Isegoria

Radar observations have revealed what appears to be a buried lake on Mars:

Discovered by a team of Italian scientists using three year’s worth of data from the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) instrument on the European Space Agency’s Mars Express orbiter, the potential lake is at least a few meters deep, and might be a fixed, steady feature of the subsurface. If confirmed, this would be the first-known reservoir of liquid water on present-day Mars—a keystone in the search for past or even present life on the Red Planet, potentially offering fresh clues about how Earth’s neighbor so profoundly transformed billions of years ago from a warmer, wetter world to its current freeze-dried state. Announced today at a press conference in Rome, the results are detailed in a study appearing in the July 26 edition of Science. Although this is just one detection, the team wrote, “there is no reason to conclude that the presence of subsurface water on Mars is limited to a single location.”

“The presence of a body of liquid water beneath Mars’s south polar cap has various implications, opening new possibilities for the existence of microorganisms in the Martian environment,” says Sebastian Lauro, a study co-author based at Roma Tre University in Rome. “Moreover, it provides a valuable confirmation that the water that once flowed abundantly over the Martian surface in the form of seas, lakes and rivers filled the voids in the subsurface.”

For the past 12 years MARSIS has mapped the Martian underground using beams of low-frequency radar pulses, which can penetrate up to several kilometers beneath the surface. Although they pass relatively unscathed through most substances, these pulses reflect back up to the spacecraft each time they encounter boundaries between different materials, such as the interface of ice and bedrock. That reflection is particularly strong at interfaces with liquid water, and shows up as a distinctively bright spot in visualizations of the data. Following up on preliminary detections of bright spots beneath Mars’s southern ice cap dating back to 2007, the Italian team reprogrammed MARSIS to employ a more intensive scanning mode, then surveyed Planum Australe 29 times with the instrument between 2012 and 2015. Time and time again across the entire observing campaign the new MARSIS readings revealed a consistent 20-kilometer-wide bright spot nestled in a bowl-like depression beneath the ice cap in Planum Australe—a feature consistent with a sizable body of liquid water (or, to be fair, with water-saturated sediments more akin to subterranean sludge). The team then spent almost 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.

Billions of years ago, Mars was a much more Earth-like place where water pooled in seas, carved enormous canyons and bubbled from hot springs. Life, many astrobiologists speculate, may have had no difficulty getting started there. But early in its promising existence the planet somehow lost its way, transforming into a desiccated orb of dried-up ocean-, river- and lakebeds. Robotic missions to the planet’s surface still find surprising echoes of that bygone time, such as patches of water-ice frost forming on rocks as well as water droplets condensing like dew on a lander’s leg. Orbiters, too, have glimpsed what might be rivulets of water flowing down sun-bathed crater walls at the height of Martian summer. Perhaps life, too, has managed to endure in some diminished, limited way. But, if so, it would have to contend with a world in which all moisture quickly vanishes in the thin, cold air, leaving the surface dry as a bone. Still, the water that once flowed across the land had to go somewhere. Some of it was likely lost to space, due to Mars’s diminutive gravitational field, but a significant fraction of the planet’s aqueous inventory never really left, instead just freezing belowground. Now it appears not all of that buried watery wealth is frozen after all.

“The really exciting thing is that this is a stable body of liquid water that was observed in the radar data over three years, not just droplets that have been observed over a short period of time,” says Anja Diez, a glaciologist at the Norwegian Polar Institute who wrote an accompanying commentary about the discovery. The subsurface lake, Diez says, may be similar those found via radar-sounding on Earth beneath ice sheets in Antarctica and Greenland.

Posted in Science | 4 Comments »