Alan Duffy, an astronomer from Swinburne University and the lead scientist of Australia's Science Channel, says the liquid water is not a lake that you would want to swim in.
The lake is about 12 miles across and may not be potable, as the researchers predict it must be extremely salty to stay liquid in the -10 and -30 Celsius temperatures.
Since everything is a competition, perhaps this exciting discovery will inspire Donald Trump to improve NASA's budget to make sure the United States wins the race to Mars. But some time in the past - probably about 3.8 billion years ago - it lost its atmosphere, stripped away by radiation and solar wind from the sun.
Many scientists have speculated that a stable body of liquid water could be present beneath the Martian polar caps, but this is the first observation of the phenomenon.
"Nobody dares to propose that there could be any more complex life form", Orosei said.
Liquid water is hiding beneath Mars' south pole glaciers, researchers reviewing radar data have confirmed.
Following news of the findings, social media was understandably enthused, with some wondering what it might mean for the search for extraterrestrial life.
Evidence for the Red Planet's watery past is prevalent across its surface in the form of vast dried-out river valley networks and huge outflow channels clearly imaged by orbiting spacecraft. But salts like magnesium, calcium and sodium already found on Mars could help the water to form a brine, which would lower the melting point to allow the lake to remain liquid. While the temperature is expected to be well below freezing point, only pure water freezes at 0 degrees, notes the release. "The problem is that this water is located 1.5km underneath the South Pole, so there is an bad lot of ice to be drilled to before you reach this liquid water", he added.
It remains to be seen if more subsurface reservoirs of water will be found or whether the newly discovered one is some sort of quirk, Orosei said. Researchers are keenly interested in such reservoirs since they are reminiscent of subglacial lakes in Antarctica, which are teeming with microbial life. Coincidentally, one of these zones lies right over the new study area where the odd signal was found, Bramson said.
The team from Italy studied radio echo sounding data recorded between 2012 and 2015 by the Mars Express spacecraft.
Jonathan Lunine, director of the Center for Astrophysics and Planetary Science at Cornell University, who was not involved with the research, said the finding transforms Mars from a dusty planet to yet another "ocean world" in the solar system.
"But there are terrestrial organisms that can survive and thrive, in fact, in similar environments".
A NASA image of Mars. SHARAD operates at different frequencies than MARSIS does, but it's also created to pick up subsurface features. It was discovered as they surveyed the Planum Australe region near Mars' southern ice cap, which is made of water ice covered by frozen carbon dioxide.
Fred Watson, from the Australian Astronomical Observatory in the Department of Industry, Innovation and Science, says Mars has many striking similarities with our own planet.