Scientists using MARSIS, a radar antenna onboard Europe's Mars Express spacecraft found what looks like a large and previously unknown reservoir of water ice below the surface of Mars.
The antenna was deployed in June 2005 and quickly detected what appeared to be water ice stretching 1.8 kilometres below the surface of the northern polar ice cap. Now, it has found what looks like water ice extending as deep as 3.5 kilometres below the southern polar cap.