Reull Vallis, Ancient River System Discovered On Mars

An extremely river-like structure, Reull Vallis, has been discovered on Mars and captured in these images by ESA’s Mars Express orbiter.


The structure looks exactly like rivers (and their associated tributaries) look on the Earth. It seems very unlikely that the structure would have been caused by something other than a liquid of similar composition and behavior to water.

Reull Vallis is theorized to have formed “when running water flowed in the distant martian past, cutting a steep-sided channel through the Promethei Terra Highlands before running on towards the floor of the vast Hellas basin. ”

The very sinuous structure, stretching almost 1500 kilometers through the martian landscape, “is flanked by numerous tributaries, one of which can be clearly seen cutting in to the main valley towards the upper (north) side.”

At some points, the structure is nearly 7 km wide and over 300 meters deep.


“The sides of Reull Vallis are particularly sharp and steep in these images, with parallel longitudinal features covering the floor of the channel itself. These structures are believed to be caused by the passage of loose debris and ice during the ‘Amazonian’ period (which continues to this day) due to glacial flow along the channel.”

“The structures were formed long after it was originally carved by liquid water during the Hesperian period, which is believed to have ended between 3.5 billion and 1.8 billion years ago.”

There are similar ‘lineated’ structures present in many of the nearby craters, which are thought to contain a lot of ice.

“In the wider context image, the tributary intersecting the main channel appears to be part of a forking of the main valley into two distinct branches further upstream before merging back into a single main valley.”


“The right (northern) part of the main image is dominated by the Promethei Terra Highlands with their high and soft-rounded mountains shown in these images, rising around 2500 meters above the surrounding flat plains.”

“This region shows a striking resemblance to the morphology found in regions on Earth affected by glaciation. For example, we can see circular step-like structures on the inner walls of the sediment-filled crater in the foreground of the second perspective view. Planetary scientists think that these may represent former high water or glacial levels, before ice and water sublimated or evaporated away in stages at various times.”

“The morphology of Reull Vallis suggests it has experienced a diverse and complex history, with analogies seen in glacial activity on Earth. These analogies are giving planetary geologists tantalising glimpses of a past on the Red Planet not too dissimilar to events on our own world today.”


It’s a very interesting find, though certainly not unexpected given all of the other evidence that has been found of Mars’ earlier wet period.

It doesn’t appear that we will be getting a closer look at the region anytime soon though, as no rovers are in the area/able to access such terrain. NASA’s Mars rover Curiosity is currently occupied with its mission at Gale Crater.

NASA is currently in the planning phases of sample return mission to the Red Planet though, this could be a very interesting place to take samples if the logistics of it make sense. It may be a difficult thing to do though, given how deep the structure is in areas.

Currently, the next mission to Mars is expected to be MAVEN mission , which will launch this year and study the atmosphere of Mars, primarily to investigate the processes that led to the planet losing its atmosphere. It’s currently thought that this was primarily due to a disappearance of the planets magnetic field as a result of the core cooling.

MAVEN will be followed by InSight, launching in 2016, which will feature a large drill, and study seismicity on the planet for the first time.

Source: European Space Agency

Image Credits: NASA MGS MOLA Science Team; ESA/DLR/FU Berlin (G. Neukum)

About the Author

‘s background is predominantly in geopolitics and history, but he has an obsessive interest in pretty much everything. After an early life spent in the Imperial Free City of Dortmund, James followed the river Ruhr to Cofbuokheim, where he attended the University of Astnide. And where he also briefly considered entering the coal mining business. He currently writes for a living, on a broad variety of subjects, ranging from science, to politics, to military history, to renewable energy. You can follow his work on Google+.

  • James Paulson

    Glad to hear that this construction was averted for the time being!

  • Terrence Healy

    Maybe there could be caverns and alot of water underground on Mars. One day they will start looking at the core of the planet and that is where it is going to get interesting. Hopefully we will find some Caverns.

    • strife

      and Martians