Far away, alone in a crater on a planet inhabited only by robots, NASA's Perseverance rover explores a dry landscape that was once a river system billions of years ago. According to a new discovery, however, the Jezero Delta on Mars is not the sole remnant of abundant water that once flowed across the surface. Perseverance's RIMFAX instrument has now probed deeper than ever beneath the Jezero crater, revealing a vast delta system fed by flowing water that existed long before the one the rover