Data suggests there is a huge reservoir of groundwater on the surface of Mars.

A vast reservoir of liquid water may exist deep beneath the surface of Mars, within fractured igneous rocks, containing enough to fill an ocean covering the entire surface of Earth’s neighboring planet.

That’s the conclusion scientists have drawn, based on seismic data obtained by NASA’s InSight robotic lander during a mission that helped decipher the interior of Mars. The water, which lies about 11.5 kilometers to 20 kilometers below the Martian surface, likely provided conditions favorable to supporting microbial life, both in the past and now, the researchers said.

“At these depths, the crust is warm enough for water to exist as a liquid. At shallower depths, water freezes,” said planetary scientist Vashan Wright of the Scripps Institution of Oceanography at the University of California, San Diego. The study’s lead author, published Monday in the journal Proceedings of the National Academy of Sciences.

“On Earth, we find microbial life deep within the Earth, where rocks are saturated with water and there is a source of energy,” added planetary scientist and study co-author Michael Manga of the University of California, Berkeley.

InSight landed in 2018 to study Mars’ deep interior, collecting data on the planet’s many layers, from its liquid metal core to its crust. InSight’s mission ended in 2022.

“InSight was able to measure the speed of seismic waves and how they change with depth,” Wright said. “The speed of seismic waves depends on what the rock is made of, where the cracks are, and what fills the cracks.”

“We combine measured seismic wave velocities, gravity measurements and rock physics models. Rock physics models are the same ones we use to measure the properties of groundwater layers on Earth or map underground oil and gas resources.”

The data suggests that this reservoir of liquid water exists within fractured igneous rocks — which form as magma or lava cools and solidifies — in the Martian crust, the planet’s outer layer.

“The middle crust, where the rocks are fractured and filled with liquid water, best explains the seismic and gravity data,” Wright said. “The water is in the fractures. If InSight were representative and extracted all the water from the fractures in the middle crust, we estimate that water would fill an ocean 1 to 2 kilometers deep on the surface of Mars globally.”

The surface of Mars is cold and barren today, but it used to be hot and wet. That changed more than 3 billion years ago. The study suggests that much of the water that was on Mars did not escape into space, but rather seeped into the crust.

“Early Mars had liquid water on its surface in rivers, lakes and possibly oceans. It’s also possible that the Martian crust was filled with water very early in its history,” Manga said. “On Earth, groundwater seeped up from the surface, and we expect this to be similar to the history of water on Mars. This occurred at a time when the upper crust was much warmer than it is today.”

Water will be a vital resource if humanity ever wants to land astronauts on Mars or establish some kind of long-term settlement. Mars harbors water in the form of ice in its polar regions and deep underground. But the depth of the apparent liquid groundwater will make it difficult to access.

“Drilling to these depths is a big challenge,” Manga said. “Looking for places where geological activity is expelling this water, perhaps the tectonically active Cerberus Fossae Zone (a region in Mars’ northern hemisphere), is an alternative to searching for deep fluids.” Although he noted that concerns about protecting the Martian environment would need to be addressed.

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