Recent studies reported the discovery of lakes of liquid water below the polar ice caps on Mars, but others later refuted the find. Fueling the debate are two new independent studies, which have reached opposite conclusions.
In 2018, scientists analyzing data from the radar instrument onboard ESA’s Mars Express orbiter reported some strange signals from near the Red Planet’s south pole. One region in particular was showing up as a bright spot in the radar image, producing a profile consistent with subglacial lakes seen beneath the ice sheets of Greenland and Antarctica.
This signal, the researchers said, indicated that there was a lake of liquid water stretching about 20 km (12.4 miles) wide, located about 1.5 km (0.9 miles) below the ice cap. This water remains liquid despite temperatures as low as -68 °C (-90 °F), thanks to the presence of large amounts of magnesium and calcium salts. Another study suggested that it’s heated by an underground magma chamber. In 2020, the scientists studied a wider section of data and found signatures of three more subsurface lakes in the area.
However, not all scientists agree, with several studies released last year refuting the lake hypothesis. One found that these radar reflections were common in the region, including at depths too shallow for liquid water to exist. The second found that deposits of clays, metal-bearing minerals and saline ice could create similar signals. And the third tested the clay hypothesis in the lab by checking the radar reflections of frozen clay samples, finding they were a close match for the Mars Express signals.
Now, two new studies have joined the discussion. The first examined the salts that are thought to keep the water from freezing, and studied how they respond to radar. The team created brines of perchlorates and chlorides, and placed them in a chamber that mimics the pressure and temperature of the Martian polar environment.
The study showed that these brines do produce the same radar signal as the orbiter observed. They might not be deep lakes, the researchers said, but the brines could be saturated between grains of ice or soil.
The second study fell in the “no water” camp. The team tweaked a radar map of Mars by adding a global ice sheet to the model, and seeing how that affected the signals from different regions. They found that bright reflections similar to the “lake” were suddenly visible all over the planet.
On closer inspection, the researchers found that many of the locations of these new bright spots corresponded to volcanic plains. Rocks produced from iron-rich lava flows can reflect radar in a similar way here on Earth, the team says, so that could be what’s happening on Mars too.
Lakes of liquid water on Mars may be the more exciting story, but unfortunately it seems that the tide is turning against the idea. More studies seem to support alternate theories, which are often more simple. But of course, further data will be needed to find out what’s really going on beneath the south polar ice caps of the Red Planet.
The first study was published in the journal Earth and Planetary Sciences Letters, while the second appeared in Geophysical Research Letters.
