Are Mars' Dark Streaks Really Evidence of Liquid Water?

The streaks, known as recurring slope lineae (RSL), occur seasonally on steep, relatively warm slopes at many locations on the Red Planet. Many researchers initially speculated that RSL may be signs of liquid water at or near the Martian surface, and this hypothesis got a big boost last year when a study reported that MRO had detected hydrated salts within the streaks. The hydrated-salts discovery generated a lot of excitement, because it suggested that some places on the otherwise dry Red Plane