Mars may have liquid water on its surface, but only when the Sun goes down. According to a new NASA report on the Curosity rover, Martian soil may absorb humidity from the atmosphere at night where it combines with salt and forms a "brine" that doesn't evaporate, i.e. stays in liquid form because salt lowers water's freezing point. When the Sun rises, scientists believe, the water evaporates. "Conditions near the surface of present-day Mars are hardly favorable for microbial life as we know it, but the possibility for liquid brines on Mars has wider implications for habitability and geological water-related processes," report author Javier Martin-Torres said.