Two years ago, researchers announced the likely discovery of a large lake of water on Mars, underneath its South Pole.
New observations have now confirmed that the lake really is there, and in fact, it’s not alone.
Multiple bodies of water have been discovered around the main lake, which is roughly 20 kilometers (12 miles) across.
The bodies are separated from each other by strips of dry land and are all located roughly 1.5 kilometers (0.9 miles) below Mars’s surface, in a region called Planum Australe.
“We have confirmed the existence of the big body of water independently and we also find the other patches, so it means that it is not an isolated, casual discovery. It is a system. And this changes things,” said corresponding author Professor Elena Pettinelli, from University of Rome 3.
How is liquid water possible on Mars?
How this water remains liquid in these lakes is a big puzzle. Their temperatures are expected to be about -68°C (-90°F).
On Earth, subglacial lakes in Antarctica remain liquid thanks to pressure from ice above.
For water to remain liquid under the frigid temperature of Mars, pressure from the above ice is not enough.
The researchers think that they must be briny lakes with high concentrations of salt. The new observations also suggest that they are not new or temporary features; they’ve been there for a geologically long time.
“We now think [the lake system] has probably survived a very long time. We are thinking for millions of years for sure. It probably got progressively covered by ice when the climate changed,” Professor Pettinelli explained.
After the 2018 discovery, there were discussions of a potential geothermal source underneath the lake to keep it liquid, but the discovery of the other three bodies of water makes this scenario less likely.
The discovery was made using the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) onboard the Mars Express spacecraft. Back in 2018, they discovered the lake using 29 observations of the areas and doing some clever data processing. The spacecraft releases radar pulses that are reflected by underground material.
Further study and potential discovery of more lakes will be difficult with current orbiters around Mars, but the team believes that it’s very likely more trapped water exists below the ice at the South Pole of the Red Planet.