Seismic waves provide evidence of ocean in Martian soil

In its early days, Mars was a planet rich in water. The question is what happened to the water. New research suggests that the water is still there – in a vast ocean beneath the surface.

An international team led by Weijia Sun from the Institute of Geology and Geophysics of the Chinese Academy of Sciences in Beijing has analyzed the data from the Mars probe InSight. The probe landed on Mars in the fall of 2018. It was equipped with a seismometer that recorded the seismic waves from two meteorite impacts in 2021 and a marsquake in 2022.

While investigating a certain type of oscillation, called shear waves, they noticed "a significant anomaly in the subsurface", write Sun and Hrvoje Tkalčić, geophysicists at the Australian National University, in an article in the online magazine The Conversation. It is said to be a layer 5.4 to 8 kilometers below the surface of Mars in which the vibrations moved more slowly. This layer presumably consists of very porous rock filled with liquid water, similar to a sponge.

Where did the water disappear to?

In the early days of Mars, between 4 billion and 3.1 billion years ago, there was a lot of liquid water on Mars – enough to cover the entire planet with an ocean 700 to 900 meters deep. As the planet's magnetic field diminished and the atmosphere thinned, most of the surface water disappeared – the question is, where did it go?

Some is now found as ice in the polar ice caps, some is trapped in minerals and finally some of the water disappeared into space. But that is not enough to explain the whereabouts of all the water that must have once existed on Mars.

The hypothesis is that it seeped into the crust and was stored there in a liquid state. According to the researchers' calculations, which they published in the journal National Science Review, the porous layer, which is around three kilometers thick, has enough capacity to hold the water that once sloshed around on Mars.

Liquid water is essential for life as we know it. Life could have developed in it and still exist today – microbes also exist on Earth in rocks filled with water. It will also be very important for possible future colonization: purified, it can serve as drinking water. It can be split into oxygen and hydrogen, which can then be used as breathing air or fuel for rockets. The question will be how to extract the water, which is stored several kilometers below the surface.

(wpl)