Tag: geology

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Cool image time! I came across this strange feature shown on the right in my normal rummaging through the archive of the high resolution camera on Mars Reconnaissance Orbiter (MRO). The photo, rotated, cropped, and reduced to post here, focuses on what they label a “cratered cone.”

The immediate thought is that this is a volcano cone, and the craters at its peak are not impact craters but calderas. In science however such a knee-jerk conclusion is always dangerous. For example, this might instead be a pedestal crater, where the surrounding terrain was worn away over eons, leaving the crater sitting high and dry.

It is therefore important to look deeper to determine what origin of this feature might be.

First, its location, as shown in the overview map below, provides us our first clue.
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The science team for the high resolution camera on Mars Reconnaissance Orbiter (MRO) today released a very cool pair of images, taken a Martian year apart, showing some significant changes that had occurred during that time in a large sand dune slope inside a crater. On the right is that pair, reduced and with the top image slightly lightened to bring out the features. As they wrote in the caption,

One large gully in particular has had major changes in every Martian winter since [MRO’s high resolution camera] began monitoring, triggered by the seasonal dry ice frost that accumulates each year.

This time there was an especially large change, depositing a huge mass of sand. The sand divided into many small toes near its end, or perhaps many individual flows descended near the same spot. Additionally, a long sinuous ridge of sand was deposited. This could be a “levee” that formed along one side of a flow, but there is not much sand past the end of the ridge, so it might also be the main body of a flow.

Nor is this dune gully the only active one in this crater, dubbed Matara Crater, located in the southern cratered highlands at about 50 degrees south latitude. If you look at the full image and compare it with an image from 2009 there are many changes across the entire slope field that extends a considerable distance to the north and south of the cropped section shown above.

At this latitude atmospheric carbon dioxide settles as frost during the winter, then sublimates away with the coming of spring. The freeze-sublimation process disturbs the sand each year, causing these avalanches.

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Cool image time! The photo on the right, cropped and reduced to post here, is a perfect example of the difficulty of explaining the alien landscapes on Mars, based on orbital imagery. It was taken by the high resolution camera of Mars Reconnaissance Orbiter (MRO) on January 23, 2020.

In this one image alone we have the following strange features, all within an area about 8 by 11 miles in size:

• Several small very obvious pedestal craters (near the top right), some located inside depressions. Pedestal craters are created because the surrounding terrain eroded away around them. Since these are pedestals, however, why are they also inside depressions?
• Two large circular mesas that appear to vaguely have terraced erosion. These might also be pedestal craters, but maybe not. They also sit much higher than the pedestal craters above. Either way, the mesas remained while the terrain around them eroded away.
• Several normal craters with a series of circular features within each. At this latitude, 34 degrees south, it is possible these craters are filled with buried ice, what scientists call concentric crater filled glaciers.
• A light-colored string of ridges aligned to almost look like a kite with tail. The light color says this ridge is not made up of the same material as the circular mesas and pedestal craters, but it too was not eroded away.
• A number of small bean-shaped depressions (just south of the biggest circular mesa and near the top left). Don’t ask me what caused them. I have no idea.

The spot is located in the Martian southern cratered highlands, as shown by the blue cross in the overview map to the right. Complicating its geological history is that it sits inside a very gigantic very old and degraded crater, with numerous newer smaller impacts overlaid on top. Any explanation needs to include these impacts, and the ejecta from them.

If you click on the image and study the full resolution photograph, you can find even more enigmatic features. For most there is a reasonable geological theory. Putting them all in one place and somehow getting all those different explanations to fit together however is far more difficult.

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Cool image time! The photograph on the right, rotated, cropped, and reduced to post here, was taken by the high resolution camera on Mars Reconnaissance Orbiter (MRO) on September 30, 2019. It shows what the image title dubs a “sinuous ridge” in a region called Tempe Terra.

