We have begun to understand the composition of worlds that are hundreds of trillions of kilometers from Earth. Astronomer Nikole Lewis is co-leader of a team that has used the Hubble Space Telescope to do this with the four Earth-like planets circling a star called TRAPPIST-1. Host Mat Kaplan talks with Digital Editor Jason Davis about a new probe designed to discover thousands of additional exoplanets. Want to win a Planetary Radio t-shirt? Answer this week’s space trivia question posed by Planetary Society Chief Scientist Bruce Betts.