Scientists have found evidence suggesting that a vast reservoir of liquid water may exist deep beneath Mars' surface within fractured igneous rocks, Reuters reported.
This reservoir could potentially hold enough water to cover the entire surface of Mars with an ocean.
This conclusion comes from seismic data collected by NASA's robotic InSight lander, which has been instrumental in exploring Mars' interior. The water is estimated to be located between 7.2 and 12.4 miles (11.5 to 20 km) below the Martian surface. According to researchers, these conditions could be suitable for sustaining microbial life, either in the past or present.
"At these depths, the crust is warm enough for water to remain in liquid form. At shallower depths, the water would freeze into ice," explained Vashan Wright, a planetary scientist at the Scripps Institution of Oceanography, University of California, San Diego, and lead author of the study published Monday in *Proceedings of the National Academy of Sciences*.
"On Earth, we discover microbial life deep underground in rocks saturated with water and an energy source," added Michael Manga, a planetary scientist at the University of California, Berkeley, and co-author of the study. The InSight lander touched down in 2018 to study the deep interior of Mars, gathering data on the planet's various layers, from its liquid metal core to its mantle and its crust. The InSight mission ended in 2022.
"InSight was able to measure the speed of seismic waves and how they change with depth. The speed of seismic waves depends on what the rock is made of, where it has cracks and what fills the cracks," Wright said.
"We combined the measured seismic wave speed, gravity measurements and rock physics models. The rock physics models are the same as the ones we use to measure properties of aquifers on Earth or map oil and gas resources underground."
The data indicated the presence of this reservoir of liquid water within fractured igneous rocks - formed in the cooling and solidification of magma or lava - in the Martian crust, the planet's outermost layer.
"A mid-crust whose rocks are cracked and filled with liquid water best explains both seismic and gravity data," Wright said. "The water exists within fractures. If the InSight location is representative and you extract all the water from the fractures in the mid-crust, we estimate that the water would fill a 1-2 km deep (0.6-1.2 miles) ocean on Mars globally."
The Martian surface is cold and desolate today but once was warm and wet. That changed more than 3 billion years ago. The study suggests that much of the water that had been on the Martian surface did not escape into space, but rather filtered down into the crust.
"Early Mars had liquid water on its surface in rivers, lakes and possibly oceans. The crust on Mars could also have been full of water from very early in its history, too," Manga said.
"On Earth, groundwater underground infiltrated from the surface, and we expect this to be similar to the history of water on Mars. This must have occurred during a time when the upper crust was warmer than it is today."
Water would be a vital resource if humankind ever is to place astronauts on the Martian surface or establish some sort of long-term settlement. Mars harbours water in the form of ice in its polar regions and its subsurface. However, the depth of the apparent underground liquid water would make it difficult to access.
"Drilling to these depths is very challenging. Looking for places where geological activity expels this water, possibly the tectonically active Cerberus Fossae (a region in the northern hemisphere of Mars), is an alternative to looking for deep liquids," Manga said, though he noted that concerns about protecting the Martian environment would need to be addressed.
