What compounds detected on RSL slopes strongly corroborated the hypothesis that these features are caused by flowing water?

Answer

Hydrated salts

The MRO spectrometer detected hydrated salts, specifically perchlorates, on the slopes when the streaks were active. These salts act as antifreeze, lowering the freezing point of water sufficiently for briny liquid to flow on the cold Martian surface.

What compounds detected on RSL slopes strongly corroborated the hypothesis that these features are caused by flowing water?
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