What caused it? At first glance the meandering nature of the ridge suggests it was originally a riverbed, formed by flowing water. Eventually the water dried up, and because that riverbed was made of harder material than the surrounding terrain, long term erosion caused that surrounding terrain to wear away, leaving a raised ridge where the river used to be. Scientists have found many such inverted channels on Mars.

Not so fast!
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Cool image time! Or I should say a bunch of cool images! The photo on the right, rotated, cropped, reduced, and annotated by me, was taken by the high resolution camera on Mars Reconnaissance Orbiter (MRO) on February 3, 2020. An uncaptioned image, it was entitled “Arabia Terra with Stair-Stepped Hills and Dark Dunes.” Arabia Terra is one of the largest regions of the transition zone on Mars between the northern lowland plains and the southern cratered highlands. It is also where Opportunity landed, and where Europe’s Rosalind Franklin rover will land, in 2022.

This image has so many weird and strange features, I decided to show them all, Below are the three areas indicated by the white boxes, at full resolution. One shows the black dunes, almost certainly made up of sand ground from volcanic ash spewed from a long ago volcanic eruption on Mars.
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The photo to the right is a small section cropped from an image taken by the high resolution camera on Mars Reconnaissance Orbiter (MRO) on January 2, 2020. It shows the rough, cratered southern highlands dubbed Tyrrhena Terra that lie between the low Isidis Basin to the north and Mars’ deepest basin, Hellas, to the south.

The image was taken not because any specific scientific request, but because MRO was doing spectroscopy over this area and it made sense to also take a photograph. Comparing the photograph with the spectroscopic data allows scientists to better understand that spectroscopy.

The white cross in the map below shows the location of this image. The map itself covers latitudes from 40 degrees north to 55 degrees south.
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Cool image time! The photo to the left, cropped to post here, was taken by the high resolution camera on Mars Reconnaissance Orbiter (MRO) on January 21, 2020, and shows several boulders at the bottom of a slope, along with the tracks those boulders made as they rolled downhill sometime in the far past.

Uphill is to the south. We know the dark spots at the end of these tracks are large boulders partly because of the wind streaks emanating away from them to the north. As the wind goes around each rock it produces eddies that produce the tracks. Based on the scale and the image resolution (about 10 inches per pixel), these boulders range in size from about one to five feet in diameter.

This image has two points of interest. First, the tracks left by the boulders seem to have a repeating pattern. My guess is that the pattern most likely formed because the boulders are not spherical in shape, and as they rolled each roll repeated a certain pattern reflecting that shape. This theory is reinforced by a close look at each boulder. Though the resolution is insufficient to resolve the boulders themselves, the pixel distribution for each strongly suggests an asymmetric shape.

Second, this image, when compared with an earlier MRO image of the same spot, taken fourteen years ago in December 2006, shows no obvious change. These tracks, and their boulders, have therefore probably sat here, as we see them, for a long time. Since there appear to be two sets of tracks, with one overlying the other, this suggests that two separate events (an earthquake or nearby impact) each time caused a bunch of boulders to break free and roll downward together, with the second set of boulder tracks crossing over the earlier set.

Establishing when those two events occurred, however, will require some on-site data, something that will likely not occur until humans roam the surface of Mars in large numbers.

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Cool image time! The photograph to the right, cropped and reduced to post here, was taken by the high resolution camera on Mars Reconnaissance Orbiter on December 22, 2019 and was titled “Contact Between Debris Apron and Upper Plains in Deuteronilus Mensae”.

The section of the full image that I have focused on shows what appears to be the downhill break-up of the surface debris covering an underlying water ice glacier. The grade is downhill to the south.

I am confident that this is buried glacial material based on recent research:

• November 22, 2019: Mars Express confirms ancient glaciers in northern Martian mid-latitudes
• December 20, 2019: More evidence of ample shallow ice in Martian mid-latitudes

Both of these reports found lots of evidence of shallow ice in Deuteronilus Mensae, a region of chaos terrain in the transition zone between the Martian northern lowlands and the southern highlands.

