Underground reservoir on Mars could fill planet's surface oceans, study says

Data from a retired NASA mission suggests the presence of an underground reservoir of water deep beneath the surface of Mars, according to a new study.

A team of scientists estimates that there could be enough water locked in tiny cracks and pores in the rock at the center of the Martian crust to fill oceans on the planet's surface. Groundwater could likely cover the entire surface of Mars, creating an ocean up to a mile deep, the study says.

The data was collected by NASA's InSight lander, which used a seismometer to study the interior of Mars between 2018 and 2022.

According to researchpublished Monday in the journal Proceedings of the National Academy of Sciences, future astronauts exploring Mars will face a number of challenges if they try to reach the water, which is located 11 to 20 kilometers below the surface.

However, the discovery reveals new details about the geological history of Mars and offers a new place to search for life on the red planet, if water can be reached.

“Understanding the Martian water cycle is critical to understanding the evolution of the climate, surface, and interior,” lead study author Vashan Wright, an associate professor and geophysicist at the Scripps Institution of Oceanography at the University of California, San Diego, said in a statement. “A useful starting point is to determine where the water is and how much of it is there.”

The Search for 'Lost' Water on Mars

Billions of years ago, Mars was likely a warmer, wetter place, as evidenced by ancient lakes, riverbeds, deltas, and water-altered rocks studied by other NASA missions and observed by orbiters. But the red planet lost its atmosphere more than 3 billion years ago, effectively ending Mars’ wet period.

Scientists are still unsure why Mars lost its atmosphere, and have designed multiple missions to learn about the history of the planet's water, where it went, and whether water ever created habitable conditions on Mars. Although water remains as ice in the planet's polar ice caps, researchers don't think that can explain all of the planet's “lost” water.

Existing theories offer several possible scenarios for what happened to Martian water after Mars lost its atmosphere: Some suggest that it turned into ice or escaped into space, others that it became part of minerals beneath the planet's surface or entered deep aquifers.

New evidence suggests that water on Mars seeped into the Martian crust.

InSight, short for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport, was a stationary probe. But it collected unprecedented data on the thickness of the red planet’s crust and the temperature of its mantle, as well as the depth and composition of its core and atmosphere. The spacecraft’s seismometer recorded the first earthquakes on another planet, called Marsquakes.

Earthquakes happen when tectonic plates shift, move, and grind against each other, but the Martian crust is like one giant plate, with faults and cracks as the planet continues to shrink and cool over time. As the Martian crust stretches, it cracks, and InSight’s seismometer has been able to detect more than 1,300 marsquakes that rumbled hundreds or thousands of miles away.

Scientists studying InSight data were able to study the speed of marsquakes as they pass through the planet, which could serve as an indicator of what materials exist beneath the Martian surface.

The speed of seismic waves depends on what the rock is made of, where the cracks are, and what fills those cracks, Wright said.

The team used this data and fed it into a mathematical model of rock physics, which is used on Earth to map underground oil fields and aquifers.

The results showed that InSight's data best matched a deep layer of igneous, or volcanic, rock filled with liquid water.

“Finding the presence of a large reservoir of liquid water provides insight into what the climate was or might have been like,” study co-author Michael Manga, a professor of earth and planetary sciences at the University of California, Berkeley, said in a statement.

“And water is essential for life as we know it. I don't see why this underground reservoir wouldn't be a habitable environment,” Manga added. “It's just like on Earth – there's life in deep mines, there's life at the bottom of the ocean. We haven't found any evidence of life on Mars, but at least we've identified a place that, in principle, should be habitable.”

If Mars' crust is uniform across the planet, then the mid-crustal zone may contain more water than “the amounts hypothesized to have filled the ancient Martian oceans,” the study's authors write.

Rocks hold clues about the planet's history, Wright said, and understanding the planet's water cycle could help researchers unravel the evolution of Mars.

While the data analysis cannot provide any information about life, past or present, if it existed on Mars, it is possible that the wet Martian crust could be habitable in the same way that deep groundwater on Earth is habitable for microorganisms, he said.

But even drilling holes 1 kilometer deep or deeper on Earth is a complex task that requires energy and infrastructure, so drilling that deep on Mars would require bringing in a huge amount of resources, Wright says.

The team was surprised to find no evidence of a frozen groundwater layer beneath Insight, since that part of the crust is cold. The researchers are still trying to determine why there is no frozen groundwater at shallower depths above the mid-crust.

Windows into Martian History

The findings add a new piece to the Martian water puzzle.

The idea that liquid water might exist deep beneath the Martian surface has been around for decades, but this is the first time that real data from a Mars mission can back up the idea, says Alberto Fairén, a visiting interdisciplinary planetary scientist and astrobiologist in Cornell University’s Department of Astronomy. Fairén was not involved in the study.

He said the water was likely “some kind of deep underground mud.”

“These new results show that liquid water does indeed exist in the Martian subsurface today, but not in the form of isolated lakes, but rather in the form of liquid-water-saturated sediments, or aquifers“,” Fairén said. “On Earth, the subsurface biosphere is truly vast, containing most of the prokaryotic diversity and biomass on our planet. Some studies even suggest that life on Earth began deep in the subsurface. So the astrobiological implications of finally confirming the existence of liquid water habitats kilometers below the surface of Mars are truly exciting.”

The result is “exactly what I was hoping to get from InSight,” said Bruce Banerdt, InSight's principal investigator.

“I was hoping that we would get data that was good enough to do studies like this, where we would look at details of the interior of Mars that are relevant to geological questions, questions about the habitability of Mars, questions about the evolution of Mars,” he said.

Banerdt, who was not involved in the study, said that while the paper's interpretation of the data is supported by strong arguments, he also believes it is still somewhat speculative and that there is almost always another way to explain any set of data.

“I was very impressed by the fact that Wright and others brought mineral physics concepts into the interpretation of seismic data,” Banerdt said.
Banerdt and Wright expressed interest in sending more seismometers to Mars and other planets and moons in our solar system in the future. While InSight’s single seismometer collected critical data, distributing it across Mars would reveal variations in the planet’s interior and provide a more complete picture of its varied and complex history, Banerdt said.

“Just like on Earth, where groundwater comes to the surface through rivers and lakes, that was certainly the case on early Mars,” Wright said. “The groundwater we see is a record of that past.”