Mars once had sprawling river systems that rivaled major watersheds on Earth, and scientists have now identified the biggest ones for the first time. Researchers mapped 16 massive drainage basins where water likely flowed long enough to support life. Even though these areas cover just 5% of ancient Martian terrain, they account for a huge share of erosion and sediment movement. That makes them some of the most promising places to search for ancient life. ...read more read less