Underground lake of liquid water detected on Mars

A lake of liquid water has been detected by radar beneath the southern polar ice cap of Mars, according to a new study by Italian researchers from the Italian Space Agency, published Wednesday in the journal Science.

Evidence was gathered by the Mars Advanced Radar for Subsurface and Ionosphere Sounding instrument, also known as MARSIS, on the European Space Agency’s Mars Express spacecraft.

Between May 2012 and December 2015, MARSIS was used to survey the Planum Australe region, which is in the southern ice cap of Mars. It sent radar pulses through the surface and polar ice caps and measured how the radio waves reflected back to Mars Express.

Those pulses reflected 29 sets of radar samples that created a map of drastic change in signal almost a mile below the surface. It stretched about 12.5 miles across and looked very similar to lakes that are found beneath Greenland and Antarctic ice sheets on Earth. The radar reflected the feature’s brightness, signaling that it’s water.

“We interpret this feature as a stable body of liquid water on Mars,” the authors wrote in the study.
The study authors ruled out any other causes for this brightness.

Previously, there have been some suggestions about water on Mars, like droplets of water condensing on the Phoenix lander or as the possible cause of recurring slope lineae, which are seasonal dark streaks on Martian slopes. But there hasn’t been evidence of stable bodies of water until now, the researchers said. However, the presence of liquid water at the base of Martian polar caps was first hypothesized in a study 31 years ago.

Given its location beneath the polar ice cap, the water is expected to be below the freezing point of water. But salts like magnesium, calcium and sodium already found on Mars could help the water to form brine, which would lower the melting point to allow the lake to remain liquid.

On Earth, lakes exist below the Antarctic ice sheet even though the mean annual temperature is around negative 76 degrees Fahrenheit. Brine lakes on Earth can remain liquid at 8.6 degrees Fahrenheit, according to the study. In comparison, salty ocean water freezes at 28.4 degrees Fahrenheit, according to the National Oceanic and Atmospheric Administration.

Much like our own ice sheets, the polar ice caps change depending on the climate and act as archives for what has happened in the past. Learning more about these caps can reveal Mars’ climate history.