Italian researchers using ground-penetrating radar have discovered an underground lake on Mars, the first such find and the solution to a three-decade-old mystery about whether liquid water might exist at its poles. Astronomers analyzed radar data from an Italian-U.S. instrument aboard the Mars Express, a European Space Agency probe that in June marked its 15th year in Martian orbit. The data revealed a 12-mile-wide liquid layer near the planet\u2019s South Pole, about a mile beneath the Martian surface. The radar showed a bright reflective area that\u2019s consistent with water and, practically speaking, nothing else. Its thickness couldn\u2019t be determined with radar. If life exists at all on Mars, \u201cthis is certainly not a very pleasant environment,\u201d said lead author Roberto Orosei of the National Institute for Astrophysics in an accompanying video. The research takes advantage of a simple fact about the Solar System. Planets are just planets, and what occurs on one may occur elsewhere, too. The scientists built upon established research that used radar to identify lakes beneath Antarctic glaciers. The forces allowing water to pool under Antarctic ice explain how the same phenomenon can happen on Mars, according to the paper, published Wednesday in the journal Science. Enormous pressures, like those under Antarctica or a mile under Mars, can lower water\u2019s freezing point. Also, the Martian soil is filled with magnesium, calcium and sodium salts, a mix that would have the effect of lowering the freezing temperature of water further still, to perhaps a minimum -60 degrees Celsius (-76 degrees Fahrenheit). No such conclusions are technically conclusive until a probe drills through the Martian soil and rock and actually takes a sip. And while that would require \u201ctechnological developments that at the moment are not available,\u201d Orosei said, the researchers nonetheless have high confidence in their results. The Planum Australe, the patch of Mars under study, registered very high brightness - at levels just like water under Antarctica and Greenland. Ground-penetrating radar on Earth is used for identifying groundwater, tunnels, unexploded bombs, ancient human-built structures and more. The principle is the same above Mars. The satellite broadcasts radar signals to the surface. The rate and strength at which the signals bounce off each stratum allows the team to try and reconstruct the spacing and composition of layers below the surface. The targeted area, which sits on the planet\u2019s southern polar ice cap, was scanned on 29 flyovers over the course of three years. Finding a body of water on another planet is novel in and of itself, and part of a larger hunt. NASA has long employed a follow-the-water strategy in its search for life. \u201cOur working concept of life should also identify environmental conditions that are most conducive to life,\u201d wrote authors of the U.S. space agency\u2019s current 10-year plan for Solar System exploration. \u201cA habitable environment must sustain liquid water at least intermittently and must also allow key biological molecules to survive.\u201d Astronomers have previously discovered water-ice and seasonal liquid water on Mars. Space aficionados also root for more water discoveries that human explorers to the red planet may need eventually to tap.