In astronomy, the rule of thumb was simple: If you can’t see it with a telescope, it’s not real. Seeing is believing. Well, tell that to the astronomers who discovered dark energy, or dark matter … or, more recently, Planet 9.  And yet we have evidence that all these things exist (although skepticism about the ninth – or is it tenth? – planet still lingers).Find out how we know what we know about the latest cosmic discoveries – even if we can’t see them directly. The astronomer who found Planet 9 – and killed Pluto – offers his evidence. And, a speculative scenario suggests that dark matter helped do away with the dinosaurs. Plus, the winner of the 2015 Nobel Prize in Physics explains why neutrinos that are zipping through your body right now may hold clues to the origin of the universe. Guests: Michael Brown - Astronomer, California Institute of Technology Michael Lemonick - science writer and an editor at Scientific American magazine Lisa Randall - Theoretical physicist, Harvard University, author of Dark Matter and the Dinosaurs: The Astounding Interconnectedness of the Universe Arthur McDonald - Astrophysicist emeritus, Queen’s University, Kingston, Ontario, and winner of the 2015 Nobel Prize in Physics Learn more about your ad choices. Visit megaphone.fm/adchoices