we're discussing invading organisms large and small. We'll talk to Dr. Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, to learn why (and how) researchers are creating new strains of flu virus. We're joined by marine invertebrate researcher Dr. Benjamin Miner, to talk about the wasting disease killing starfish on the west coast of North America. And we'll talk to physicist Ross Lockwood about the HI-SEAS project, exploring the psychological conditions facing a human crew on a mission to Mars.