Doubt has been cast on the possibility of a lake of liquid water buried beneath Mars' southern ice cap by new computer simulations, which suggest that closely compacted layers of ice could produce the same radar reflections that liquid water would.
In 2018, the European Space Agency's Mars Express orbiter used its MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) instrument to identify what appeared to be a 20-kilometer-wide (12.4 miles) lake of liquid water buried deep beneath 1.5 km (0.93 miles) of ice in a region called Planum Australe, in the southern polar plain on Mars. Similar evidence subsequently came to light for potentially dozens of lakes, but some are so close to the surface that it seemed impossible for water to be a liquid there.
