It's the first time that scientists have ever discovered a stable body of liquid on the planet.
"This is a stunning result that suggests water on Mars is not a temporary trickle like previous discoveries but a persistent body of water that provides the conditions for life for extended periods of time", he said.
After seeing what possibly could be dark streaks of salty water that flowed down the Martian dune during warm seasons, the planetary scientists were certainly delighted.
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.
Given its location beneath the polar ice cap, the water is expected to be below the freezing point of water.
On Earth, lakes exist below the Antarctic ice sheet even though the mean annual temperature is around negative 76 degrees Fahrenheit.
A massive underground lake has been detected for the first time on Mars, raising hopes that more water - and maybe even life - exists there, worldwide astronomers said Wednesday. In 2020, the European Space Agency plans to send a rover to Mars that will search for more evidence of the presence of water or life. It's the same as when you put salt on a road, said Kirsten Siebach, a planetary geologist at Rice University who wasn't part of the study.
It has been known from earlier measurements by spacecraft, including the European Space Agency's Mars Express orbiter, that there is water ice at the poles of Mars. "There are microorganisms on Earth that are capable of surviving even in ice".
"That doesn't mean that there will be life there - but it does suggest that a lake on Mars would be a ideal place to look".
Previously, there has been some suggestions about water on Mars, like droplets of water condensing on the Phoenix lander or as the possible cause of recurring slope lineae, which are seasonal dark streaks on Martian slopes.
However, Stillman, who was not involved in the research, said another spacecraft, or other instruments, need to be able to confirm the discovery.
While the Martian landscape is covered in signs of water from the distant past, the planet's climate is now far too cold for liquid water to exist on the surface. "What helped the liquid water to be stable?"
"This is the first body of water it has detected, so it is very exciting", David Stillman, a senior research scientist in the Department of Space Studies at Southwest Research Institute in San Antonio, Texas, told AFP in an email. "Most importantly, this allows liquid water, essential for life", said Patel.