European Mars-orbiting radar detects subsurface liquid water

For the first time, evidence of liquid water on Mars has been detected. Previous studies have suggested that liquid water might exist on the surface under certain conditions, but although Mars is scarred with remains of river valleys and channels where water once flowed, major changes in the planet’s climate mean that it cannot exist today in any persistent form.

The Mars Express orbiter, which has been studying Mars since 2003, carries a radar sounding instrument called MARSIS (Mars advanced radar for subsurface and ionosphere sounding), which uses ground-penetrating radar to map the subsurface topography of the planet. This technique, also widely used by engineers on Earth, sends radar pulses towards the surface and times how long it takes for them to be reflected back, and analyses the reduction in the strength of the returning signal. This gives clues on the composition of the material through which the radar pulse travelled before being reflected.