Exploration: It’s exciting, it’s novel, and you can’t always count on a round-trip ticket.  You can boldly go, but you might not come back.  That’s no showstopper for robotic explorers, though.  Spacecraft go everywhere. While humans have traveled no farther than the moon, our mechanical proxies are climbing a mountain on Mars, visiting an ice ball far beyond Pluto, plunging through the rings of Saturn, and landing on a comet.  Oh, and did we mention they’re also bringing rock and roll to the denizens of deep space, in case they wish to listen. We consider some of the most daring explorers since the 16th century – made of metal and plastic - venturing to places where no one else could go.  What have they done, what are they doing, and at what point do they declare “mission accomplished” and head for that great spacecraft graveyard in the sky? Guests: Matt Tiscareno– Planetary Scientist at the SETI Institute Mark Showalter– Senior Research Scientist, SETI Institute Jonathan Amos– BBC Senior Writer and Science Correspondent Ashwin Vasavada– Curiosity Project Scientist at the Jet Propulsion Laboratory