Mars’ giant sinkholes

The floor of one of Mars' giant sinkholes

Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on June 27, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows a small section of the floor and northern slope of Hebes Chasma, one of the many very large enclosed pits that can be found to the north of Valles Marineris, the largest canyon in the solar system. Though Hebes seems small next to the 1,500 mile long Valles Marineris, it still is 200 miles long by 80 miles wide, and could easily fit a half dozen Grand Canyons within it.

For example, the Grand Canyon is from 4,420 to 5,400 feet deep, hiking down from the south and north rim lodges respectively, which sit about ten miles apart. On this picture, the peak on the right sits about 5,300 feet above and only about 3.8 miles from the low spot on the bottom left, which means this one small picture encapsulates the Grand Canyon. And yet, the northern rim of Hebes sits another 21,000 feet higher and twelve miles away. And the entire chasma itself extends 50 miles to the west, 150 miles to the east, and 50 miles to the south.
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Striped terrain on Mars

Overview map

Striped terrain on Mars
Click for original image.

Today’s cool image will be a mystery with the answer below the fold. Before you look at the answer, however, you must try to come up with your own explanation for the picture to the right, cropped to post here, that was taken on September 25, 2018 by the high resolution camera on Mars Reconnaissance Orbiter (MRO).

What we see in this picture is what looks like a striped terrain, alternating bands of light and dark. What caused the bands? Why the different colors?

The overview map above provides some clues. The white rectangle inside Juventae Chasma near the map’s center marks the area within which this picture was taken, though the picture to the right covers only about a pixel inside that rectangle.

Can you guess what these stripes reveal, from this little information? For this quiz to work you must make a guess, but be prepared to be wrong and quickly reassess your conclusions. Such is the real scientific method, so rarely taught now in schools.
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Martian ice sheets sublimating like peeling paint?

Overview map

Martian ice sheets resembling paint peeling
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Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on September 19, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO).

The features are described as “ribbed terrain” in the label. To my eye they more resemble flakes of peeling paint, most especially the mesas in the lower left. On the full image there are many more examples that resemble old paint peels, barely attached to the wall.

The white dot on the overview map above marks the location, deep inside the 2,000-mile-long strip in the northern mid-latitudes I dub glacier country, because everything seems covered by glacial features. This location is at 42 degrees north latitude, where plenty of near-surface ice features are found on Mars.

At first glance it looks like the top “paint-peel” layers to the south have been slowly sublimating away, leaving behind the smooth plain to the north. The problem is that this smooth area in the full image actually appears to be a glacial ice sheet of its own, filling all the low areas between mesas.

In other words, we are probably looking at layers and layers of ice sheets, each created during a different Martian climate cycle, caused by the wide swings of the planet’s rotational tilt, or obliquity.

The location is within Arabia Terra, the largest transitional zone on Mars between the northern lowland plains and the southern cratered highlands. Thus it sits above the glaciers that fill the lower regions of chaos to the north. What we have here is terrain that will eventually become chaos terrain, as the narrow faults and cracks are slowly widened into canyons by the cycles of glacial activity.

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Ancient volcanic vent on Mars

Volcanic vent on Mars
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Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on May 28, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO).

The picture label describes it as a “Low Shield Vent and Pit Northeast of Arsia Mons,” suggesting these depressions are volcanic in nature. We know the pit in the lower left is not an impact crater because it has no raised rim of ejecta. Instead, it looks like a collapsed sinkhole, formed when the ceiling above a void could no longer support its weight. Similar, the trench to the northeast is aligned with the downhill grade to the northeast, with its features suggesting a vent draining in that direction.

The ample dust inside the trench and pit suggest that it has been a very long time since this vent was active. Research suggests volcanic activity last occurred in this region from 10 to 300 million years ago, so that gives us a rough estimate of this vent’s age. Since then any dust that is blown into it will tend to become trapped there.
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The southernmost extent of Mars’ youngest lava flood event

The southernmost edge of Mars' youngest lava event
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Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on August 24, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO).

Labeled “flow margin in Elysium Planitia,” it shows the very edge of what scientists believe was the most recent large lava event on Mars, dubbed the Athabasca Valles, that is thought to have occurred only 600 million years ago. In only a matter of weeks the fast flowing lava covered a region about the size of Great Britain. What we see here is the southernmost edge of that flow, with the smooth terrain on the west an older lava flood plain, covered by the new flood lava from Athabasca on the east.

