Advanced radar on board the Mars Express probe has detected signs of an underground ice lake near the north polar of the red planet, an international research team said on Wednesday.
The Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) also found more evidences of past water on the red planet, reported scientists from Italy, France, Germany, and the United States. Their findings appeared in the early online edition of the Journal Science.
The results of the radar's first scan of the red planet, made in July this year, have shown what scientists believe to be an impact crater, up to 250 km across and buried 1.5-2.5 km below the surface, in the Chryse Planitia lowland near Mars' north polar.
"In the mid-latitude Chryse Planitia, MARSIS has detected a 250-km-diameter circular structure, presumably of impact origin. Embedded in this structure is a continuous reflector that may be the basin floor beneath a thick volume of low-loss material," reported the scientists.
Radio waves from the radar's 20-meter antennae penetrate the planet's surface before reflecting off layers of different materials. The strength and time delay of these echoes could help scientists to locate deposits of ice, or even trapped aquifers of liquid water.
The basin is at least partly filled with ice-rich material, the researchers concluded after analyzing the echoes. The researchers also suggested that water may have once flowed into the crater.
"In its only observation of the north polar layered deposits, the sounder has apparently penetrated over 1 km of the ice-rich deposits, likely imaging the basal contact. The low attenuation observed in the north polar lowland indicates a composition of nearly pure, cold water ice, " they wrote in the paper.
Water is a key ingredient to life. While there is no firm evidence that biology has ever existed on Mars, scientists are seeking locations that may once have held standing water as logical start point for future missions.
Signs of a wet Martian history had been detected by the Mars Express probe and two rovers of US National Aeronautics and Space Administration (NASA). The Mars Express, launched by the European Space Agency in June, 2003, is now still orbiting the red planet.
But the new findings are surprising because the lowland lies in a relatively temperate mid-latitude region, where no ice is seen at the surface. Scientists had expected to find liquid water beneath.
"Other explanations cannot be ruled out," cautioned the researchers, while adding that they have planned further detection next year.