by New computer simulations have cast doubt on the possibility of a lake of liquid water trapped under the southern ice of Mars, suggesting that dense layers of ice could produce the same radar reflections as liquid water.
In 2018, the European Space Agency did Mars Express orbiter used its MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) instrument to identify what appeared to be 20 kilometers wide (12.4 miles) a lake of liquid water buried deep under 1.5 km (0.93 miles) of ice in a region called Planum Australe, in the south polar plain of Mars. Similar evidence subsequently emerged for the many lakes that could existbut some are so close to the surface that it seemed impossible for water to be a liquid there.
That’s because of a surface Mars yes too cold and the atmosphere pressure too low to allow liquid water to stand too close to the surface. However, at the base of the south polar ice cap, the temperature and pressure conditions, with the help of a little natural antifreeze, could allow for the existence of glacial lakes.
Related: Water on Mars: Exploration & Evidence
This antifreeze could come in the form of calcium and magnesium perchlorate, a chemical compound found by NASA on the surface of Mars. phoenix mission in 2008. Magnesium and calcium perchlorate, when dissolved in water, would lower its freezing point to a minimum of 68 degrees and minus 75 degrees Celsius (minus 92 and minus 103 degrees Fahrenheit) respectively — very close to the predicted temperature of minus 68 degrees C (minus 90 degrees F) at the base of the ice cap. Therefore, it is not too much to imagine local conditions of temperature, pressure and concentration of perchlorate that allow large pools of liquid water on Mars.
Additional evidence for such lakes came from measurements of surface ice undulations; liquid water lowers the amount of friction between an ice sheet and the underlying bedrock, allowing the ice sheet to flow faster over the bedrock. This increase in flow rate results in troughs and peaks in the surface ice, as it were exactly what is seen in Planum Australe.
Despite all this evidence, however, many in the planetary science community were skeptical; the presence of liquid water on Mars would be unusual, and unusual evidence would be required. Now, a team of scientists from Cornell University have fanned the flames of this doubt with new results that offer another explanation for the radar echoes.
“I can’t say that it is impossible that there is liquid water down there, but we are showing that there are much simpler ways to get the same views without having to stretch so far, using mechanisms and materials which we already know there,” said Cornell’s Daniel Lalich in a statement. Lalich is the lead author of new research that suggests that compacted ice layers may return a strong radar signal that looks just like the radar echo from a liquid layer.
A large body of water is able to reflect radar back to its source because of the flatness of a lake, and so on World A bright radar reflection of the kind detected by MARSIS would certainly mean liquid water, like pockets of water under Antarctica, for example Lake Vostok. However, planetary scientists must be careful about assuming that what is true for Earth is true for other planets, where conditions are not the same.
RELATED STORIES:
— Water on Mars carved deep gullies and left a ‘great puzzle’ for the Red Planet’s history
— Water on Mars could have flowed for a billion years longer than thought
— Mars may hide oceans of water under its crust, according to a study
Lalich’s group ran thousands of simulations to test whether multiple dense ice layers could mimic a lake’s radar signal. Each simulation changed the thickness of the ice layers and their composition (meaning, how dirty they were). They found that, in several cases, layers of tightly packed ice deposited long ago and crushed under the weight of the ice cover can produce bright radar reflections just like those detected by MARSIS.
The trick is to “constructively interfere” with the 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 part of the radar beam back, and because the layers are pressed so tightly together, the radar echoes overlap and combine, increasing their strength and making them appear brighter.
“This is the first time we have a hypothesis that explains the entire population of observations below the ice cap without introducing anything unique or odd,” said Lalich. “This result is when we get a bright reflection scattered all over the place exactly as you would expect from a thin layer interference in the radar.”
So far, the question of whether there is a dreamlike lake beneath the south pole remains unanswered, but Lalich insists that the simulations at least offer a much simpler and, in his eyes, more likely explanation than a lake.
“The idea of liquid water even slightly near the surface would be very exciting,” said Lalich. “I don’t think it’s there.”
The results of Lalich’s team were published on June 7 in the journal Scientific Progress.
