ESA's Mars Express orbiter has found evidence of more liquid water beneath the ice cap in the south polar region of Mars. Based on data from the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) radar instrument, researchers found three new subsurface ponds, with the largest measuring 20 x 30 km (12 x 19 mi).
In 2018, the Mars Express team discovered that the Martian ice caps are not ice throughout, but actually have large, subsurface lakes of liquid water. Using the MARSIS instrument to probe beneath the southern polar cap from May 2012 and December 2015, the orbiter mapped out a lake 20 km (12.4 mi) wide under 1.5 km (0.9 mi) of solid ice. Now, more ponds are being revealed at the same depth by a reanalysis of the same data.
According to ESA, the lake and the collection of smaller ponds are similar to the subglacial lakes found under ice caps in Greenland, Canada, and Antarctica. However, because of the freezing temperatures in the Martian polar regions, the water is probably very salty to remain a liquid.
This water is likely so salty that the ponds may be as dead as the salt lakes on Earth, however, there are extremophile microbes on Earth that can live in very hostile conditions, so it is possible that there is some sort of life in the Martian subsurface polar lake systems.
Today, the extremely thin Martian atmosphere means that there can't be any liquid water on the surface, but ESA says that subsurface water may have survived millions or billions of years – dating back to the era when Mars was much warmer and wetter and had lakes, rivers, and oceans.
The video below provides an overview of the discovery.
Source: ESA