Scientists discover ‘hidden water’ just three feet below Mars’ Grand Canyon

The European Space Agency’s ExoMars orbiter has found evidence of a huge deposit of water underneath the Valles Marineris Martian canyon system, which is one of the Solar System’s largest canyons—about five times as deep and ten times as long as the Grand Canyon in Arizona.

Scientists assessed data recorded by the Trace Gas Orbiter’s (TGO) Fine-Resolution Epithermal Neutron Detector (Frend) instrument, which maps hydrogen in the uppermost metre of Mars’ soil—a measure of water content—to make the discovery.

The research, accepted for publication in the journal Icarus, revealed an area in the canyon, about the size of the Netherlands, with an unusually large amount of hydrogen.

“Assuming the hydrogen we see is bound into water molecules, as much as 40 per cent of the near-surface material in this region appears to be water,” study lead author Igor Mitrofanov of the Russian Academy of Sciences in Moscow, said.

“With TGO we can look down to one metre below this dusty layer and see what’s really going on below Mars’ surface—and, crucially, locate water-rich ‘oases’ that couldn’t be detected with previous instruments,” Dr Mitrofanov added.

While previous studies have found hints of water deeper underground in the Red Planet’s mid-latitudes, as well as evidence of deep pools of liquid water under the Martian south pole, these potential deposits are few kilometres below ground and less accessible to future exploration than any found just below the surface.

The new study has revealed evidence of a “large, not-too-deep, easily exploitable reservoir of water” in this region of Mars.

A central part of Valles Marineris, the scientists believe, could be packed full of water—similar to the Earth’s permafrost regions like Siberia, where water ice permanently persists under dry soil because of the constant low temperatures.

In the study, the researchers analysed data recorded from May 2018 to February 2021 by the Frend instrument that mapped the hydrogen content of Mars’ soil by detecting neutrons.

“Neutrons are produced when highly energetic particles known as ‘galactic cosmic rays’ strike Mars; drier soils emit more neutrons than wetter ones, and so we can deduce how much water is in a soil by looking at the neutrons it emits,” study co-author Alexey Malakhov from the Russian Academy of Sciences explained.

“Frend’s unique observing technique brings far higher spatial resolution than previous measurements of this type, enabling us to now see water features that weren’t spotted before,” Dr Malakhov added.

The observed deposits of water, the researchers believe, could either be in the form of ice, or water that is chemically bound to other minerals in the soil.

But based on other studies, they say the minerals seen in this part of Mars usually contain only a few percentage of water—“much less than is evidenced by these new observations”.

“Overall, we think this water more likely exists in the form of ice,” Dr Malakhov said.

However, researchers added that further studies of this part of the canyon were needed to confirm what form of water these deposits hold.

While water ice usually evaporates in this region of Mars due to the temperature and pressure conditions near the equator, scientists say the right combination of temperature, pressure and hydration must be there to prevent water loss from the region.

They say a “special, as-yet-unclear mix of conditions” is likely present in Valles Marineris to preserve the water.

Alternatively, the researchers speculate the water is somehow being replenished by an as-yet-unknown process.

“This finding is an amazing first step, but we need more observations to know for sure what form of water we’re dealing with,” study co-author Håkan Svedhem of ESA’s ESTEC in the Netherlands added.

“Regardless of the outcome, the finding demonstrates the unrivalled abilities of TGO’s instruments in enabling us to ‘see’ below Mars’ surface,” Dr Svedhem added.