The polygon cracks likely indicate cracks that formed during the hardening process (like the polygon cracks in drying mud). Hot lava then pushed up from below to form the ridges. It is also possible the ridges are what scientists call “wrinkle ridges,” formed when material shrinks during the drying process.
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Lava/ice eruptions on Mars

Lava/ice eruptions on Mars
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Cool image time! The picture to the right, cropped, reduced, and sharpened to post here, was taken on August 1, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). Labeled by the science team as showing “possible lava-ice interaction,” the photo features some pimply-looking mounds that, though round like craters, sit above the surrounding landscape like small volcanoes.

That these are likely not ancient pedestal impact craters that now sit higher because their material is packed and can resist erosion is illustrated by the bridge-like mound in the lower right. This mound was likely once solid, but its north and south sections have disappeared, either by erosion or sublimation. If formed by an impact the mound would have had a depression in its top center, and would have only eroded outside the rim.
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The caldera wall of a Martian giant volcano

The caldera wall of Pavonis Mons
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Cool image time! The picture to the right, rotated, cropped, reduced, and enhanced to post here, was taken on June 8, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows the top half of the northwestern interior wall of the central caldera of Pavonis Mons, the center volcano in the string of three giant volcanos found in Mars’ equatorial regions.

The elevation change from the top to the bottom of this picture is about 7,000 feet, though this covers only half the distance down to the floor of the caldera. The picture was taken as part of a survey of this caldera wall.

Volcanic activity here is thought to have ended more than a billion years ago. Thus we are looking at relatively old terrain that has had many eons to be reshaped since the last eruption.
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The strange craters in the high northern latitudes of Mars

The strange craters in the Martian northern lowlands
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Cool image time! The picture to the right, rotated, cropped, reduced, and enhanced to post here, was taken on August 22, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). I have also inserted data from a July 28, 2008 context camera image into the blank strip that now exists in the center of high resolution camera images due to the failure of one sensor.

This photo is what the camera team calls a terrain sample, and was probably taken not as part of any specific request but to fill a gap in the camera’s schedule in order to maintain its proper temperature. When the camera team does this they try to find locations that either have not been observed in much detail previously or have interesting features. In this case the team accomplished both. The interesting features are the two pedestal craters, both surrounded by splash aprons. Neither has been observed in high resolution previously, and the context camera has only taken two pictures of this location in total.
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Strange meandering ridge amidst Martian glaciers

Overview map

Strange meandering ridge in glacier country

Cool image time! The picture to the right, cropped, reduced, and sharpened to post here, was taken on June 21, 2023 by the high resolution camera on Mars Reconnaissence Orbiter (MRO). Its focus is the meandering ridge in the center of the picture, which the scientists intentially describe vaguely as a “ridged flow-like feature”.

The elevation difference between the high and low points within the picture is about 500 feet, though most of that slope occurs in the lighter terrain on the right. The darker area where the ridge is located has no clear elevation trend, though there are hints of depressions and rises within it.

The yellow dot on the overview map above marks this location, deep within the chaos terrain dubbed Deuteronilus Mensae, on the western end of the 2,000 long northern mid-latitude strip I dub glacier country, because practially every image from there shows glacial features.

To underline this fact, the red and white dots mark previous cool images from 2020 and 2021, with the first showing an eroded glacier and the second glacial ice sheets.

The mesa to the east of this picture rises more than 6,000 feet to its peak, as indicated by the black dot. This is also the highest point for this entire grouping of mesas. All are surrounded by a single large apron of material, likely a mixture of alluvial fill and ice.

What however caused the narrow ridge in the picture above? Is it ice or bedrock? If ice why is it so different than the glacial material that seems to surround it? If bedrock, it suggests it is instead an ancient inverted channel created when that ridge was a canyon through which ice or water flowed, compacting the canyon floor. When the terrain around it eroded away it was more resistent and became a ridge instead.

I have no answer. The colors suggest the ridge is rock, not ice, but that is not conclusive.

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The grand Valles Marineris of Mars

The grand canyon of Mars
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Time for another cool image of the grand canyon of Mars, Valles Marineris. The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on May 24, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows a small section of the floor of this gigantic canyon, where orbital data has detected light-toned materials. From the caption:

Many of the Valles Marineris canyons, called chasmata, have kilometer-high, light-toned layered mounds made up of sulfate materials. Ius Chasma, near the western end of Valles Marineris, is an exception.

The light-toned deposits here are thinner and occur along both the floor and walls, as we see in this HiRISE image. Additionally, the sulfates are mixed with other minerals like clays and hydrated silica. Scientists are trying to use the combination of mineralogy, morphology, and stratigraphy to understand how the deposits formed in Ius Chasma and why they differ from those found elsewhere in Valles Marineris.

