Compelling new evidence supports the presence of liquid water deep beneath Mars’ surface, based on a fresh analysis of seismic data from NASA's InSight mission. In 2024, researchers had proposed that between 7.1 and 12.4 miles (11.5 to 20 kilometers) below the surface, Mars’ subsurface could be saturated with water. This conclusion was drawn from the behavior of seismic waves generated by marsquakes.

Building on this, Ikuo Katayama from Hiroshima University and Yuya Akamatsu of Japan’s Research Institute for Marine Geodynamics found further support for this hypothesis. Katayama emphasized that while many studies point to ancient water on Mars, their model indicates liquid water exists today.

Their findings, like prior research, are grounded in data from InSight’s SEIS (Seismic Experiment for the Interior Structure) instrument, which measured three seismic wave types: fast-moving P-waves, slower S-waves (which cannot pass through liquids), and surface waves. By analyzing the P- and S-waves, which reflect underground composition based on travel speed and intensity, they identified two transitional zones between 6.2 and 12.4 miles deep where seismic properties suddenly shift — consistent with the presence of water.

While earlier theories attributed these seismic changes to transitions from volcanic to impact ejecta layers or from porous to solid rock, Katayama and Akamatsu suggest the porous rock between 10 and 20 kilometers deep is water-filled.

To test this, they examined diabase rocks from Sweden — analogs to Martian rock — and found that their seismic responses in wet conditions matched what SEIS recorded on Mars.

Past estimates suggest Mars could hold enough underground water to create a global ocean 0.62 to 1.24 miles (1 to 2 kilometers) deep. If this water exists, it may even support microbial life. However, current technology doesn’t allow us to reach or study this deep water directly, leaving Mars’ water — and its potential for life — hidden for now.

Their findings are published in Geology.