The complex pattern left behind by liquid water flowing through sand under Martian atmospheric pressures. (credit: M. Massé) We now know that there is liquid water on the surface of Mars. Streaks of dark material flow down crater walls, appearing and disappearing with the seasons. Imaging from orbit has confirmed that these features contain hydrated salts, leading researchers to conclude that the water took the form of a salty brine, which would prevent it from immediately evaporating into Mars' cold, thin atmosphere. But a new paper released today argues that we might want to rethink the role of brine.