Mars Lakes :
If you have the thought of swimming on Mars, you just have to hold off your idea. Two new studies have put forward the idea that there aren’t any lakes deep in the red planet’s southern polar cap with potentially habitable liquid water.
The possibility of Mars lakes or subsurface lakes with a diameter of about 20 kilometers was first talked about in 2018 when the Mars Express spacecraft of the European Space Agency searched the planet’s southern polar cap using radar and Mars Advanced Radar for Subsurface and Ionosphere Sounding, or MARSIS.
The probe detected bright spots in the south pole indicating the presence of a large mass of liquid water beneath 1.5 km of solid ice that could potentially be home to living organisms. Later work argued the evidence of additional ponds surrounding the main lake basin.
Image credit: NASA/JPL-Caltech
But the planetary scientific community was skeptical about the existence of lakes, which would require some kind of permanent geothermal heating to maintain subglacial conditions on Mars.
Under the ice, the average temperature is -68°C, well below the freezing point of water, even if the lakes are made of saltwater and contain healthy amounts of salt, which lowers the water’s freezing point, it would still be impossible for water to remain in a liquid state.
In order for the Mars lakes to survive, only the underground magma pools would be able to keep the region fluid, which is unlikely given the current shortage of volcanoes on Mars.
“If the water is not liquid, is there anything else that could explain the bright radar reflections we see?” asked planetary scientist Carver Pearson of Arizona State University at Tempe.
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In a study published in Geophysical Research Letters, Pearson and colleagues describe two other substances that may explain otherwise. The reflectivity of a radar depends on the conductivity of the material through which the radar signal passes.
Liquid water has a fairly distinct radar signature, but studies of the electrical properties of clay minerals and frozen brine have shown that these materials can mimic this signal.
“I really don’t believe that the lake idea holds water, so an alternative was needed… smectites are abundant on Mars and heavily studied by spectroscopists, but they’ve been mostly neglected by the radar community. My hope is that we consider them more fully in the future and even revisit some of our previous work in light of these new results,” said Isaac Smith, a planetary scientist at York University and lead author of the new paper said to Gizmodo.
An independent cohort study on Mars lakes published in the same issue of Geophysical Research Letters added weight to the non-lake explanations.
The preliminary hydrological results of 2018 were based on MARSIS data on a small portion of the southern ice cap, but the instrument has now built 3D maps of the entire region, showing hundreds or thousands of additional bright spots.
“We find them literally everywhere,” planetary scientist Aditya Khuller from Arizona State University said about Mars lakes.
Creating plausible scenarios for maintaining fluid in all of these locations will be challenging. Khuller and Bierson believe that MARSIS is likely to target the type of generalized geophysical process that results in the formation of frozen minerals or brines.
Researchers stated that to date, no other agreeable explanations were presented on Mars lakes. And only the presence of clay minerals was demonstrated.
Although previous work on Mars lakes has already raised questions about the interpretation of the lake, this additional data may represent a death sentence for the existence of basins theory.
However, if the Lakes existed, they would most likely be extremely cold and contain up to 50% salt – conditions in which no known organism on Earth could survive. In this light, ponds won’t be a strong astrobiological target anyway, said Rivera Valentine.
Bierson stated that lab work to study how materials interact with conditions in the ice sheet of Mars’ south pole could further help reduce the formation of bright radar spots.
Meanwhile, Khuller is already working on seeing other habitats on the Red Planet, such as warmer mid-latitudes, where satellites have seen evidence of ice melting under the sun. “I think there are places today where there could be liquid water on Mars,” he said. “But I don’t think he’s in the south pole.”
“Everyone would love to find liquid water, but unfortunately, I don’t think we’re going to find any with current instrumentation,” Smith added about Mars lakes.