This undated photo provided by NASA and taken by an instrument aboard the agency's Mars Reconnaissance Orbiter shows dark, narrow, 100 meter-long streaks on the surface of Mars that scientists believe were caused by flowing streams of salty water. Researchers said Monday, Sept. 28, 2015, that the latest observations strongly support the longtime theory that salt water in liquid form flows down certain Martian slopes each summer. (NASA/JPL/University of Arizona via AP)