ESA’s Trace Gas Orbiter Finds Water in Martian Canyon System

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Planetary researchers using the Fine Resolution Epithermal Neutron Detector (FREND) instrument onboard ESA’s Trace Gas Orbiter (TGO) have found evidence for very high content of hydrogen in the soil — the mean water equivalent hydrogen value as large as 40.3 wt% — in Candor Chaos, central part of Valles Marineris.

Mars; the center of the scene shows the entire Valles Marineris canyon system. Image credit: NASA Goddard Space Flight Center.

“With TGO we can look down to one meter 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,” said Dr. Igor Mitrofanov, a researcher at the Space Research Institute.

“FREND revealed an area with an unusually large amount of hydrogen in the colossal Valles Marineris canyon system: assuming the hydrogen we see is bound into water molecules, as much as 40% of the near-surface material in this region appears to be water.”

Dr. Mitrofanov and his colleagues analyzed FREND data obtained from May 2018 to February 2021, which mapped the hydrogen content of Mars’ soil by detecting neutrons rather than light.

“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,” said Dr. Alexey Malakhov, also from the Space Research Institute.

“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.”

“We found a central part of Valles Marineris to be packed full of water — far more water than we expected.”

“This is very much like Earth’s permafrost regions, where water ice permanently persists under dry soil because of the constant low temperatures.”

“This water could be in the form of ice, or water that is chemically bound to other minerals in the soil.”

“However, other observations tell us that minerals seen in this part of Mars typically contain only a few percent water, much less than is evidenced by these new observations.”

Valles Marineris can be seen stretching across this frame, overlaid by colored shading representing the amount of water mixed into the uppermost meter of soil (ranging from low amounts in orange-red to high in purple-blue tones, as measured by TGO’s FREND instrument). The colored scale at the bottom of the frame shows the amount of ‘water-equivalent hydrogen’ (WEH) by weight (wt%). As reflected on these scales, the purple contours in the center of this figure show the most water-rich region. In the area marked with a ‘C,’ up to 40% of the near-surface material appears to be composed of water (by weight). The area marked ‘C’ is about the size of the Netherlands and overlaps with the deep valleys of Candor Chaos, part of the canyon system considered promising in our hunt for water on Mars. The underlying gray shading in this image represents surface topography, and is based on data from the Mars Global Surveyor Mars Orbiter Laser Altimeter (MGS/MOLA). The axes around the frame show location (latitude and longitude) on Mars. Image credit: Mitrofanov et al., doi: 10.1016/j.icarus.2021.114805.

Valles Marineris can be seen stretching across this frame, overlaid by colored shading representing the amount of water mixed into the uppermost meter of soil (ranging from low amounts in orange-red to high in purple-blue tones, as measured by TGO’s FREND instrument). The colored scale at the bottom of the frame shows the amount of ‘water-equivalent hydrogen’ (WEH) by weight (wt%). As reflected on these scales, the purple contours in the center of this figure show the most water-rich region. In the area marked with a ‘C,’ up to 40% of the near-surface material appears to be composed of water (by weight). The area marked ‘C’ is about the size of the Netherlands and overlaps with the deep valleys of Candor Chaos, part of the canyon system considered promising in our hunt for water on Mars. The underlying gray shading in this image represents surface topography, and is based on data from the Mars Global Surveyor Mars Orbiter Laser Altimeter (MGS/MOLA). The axes around the frame show location (latitude and longitude) on Mars. Image credit: Mitrofanov et al., doi: 10.1016/j.icarus.2021.114805.

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

“Water ice usually evaporates in this region of Mars due to the temperature and pressure conditions near the equator.”

“The same applies to chemically bound water: the right combination of temperature, pressure and hydration must be there to keep minerals from losing water.”

“This suggests that some special, as-yet-unclear mix of conditions must be present in Valles Marineris to preserve the water — or that it is somehow being replenished.”

“This finding is an amazing first step, but we need more observations to know for sure what form of water we’re dealing with,” said Dr. Håkan Svedhem, a researcher at ESA’s ESTEC.

“Regardless of the outcome, the finding demonstrates the unrivalled abilities of TGO’s instruments in enabling us to ‘see’ below Mars’ surface — and reveals a large, not-too-deep, easily exploitable reservoir of water in this region of Mars.”

The findings appear in the journal Icarus.

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I. Mitrofanov et al. 2022. The evidence for unusually high hydrogen abundances in the central part of Valles Marineris on Mars. Icarus 374: 114805; doi: 10.1016/j.icarus.2021.114805

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