With this image we see what appears to be the slippage of that ice downslope, causing breakage and cracks on the surface, with much of that surface made up of the dust and debris that covers the ice and protects it. Towards the bottom of the image it even appears that the disappearing ice is unveiling the existence of a bunch of buried bedrock mesas, typical of chaos terrain, previously hidden by the ice because it filled the surrounding canyons.

Below is a close-up of the photograph’s most interesting area of break-up.
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Cool image time! The photo on the right, rotated, cropped, and reduced to post here, was taken by the high resolution camera on Mars Reconnaissance Orbiter on November 21, 2019. The uncaptioned image was simply entitled “Ice-filled Graben.”

The location is on the lower flanks of the giant volcano Alba Mons, which in itself sits north of Olympus Mons and the volcanic Tharsis Bulge. The canyon is called a graben because it was formed when a section of the crust slips downward along parallel faults. It does not have the features of a rill, or lava flow, as it starts and stops suddenly. It probably formed due to the rise of the volcano, pulling apart its flanks along faults, causing some sections then to slip downward.

How do the scientists know this is ice-filled? I suspect they have other data that indicates the presence of water, but there are also clear features inside this canyon that resemble the glacial features found elsewhere on Mars. For example, note the parallel lines near the canyon walls. These indicate past surface levels as well as layers within the ice from cyclic climate processes. The line of pits along the southwest wall, where the surface gets more sunlight, also suggests that this sunlight is causing more ice to sublimate away.

Finally, the graben is located at 46 degrees north latitude, definitely far enough north for such ice to exist, based on ample other research.

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The image to the right, rotated, cropped and reduced to post here, was taken on December 19, 2019 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). Labeled “Head of Mamers Valles”, it shows the very end of one side canyon to this very extensive canyon system made up of the fractured fissures and mesas of chaos terrain.

Mamers Valles itself sits in the transition zone between the northern lowland plains and the southern cratered highlands. This specific canyon is close to those lowlands, at a latitude of 40 degrees north, where scientists believe there are many buried inactive glaciers of ice.

The image reinforces this belief. The entire canyon appears practically filled with what looks like ice. In fact, it almost looks like we are looking down at a frozen lake with a layer of snow on top of it. In this case, the layer is not snow, but dust and dirt and debris that covers the ice to protect it and prevent it from sublimating away.

The overview map below shows the location of this canyon, by the red cross, within Mamers Valles.

Mamers Valles is actually a very large collection of miscellaneous canyons, flowing into the lowlands. In some areas it looks like very old chaos terrain, with the canyons so eroded that all we see are scattered mesas. In other places the canyons more resemble meandering river canyons sometimes interspersed with crater impacts.

Scientists have analyzed the canyons in Mamers Valles, and from this concluded that they were likely formed from “subsurface hydrologic activity”. which in plain English means that flowing water below ground washed out large underground passages, which eventually grew large enough for their ceilings to collapse and form the canyons we see today.

Yesterday I posted an image of a string of pits that could very well be evidence of this same process in its early stages of canyon formation. In Mamers Valles the process is far more advanced, and the canyons have existed for a long time, long enough for the planet’s inclination to go through several cycles of change, from a low of 25 degrees tilt (what it is now) to has high as 60 degrees. At that high inclination the mid-latitudes were colder than the poles, so that ice would sublimate from the poles to fall as snow in the mid-latitudes, forming active glaciers within canyons such as this.

Now that the planet’s inclination is similar to Earth’s, 25 degrees, the poles are slightly colder than the mid-latitudes, and the glaciers in this canyon are either inactive (if buried) or slowly sublimating away so that the water can return to the poles.

Here however the surface debris appears to be protecting the glaciers, leaving the canyon filled mostly with ice. For future settlers this ice would likely be relatively accessible, and at a latitude where the environment is also relatively mild, for Mars.