Tag: geology

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Today’s cool image is once again another of what I dub a “what the heck?” photo. The picture to the right, cropped to post here, was taken on December 17, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO) and captures some very strange ridges on the plateau above Mars’ biggest canyon, Valles Marineris.

The image, labeled merely as a “terrain sample,” was taken not as part of any specific research project but scheduled by MRO’s science team in order to maintain the camera’s temperature. When they do this they try to take pictures covering something interesting, but often it is a potshot that sometimes shows little of interest.

In this case the photo shows something very strange. The ridges in the sample are packed into one area only, but if you look at the full image you will see that they are also scattered about randomly and sometimes isolated on the flat plains surrounding this spot.

Interestingly, these ridges resemble the first “What the heck?” image I ever posted in 2019. That photo was located at about the same elevation as these ridges, but due west in the volcanic plains near Mars’s giant volcanoes and just off the western edge of the overview map below.
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British biologist John Haldane once once wrote, “The universe is not only queerer than we suppose, but queerer than we can suppose.”

Today’s cool image to the right, cropped to post here, is a fine example of Haldane’s words. It was taken on January 15, 2021 by the high resolution camera on Mars Reconnaissance Orbiter of a single lone mesalike feature sticking up in a flat expanse of Mars’ south polar dry ice/water ice cap.

I emailed Shane Byrne of the Lunar and Planetary Lab University of Arizona, who had requested the photo, to ask him what he thinks we are looking at. His response:

This region has a thick layer of CO2 ice sandwiched between water ice that’s above and below. CO2 ice is denser than water ice so I think a fragment of water ice of the underlying layer has risen up through the denser CO2 ice that covers this area (what geologists call a diapir).

Byrne also admits this remains merely “just a wild theory,” not yet confirmed.

Assuming this theory to be right, in a sense then this mesa is not really a mesa at all but an iceberg of water, floating not in a saltwater liquid ocean as on Earth but on a frozen sea of dry ice. Talk about queer! The wider shot below, taken by MRO’s context camera, illustrates how isolated this water iceberg is on that dry ice sea.
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Cool image time! The pit shown in the high resolution photo to the right (image rotated, cropped, and reduced to post here) was taken on January 25, 2021 and labeled by the Mars Reconnaissance Orbiter (MRO) “Collapse Pit in Graben with Ice Fill.”

There is a lot of information in that title. First, a graben is a geological feature where a section of terrain drops relative to the surrounding terrain, producing a depression. Second, it appears the graben in this region is mostly filled with debris, probably wind-blown dust or sand or volcanic ash.

Third, at this particular spot the filling material sank, like a sinkhole on Earth, creating the pit.

And fourth, and maybe most intriguing, the scientists think that this pit is now filled with ice. At 47 degrees north latitude, the location is prime for such ice, and the interior material resembles similar glacial features seen in many other mid-latitude craters.
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Boxwork inside Wind Cave, South Dakota, mere inches across.

Anyone who has ever visited either Wind or Jewel caves in South Dakota has likely seen some wonderful examples of the cave formation boxwork, formed when the material in cracks is more resistant to erosion that the surrounding bedrock, which once eroded away leaves behind the criss-crossing ridges seen in the picture to the right.

Today’s cool image provides us what appears to be an example of boxwork on Mars. However, unlike on Earth it is not in a cave but on the surface. It is also much larger. Instead of the ridges being almost paper thin and stretching for inches or feet, this Martian boxwork is feet wide with ridges extending hundreds of feet in size, as shown by today’s cool image below.
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Cool image time! Last week the MRO science team posted a new captioned image entitled “Bright and Dark Dunes” featuring a particularly large single dune in the floor of a 25-mile-wide unnamed crater located at about 68 degrees south latitude. The photo to the right, rotated, cropped, reduced, and color enhanced to post here, shows that dune. According to the caption, written by Colin Dundas of the U.S. Geological Survey’s Astrogeology Science Center in Arizona,

This image shows a large sand dune with bright patches. Martian dunes near the poles often have bright patches in the spring, when seasonal frost is lingering. However, this image is from late summer, when frost is long gone. What is going on here?

A close-up look with [MRO’s high resolution camera] provides some clues. The bright patches are made up of large ridges that look like wind-blown bedforms. Additionally, the bright patches are yellowish in the infrared-red-blue image. In enhanced color, most sand on Mars is blue but dust is yellow. This suggests that the bright bedforms are either built from, or covered by, dust or material with a different composition.

Thus, the bright patches reveal either aspect of the dune’s underlying structure, either inherent in the bedrock itself, or the texture of its surface that allows it to hold more dust. As Dundas adds, “I think more study would be needed to determine the answer in this particular case.”

There are other aspects of this dune that can be seen by a look at the wider view afforded by MRO’s context camera below.
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