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Using seismic activity to probe the interior of Mars, geophysicists have found evidence of a vast underground reservoir of liquid water, enough to fill the planet’s oceans. Using data from NASA’s InSight lander, the scientists estimate that the underground water could cover the entire planet to a depth of between one and two kilometers. While that’s good news for those watching the fate of the planet’s water after the oceans disappeared more than 3 billion years ago, the reservoir wouldn’t be of much use to anyone trying to tap into it to power a future Martian colony.
It’s found in tiny cracks and pores in rocks in the middle of the Martian crust, between 11.5 and 20 kilometers below the surface. Even on Earth, drilling a hole a kilometer deep is a challenge. Still, the discovery points to another promising place to look for life on Mars, if the reservoir can be reached. For now, it helps answer questions about the planet’s geological history. “Understanding the water cycle on Mars is crucial to understanding the evolution of its climate, surface, and interior,” said Vashan Wright, a former UC Berkeley postdoctoral researcher who is now an assistant professor at the Scripps Institution of Oceanography at the University of California, San Francisco. “A useful starting point is to determine where and how much water is present.” Wright, along with colleagues Michael Manga of UC Berkeley and Matthias Morsfeld of Scripps Oceanography, detail their analysis in a paper that will appear this week in the Proceedings of the National Academy of Sciences.
The scientists used a mathematical model of rock physics, similar to those used on Earth to map aquifers and oil fields, to conclude that InSight’s seismic data could best be explained by a deep layer of fractured igneous rocks saturated with liquid water. Igneous rocks are hot, cooled magma, like the granite found in the Sierra Nevada. “By demonstrating that there is a large reservoir of liquid water, we get an idea of what the climate was or could have been like,” said Manga, a professor of earth and planetary sciences at the University of California, Berkeley. “And water is essential to life as we know it. I don’t see why [het ondergrondse reservoir] “It wouldn’t be a habitable environment. That’s certainly true on Earth. Deep mines harbor life, the ocean floor harbors life. We haven’t found evidence of life on Mars, but we’ve at least found a place that should be able to support life in principle.” Manga was Wright’s postdoctoral advisor. Morsfeld, a former postdoctoral researcher in the mathematics department at UC Berkeley, is now an associate professor of geophysics at Scripps College of Oceanography.
Manga noted that a wealth of evidence, including river channels, deltas, and lake deposits, as well as water-altered rocks, supports the hypothesis that water once flowed on the planet’s surface. But that wet period ended more than 3 billion years ago, when Mars lost its atmosphere. Planetary scientists on Earth have sent numerous probes and landers to the planet to find out what happened to that water — the frozen water in Mars’ polar caps can’t explain everything, including when it happened and whether life ever existed on the planet. The new findings suggest that much of the water didn’t escape into space, but rather seeped into Earth’s crust. NASA sent the InSight lander to Mars in 2018 to explore the crust, mantle, core, and atmosphere, gaining invaluable information about the Martian interior before the mission ends in 2022. “The mission has exceeded my expectations by far,” Manga said. “By looking at all the seismic data Insight has collected, they figured out the thickness of the crust, the depth of the core, the composition of the core, and even a little bit about the temperature in the mantle.”
InSight has detected Martian earthquakes up to magnitude 5, meteorite impacts and rumbling sounds from volcanic regions, all of which have produced seismic waves that have allowed geophysicists to probe its interior. A previous study reported that above a depth of about 5 kilometers, the upper crust contains no water ice, as Manga and others suspected. This could mean that there is little accessible groundwater ice beyond the polar regions. The new paper analyzed the deeper crust and concluded that “the available data are best explained by a water-saturated middle crust” beneath InSight’s location. Assuming the crust is the same across the planet, the team argues that there must be more water in this middle crustal region than “the volumes thought to have filled the ancient Martian oceans.”
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