Tag: geology

Circling the north pole of Mars is a gigantic dune field dubbed Olympia Undae, with its densest regions (marked in red on the overview map to the right) estimated to be 700 miles long and covering 120 degrees of longitude.

Where does all the sand come from that created this dune ocean? We now have a rough idea. The arrows on the map to the right indicate the direction of the prevailing winds, as recently determined by scientists studying the orientation of dunes. From this it appears that much of the dust comes from the north polar icecap itself, from its lower layers where dust and ice are cemented together. The prevailing winds, especially in the canyons that cut into the icecap, drive that dust out from the lower layers, where it over eons has piled up in that circular ocean of sand.

The white cross marks the location of today’s cool image, an attempt by scientists to photograph at high resolution one of the sources of this sand, on the edge of the icecap.
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Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on July 6, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO).

This 500-to-600-foot-high hill represents what is likely the top of a much larger mountain, now buried by the flood lava that surrounds it. The edge of that flood lava can be seen best along the base of the hill’s northern slope, where this now hardened lava had washed up against that slope.

That this Martian mountain is very old can be discerned from two features. One, it had to have been there when the lava flowed, and scientists estimate these lava flows are at least one billion years old. Second, peak’s rounded shape and eroded edges (showing terraced layers) suggest it has been here for far longer, allowing Mars’ thin atmosphere and climate to weather it down.
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Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on June 30, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). The scientists label it “Mesas in shallow trough,” but that is only describes a small part of what can be seen here, as I interpret it.

The picture itself shows a small portion of the floor of an unnamed 32-mile-wide crater, with the crater’s southeast interior rim beginning its rise in the lower right. First, note the meandering hollow in the upper left, suggesting some past flow. Second, note the pattern of small ridges on the flat crater floor, suggesting some past drying process that left cracks that later filled with material that formed the ridges at a later time. Third, the mesas themselves suggest chaos terrain, often formed on Mars in connection with glacial flows. Fourth, note that the trough which holds the mesas is on the edge of the crater floor, suggesting the trough and mesas mark the erosion that once occurred at the edge of some material, possibly ice, that once filled that floor.

The trough and small meander also signify something far larger that can only be seen when we zoom out.
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Cool image time! The picture to the right, cropped to post here, was taken on June 21, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO).

The scientists label the strange tubelike features that are scattered throughout this picture as “landforms,” which is correctly vague because their origin is utterly inexplicable. The ground here is on the eastern slope of a small 20-mile-wide very flat shield volcano located about 150 miles northwest of the giant volcano Ascraeus Mons. The dark wind streaks point down that grade to the east, away from the shield volcano’s peak about 1,000 feet away. (If you look at the full image this indistinct peak is at dead center, with a linear depression (the volcano’s vent) beginning there and heading to the northeast for about four miles.)

Why these many tubes are all oriented in a northwest-southwest direction, at right angles to the slope, is baffling, especially because they hold to that same orientation all across the shield volcano, no matter the downward direction of the slope.
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Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on June 28, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). The intended science focus of the image is likely the floor of this canyon on the lower right, showing what appears to be a patch of uprised topography surrounded by what looks like glacial debris, which at this latitude of 39 degrees north is expected on Mars.

The grade at this location is downhill to the southwest, so if this is a glacier it is flowing in that direction.

The cliff is about 3,000 feet high, dropping that distance in about a mile and a half. Thus, this is only slightly less steep than the very steep cliff wall of the caldera of Olympus Mons, highlighted as a cool image two days ago.

What makes this canyon interesting — besides its spectacular scenery — is its larger context, recognized when one looks at this location from afar and thus sees how it shaped a vast portion of the global surface of Mars.
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Cool image time! The picture to the right, cropped, reduced, and sharpened to post here, was taken on July 14, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), and shows what appear to be horizontal layers in the inner wall of a small one-mile-wide and 150-foot deep unnamed crater on Mars. I have included the color version below, zoomed in to make those layers and their colors very clear.

As I have not contacted the scientists who requested this picture, I can only guess at its purpose. My guess however relates to those horizontal blue layers, reminiscent of the ice layers seen in Martian scarps at the high latitudes at about 50 to 55 degrees.

Normally it is rare to see horizontal layers like this in craters on Mars. Instead, what you usually see are downward-pointing gullies along with drainage and avalanche-type patterns, though the latter two might not be formed by either drainage or avalanches.

