Groundwater on Mars defies expectations

A new analysis Seismic data from NASA’s Mars InSight mission revealed some surprises.

First surprise: the first 300 meters of the basement under the landing site near the Martian equator contain little or no ice.

“We find that the crust of Mars is weak and porous. The sediments are not well cemented. And there’s no ice or not a lot of ice filling the porous spaces,” said geophysicist Vashan Wright of the Scripps Institution of Oceanography at the University of California, San Diego. Wright and three co-authors published their analysis in Geophysical Research Letters.

“These results do not rule out that there may be grains of ice or small balls of ice that do not cement other minerals together,” Wright said. “The question is, what is the probability that the ice is present in this form? »

The second surprise contradicts a central idea about what happened to water on Mars. The Red Planet may have hosted oceans of water early in its history. Many experts suspected that much of the water was part of the minerals that make up underground cement.

“If you put water in contact with rocks, you produce a whole new set of minerals, like clay, so water is not a liquid. It’s part of the mineral structure,” said study co-author Michael Manga of the University of California (UC) Berkeley. “There is cement, but the rocks are not full of cement.”

“Water can also penetrate minerals that don’t act like cements. But uncemented subsoil removes a way of keeping a record of biological life or activity,” Wright said. Cements , by their very nature, hold rocks and sediments together, protecting them from destructive erosion.

The lack of cemented sediments suggests a water shortage in the 300 meters below InSight’s landing site near the equator. The average below-freezing temperature at Mars’ equator means conditions would be cold enough to freeze water if it were there.

Many planetary scientists, including Manga, have long suspected that the Martian subsoil would be full of ice. Their suspicions dissipated. Yet large ice caps and frozen ground ice remain at the Martian poles.

“As scientists, we are now faced with the best data, the best observations. And our models predicted that there should still be frozen ground at that latitude with aquifers below,” said Manga, professor and chair of Earth and Planetary Sciences at UC Berkeley.

The InSight spacecraft landed on Elysium Planitia, a flat, smooth plain near the Martian equator, in 2018. Its instruments included a seismometer that measures vibrations caused by earthquakes and falling meteorites.

Scientists can link this information to a huge body of knowledge about the surface, including images of Martian landforms and temperature data. Surface data suggests that the subsoil may consist of sedimentary rocks and lava flows. Yet the team had to account for uncertainties in subsurface properties such as porosity and mineral content.

Seismic waves from earthquakes provide clues to the nature of the materials they pass through. Possible cementing minerals, such as calcite, clay, kaolinite, and gypsum, affect seismic velocities. Wright’s team at Scripps Oceanography applied computer modeling of rock physics to interpret velocities derived from InSight data.

“We ran our models 10,000 times each to incorporate uncertainties into our answers,” said co-author Richard Kilburn, a graduate student working at the Wright-led Scripps Tectonorockphysics Lab. Simulations showing a subsoil composed mainly of uncemented materials fit the data best.

Scientists want to probe underground because if life existed on Mars, that’s where it would be. There is no liquid water on the surface and underground life would be shielded from radiation. Following a sample return mission, a NASA priority for the next decade is the Mars Life Explorer mission concept. The goal is to drill two meters into the high-latitude Martian crust to search for life where ice, rock and atmosphere come together.

The international Mars Ice Mapper robotic mission is already under consideration to help NASA identify potential scientific goals for the first human missions to Mars. Scripps Oceanography helps prepare young scientists to contribute to such missions.

“All my life growing up, I heard that the Earth could become uninhabitable,” said study co-author Jhardel Dasent, another graduate student in the Wright-led lab. “I am now at the age where I can contribute to producing the knowledge of another planet that could lead us there.”

This research was funded by the National Science Foundation, NASA, and the CIFAR Earth 4D program.

– This press release was originally published on the University of California – San Diego website

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