It was one of the most exciting planetary science announcements in 2018: Radar from an orbiting spacecraft might have found large pools of liquid water under the Martian south pole. But good science doesn’t end with first conclusions. Jeffrey Plaut and Isaac Smith are among the researchers who have found that a form of clay may better explain these reflections. We also talk with The Planetary Society’s Rae Paoletta about the Earth-like worlds found across our corner of the galaxy. Your chance to win the coveted Planetary Society rubber asteroid returns in this week’s What’s Up. Discover more at  https://www.planetary.org/planetary-radio/jeffrey-plaut-isaac-smith-mars-polar-clay