The largest canyon in the Solar System, Valles Marineris deeply marks the surface of Mars; a tectonic crack subsequently widened by erosion and marked by nearby channels potentially carved by water. Now, it turns out, some of that water might still be there. Orbital observations suggest a hidden reservoir of water is present beneath the soil at the bottom of this vast canyon.  

The ESA-Roscosmos ExoMars Trace Gas Orbiter (TGO) has been measuring the presence of hydrogen over the surface of the Red Planet. Hydrogen is a possible proxy for water. Using the FREND instrument on board TGO, the team has identified a region where if the hydrogen detected is in the form of water ice, it could make up as much as 40 percent of the near-surface material.

As published in Icarus, the potentially water-rich region is found overlapping the Candor Chaos, an area that had already been considered a promising place to hunt for water. Previously, scientists looking for near-surface water on Mars have only explored the very surface, looking for ice-covered dust grains in the soil. The new research digs deeper, so to speak. 

“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,” lead author Igor Mitrofanov of the Space Research Institute of the Russian Academy of Sciences, said in a statement.

“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.” 

Mars is a frigid desert but the equatorial regions are still not cold enough to maintain exposed water ice, as is found at the poles. Valles Marineris extends for more than 4,000 kilometers (2,500 miles) in length just south of the equator so the presence of water in the soil is very exciting. More observations will be needed to confirm this detection and to understand what type of water the researchers believe has been found on Mars. At those latitudes, the water could be in the form of buried ice or trapped in minerals.  

“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,” co-author Alexey Malakhov said. “Overall, we think this water more likely exists in the form of ice.”  

"Knowing more about how and where water exists on present-day Mars is essential to understand what happened to Mars' once-abundant water, and helps our search for habitable environments, possible signs of past life, and organic materials from Mars' earliest days," added ExoMars Trace Gas Orbiter project scientist Colin Wilson.