Tag: geology

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Today’s cool image, rotated, cropped, and contrast-enhanced to post here, focuses on polygons found near the equator of Mars. It was taken by the high resolution camera on Mars Reconnaissance Orbiter (MRO) on May 22, 2020, and shows what the science team labels as “well-preserved polygons.”

Previously I have posted cool images showing polygons (here and here), but those images were located in the northern mid-latitudes, and were thought to have been formed in connection with some form of freeze-melt-drying water process in permafrost.

Today’s image however is likely not related to water. It is located in the equatorial regions, where little water is expected. It also has a more permanent nature, which suggests that it is the result of some sort of volcanic or tectonic process. That the polygons are depressions suggests the latter, since a volcanic process is more likely to have filled cracks and left ridges more resistant to erosion, as explained by this article.

In this case the topography suggests instead some form of spreading and cracking process that left behind these polygon-shaped cracks. In mud, such polygons are found when the mud dries, but once again, these are in a very dry region. If formed in that manner they must have formed a very very long time ago, when the climate here was very different, and were somehow preserved for eons since.

The location, as shown in the overview map below provides some context, though it really doesn’t answer any questions..
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Cool image time! The photo to the right, rotated, cropped, and reduced to post here, shows what the scientists from the high resolution camera on Mars Reconnaissance Orbiter (MRO) label “fretted terrain.” In an earlier post describing evidence found by Europe’s Mars Express orbiter of glaciers in the northern mid-latitudes of Mars, fretted terrain was described as follows:

As is common with fretted terrain, it contains a mix of cliffs, canyons, scarps, steep-sided and flat-topped mounds (mesa), furrows, fractured ridges and more, a selection of which can be seen dotted across the frame.

These features were created as flowing material dissected the area, cutting through the existing landscape and carving out a web of winding channels. In the case of Deuteronilus Mensae, flowing ice is the most likely culprit. Scientists believe that this terrain has experienced extensive past glacial activity across numerous martian epochs.

In that case the fretted terrain was in the transition zone between the northern lowland plains and the southern cratered highlands, and actually resembled chaos terrain. What we see here looks far different, a surface that resembles the bubbly surface of a vat of thick molten stew.

This image is also deep in the cratered southern highlands, though still in the mid-latitudes at 41 degrees south latitude. While the presence of ice close to the surface is possible at this latitude and could definitely explain what this image shows, it would be a big mistake to accept this explanation without skepticism. A lot is going on here, and much of it suggests volcanic-type processes. The volcanoes might have been spewing mud or ice instead of molten lava, but then again, all is uncertain.

What is certain is that I can’t help thinking of the pock-marked skin of an adolescent teenager when I look at this photo. And for all we know, the processes that produce both surfaces could be in many ways similar.

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Cool image time! The photo to the right, cropped and reduced to post here, is a great example of how a well known geological process on Earth, glaciers, can form features on Mars that appear most inexplicable.

The image was taken on May 13, 2020 and highlights the geology found in a depression, likely an eroded crater, on the northwest flanks of one of Mars’ largest basins, Argyre Planitia, located in the planet’s southern cratered highlands. The basin is thought to have been formed by a giant impact during the Late Heavy Bombardment around 3.9 billion years ago, when the inner terrestrial planets were sweeping up the last remnants of the Sun’s accretion disk, with that process causing the many craters we see on the Moon, Mercury, and Mars

This particular depression is at 41 degrees south latitude, in the mid-latitudes where scientists have found much evidence of buried glaciers. This is likely what we are looking at here. The section I’ve cropped has a dip to the south, which somewhat fits these flow features. If you look at the full image, you will see comparably weird flow features south of this section, flowing downhill in the opposite direction, to the north.

The problem is that not all the features fit the direction of flow, or any flow at all. I suspect we are seeing evidence of the waxing and waning of glaciers over this terrain over many eons. Disentangling that history however is confounding, especially when we are limited to only studying such objects from orbit.

I must also add that this image was labeled by the MRO science team a “terrain sample,” which means it wasn’t specifically requested by any scientist studying this geology. Instead, they needed to take an image to maintain the spacecraft’s camera temperature, and picked this spot for that snapshot. Their choice wasn’t random, but it also wasn’t based on any focused research.

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Cool image time! The image to the right, cropped and reduced to post here, was taken by Mars Reconnaissance Orbiter (MRO) on May 1, 2020, and shows a truly intriguing crater that they dub a “Crater Hanging on Mesa Wall.”

Located in Deuteronilus Mensae, a chaos region of mesas and cross-crossing canyons in the transition zone between the northern lowland plains and the southern cratered highlands, the crater literally overhangs the edge of this canyon’s cliff. The overview map to the right, with this location indicated by the red box, illustrates what this region’s geology is like.

The most likely explanation is that the impact occurred prior to the creation of the canyon, and when the canyon eroded, the material in and of this crater was more resistant, probably because the impact had packed it together to increase its density.

At the same time, the features inside both craters in the photo, as well as below them on the floor of the canyon, suggest the presence of buried glaciers, something not unlikely at the 45 degree north latitude where this crater sits.

So, here’s a guess at the geological history. First we had the impact, then during the eons of glacial ebb and flow on Mars due to wide swings in the planet’s obliquity (its rotational tilt), the canyon was cut, with that erosion leaving the crater sitting high above the canyon floor below it.

One more curious detail: The material in the canyon seems asymmetric, suggesting that the crater actually dips down toward the canyon, as if it as a unit has tilted to the east as the canyon was worn out below it.