The proposed "lake" sits beneath the planet's south polar ice cap, and is about 20km (12 miles) across.
The presence of liquid water at the bottom of the Martian polar ice caps was first theorized more than 30 years ago, the researchers said, but it had been "inconclusively debated ever since". With such encouraging results now published, those involved with the hunt are sure to be emboldened. On Earth, microbial life persists down in the dark, frigid waters of one such lake. Subsurface echo power is color coded and deep blue corresponds to the strongest reflections, which are interpreted as being caused by the presence of water. The team then spent nearly a year analyzing the data, and another two years writing their paper and attempting to rule out non-aqueous explanations for what they had seen.
"We don't see the same reflector with SHARAD, not even when we recently summed together [thousands] of observations to create CATSCAN-like 3-D views of both polar caps", Nathaniel Putzig, Mars Reconnaissance Orbiter SHARAD deputy team leader and senior scientist at the Planetary Science Institute, said in an email. In the years to come you will likely hear more and more about this next close encounter as NASA and other space agencies make plans to actually visit the Red Planet.
This is when the Red Planet will shine its brightest since 2003.
Green said that a lander mission called InSight that's already on its way to Mars might be able to help provide corroborating evidence. Perhaps life, too, has managed to endure in some diminished, limited way.
Mars is now cold, barren and dry but used to be warm and wet. Hang on though, don't book your Mars vacation plans just yet. Now it appears not all of that buried watery wealth is frozen after all.
Scientists have discovered a body of liquid water on Mars for the first time, raising the possibility that the planet could sustain life.
European Space Agency's Mars Express spacecraft is depicted in orbit around Mars in artist's concept stereo illustration
"A similar situation has been discovered here on Earth, 4km below the ice of Antarctica, in Lake Vostok, where scientists have observed very primitive life in an area that is equally devoid of light and likely at similar temperatures", he says.
Until now, the stuff has only been found in the form of ice and in small quantities in the atmosphere. The weight of kilometres worth of ice above it could also be keeping the water in a liquid state, the researchers say.
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.
So while the findings suggest water is present, they do not confirm anything further. Orosei estimated the water temperature at somewhere between 14 degrees Fahrenheit (minus 10 degrees Celsius) and minus 94 degrees Fahrenheit (minus 70 degrees Celsius). When pointed at the surface ice caps of the planet, it measures how radio waves penetrate and reflect back to the spacecraft.
That life, however, would have to contend with another key factor making its aquatic environs possible: mineral salts that leach out of rocks and sediments to act as antifreeze. In recent years, that has led the space agency to contemplate robot probes to the moons of Jupiter and Saturn, like Europa or Enceladus, where it is now known that salty oceans exist underneath thin shells of ice and where imaginative astrobiologists can envision microbes or more complex creatures. A member of the MARSIS team who is not an author of the study, Jeffrey Plaut of NASA's Jet Propulsion Laboratory, told Science that "the interpretation is plausible, but it's not quite a slam dunk yet".