More than 50 years of missions to Mars paint a clear picture of a cold, dry, desert planet. And at the same time, photographs, minerals, and other data tell scientists that Mars once had as much water as Earth, or even more. Why are the two planets so different today? In this episode of Stereo Chemistry, we talk to scientists about the latest research on Mars’s water and where they think the water went. Listen to the end of the episode for an announcement about the future of Stereo Chemistry. Sign up for C&EN’s newsletter at bit.ly/chemnewsletter. A transcript for this episode is available at bit.ly/3hPfHcP. Image credit: Kevin Gill/Flickr based on data from NASA/JPL/University of Arizona/USGS