For today’s cool image, we are going to start from afar and zoom in, because I think that might be the best way to gain at least a rudimentary understanding of the strange geology visible at this one particular Martian location.
The first image, to the right, is the overview map. The red cross indicates our target, a chaotic canyon that flows into the larger Kasai Valles, one of Mars’ largest and longest canyons and possibly only exceeded in size by Valles Marineris. This part of Kasai is near its end, where it drains out into the vast northern lowland plains of Mars.
The second image, below, comes from the wide angle camera on Mars Reconnaissance Orbiter (MRO).
Click for full image.
Click for full image.
This camera doesn’t take images at the highest resolution. Instead, it captures a wider area in order to give context. As you scroll down, you go from the center of the wide southern channel of Kasei Valles into a wide box canyon about ten miles across flowing southward into Kasei. At the end of this box canyon the terrain transitions into a jumbled series of mesas and criss-crossing canyons, terrain that is very typical of what scientists call Martian chaos terrain.
The most popular theory for decades for the formation of Kasei Valles in this region was that it formed by catastrophic floods. More recently scientists have added the component of glacial processes. Even more recent research suggests that those glacial processes might have been dominant, though this hypothesis is not yet documented well.
The flood nature of Kasei’s channels in this area appears very obvious, with much of it reminiscent of the channels carved into wet sand at the beach, after a wave recedes. Some scientists [pdf] tie these catastrophic floods to the breaking of an ice dam higher upstream.
Scientists also believe that volcanic processes contributed to Kasei Valles’ formation, especially in its upstream regions near Mars’ giant volcanoes.
As we scroll down the wide context image to the right, we move into the chaos sections of this canyon, areas where instead of flash floods, glacial activity probably dominated. The glaciers eroded faults or cracks in the ground that appear patterned like the cracks one sees when one shatters tempered glass.
We also could be seeing the leftover ancient remains of polygons, which are Mars resemble mud cracks found when wet mud dries. The glaciers would have favored the cracks for finding routes downhill, and would then have widened them over time, creating the chaotic patterns we see today.
The white box delineates the area covered by the high resolution MRO image, taken on July 12, 2020. More on that below.
South of this initial chaos terrain we start to see a return to large flow channels that suggest again some form of catastrophic flood. Or maybe these channels were also carved by glaciers over a very long period of time. The truth at this point is unknown. Too little is presently known.
Finally below the long context image strip is today’s cool image, a close up of the strange chaotic terrain in the white box.
What makes the geology in this close-up image especially mysterious is how it seems so localized. To the west we have a smooth relatively flat plateau, disturbed only by a scattering of craters.
Then suddenly we are at a rim, looking down at a bunch of mesas and canyons. Sand dunes cover the canyon floors, indicating that when dust and sand gets blown into these canyon it gets trapped there.
Why the chaos terrain should start so suddenly is to me very baffling. It seems reasonable to expect the underlying geology below the plateau to be similar to that where there is chaos, but the existence of the chaos one place and not another suggests otherwise.
The color strip for this image reveals more details. It appears that the canyon floors here have a blue tint, which suggests either rougher terrain or the presence of water. The latter is more likely, especially because the transition from orange/gold to blue is often sharp. For example, there are sand dunes that are orange/gold right beside blue areas, suggesting that the dry sand dunes are covering icy ground.
Regardless, here we are looking at the sudden edge of chaos terrain, beginning abruptly for no apparent reason. It is all quite perplexing, which is of course one of the reasons the image is so cool.
I could go on, puzzling about other features in the image, but I will leave further puzzling to my readers. Make sure you click on the full image. At higher resolution other features become apparent, though this added detail does not necessarily help explain much.