https://motherboard.vice.com/en_us/article/vbj7zb/scientists-find-evidence-of-liquid-water-on-mars

On Wednesday, a team of European scientists announced it had found strong evidence of a vast reservoir of liquid water hiding under the ice cap on the south pole of Mars.

As detailed in Science, the buried lake was detected using ice-penetrating radar from the European Space Agency’s Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) satellite. MARSIS has been in orbit around the Red Planet since 2003 and uses high frequency radio pulses to map Mars’ subsurface geology.