Science & Technology

Clay, not water, is likely to be the source of Mars’ “lakes” – so watt-up?


Taken by NASA’s Mars Reconnaissance Orbiter, this image shows an ice sheet in the South Pole of Mars. The spacecraft has detected clay near this ice. Scientists suggest that such clay is the source of radar reflections, previously interpreted as liquid water. Credits: NASA / JPL-Caltech / University of Arizona / JHU

Three studies published last month question the premise of an underground lake beneath the South Pole of Mars.

Where there is water, there is life. That’s at least the case of Earth, and that’s why scientists continue to be intrigued by the evidence that there is liquid water on cold, dry Mars. The red planet is a difficult place to find liquid water. Water ice is abundant, but water warm enough to liquid on the surface lasts only a few seconds before turning into steam in the faint air of Mars.

Therefore, interest grew in 2018 when a team led by Roberto Orosei of Istituto Nazionale di Astrofisica in Italy announced that they had found evidence of an underground lake deep in the Martian Antarctic ice cap. The evidence they quoted came from radar equipment on board the ESA (European Space Agency) Mars Express Orbiter.

Colored dots represent sites where bright radar reflections have been detected
The colored dots represent where bright radar reflections were discovered by ESA’s Mars Express Orbiter in the Antarctic crown of Mars. Such reflections were previously interpreted as underground liquid water, but their prevalence and proximity to frigid surfaces suggest that they may be different. Credit: ESA / NASA / JPL-Caltech

Radar signals that can penetrate rocks and ice change when reflected by a variety of materials. In this case, they produced a particularly bright signal under the polar cap. This can be interpreted as liquid water. The potential of the environment in which microorganisms could live was exciting.

However, after scrutinizing the data along with experiments here in the cold laboratories of the Earth, some scientists now suspect that clay, not water, is creating the signal. Last month, three new treatises may have unraveled a mystery and depleted the lake hypothesis.

Isaac Smith at York University in Toronto
Isaac Smith of York University in Toronto bundled and frozen smectite clay in liquid nitrogen while working in the lab to test how it reacts to radar signals. The results challenged the hypothesis that an underground lake could be found in the South Pole of Mars.Credits: University of York / Craig Reza

Scientific ecosystem

Such gatherings provide the opportunity to test new theories and challenge each other’s perspectives. “Communities can create their own small scientific ecosystem,” said Jeffrey Prout of NASA’s Jet Propulsion Laboratory, one of the scientists at the conference. He is also a co-principal researcher for the equipment behind an interesting radar signal called MARSIS, or Mars altitude radar for underground and ionospheric exploration, along with Orosei. “These communities can be self-reliant,” he continued. “It helps you to ask someone a question and probably find the answer in a year or two.”

Polar scientists on Mars belong to a small and intimate community.Shortly after the Lake’s treatise was published, about 80 of those scientists International Conference on Mars Polar Science and Exploration It is located in Ushuaia, a seaside village on the southern tip of Argentina.

There were many stories centered around the underground lake. How much heat does it take to keep the water liquid under all that ice? Can salt water keep the liquid low enough to lower the freezing point of the water?

Of course, this isn’t the first time an exciting water-related hypothesis has rushed to investigate. In 2015, NASA’s Mars Reconnaissance Orbiter discovered what appears to be a streak of moist sand flowing down a slope, a phenomenon called “repeated slope lines.”However, repeated observations using a spacecraft HiRISE – Or high-resolution imaging science experiments – cameras have revealed that this is likely to be the following result: Sand flows.. A paper published earlier this year discovered many repetitive slopes after a global sandstorm on Mars in 2018. This finding suggests that the dust that accumulates on the slopes causes a stream of sand, which in turn exposes darker underground material that gives the lines a distinctive color. ..

Similar to the wet sand hypothesis, some scientists have begun to think of ways to test the underground lake hypothesis. “I felt like I should try to deal with this,” said Isaac Smith of York University in Toronto, who hosted the conference in Ushuaia and led the latest research showing that clay can explain the observations. ..

Too cold for the lake

Among those scientists was Prout. He and Aditya Khuller, a PhD student at Arizona State University who was an intern at JPL, analyzed 44,000 radar echoes from the base of the polar cap over 15 years of MARSIS data. They showed dozens more bright reflections, as in the 2018 survey. but, Their recent treatise In Geophysical Research Letters, they should be too cold for water to remain liquid, even when mixed with perchlorate, a type of salt commonly found on Mars that can suppress freezing. We found many of these signals in the region near the surface of the water temperature.

Next, two separate teams of scientists analyzed the radar signals to determine if anything else could be producing those signals.

ASU’s Carver Bierson has completed a theoretical study that suggests: Some possible materials It can cause signals such as clay, metal-containing minerals and salt water. But Isaac Smith of the University of York went further in another third treatise, learning that a group of clay called smectite was ubiquitous on Mars. He measured the properties of smectite in the laboratory.

Smectite looks like ordinary rock, but long ago it was formed by liquid water. Smith put some smectite samples in a cylinder designed to measure how radar signals interact with them. He also soaked them in liquid nitrogen and frozen them to minus 58 degrees Fahrenheit (-50 degrees Celsius). This is a temperature close to the South Pole of Mars.

“The lab was cold,” Smith said. “It was winter in Canada at the time. When I pumped liquid nitrogen into the room, it got cold. Because of COVID-19, it was bundled in a hat, jacket, gloves, scarf, and mask. It was pretty uncomfortable. . “

After freezing the clay samples, Smith found that their responses were almost in perfect agreement with MARSIS radar observations. He and his team then checked the clay present on Mars near those radar observations. They relied on data from MROs equipped with a mineral mapper called a compact observation imaging spectrometer. CRISM..

bingo. CRISM cannot look into the ice, but Smith found smectites scattered near the Antarctic ice cap. Smith’s team has demonstrated that frozen smectites can reflex and do not require extraordinary amounts of salt or heat, and that they are present in Antarctica.

There is no way to see what a bright radar signal is without landing on the South Pole of Mars and digging miles of ice. However, recent treatises provide a plausible explanation that is more logical than liquid water.

“In planetary science, we are often closer to the truth,” Prout said. “The original treatise did not prove that it was water, and these new treatises did not prove that it was not. But to reach consensus, try as much as possible. I’m narrowing down. “

Details of MRO

For more information on the Mars Reconnaissance Orbiter, please visit:

Clay, not water, is likely to be the source of Mars’ “lakes” – so watt-up? Clay, not water, is likely to be the source of Mars’ “lakes” – so watt-up?

Back to top button