Liquid Water on Mars. Where Is It Hiding?

Scientists say many of Mars' rock formations—river channels, deltas, lake deposits, water-altered rocks—support the hypothesis that water long ago flowed across the planet's surface. But that wet period ended more than 3 billion years ago, after Mars lost its atmosphere.

To find out what happened to Martian water, many probes and landers have been sent to the planet's surface. Data collected by one of the devices allowed us to determine that a reservoir of liquid water may exist on Mars. The study was published in the journal Proceedings of the National Academy of Sciences.

Scientists used a mathematical model of rock physics, identical to those used on Earth to map underground reservoirs of water and oil, and analyzed seismic data collected by the InSight lander to explain specific signals that the crust is not made of just rocky material.

As it turned out, the data most closely matched the model that assumed the existence of a layer of fractured igneous rock saturated with liquid water. This most likely occurs in the middle crust of Mars, between 11.5 and 20 kilometers below the surface. The amount of water stored there would probably be enough to cover the planet with an ocean 1 to 2 kilometers deep.

“The finding that there is a large reservoir of liquid water there gives us some insight into what the ancient climate of Mars was or might have been,” said Michael Manga of the University of California, Berkeley, one of the study’s authors. He said water is essential for life as we know it. An underground reservoir would also be a potentially habitable environment.

– It's certainly the case on Earth: deep mines are habitats for life, the ocean floor is habitats for life. We haven't found any evidence of life on Mars, but at least we've identified a place that should be able to support life, in principle, he explained.

Lead author Vashan Wright of the University of California, San Diego, explained that understanding the Martian water cycle is key to understanding the evolution of the planet's climate, surface, and interior. “A useful starting point is to determine where the water is and how much of it there is,” he said.

This is the first evidence of liquid water on Mars – until now, scientists have only found it in solid and gaseous states. Unfortunately, the reservoir is unlikely to be of much use to future Martian colonies. The depth at which it is located makes it difficult to obtain water – on Earth, drilling a hole a kilometer deep is a big challenge, and in the case of the Red Planet, resources are much deeper.

The InSight lander was sent by NASA to Mars in 2018 to study the crust, mantle, core, and atmosphere. It acquired invaluable information about Mars' interior before ending its mission in 2022. The lander detected Martian earthquakes, meteor impacts, and volcanic tremors that created seismic waves that allowed geophysicists to study the planet's interior.