In 2024, scientists made headlines when they found evidence of copious amounts of water inside a layer of the Martian crust. This layer lies 11.5 to 20 kilometers below the surface and is about 1-2 km thick. Now, these findings have been backed by a new study from Japan.

Using seismic data from NASA’s InSight lander, researchers Ikuo Katayama of Hiroshima University and Yuya Akamatsu of the Research Institute for Marine Geodynamics have uncovered compelling evidence of water trapped within the Martian subsurface. 

“Many studies suggest the presence of water on ancient Mars billions of years ago,” Katayama said. “But our model indicates the presence of liquid water on present-day Mars.”

Listening to the Pulse of Mars

Like the previous study performed by U.S. scientists, the new study hinges on data from the Seismic Experiment for the Interior Structure (SEIS), a sensitive seismometer deployed by the InSight lander since 2018. SEIS was designed to detect marsquakes — tremors caused by the planet’s internal activity — and the shockwaves from meteorite impacts. These seismic waves, much like ripples in a pond, carry clues about the materials they pass through.

When “X-raying” a planet’s interior, scientists mostly care about two types of seismic waves: P-waves, which compress and expand like sound waves, and S-waves, which move perpendicular to their direction of travel. S-waves cannot travel through liquid, while P-waves slow down in less dense materials. By analyzing the speed and behavior of these waves, scientists can map the planet’s interior.

Katayama and Akamatsu focused on two distinct boundaries in the seismic data, where the waves’ behavior changed abruptly. They think these transitions could indicate the presence of water filling cracks and pores in the rock.

To test this assumption, they turned to diabase rocks from Rydaholm, Sweden — a close analog to Martian crust. In laboratory experiments, they measured how seismic waves traveled through these rocks under dry, wet, and frozen conditions. Indeed, the results mirrored the seismic patterns observed on Mars.

What the Findings Mean

Mars might hold enough subsurface water to cover its surface in a global ocean between 0.62 to 1.24 miles (1 to 2 kilometers) deep. But because this water is trapped in rock, it cannot be easily extracted — if at all. However, its existence raises tantalizing questions about the possibility of microbial life.

“If liquid water exists on Mars,” Katayama said, “the presence of microbial activity is possible.”

This study is just the latest evidence in a growing body of science that shows Mars was once — and may still be in some respects — a watery world. Orbital images reveal ancient river valleys and lakebeds, while rovers like Curiosity have found minerals that form in water. Last month, researchers found the first evidence of Martian beaches.

Despite the excitement, the findings come with caveats. The water, if it truly exists, is locked deep underground, far beyond the reach of current technology. Drilling to such depths on Mars would require unprecedented feats of engineering. Moreover, the seismic data alone cannot definitively prove the presence of water; other explanations, such as changes in rock composition, remain possible.

Still, it’s remarkable that even though its mission ended in 2022, the InSight mission is still delivering amazing science. In fact, the huge amounts of seismic data that it gathered could keep NASA scientists busy for a decade to come.

The findings were reported in the journal Geology.