ESA’s Mars Express has used radar signals bounced through underground layers of ice to identify a pond of water buried below the surface.
This image shows an example radar profile for one of 29 orbits over the 200 x 200 km study region in the south polar region of Mars. The bright horizontal feature at the top corresponds to the icy surface of Mars. Layers of the south polar layered deposits – layers of ice and dust – are seen to a depth of about 1.5 km. Below is a base layer that in some areas is even much brighter than the surface reflections, while in other places is rather diffuse. The brightest reflections from the base layer – close to the centre of this image – are centred around 193°E/81°S in all intersecting orbits, outlining a well-defined, 20 km wide subsurface anomaly that is interpreted as a pond of liquid water.