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“Lake” under the South Pole of Mars: a muddy photo?


The bright white area of ​​this image shows the ice cap covering the South Pole of Mars. It consists of frozen water and frozen carbon dioxide.Credit: ESA / DLR / FU Berlin / Bill Dunford

Two research teams using data from the European Space Agency’s Mars Express Orbiter recently published results suggesting that what was thought to be an underground lake on Mars may not be one at all. did.

In 2018, scientists working with data from Mars Express Orbiter announced an astonishing discovery: Radar device It seems that a liquid underground lake has appeared, reflecting off the South Pole of the red planet. Since then, several other such reflections have been announced.

therefore New paper Published in the American Geophysical Union Geophysical research letterAditya Khuller, a graduate student in the School of Earth and Space Exploration at Arizona State University, and Jeffrey Plaut of NASA’s Jet Propulsion Laboratory (JPL) analyzed a wide range of data from Mars Express before to do it around the South Pole. Explain that we have discovered dozens of radar reflections. ..But many are in areas that should be too cold the water Leave it liquid.

The signal is Liquid water It is also being considered by a team of scientists led by Carver Bearson, ASU postdoctoral researcher in Earth and space exploration. Their research too Recently published AGU Geophysical research letter We then determined that these bright reflections could be caused by underground clay, minerals containing metals, or saltwater ice.

The Mars Express is NASA’s second oldest and continuously active spacecraft to orbit non-Earth planets, following NASA’s 2001 Martian Odyssey. While the Mars Express orbiting Mars, it continues to provide important data on the subsoil, surface and atmosphere of the Red Planet.

On board this spacecraft is a Mars altitude radar for underground and ionospheric exploration, or a device called MARSIS for short. This device uses a radar sounder to assess the underground composition of Mars.

MARSIS has been collecting data around Mars, including Antarctica, since 2004, allowing scientists to construct a three-dimensional view of the Antarctic region. “We wanted to look under the Antarctic ice and use the MARSIS data to characterize the ancient terrain below,” says Khuller.

In other recent studies using MARSIS data, researchers have found areas where underground reflections are brighter than surface reflections. This is not what scientists expect.

“Usually, radar waves lose energy as they pass through matter, so deep reflections should be less bright than surface reflections,” he said along with an internship at JPL under the Prout’s instructions. Khuller said. “There are several possible reasons for the unusually bright underground reflections, but these two studies conclude that the liquid water component appears bright on radar and that the liquid water component is responsible for these bright reflections. I tied it up. “

The colored dots represent where the bright radar reflections were discovered by ESA’s Mars Express orbiter in the Antarctic cap of Mars. Credit: ESA / NASA / JPL-Caltech

Frozen time capsule

Radar signals, originally interpreted as liquid water, have been discovered in the area of ​​Mars known as the Antarctic layered sediments. It gets its name from an alternating layer of water ice, dry ice (frozen carbon dioxide) and dust that has settled there for millions of years. These layers believe they hold a record of how the tilt of the axis of Mars has changed over time, just as changes in the tilt of the Earth have created ice ages and warmer periods all over the place. throughout the history of our planet. Was done. As the obliquity angle of Mars decreased, layers of snow and dust accumulated in the area, ultimately forming the thick layers of ice found there today.

The area originally believed to contain liquid water is a relatively small area of ​​Martian Antarctic sediment that spans about 6 to 12 miles (10 to 20 kilometers). Khuller and Praut extended the search for similar powerful radio signals to 44,000 measurements over 15 years of MARSIS data in southern Mars. Polar region..

Unexpected “lake”: a muddy photo?

New, in-depth study by Khuller and Plaut reveals dozens of additional light radar reflections over an area and depth much wider than ever before. In some places, temperatures were less than a mile from the surface, estimated at minus 81 degrees Fahrenheit (minus 63 degrees Celsius). Even though it contained a salty mineral called perchlorate, it was cold enough to freeze water. You can lower the freezing point of water.

“I don’t know if these signals are liquid water, but they appear to be much more prevalent than the original article found,” said co-author, co-principal investigator of Orbiter’s MARSIS instrument. said Prout. .. “What liquid water is flowing under the South Pole of Mars, these signals point to something else.”

Further Khuller Beware of the 2019 treaty The researchers calculated the heat required to melt underground ice in the region and found that only recent volcanic activity below the surface can explain the potential existence of liquid water beneath Antarctica. ..

“They discovered that it takes twice as long as Mars’ estimated geothermal heat flow to keep this water liquid,” Khuller said. “One possible way to get this amount of heat is volcanic activity, but since there’s really no solid evidence of recent volcanic activity in Antarctica, volcanic activity causes liquid water to flow underground. It seems unlikely that it exists in this whole area. “

The next step for Khuller and Plaut in this series of studies is to study the discovery of the second deeper layer beneath some. Antarctic It represents the ancient buried land of Mars, called the Dolsa Argentavis, as scientists believe. It is believed to have been modified by ancient glaciers that once existed in the area, and they are trying to determine its composition and age more accurately.

Research examines Martian groundwater signals in more detail

For more information:
Aditya R. Khuller et al, Basal Interface Characteristics of Martian Antarctic Sediments, Geophysical research letter (2021). DOI: 10.1029 / 2021GL093631

CJ Bierson et al, strong MARSIS radar reflections from the base of the Martian Antarctic Crown, may be due to conductive ice or minerals. Geophysical research letter (2021). DOI: 10.1029 / 2021GL093880

Michael M. Sori et al, Martian water, grains of salt: the basic melting of the ice in Antarctica today requires local thermal anomalies. Geophysical research letter (2019). DOI: 10.1029 / 2018GL080985

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