The ESA findings were published in Science – Italian astronomers have found evidence of a 12-mile-wide lake under the southern ice cap:
The presence of liquid water at the base of the martian polar caps has long been suspected but not observed. We surveyed the Planum Australe region using the MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) instrument, a low-frequency radar on the Mars Express spacecraft. Radar profiles collected between May 2012 and December 2015 contain evidence of liquid water trapped below the ice of the South Polar Layered Deposits. Anomalously bright subsurface reflections are evident within a well-defined, 20-kilometer-wide zone centered at 193°E, 81°S, which is surrounded by much less reflective areas. Quantitative analysis of the radar signals shows that this bright feature has high relative dielectric permittivity (>15), matching that of water-bearing materials. We interpret this feature as a stable body of liquid water on Mars.
You can read more about the findings at Nature, here, including things like:
“It’s a very promising place to look for life on Mars,” says Roberto Orosei, a planetary scientist at the National Institute of Astrophysics in Bologna, Italy. “But we do not know for sure if it is inhabited.” On Earth, similar ‘subglacial’ lakes are home to microbial life.
The lake is about 1.5 kilometres beneath Mars’s surface and is at least 1 metre deep. To keep from freezing, the water must be very salty, Orosei says — perhaps similar to super-salty subglacial lakes reported in the Canadian Arctic earlier this year. Salt-rich rocks beneath the Canadian lakes infuse the water and allow it to remain liquid, says Anja Rutishauser, a glaciologist at the University of Alberta in Edmonton. On Mars, salts known as perchlorates might be what’s making the brine; in 2008, NASA’s Phoenix spacecraft found perchlorates in soils near the planet’s northern polar ice.