Vast Liquid Water Reservoir Found Deep in Martian Crust

Scientists have made a transformative discovery that could rewrite our understanding of Mars’s water history and potential for habitability.

Using high-frequency seismic data from NASA’s InSight mission, researchers have identified compelling evidence of a significant liquid water reservoir 5.4 to 8 kilometers beneath the Martian surface – potentially equivalent to a global ocean hundreds of meters deep. This breakthrough finding may finally solve the longstanding mystery of where Mars’s ancient surface water disappeared to when the planet transitioned from wet to dry billions of years ago.

Hidden Aquifer Revealed Through Marsquakes and Meteorite Impacts

The international research team, led by Dr. Weijia Sun from the Institute of Geology and Geophysics at the Chinese Academy of Sciences, analyzed seismic data from two notable meteorite impacts (designated S1000a and S1094b) and the largest marsquake ever recorded (S1222a). Unlike previous studies that used lower-frequency data, this research captured high-frequency seismic waves up to 4 Hz, significantly enhancing resolution of the planet’s subsurface structure.

“The water involves profound questions about life and humanity’s future on the Red Planet,” said Dr. Hrvoje Tkalčić from The Australian National University, one of the study’s co-authors.

The team employed two distinct inversion methods—deterministic and statistical Bayesian—to analyze how seismic waves traveled through Mars’s upper crust. Both approaches revealed a distinctive low-velocity zone between 5.4 and 8 kilometers deep, where shear waves slowed significantly. This anomaly strongly indicates the presence of highly porous, water-saturated rock.

The Perfect Conditions for Liquid Water

Why would liquid water exist at this particular depth? The answer lies in Mars’s temperature profile. At depths shallower than 5 kilometers, Martian temperatures remain below water’s freezing point, meaning any water present would exist as ice. However, at depths greater than 5 kilometers, temperatures rise above freezing, allowing water to remain liquid.

The researchers note that the temperature and pressure conditions at the base of the upper crust (45-70 MPa, 10-30°C) are ideal for maintaining liquid water. These conditions ensure the water doesn’t reach supercritical levels that would change its properties.

Solving Mars’s Missing Water Mystery

This discovery potentially solves one of the greatest mysteries in planetary science: what happened to Mars’s abundant surface water? Evidence shows that during the Noachian and Hesperian periods (4.1 to 3 billion years ago), Mars featured rivers, lakes, and possibly even oceans. When the planet’s climate shifted during the Amazonian period, this surface water disappeared.

Scientists have proposed several mechanisms for this water loss:

• Escape into space through interaction with solar wind
• Crustal hydration through irreversible chemical weathering
• Sequestration into the crust in deep aquifers
• Storage as subsurface ice

The team’s calculations suggest the liquid water volume preserved at the upper crust base could range from 520 to 780 meters of global equivalent layer (GEL)—essentially the depth if all this water were spread evenly across the planet’s surface. This aligns remarkably well with the estimated 710-920 meters GEL of “missing” water calculated from other multidisciplinary studies.

How Did Water Reach These Depths?

The researchers propose that water infiltrated Mars’s upper crust during the Noachian period through fractures created by intense meteorite bombardment. Mars’s cooling over time may have subsequently reactivated these fractures through planetary contraction, maintaining pathways for water movement.

Crucially, this water infiltration would have occurred before Mars cooled to its current state, where upper layers would freeze and prevent further water percolation from the surface.

Implications for Mars Exploration and Habitability

This discovery has profound implications for our understanding of Mars and future exploration efforts. A significant subsurface water reservoir dramatically increases the potential for past or even present microbial life on Mars, as liquid water is essential for all known life forms.

“Our results provide the first seismic evidence of liquid water at the base of the Martian upper crust, shaping our understanding of Mars’s water cycle and the potential evolution of habitable environments on the planet,” the researchers write in their paper published in National Science Review.

The findings could also inform planning for future human missions to Mars, as accessible subsurface water would be a critical resource for sustaining long-term habitation. However, the researchers caution that their estimates are based on measurements at a single location—beneath the InSight landing site in Elysium Planitia.

Future missions with additional seismometers could verify whether this water-saturated layer exists globally and map its distribution across the planet, potentially revealing even more about Mars’s fascinating hydrological history and its capacity to support life beyond Earth.