To find water on Mars, listen to marsquakes

Water on Mars: Cutaway view of rocky ground subsurface with blue-colored region halfway down.
View larger. | Artist’s concept of an aquifer of liquid water on Mars, deep below the surface. A new study from researchers at Penn State University in Pennsylvania shows it could be possible to find such aquifers by listening to marsquakes. Image via ESA/ Medialab.
  • If Mars still has any liquid water, it could be found deep underground in aquifers using the seismoelectric method, say researchers at Penn State University.
  • Seismic waves from marsquakes would move through water, creating unique electromagnetic signals.
  • Future probes could use the same technique to study the subsurface oceans of moons like Europa and Enceladus.

Finding underground water through marsquakes

Scientists say Mars once had oceans, but today its surface is basically bone-dry. However, Mars might still have liquid water deep underground in aquifers. On June 17, 2024, researchers at Penn State University in Pennsylvania said it would be possible to find such aquifers by listening to marsquakes, Mars’ version of earthquakes. The quakes would produce certain electromagnetic signals when moving through the water deep below the surface.

The researchers published their peer-reviewed findings in JGR Planets on May 5, 2024.

Water on Mars may be deep underground

Mars is cold and extremely dry on its surface today, basically a planet-wide desert. But scientists have suggested there might still be some aquifers of liquid water far below the surface where it is warmer. If so, it is likely too deep for traditional methods like ground-penetrating radar to find it. Orbiting spacecraft using radar have found extensive ice deposits on Mars, however.

So, how could we find the water, if it’s there? The Penn State researchers said we could listen to marsquakes. When quakes pass through bodies of liquid water, they produce electromagnetic signals. By examining marsquake data, scientists could detect subsurface aquifers, if they exist.

Nolan Roth is the study’s lead author in the Department of Geosciences at Penn State. He said:

The scientific community has theories that Mars used to have oceans and that, over the course of its history, all that water went away. But there is evidence that some water is trapped somewhere in the subsurface. We just haven’t been able to find it. The idea is, if we can find these electromagnetic signals, then we find water on Mars.

Listening to marsquakes to find water on Mars

The researchers said instead of a regular ground-penetrating radar, they suggest using the seismoelectrical method. It’s a newer technique, still under development, to non-invasively characterize Earth’s subsurface. Sensors placed on the surface can detect the electromagnetic signals produced when seismic waves from an earthquake pass through liquid water. Differences in how rocks and water move from the seismic waves produce distinct electromagnetic fields. When an aquifer is found, the data from these sensors reveal an aquifer’s depth, volume, location and chemical composition. A future rover or lander could use this technique on Mars, as Roth noted:

If we listen to the marsquakes that are moving through the subsurface, if they pass through water, they’ll create these wonderful, unique signals of electromagnetic fields. These signals would be diagnostic of current, modern-day water on Mars.

In fact, it would be even easier to do on Mars than on Earth. That’s because water in Earth’s subsurface isn’t limited to just aquifers. This other water can create different electromagnetic signals. So, to find aquifers, scientists need to filter out this other “background noise”. But on Mars, there is no other liquid water in the ground, closer to the surface. This means any signals of aquifers would be cleaner and more distinct. Co-author Tieyuan Zhu at Penn State said:

On Mars, where the near-surface is certainly desiccated, no such separation is needed. In contrast to how seismoelectric signals often appear on Earth, Mars’ surface naturally removes the noise and exposes useful data that allow us to characterize several aquifer properties.

So, if a future Mars mission used this seismoelectrical technique, then it should be fairly easy to find aquifers, if they exist.

Modeling the Martian subsurface

To test just how well the technique would work on Mars, the researchers created a computer model of the subsurface. They then added aquifers to the model. The results indicated the technique should be able to find deeply buried aquifers on Mars. In fact, it could reveal how thick or thin they are, their salinity (amount of dissolved salt they contain) and other physical properties. Roth said:

If we can understand the signals, we can go back and characterize the aquifers themselves. And that would give us more constraints than we’ve ever had before for understanding water on Mars today and how it has changed over the last 4 billion years. And that would be a big step ahead.

Small white metallic dome with long tether attached sitting on reddish dusty ground with small rocks and dusty sky.
View larger. | NASA’s InSight lander took this image of its seismometer on sol 96 (March 5, 2019). InSight detected many marsquakes in the subsurface but not aquifers. If they exist, they are probably too deep down for detection with a regular radar. Image via NASA/ JPL-Caltech.

What about InSight?

NASA’s InSight lander, which landed in 2018 and ended its mission in 2022, detected many marsquakes with its seismometer. It also mapped the subsurface. But there were limitations. Any aquifers would probably be too deep to detect with its instruments, and seismometers can have problems distinguishing between water, gas and rock. It also had a magnetometer though, which measures magnetic fields. If scientists combined the data from the magnetometer and seismometer, it could potentially reveal seismoelectric signals. That will probably require more studies back on Earth, and a dedicated seismoelectrical instrument on a future Mars mission would still be preferable.

Ocean moons

The same technique could also be used elsewhere; for example, on ocean moons. A landed probe on Europa or Enceladus could then measure how thick (deep) the moons’ oceans are. Zhu said:

This shouldn’t be limited to Mars, the technique has potential, for example, to measure the thickness of icy oceans on a moon of Jupiter. The message we want to give the community is there is this promising physical phenomenon – which received less attention in the past – that may have great potential for planetary geophysics.

This could help scientists determine just how habitable those oceans might be. But instead of being buried deep in a rocky subsurface, these oceans are covered by a crust of water ice.

In 2018, the Mars Express orbiter found the first evidence for possible lakes of salty liquid water beneath the ice cap at the planet’s South Pole. Other studies, however, cast doubt on that interpretation of the radar data. Yet others have supported it. The debate continues.

Bottom line: Is there still any liquid water on Mars? A new study suggests scientists could find aquifers deep below the surface by listening to marsquakes.

Source: Characterizing Liquid Water in Deep Martian Aquifers: A Seismo-Electric Approach

Via Penn State

Read more: Marsquakes reveal red planet’s deep secrets

Read more: Liquid water on Mars beneath polar ice?

July 3, 2024

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