The Valles Marineris in equatorial Mars and is one of the the largest canyon in the solar system.  It is surpassed in length only by the rift valleys of Earth. (NASA)

That early Mars was much wetter and warmer than it is today has been well established by numerous missions.  Water ice is visible at the poles and many fossil rivers have been found in the southern highlands of Mars.  The Curiosity rover found as well that the large crater where it landed — Gale Crater – once had a lake and in-flowing streams.

But the presence of water, or proof that water once flowed, has been missing in the equatorial latitudes  of the planet.

However, now a paper based on data from the European/Russian Trace Gas Orbiter (TGO) strongly suggests that the Candor Chasma, located near the heart of the massive canyon system called Valles Marineris, has either large deposits of a kind of permafrost water ice just below its surface or of rocks formed in water and now containing that H₂O in their structure.

The article to appear in the journal Icarus says that the discovery of large amounts of hydrogen in the region speaks of this aqueous  past.

“We found a central part of Valles Marineris to be packed full of water – far more water than we expected,” Alexey Malakhov, of the Russian Space Research Institute and a co-author of the study, said in a statement.

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

Valles Marineris, seen at an angle of 45 degrees to the surface in near-true color and with four times vertical exaggeration. The image covers an area of about 400,000 square miles. The largest portion of the canyon, which spans right across the image, is known as Melas Chasma. Candor Chasma is the connecting trough immediately to the north. The digital terrain model was created from 20 images taken by the High Resolution Stereo Camera of the Mars Express Orbiter. (ESA)

Valles Marineris is 10 times longer and 4 times deeper than our Grand Canyon.  Geologists have theorized that Valles Marineris began to open along geological faults about 3.5 billion years ago. The faulting may have been caused by the tectonic activity that accompanied the growth of the giant volcanoes in Tharsis, lying just to the west.… Read more