New computer simulations that suggest tightly packed layers of ice could produce the same radar reflections as liquid water cast doubt on the possibility of a lake of liquid water buried beneath Mars’ southern ice cap.
In 2018, the European Space Agency Mars Express the orbiter used its MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) instrument to identify what appeared to be a 20-kilometer-wide (12.4 mi) lake of liquid water buried deep under 1.5 km (0.93 mi) of ice in an area called Planum Australe, in the south polar plain on Mars. Similar evidence subsequently came to light potentially dozens of lakesbut some are so near the surface that it seemed impossible for water to be a liquid there.
That’s because the surface Mars Yippee too cold and atmospheric pressure too low for liquid water to stay too close to the surface. However, at the base of the southern polar ice cap, the temperature and pressure conditions, with the help of a little natural antifreeze, could allow salt lakes to exist.
Related: Water on Mars: Exploration and Evidence
That antifreeze could come in the form of calcium magnesium perchlorate, a chemical compound found by NASA on the surface of Mars. The Phoenix Mission in 2008. Magnesium perchlorate and calcium perchlorate, when dissolved in water, would lower their freezing points to at least minus 68 degrees and minus 75 degrees Celsius (minus 92 and minus 103 degrees Fahrenheit), which is very close to the predicted temperature of minus 68 degrees. degrees C (minus 90 degrees F) at the base of the ice cap. As a result, it is not too difficult to imagine localized conditions of temperature, pressure, and perchlorate concentration combining to allow large pools of liquid water on Mars.
Further evidence for such lakes came from measurements of surface ice ripples; liquid water reduces the amount of friction between the ice sheet and the bedrock below, allowing the ice sheet to flow faster over the bedrock. This increase in flow results in depressions and peaks in the surface ice, which is exactly what is seen in Planum Australe.
Despite all this evidence, however, many in the planetary science community are skeptical; the presence of liquid water on Mars would be an extraordinary find and require extraordinary evidence. Now, a team of scientists from Cornell University has fanned the flames of that skepticism with new findings that provide an alternative explanation for radar echoes.
“I can’t say it’s impossible for there to be liquid water down there, but we’re showing that there are much simpler ways to get the same observations without having to stretch so far, using mechanisms and materials that we already know they exist there.” said Daniel Lalich of Cornell Va declaration. Lalich is the lead author of new research that suggests compacted layers of ice could return a strong radar signal that looks just like a radar echo from a layer of liquid.
A large body of water is able to reflect the radar back to its source because of how flat the lake is, and beyond Earth bright radar reflections of the type detected by MARSIS would almost certainly indicate liquid water, similar to pockets of water under Antarctica, such as Lake Vostok. However, planetary scientists must be wary of assuming that what is true for Earth is true for other planets where conditions are not the same.
Lalich’s group ran thousands of simulations to test whether multiple tightly packed layers of ice could mimic the lake’s radar signal. Each simulation varied both the thickness of the ice layers and their composition (that is, how dirty they were). They found that in many cases, tightly packed layers of ice deposited a long time ago and crushed under the weight of the ice sheet can produce bright radar reflections just like those detected by MARSIS.
The trick is “constructive interference” of radar waves. The spatial resolution on MARSIS is limited, and if the ice layers are too thin, the radar instrument cannot distinguish them. Each layer would reflect a portion of the radar beam back, and because the layers are crushed so tightly, the radar echoes overlap and combine, amplifying their strength and appearing brighter.
“This is the first time we have a hypothesis that explains the entire population of observations under the ice cap without introducing anything unique or special,” Lalich said. “This result, where we get bright reflections scattered all over the place, is exactly what you would expect from thin layer interference in radar.”
For now, the question of whether there is a salt lake under the South Pole remains unanswered, but Lalich says the simulations at least provide a much simpler and, in his eyes, more likely explanation than a lake.
“The idea of ​​liquid water even a little bit near the surface would be really exciting,” Lalich said. “I just don’t think it’s there.
The findings of Lalich’s team were published June 7 in the journal Scientific advances.