In this case these horizontal layers are clear and pronounced, making this crater a possibly important and somewhat unique find, based on its location.
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Cool image time! The picture to the right, cropped, reduced, and sharpened to post here, was taken on May 29, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows what the science team labels an “unusual shaped hill” that is estimated to be about 20 to 40 feet high.

What makes it unusual? First, it sticks up out of the endless northern lowland plains for no obvious reason, though its shape suggests the existence of bedrock topography that is now buried by the dust and debris that coats the surface of those plains.

Second, the hill itself suggests that it formed after it was covered with debris. Note the crater near its northeast cliff. It appears that the cliff chopped off part of the crater, suggesting that the hill was once level with the surrounding terrain. Some later underground pressure pushed it upward, with its angled sides determined by existing faults.

Why those forces tilted the hill upward as it did, with only its eastern fringes raised, is a question a wide view might answer.
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Cool image time! Only yesterday I posted an image of polygons in the dry equatorial regions of Mars, where little evidence of near-surface ice is found and are thought to be the remnants from a long-dried lakebed.

Today we take a look at some polygons in the mid-latitudes of the icy northern lowland plains, where near-surface ice appears ubiquitous and as it sublimates away with the changing seasons causes all kinds of strange formations, including polygons.

The picture to the right, cropped, reduced, and sharpened to post here, is a good example, centered on a 0.6-mile-wide bright crater that appears to be filled with glacial ice. The image was taken on June 22, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), and is located at 44 degrees north latitude on the western edge of Utopia Basin. As noted by the MRO science team in 2006 for a different MRO picture with similar features:
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Cool image time! The picture to the right, cropped, reduced, and sharpened to post here, was taken on June 26, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). The science team calls the features surrounding these small 20 to 60 foot high hills “polygon features,” an apt description and a geological feature that is seen in many places on Mars.

When these features are found in the icy higher latitudes, it is believed they are formed in connection to the freeze-thaw cycle that causes cracks in the near surface ice. When found in the dry equatorial regions, where these polygons are located, they are usually thought to be ancient evidence of past standing water that left behind these cracks, much like the cracks seen in mud after the water has evaporated away on Earth.

The formation of these tiny hills is a bit more complex.
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Cool image time! The picture to the right, cropped, reduced, and sharpened to post here, was taken on April 7, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows what planetary scientists label somewhat vaguely as “layered deposits,” because though the features inside both of these craters strongly resemble glacial ice features, until this is confirmed a good scientist remains skeptical.

I can be more bold, and call the layers glacial in both of these small and very shallow craters (less than a 100 feet deep). To explain this it is important to understand that the lighting and shadows make it hard to distinguish the high points of these layers. Based on the elevation data from MRO, the ground descends to the south, and the mesa in the southern half of each crater’s floor is actually far below the layers and material to the north.

This elevation data suggests that the layered material is surviving best against the crater’s northern interior wall, which at this latitude, about 36 degrees south, will be in shadow the most.
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Cool image time! The picture to the right, cropped, reduced, and sharpened to post here, was taken on February 1, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows what the camera team labels “Circular Mounds Surrounded by Moats,” which when all the known data is considered are probably caused by a spray of small meteorites landing on a field of ice.

Why ice? The location is at 37 degrees south latitude, in the cratered southern highlands of Mars, where many images show glacial-type features inside many craters. In fact, all the nearby craters at this location appear to have such features, suggesting the presence of near-surface ice trapped in these craters.

The picture actually looks at the floor of another such crater, with the mounds in the image’s upper left the crater’s indistinct central peaks. Though only 8.5 miles wide, the crater is deep, with interior walls that quickly rise 2,800 feet to the rim. That depth further suggests ice, as any snow that fell here in the far past could easily become trapped, inside what could be thought of a cold trap.
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Cool image time! The picture to the right, cropped, reduced, and sharpened to post here, was taken on June 8, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows some of the more unusual terrain found at the higher latitudes in the Martian northern lowland plains.

How do we explain this strange landscape? Based on what little we presently know about Mars, at 40 degrees north latitude this bubbly-looking surface probably indicates the presence of a lot of near-surface ice that at some time in the past was heated for some reason and thus bubbled upward to form these mounds. Think of tomato soup simmering.

Unlike simmering tomato soup, this terrain is solid and no longer bubbling. We are looking at a soup that has frozen even as it bubbled. The process could have been like an ice volcano, the ice turning to thick slurry that froze quickly, like lava. Or it could have happened fast, and then froze to remain unchanging in the eons since.
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