Geological features and orbital images show that ancient Mars hosted rivers, lakes and possibly oceans, indicating a much wetter past that shaped its surface
Geological evidence
Orbital imagery and surface geology reveal valley networks, delta deposits and layered sediments that are best explained by flowing and standing liquid water on ancient Mars, suggesting sustained surface water in the planet’s early history.
Present day water
Today most of Mars’ water is frozen as polar caps and subsurface permafrost, with only trace amounts of water vapour in the atmosphere. Exposed liquid water on the surface is extremely scarce because of the cold temperatures and low atmospheric pressure.
Subsurface and salty water
Recent studies and seismic analyses indicate reservoirs of liquid water may exist beneath the crust or as salty brines in the shallow subsurface, raising the possibility of substantial hidden water stores that persist in liquid form due to salts and local geothermal conditions.
Implications for habitability
Because liquid water is essential for life as we know it, evidence for past surface water and potential subsurface liquids makes Mars a prime target to search for past habitability and possible extant microbial ecosystems beneath the surface.