Water + salts + iron + sulfur = microbes partying on!
Microbes with unusual (for Earth) metabolisms thriving in frigid conditions. Subsurface Maahs, Enceladus and Europer come to mind.
With the ample evidence for briney water below Mars' surface, I'm re-assesing my opinion yet again, leaning towards think that there may actually be life extant under the Martian surface. Did it come from here? Or as I think likely, our life first came from Mars which cooled down over a hundred million years earlier than Earth.