There might be vast quantities of liquid water beneath Mars’ surface

There’s no water on the surface of Mars, but vast quantities of it might be hiding underground – enough to cover the red planet in a global ocean, a group of scientists says in a new paper.

The generally accepted theory holds that there used to be plenty of water on the surface of Mars – it might even have been a river-laden world – but it then either evaporated into space or somehow landed in the planet’s crust very deep underground.

But now, a group of scientists say liquid water may be locked in rock just a few kilometres beneath Martian ground – much closer to the surface than previously thought.

A China-led international team of researchers – from China’s Academy of Sciences, the Australian National University, and the University of Milano-Bicocca – used data from NASA’s now-retired InSight lander to analyze seismic waves from “Marsquakes” and meteorite impacts recorded between 2018 and 2022.

What they found was a mysterious zone in Mars’ crust, allegedly best explained by a layer of water-saturated rock.

“This zone is interpreted as a 23 high-porosity, water-saturated layer, and is estimated to hold a liquid water volume of 520–780 24 m of global equivalent layer,” the researchers write in a paper published by the National Science Review (PDF).

According to the scientists, the aforementioned incidents produced seismic waves that slowed as they passed through a layer between 5.4 and 8 kilometers (between 3.3 and 5 miles) below the surface.

That clear drop in wave speed meant there probably was a layer of porous rock filled with liquid water. At that depth, conditions on Mars are warm and pressurized enough for water to stay liquid.

“Our results provide the first seismic evidence of liquid water at the base of the Martian upper crust, shaping our understanding of Mars’ water cycle and the potential evolution of habitable environments on the planet,” said the researchers.

For four years, the InSight lander – which arrived on Mars in 2018 – used a sensitive seismometer to detect subtle ground movements caused by crustal stress and meteorite impacts. Scientists back on Earth then studied the information.

According to the researchers, the mysterious zone might be a kind of “last refuge” for liquid water on Mars. However, the water – even if it’s there – is, of course, far too deep to be accessed with existing drilling technology.

The scientists are optimistic: “Liquid water is essential for life as we know it. On Earth, microbes thrive in deep, water-filled rock. Could similar life, perhaps relics of ancient Martian ecosystems, persist in these reservoirs? There’s only one way to find out.”