Nanedi Valles: A River on Mars

Like Finding A Fossil on Mars

I can remember the feeling I got when I first saw a picture of Nanedi Valles. I was early in the research for my master’s thesis investigating the properties of Martian valley networks and comparing them to properties of terrestrial draining networks. My hypothesis was that the Martian valley networks were formed by water drainage but I needed the data to tell me that. All of a sudden I find this picture:

nanedi valles full

Figure 1. Section of Nanedi Valles

It was like looking down on the Martian ground and finding a dinosaur fossil!   In the bottom of this valley is an unmistakable dry river bed! While one could try to debate that the formation of large valley could have been the result of ground water sapping instead of surface water drainage, there is no doubt about the meandering river bed at the bottom of it. At some point in history of Mars water flowed down bottom of Nanedi Valles. Case closed. Time to pack up and go out for a drink.

valley with river annotated

Figure 2. – Dry River Bed in the Bottom of Nanedi Valles

But wait, the surface of Mars is nearly at vacuum. Oh, and Mars is cold. Very cold. Put the laptop back on the table and get back to work. The mystery has not been solved. When this river was flowing, what did Mars look like? Was the river flowing beneath a glacier or was the surface pressure and temperature much higher than it is today, allowing for liquid water on the surface like it does on Earth? There is still a puzzling mystery here to be investigated and debated, but I’m not going to try to tackle that one here. Instead, I want to take a closer look at Nanedi Valles. Here’s a great picture to consider, it is a side-by-side comparison of the Grand Canyon next to Nanedi Valles.

Nanedi close at angle

Figure 3. – Side by Side Comparison of the Grand Canyon and Nanedi Valles

If you were to scour the Grand Canyon with dust, smoothing out it’s features, it’s easy to see how it could be transformed into something that looks like Nanedi Valles. Using the scale in the Nanedi Valles side of the figure you can estimate the river bed at a couple hundred meters wide, very comparable to a number of terrestrial rivers.

Nanedi Valles highlights one of the challenges of searching for more clues about Mars’s past. We can only see a short section of the dry river bed because the rest has been filled in by dust. When scanning the surface of Mars to find more ancient river system we are likely being misled by the fact that dust has obscured features from our sensors and cameras.

Putting the Puzzle Pieces Together

William K. Hartmann, in Mars: The Mysterious Landscapes of the Red Planet, made out an excellent assessment of the exposed river bed in Nanedi Vallis.   In his treatment he considered the closeup view below.

nanedi unmarked

Figure 4. – Close up of Nanedi Valles Meandor with Exposed Dry River Bed

Hartmann puts forth a geologist perspective of this scene, and he lays it out a theory of how Nanedi Valles could have been formed entirely by running water. To relay his discussion I’ve annotated a version of the picture. For sense of scale, the channel at marker (4) is about 0.5 km wide.

Capture

Figure 5. – Annotated Region of Nanedi Valles

The sequence of events according to Hartmann goes like this.

Marker 1: Flowing torrents of water eroded the landscape to form Nanedi Valles. This very wide river initially flows through Markers 2 and 3 and onward to the north.

Marker 2: A highly resistive rock layer, indicated by the dark strata in valley wall is encountered. In some areas, like at Marker 1) the river is able to erode through this layer but at Marker 3) this resistive layer causes the river to meander and flow towards Marker 4).

Marker 3: When the river meandered to the east, it left this stopped eroding this area. The resulting meander left behind the triangular shelf we see today.

Marker 4: The river now bends abruptly here, though you can still see where continuing flow nearly turned this bend into an oxbow lake. Rivers don’t like ninety degree turns!

Marker 5: At some point the heavy water flow in Nanedi Valles decreased to a fraction of it’s original size, or, alternatively, the flow stopped entire and reactivated some time later at a much lesser amount. In any event the smaller channel exposed here is the result of the last stage of the formation of Nanedi Valles. Over the billions of years since the valley went dry dust scoured the valley walls eventually settling into the bottom of it.

Hartmann points out that the missing element to this sequence of events is the time over which they occurred. Was it all created in weeks, years, centuries or millions of years? We’ll probably never know.

Researchers like Hartman, Malin and Edgett have highlighted Nanedi Valles as probably the best proof that water once flowed on the surface of Mars.

Possible Option for a Human Landing Site

Given the exposed nature of this particular section of Nanedi Valles, and the geologic record it presents, I would conjecture that this area would be an excellent candidate for human landing and exploration. I could imagine establishing a habitat base at the top of the ridge leading down to the shelf. The promontory point between markers (2) and (3) would afford an excellent view of the valley to the north, east and south.

Nanedi Base3

Figure 6. – Notional Location of a Human Habitat (red dot) with Possible Routes to Points of Interest.

Figure 6 is a notional diagram of where the human habitat could be located along with possible paths to nearby points of interest. Blue lines lead to craters almost half a kilometer in diameter. Green lines lead to the exposed river bed in the bottom of the valley. The purple path leads up a short tributary and backup up to the plains to the east of Nanedi Valles. The lower green path also provides an excellent opportunity to examine the exposed dark strata in the valley wall.

After considering the benefits of this location for a manned landing site I checked the proceedings of the “First Landing Site/Exploration Zone Workshop for Human Missions to the Surface of Mars” held in October of 2015 to see if it was one of the locations discussed. Surprisingly it was not on the list.

Stepping Back

To put this location in context, I wanted to review where Nanedi Valles is located on Mars. Here are a series of figures to illustrate the location.

mercatormola with nanedi valles

Figure 7.- MOLA Elevation Map of Mars.

Figure 7 is a Mars Observer Laser Altimeter (MOLA) elevation map of Mars. Nanedi Valles is located in Xanthe Terra (purple star). It is in the equatorial region which would make it very accessible from a landing site perspective. It also sits near the divide between the southern highlands and northern lowlands which means it could be near the shores of what is theorized to have been a huge northern ocean. Overland trips from a Nanedi outpost could be made to investigate these ancient shorelines.

Xanthe Region

Figure 8. – Elevation map of Xanthe Terra. Red circle is the approximate locate of the section of Nanedi Valles I’ve been studying.

Zooming in on Xanthe Terra we see the mighty river valley of Shalbatana Vallis which leads to the northern lowlands. Nanedi Valles is to the west of this larger valley system. The particular meander I’ve been discussing is within the red circle. At the increased level of detail in this map, one can see the great number of craters, and what appears to be an ancient lake bed in Simud Vallis, in addition to Shalbatana Vallis, that are all accessible from the landing site at Nanedi Valles.

cropped nanedi view

Figure 9.- Section of Nanedi Valles. The meander I’ve been studying is at the very bottom of this image.

Figure 9 zooms in one more time. The section with the exposed river bed is located at the lower end of the image. This image shows that Nanedi Valles continues to meander along its entire course. Each exposed ridge in a meander provides the potential for a discovery of the millennia: fossilized life on Mars.

Conclusion

Nanedi Valles is a fascinating, ancient drainage network in the equatorial region of Mars. An exposed, meandering river bed at the bottom of it provides definitive proof that water once flowed on the surface of Mars. This location would be an excellent candidate for human landing and exploration. Not only does it provide the river valley for investigation, but nearby craters, valley systems and lake beds provide more than enough opportunity for discovery.

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