Scientists have long known that Mars has water in the form of ice and certain minerals.
The discovery was made using a radar instrument on board the European Space Agency's Mars Express orbiter, which launched in 2003. They do not know whether it's an underground pool or just a layer of sludge.
"If life ever arose on Mars, I would say that what has been discovered today, that subsurface lake, is probably one of the best spots where we could find life", Chevrier said.
If large bodies of liquid water lie beneath Martian polar ice, they could theoretically harbour living microbes to this day.
"On Earth, it's nearly a given that if a ground-penetrating radar spots stronger reflections from the sub-surface than from the surface of the polar ice, then you are seeing liquid water".
Between 2012 and December 2015 the Planum Australe region was mapped by the Mars Advance Radar for Subsurface and Ionosphere Sounding (Marsis) instrument carried on the orbiter.
But dissolved salts of magnesium, calcium, and sodium - known to be present in Martian rocks - are thought to maintain the briny miniature sea by reducing the melting point of water to minus 74C.
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"This is the place on Mars where you have something that most resembles a habitat, a place where life could subsist", said planetary scientist Roberto Orosei of Istituto Nazionale di Astrofisica in Italy, who led the research published in the journal Science.
The tool is called the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS), and was created to find subsurface water by sending radar pulses that penetrate the surface and ice caps. The Martian water news cycle is pretty active, thanks to multiple discoveries of ice deposits on the surface and frozen vapor in the atmosphere.
Speaking in a recorded interview released by Science, Prof Orosei revealed that his team spent years checking their results before being confident enough to announce the discovery.
Marsis was not able to measure the depth of lake, but the scientists estimate that it must be at least one metre thick.
"That water could be sourced from asteroids, the moon, or Mars".
On Earth, lakes exist below the Antarctic ice sheet even though the mean annual temperature is around negative 76 degrees Fahrenheit.
Professor Dempster said Australia had taken a leadership position on the matter, with University of New South Wales researchers examining business cases, mining methods, earth analogues, asteroid selection, asteroid navigation and other resources such as platinum. "But there are terrestrial organisms that can survive and thrive, in fact, in similar environments".