Tag: geology

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Cool image time! The photo to the right, rotated, cropped, reduced, and sharpened to post here, was taken on August 21, 2022 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows what the scientists label as a “layered mound.” It also shows a plethora of geological mysteries, all of which relate to the as yet not quite understood geological history of Mars.

First, note the different colors north and south of the ridgeline. According to the science team’s understanding of what these colors mean [pdf], the orange-red to the north suggests dust, while the bluish-green to the south suggests coarser materials, such as rocks and sand. Though frost and ice are generally bluer, such things are generally found on the pole-facing slopes where there is less sunlight. Thus the bluish-green material to the south is unlikely to be ice or frost, though this is not impossible, as the picture was taken in the winter and the latitude is 35 degrees north.

Why however is there such a dichotomy of rocks, sand, and dust between the north and south slopes? And if frost and ice, why is it more prominent to the south, when it should instead be more prominent to the north?

Other mysteries: Is the circular depression on the ridgetop an impact crater or a caldera? If the latter, this suggests the mound is some kind of volcano, likely mud, though lava is not excluded. If so, however, why is there no caldera on top of the ridge to the south?

The location, as shown in the overview map below, reveals other puzzles.
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Cool image time! The photo to the right, cropped, reduced, and enhanced to post here, was taken on August 26, 2022 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). Though the science team labels this image vaguely as showing “Features in Mamers Valles,” the features are likely glacial ice since this location is at the western end of the 2,000-mile-long northern mid-latitude strip I dub glacier country, where glacial features are seen everywhere.

The white dot marks this picture’s location in Mamers Valles, as shown on the overview map above. This particular Martian channel, that meanders in a wildly random manner (including a few sharp ninety degree turns), is theorized [pdf] by some scientists to have formed not by surface flows but by a subterranean drainage that created voids. On the surface the voids caused sagging, collapses, and the eventual formation of the surface channel.

Under such conditions, any ice in the channel would not necessarily have a clear flow direction, thus providing an explanation (though hardly certain) of the eddy-like shape of these features.

Cool image time! The photo to the right, rotated, cropped, reduced, and enhanced to post here, was taken on September 2, 2022 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). The science team titled this picture “Gullies with Terminal Ridges on Glacial Crater Fill,” a title that in one phrase encapsulates everything we see here of this unnamed 8-mile-wide crater’s western rim and interior.

The crater is located at 46 degrees south latitude inside the much larger 145-mile-wide Kepler Crater, and about 1,500 miles east of Hellas Basin in a region where a lot of glacial ice is found. A context camera image taken in July 2020 shows the entire crater floor apparently covered with glacial fill that on the edges appears to be eroding away.

Today’s high resolution photo focused on the western part of the crater, where that eroding edge was instead replaced by a meandering ridge reminiscent of a moraine. The gullies on the interior slope to the west, as well as the parallel north-south cracks, suggest that debris falling and sliding down from that rim had pushed up against this glacial ice and created that ridge.

There is a lot more to this geology however.
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Cool image time! The photo to the right, rotated, cropped, reduced, and sharpened to post here, was taken on August 13, 2022 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It is another fine example of the wind-blown sculpted terrain that one finds routinely in Mars’ largest volcanic ash field, dubbed the Medusae Fossae Formation. About the size of India, this gigantic field is thought to be the source of most of the dust on Mars.

This particular location sits on the northernmost edge of that huge field. The elongated mesas mark the field’s edge, disappearing to the north but becoming thick and extensive to the south. The prevailing southeast-to-northwest winds have acted to clean most of the ash away.

We can get an idea about how deep and pervasive that field once was at this location by the pedestal crater in the middle right. Once, the floor of that crater was below the top of the ash field. At that time, the top of the dunes marked the general ground level across this entire image. Over time, the winds blew most of this material away, but the denser packed floor of the crater resisted that erosion, and thus now stands above the surrounding terrain.

The more normal-looking craters nearby could have occurred before the ash was deposited, or after it was blown away. The impact that created the pedestal crater however occurred when the ash covered everything here.
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Cool image time! The photo to the right, rotated, cropped, and reduced to post here, should at first glance be one of my “What the heck!?” images. However, a little detective work quickly provides us some understanding of the inexplicable geology seen at this particular location on Mars.

The picture was taken on August 29, 2022 by the high resolution camera on Mars Reconnaissance Orbiter (MRO) and was labeled by the science team a “Lobate Debris Apron in Deuteronilus Mensae.” This mensae region is the western part of the 2,000-mile-long strip in the northern mid-latitudes of Mars that I label glacier country, since almost every high resolution picture taken in this strip shows extensive glacial features.

This picture is no different, showing what appears to be glaciers, but by itself it is still difficult to make sense of it. Glaciers flow downhill, like rivers. In this high resolution image the direction of flow is somewhat unclear.

As always, a wider view clarifies the picture.
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Cool image to end the week! The picture to the right, rotated, cropped, reduced, and enhanced to post here, was taken by on July 18, 2022 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows the bedrock layers on one of two very large mesas that jut out into the floor of 108-mile-wide Terby Crater.

I want to focus your eye on the spoon-shaped mesa near the top right of the photo. Note how the layers can be seen on both sides, even though the top of the mesa seems to be concave. This is strange and complex geology, made even more fascinating in that the two mesas almost reach the center of the crater floor. Why are they here? Why were they not flattened during impact, like the rest of the crater floor? Or maybe the original crater floor is the mesa top, but if so, why did the rest of the crater interior get eroded away.

The overview map below provides some context, and helps fill in some details, even if it fails to answer any of these questions.
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