The possibility of a lake of liquid water buried under the southern Martian ice cap has been cast into doubt by new computer simulations, which suggest that tightly packed layers of ice could produce the same radar reflections that water would. liquid.
In 2018, the European Space Agency March Express the orbiter used its MARSIS (Mars Advanced Radar for Subsurface Sounding and Ionosphere) instrument to identify what appeared to be a 20-kilometer (12.4-mile) wide liquid water lake buried deep under 1.5 km (0.93 miles) of ice in a region called Planum Australe, in the south polar plain on Mars. Similar evidence came to light later on potentially dozens of lakesbut some are so close to the surface that it seemed impossible for water to be a liquid there.
This is because the surface of March IS very cold AND weather pressure too low to allow liquid water to stay too close to the surface. However, at the base of the southern polar ice cap, temperature and pressure conditions, with the help of a little natural antifreeze, may allow salt lakes to exist.
Connected: Water on Mars: Exploration and Evidence
This antifreeze can come in the form of calcium magnesium perchlorate, which is a chemical compound that was found on the surface of Mars by NASA. The Phoenix Mission in 2008. Magnesium and calcium perchlorate, when dissolved in water, would lower the freezing point to a minimum of minus 68 degrees Celsius and minus 75 degrees Celsius (minus 92 and minus 103 degrees Fahrenheit)—very close to the predicted temperature of minus 68 degrees C (minus 90 degrees F) at the base of the ice cap. Consequently, it is not too difficult to imagine localized conditions of temperature, pressure, and perchlorate concentration conspiring to allow large pools of liquid water on Mars.
Further evidence for such lakes came from measuring surface ice ripples; liquid water decreases the amount of friction between an ice sheet and the bedrock beneath it, allowing the ice sheet to flow more quickly over the rocks. This increase in flow velocity results in troughs 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 have been skeptical; the presence of liquid water on Mars would be an extraordinary discovery and require extraordinary evidence. Now, a team of scientists from Cornell University have fanned the flames of this skepticism with new findings that offer an alternative explanation for radar echoes.
“I can’t say it’s impossible that there’s liquid water down there, but we’re showing that there are much simpler ways to get the same observations without having to go that far, using mechanisms and materials that we already have. we know they exist there.” Cornell’s Daniel Lalich said in a STATEMENT. Lalich is the lead author of new research that suggests that compressed ice layers can return a strong radar signal that looks exactly like the radar echo from a layer of liquid.
A large body of water is able to reflect radar back to its source because of how flat a lake is, and further earth Bright radar reflections of the type detected by MARSIS would almost certainly mean liquid water, similar to pockets of water under Antarctica, such as Lake Vostok. However, planetary scientists must be careful to assume 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 layers of tightly packed ice could mimic the radar signal of a lake. 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 long ago and crushed under the weight of the ice sheet can produce bright radar reflections like those detected by MARSIS.
The trick is “constructive interference” of radar waves. The spatial resolution in MARSIS is limited, and if the ice layers are too thin, the radar instrument cannot distinguish them. Each layer would reflect back a portion of the radar beam, and because the layers are pressed so tightly together, the radar echoes overlap and combine, amplifying their strength and making them appear brighter.
“This is the first time that we have a hypothesis that explains the entire population of observations under the ice cap without having to introduce anything unique or strange,” 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 beneath the south polar cap remains unanswered, but Lalich argues that the simulations at least offer a much simpler and, in his eyes, more likely explanation than a lake.
“The idea that there would be liquid water even somewhat close to the surface would have been really exciting,” Lalich said. “I just don’t think it’s there.”
Lalich’s team’s findings were published June 7 in the journal Advances in science.
#huge #underground #lake #south #pole #Mars
Image Source : www.space.com