Seismic data from the Insight lander indicate deep, porous rock filled with liquid water.

BERKELEY, Calif. — Geophysicists have used seismic activity to study the interior of Mars and found evidence of a large underground reservoir of liquid water – large enough to fill the oceans on the planet’s surface.

Using data from NASA’s Insight lander, scientists were able to estimate that the amount of groundwater could cover the entire planet to a depth of one to two kilometers.

While that’s good news for those tracking the fate of the planet’s water after the oceans disappeared more than three billion years ago, the reservoir won’t be of much use to someone trying to tap it to supply a future Mars colony. It’s located in tiny cracks and pores in the rock in the middle of Mars’ crust, between 11.5 and 20 kilometers below the surface. Even on Earth, drilling a hole one kilometer deep is a challenge.

However, the discovery does reveal another promising location for the search for life on Mars, provided the reservoir is accessible. For now, it helps answer questions about the planet’s geological history.

“Understanding the Martian water cycle is critical to understanding how the climate, surface and interior evolve,” said Vashan Wright, a former UC Berkeley postdoctoral fellow who is now an assistant professor at UC San Diego’s Scripps Institution of Oceanography. “A useful starting point is identifying where water is and how much of it there is.”

Wright, along with colleagues Michael Manga of UC Berkeley and Matthias Morzfeld of Scripps Oceanography, detailed his analysis in a paper appearing this week in the journal Proceedings of the National Academy of Sciences.

The scientists used a mathematical model of rock physics that is identical to the models used on Earth to map underground aquifers and oil fields. They concluded that Insight’s seismic data was best explained by a deep layer of fractured igneous rock saturated with liquid water. Igneous rocks are cooled hot magma, such as the granite of the Sierra Nevada.

“Finding that there is a large reservoir of liquid water gives insight into the climate that was or could be there,” said Manga, a professor of earth and planetary sciences at UC Berkeley. “And water is necessary for life as we know it. I see no reason why (the underground reservoir) shouldn’t be a habitable environment. It certainly is on Earth — deep, deep mines host life, the seafloor hosts life. We haven’t found evidence of life on Mars, but at least we’ve identified a place that could, in principle, support life.”

Manga was Wright’s postdoctoral fellow. Morzfeld was formerly a postdoctoral fellow in the mathematics department at UC Berkeley and is now an associate professor of geophysics at Scripps Oceanography.

Manga noted that there is a wealth of evidence — riverbeds, deltas and lake deposits, as well as water-altered rocks — to support the hypothesis that water once flowed on the planet’s surface. But that wet period ended more than 3 billion years ago, after Mars lost its atmosphere. Planetary scientists on Earth have sent many probes and landers to the planet to figure out what happened to that water — water frozen in Mars’ polar caps can’t explain everything — and also when it happened and whether life exists or has existed on the planet.

The new findings suggest that much of the water did not escape into space but seeped into the Earth’s crust.

The Insight lander was sent to Mars by NASA in 2018 to study the crust, mantle, core and atmosphere, and recorded valuable information about Mars’ interior before the mission ends in 2022.

“The mission has far exceeded my expectations,” Manga said. “By analyzing all the seismic data collected by Insight, they were able to determine the thickness of the crust, the depth of the core, the composition of the core, and even a little bit of the temperature in the mantle.”

Insight recorded earthquakes on Mars with a magnitude of up to 5, meteorite impacts, and rumblings from volcanic areas. All of these earthquakes generated seismic waves that allowed geophysicists to study the interior.

A previous study reported that the upper crust does not contain water ice above a depth of about 5 kilometers, as suggested by Manga and others. This may mean that there is little accessible frozen groundwater outside the polar regions.

The new paper analyzed the deeper crust and concluded that the “available data are best explained by a water-saturated mid-crust” under Insight. Assuming the crust is similar across the planet, the team argued, there should be more water in this mid-crust zone than the “amounts that are thought to have filled the hypothetical ancient Martian seas.”

The Canadian Institute for Advanced Research, the National Science Foundation and the US Office of Naval Research supported the work.

Robert Sanders writes for the UC Berkeley News Center.