The picture however gives no sense of the monumental terrain that surrounds it.
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Martian lava that buried a crater

Martian lava flow through crater
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Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on June 24, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows a lava flow that cut through an older 2-mile-wide crater, mostly burying it as it burst through the crater’s southwest and northeast rims. From the caption:

A lava channel extends from the feature and continues 60 kilometers to the northeast, growing deeper along its path. The circular formation is likely an eroded impact crater whose walls have been breached by the lava as it surrounded the rim and then infilled the crater. Alternatively, it could represent the location of a volcanic vent that sourced some of the lavas that formed the channel.

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Mars geology that only makes sense by digging deeper

Not-so baffling Martian geology
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Today’s cool image is a perfect example of why nothing in science research should ever be taken at face value, without digging a bit deeper. The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on October 5, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO).

First an important technical point. Though the electronics unit for one of the camera’s color filters is still not working — causing a blank strip down the center of all black & white images, the camera team has gotten around this problem by inserting in that strip other color filter data, thus creating a complete image as you see to the right. This work-around means that MRO’s capabilities, though showing signs of age, will continue almost as good as before.

As for the image itself, when I first looked at it, I was baffled by the striking contrast between the mottled and rough ground in the lower left, and the almost featureless and smooth terrain everywhere else. Why this sudden transition? What could cause it? That inexplicable contrast demanded I post it as a cool image.
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A seasonal map of the cloudy parts of Mars

Seasonal map of the cloudy parts of Mars
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Though Mars’ very thin atmosphere (1/thousandth that of Earth) is generally clear, it does have clouds that come and go. A project begun in 2022 using citizen scientists to identify these clouds and the seasons they appear the most, dubbed Cloudspotting on Mars, has now published its first paper, available here.

The graph to the left, Figure 9 in the paper, shows two seasonal Mars maps, one indicating the daytime seasonal frequency of clouds and the other their nightime frequency. From the paper:

The seasonal evolution of all clouds as a function of latitude for both daytime and nighttime are shown in Fig. 9. During the clear season until [mid-summer in the northern hemisphere] … there are several regions where clouds occur frequently: in the equatorial region (annotated as 1), at mid-latitudes (2), in the southern polar region (3), and to a lesser extent in the northern polar region [at the start of summer]. From [late fall to mid-autumn in the north], daytime clouds occur primarily at mid-latitudes, but are observed at nearly all latitudes between 70°S and 60°N (4). At night, there is one broad population from 30°S to 30°N (clouds are more frequent in the equatorial region at night), but [in autumn], clouds occur frequently between 30°N and 50°N as well. [In mid-spring] the number of observed nighttime clouds increases in the southern hemisphere, especially near 50°S. There is a strong decrease in the number of peaks just before [the late northern autumn and the late southern sping] at nearly all latitudes except around 50°S and 20°N at night. [Once northern winter arrives], clouds are observed between about 60°S and 60°N as well as both polar regions, although nighttime clouds between 0°N and 30°N occur relatively less frequently.

The low-latitude clouds during the clear season (1), which are observed more frequently at night, occur at high altitudes, 65–80 km during the day and 55–70 km at night; this is the aphelion equatorial mesospheric cloud population studied in depth by Slipski et al. (2022) and in which previous observations have spectrally confirmed CO2-ice.

Martian seasons

The bracketed words indicating seasons above replace the longitudal numbers the scientists use to indicate the seasons, and are used on these two graphs. The figure to the right shows what the longitude numbers represent in the graphs’ X-axis.

The project continues if any of my readers want to join in.

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A Martian splash crater in the northern lowland plains

A Martian splash crater
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Cool image time (necessary when there is no real space news to report)! The picture to the right, cropped, reduced, and sharpened to post here, was taken on June 29, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows what the scientists label as “steep crater walls.”

And the interior slopes of this 5-mile-wide unnamed crater are steep, about 600 feet high and descending at a grade of 10 to 13 degrees, getting steeper as you go down. In fact, the floor of the crater itself continues that slope downward to the west until it reaches the base of its western interior wall. For some reason the glacial material within it is piled up higher on its eastern end.

The dark streaks on the crater interior walls are either slope streaks or recurring slope lineae, with the former appearing somewhat randomly and the latter seasonal in nature. Both remain unexplained unique phenomenons of Mars. This new picture was likely a follow-up of a January 2014 MRO picture to see if anything had changed in the past decade.

To my eye it is difficult to detect any changes, but I am not looking at the highest resolution version of the picture. The lack of changes suggests the streaks are seasonal lineae, as both images were taken in the northern spring and the streaks in both appear much the same.
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Scour pits of volcanic Martian ash

Scour pits in volcanic ash
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Cool image time! The picture to the right, cropped, reduced, and sharpened to post here, was taken on June 16, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). The science team describes this as “clusters of scour pits,” which means the pits here were formed by the prevailing winds, which according to a global analysis of dunes on Mars, is probably blowing from the west to the east at this location.

