The duo found signs of groundwater seepage and surface runoff in hundreds of locations, mostly in high latitudes and in the southern hemisphere. The sites include gullies and alluvial fans within the walls of pits, valleys and impact craters. Malin Space Sciences operates a camera onboard the NASA satellite, which has orbited Mars since 1997. Scientists have long thought Mars' surface coursed with water billions of years ago, based on evidence of liquid erosion and signs of ancient channels and seas. But the water all but disappeared as the planet cooled and its atmosphere thinned.
Water is known to exist today as ice in the northern polar cap and as vapor in faint clouds.
But the presence of liquid water near the surface could strengthen the theory that life exists or once existed on Mars. Low-flying airplanes or robotic balloons could make closer observations of the seepage features, suggested U.S. Geological Survey scientist Kenneth Tanaka in Science. Liquid water on Mars would also make travel to the planet easier. Astronauts could convert water into hydrogen and oxygen, using both as rocket fuel and the second for breathing gas. NASA last tried to search for water on the red planet in 1999.