In May and June, NASA will be launching two new landers to the Red Planet, but until late last week the agency hadn’t decided where to send them. After years of analysis and debate, Mars scientists and NASA have agreed to set the twin Mars Exploration Rovers down in two places where liquid water seems to have flowed in the past. The first Mars Exploration Rover (MER-A) will land inside Gusev Crater, which may have at one time held a lake. Located a little less than 15 degrees south of the martian equator, the 160-kilometer (100-mile) impact crater lies at the end of a 900-kilometer-long (550-mile) fluvial channel called Ma’adim Vallis. Some scientists have suggested that Ma’adim Vallis may have once fed water into a lake within Gusev Crater.