Are Mars’ subsurface lakes really lakes?

 The European Space Agency’s Mars Express spacecraft located the first proof of an underground lake in 2018. The lake was located deep beneath the Antarctic ice cap. What an exciting discovery! Then in 2020, space scientists reported that they had discovered three more lakes near the first one. The presence of lakes on Mars, even cold, salty, and dark ones, increases the likelihood of life on the Red Planet. But are the lakes beneath Mars lakes?

A new study by two different research teams has cast doubt on this initial finding. Scientists from Arizona State University (ASU) and the ASU School of Earth and Space Exploration further studied the Mars Express data. They found some evidence that the lake may not be a lake at all.

The researchers published their peer-reviewed results in two new papers in Geophysical Research Letters on June 16, 2021, and June 28, 2021.

When it was first discovered, a possible lake appeared on the Mars Express radar image as a bright reflection consistent with liquid water. This was hard to believe, given the cold temperatures on Mars, deep beneath the Antarctic ice cap. However, scientists concluded that the lake was most likely water kept liquid by salts. The lake was found beneath a layered Antarctic deposit of alternating layers of water ice, dry ice (frozen carbon dioxide), and dust.

ASU researchers examined Mars Express MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) data and found dozens more similar lakes(?). were found. They expanded their search for similar radar signals to 44,000 measurements spanning 15 years of MARSIS data. The search covers the entire south polar region of Mars. Lead author Aditya Khuller said, “We are very pleased with the results.

We wanted to use the MARSIS data to look beneath the Antarctic ice and characterize the old terrain.

That sounds like fun, but there is a problem. There are too many lakes. Many of the new lakes are in places where the subsurface is too cold for liquid water to exist, even with the help of salt. But they looked just like any other bright reflection seen on radar and interpreted as a lake.