This image only covers a small section of these scour pits. The full field extends about 20 by 18 miles across, and appears to be the southeastern flank of a mile-high dome. The scour marks could therefore also be evidence of some sagging of this material downhill along that flank.

It is also possible that the flow of the prevailing winds across this southeastern downhill slope is causing the pit formation. Unlike this flank, the rest of this dome is relatively smooth.
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A new global map of the near-surface ice on Mars

Global map of near-surface ice on Mars
Click for interactive map.

A project begun in 2019 to use all the presently available orbital data to compile a global map of the near-surface ice on Mars has now been released that global map, shown by the graphic above, taken from Figure 16.7 from the project’s science paper.

The various areas in blue show the evidence of ice down to about 5 meters, or about 15 feet, with darker blue areas indicated ice at greater depth. The study focused on latitudes below 60 degrees latitude, while also blocking out areas above one kilometer in elevation (as indicated in black on the map above). As the paper noted,
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The icy terrain near one of Starship’s prime candidate landing spots on Mars

The icy terrain near Starship's prime landing spot on Mars
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Cool image time! The picture to the right, cropped to post here, was taken on August 22, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). The camera team labeled the picture a “terrain sample,” which generally means it was not taken as part of any scientist’s specific research request, but to fill a gap in the schedule so as to maintain the camera’s proper temperature. When the team needs to do this, they try to pick a location in the gap that might have some interesting features. Sometimes such pictures show relatively boring features. Sometimes the results are fascinating.

In this case the location chosen was in the northern lowland plains of Mars, in a region called Amazonis Planitia. At 38 degrees north latitude it is not surprising that the photo shows ice features. All the depressions here appear to have an eroding glacier, while the surrounding plateau resembles an untouched snow field in the very early spring, the snow beginning to sublimate away to leave the top rough and stuccoed. Note too that these depressions are likely not impact craters (they have no upraised rims and many are distorted in shape), but were likely formed by that same sublimation process.
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Perseverance looks ahead, beyond Jezero Crater

Perseverance looks ahead, beyond Jezero Crater
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Overview map
Click for interactive map.

Cool image time! The panorama above, enhanced and annotated to post here, was taken on October 21, 2023 by one of the navigation cameras on the Mars rover Perseverance. As shown on the overview map to the right, it looks to the west, at the gap in the rim of Jezero crater, dubbed Neretva Vallis, through which the delta in the crater had once poured.

The blue dot marks the location of Perseverance. The green dot marks the location of Ingenuity, which suggests it is visible within the panorama. I have indicated two features on the panorama that could be the helicopter, but the resolution of this navigation camera image is not good enough to determine with certainty if either is the helicopter or simply a rock.

Beyond the gap can be seen several small mountains, a hint at the generally rough terrain that sits to the west of Jezero that Perseverance will eventually enter and explore. This region is also an area where orbital images suggest a wide variety of minerals, making it a potentially valuable mining location for future Martian settlers.

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A low mid-latitude crater on Mars apparently filled to overflowing with ice

ice filling a Martian crater to overflowing
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Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on June 18, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows a steep 1,000-foot-high cliff with what appears to be extensive glacial material at its base.

The many layers all suggest past climate cycles, where snow was deposited and the glacier grew, followed by a period when no snow fell and the glacier either shrank or remained unchanged. The terraced nature of the layers near the base of the cliff suggest that with each active cycle less snow was deposited and the glacier grew less.

The latitude is 33 degrees south, which puts it just outside the dry equatorial regions of Mars and inside the mid-latitude region where many such glacial features are found. Its closeness to the tropics however is significant, because by this point we should be seeing a diminishment of such features. Instead, the wider view shows us that the near surface ice in this region is extensive and in fact appears to cover everything.
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The fractured floor of the south Utopia Basin

The fracture floor of South Utopia Basin

Cool image time! The picture to the right, rotated, cropped, reduced, and enhanced to post here, was taken on August 5, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). The central darker strip however comes from a September 27, 2008 image by MRO’s lower resolution context camera, inserted to fill in the blank section where one component on the high resolution camera has failed.

The picture focuses on what the scientists call a “pit interacting with a mound.” The 100-foot-deep pit is one of a very long meandering string of such pits, all of which suggest the existence of an buried river canyon into which debris is sinking. Altogether this particular string runs from several dozen miles, and its interaction with the triangular 300-foot-high mound suggests at first glance that the river that created the canyon did a turn to the left to avoid a large underground mountain, now mostly buried but revealed by its still exposed peak.

As is usual in planetary research, the first glance is often wrong. The overview map below provides a different answer, which says the formation of the aligned pits is related to the formation of the mound itself.
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