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. Learn more about this week’s topics and see images here: http://www.planetary.org/multimedia/planetary-radio/show/2018/0411-nikole-lewis-trappist-worlds.htmlLearn more about your ad choices. Visit megaphone.fm/adchoices

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