Billions of years ago, Mars may have looked less like the barren red desert we know today and more like Earth—with a blue sky, flowing rivers, and even seas. What happened to turn a once-habitable world into the frozen, lifeless planet we see now?

On this episode of Big Brains, University of Chicago geophysical scientist Edwin Kite takes us on a journey through Mars’ hidden past. From evidence of a lost carbon cycle to theories about ancient climate swings, Kite’s research is rewriting the story of the Red Planet. But it’s not just about the past—his work is also at the forefront of a provocative question: could humanity one day terraform Mars and make it a living world again?