Water discovered 1.5km beneath surface of Mars

摘要

An instrument on board ESA's Mars Express orbiter spacecraft has detected a wide body of water 1.5km below solid ice and dust nearthe south pole of Mars.The planet is scarred with remains of river valleys and channels where water flowed, but changes in its climate mean that it cannot exist today in any persistent form.An onboard instrument called MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) uses ground-penetrating radar to map Mars's subsurface topography. It sends radar pulses towards the surface and times their reflection. It then analyses the reduction i n the strength of the returning signal, giving clues on the composition of the material through which the radar pulse travelled before being reflected. The discovery was made during an investigation of a 200km-wide area composed of alternating layers of ice and dust.