Radar data from the European Space Agency Mars Express was analyzed to reveal the lakes. The Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) sent radio waves that bounce off layers of material in the planet's surface and subsurface. Areas of high reflectivity indicate bodies of liquid water trapped under more than one kilometer of Martian ice.
The lakes are spread over about 75,000 square kilometers — an area roughly one-fifth the size of Germany. The largest, central lake measures 30 kilometers across and is surrounded by 3 smaller lakes. Each of the smaller lakes is a few kilometers wide.
Earth lakes with salt content about 5 times that of sea-water can support life. There is no life in earth water when salt concentration approaches 20 times that of sea-water.