In showing my readers today’s cool image, I want to present it as it is seen by scientists, first from a far distance that with time increasingly zooms in to reveal mysteries on a very human scale.
The overview map to the right essentially gives us the view of Mars as seen by scientists following the Mariner 9 orbiter mission that began mapping the Martian surface in late 1971 after the conclusion of a global dust storm that had hidden its surface initially. As the first high resolution map of Mars, the orbiter revealed numerous puzzling and surprising features, including the largest volcanoes and canyons in the solar system. The orbiter also found that the red planet’s surface was comprised of two very different regions, the northern lowland plains and the southern cratered highlands.
The overview map, covering from about 13 degrees south latitude to about 34 degrees north latitude, shows us all but the southern cratered highlands. The white box in Kasei Valles is where today’s cool image is located. Both Kasai and Valles Marineris represent those giant canyons, all invoking to Earth eyes the possibility of catastrophic floods of liquid water sometime in the past.
Ascraeus Mons is the northernmost of the three giant volcanoes east of the biggest volcano of all, Olympus Mons. All sit on what scientists now call the Tharsis Bulge.
Chryse Planitia, where Viking-1 landed in 1976, is part of those northern lowlands that some scientists believe might have been once had an intermittent ocean sometime in the past. Today’s image is about 600 miles from the outlet into Chryse Planitia.
The geological mystery of all these features demands a closer look, something that scientists have been pursuing now for more than a half century.
The photo to the right, rotated, cropped, and reduced to post here, was taken by the context camera on Mars Reconnaissance orbiter (MRO), designed to map the entire planet at wide-angle at lower resolution. The data is similar to the cameras on the Viking orbiters from 1976-1980, and Mars Global Surveyor from 1997 to 2006, though the coverage is far more complete. While Viking did image this location, it did so at a lower resolution, with incomplete coverage.
The context camera tells scientists where they might find interesting things to look at in greater detail. This context image of the area of the white rectangle above certainly does that, as all the mesas visible apparently are surrounded by a strange moat. Moreover, the mesas sit in what looks like a relatively young, flat, and featureless plain, as indicated by its lack of craters.
The implication of the mesas are that they are an older feature that was resistant to erosion. The overview map above suggests the first major cause of that erosion, the catastrophic flood that some scientists believe poured through Kasai Valles when a giant ice dam broke farther upstream and released a large lake in a sudden flood.
But why the moats? I can guess, but I have zero confidence on any theory. Maybe the flat plain is covered with the mud washed downstream by the flood that has now dried and can be lifted up by wind. As the wind blows it flows around the mesas, getting concentrated near the mesa and picking up speed so that it has the ability to pick up more sand and create these moats. You see something similar on beaches with rocks sitting on the sand. The waves are more efficient at pulling sand from the margins around the rocks, so they have moats.
That the moats are generally the same size on all sides suggests that the winds in this wide part of Kasai Valles have no prevailing direction. Depending on weather and season, they can blow in any direction.
To prove or disprove these theories, however, requires even closer photos.
The image to the right, rotated, cropped, and reduced to post here, is today’s cool image. It zooms in on the southernmost and largest mesa, and was taken on December 2, 2020 by the high resolution camera on MRO.
This photograph raises more questions than it answers. The mesa top appears as young and featureless as the surrounding plain, with what appear to be about the same number of craters. Similarly, the moat on the mesa’s south side also appears to have a similar crater count. This suggests that the mesa, the plains, and even the moats are of approximately the same age, something that seems unlikely and if true makes all my suppositions above invalid.
Covering all the mesa’s slopes are slope streaks, a feature that even today remains unexplained and unique to Mars. At first glance you think they are avalanches, but a close look shows that they do not change the topography of the surface and leave no boulder piles at their base. Instead, they appear at high resolution to merely be a discoloration of the surface.
However, monitoring at high resolution of these slopes shows that the streaks are caused suddenly, like avalanches. Something triggers a flow of some kind down hill, that discolors the surface and over time fades.
If you look at the full image from the context camera, you can see that all the mesas in this area appear to have slope streaks. Why? What makes this location so favorable for these strange features?
At this moment no one knows. The data is too incomplete. We will have to get much closer, to the point of actually touching these features, to really find out.
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