Tag Archives: Mars Reconnaissance Orbiter

How last year’s global dust storm changed one spot on Mars

One spot on the western flank of  Olympus Mons, August 2017
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To the right is an image taken by the high resolution camera on Mars Reconnaissance Orbiter (MRO) back in August 2017, cropped, rotated, and reduced to post here. It shows a particular spot on the western slope of the giant volcano Olympus Mons. The uncaptioned image release is entitled “Dark and Possibly Stationary Ripples in Anomalous Terrain.” The image was probably taken as a follow-up to this 2009 image to see if the the dark patches near the peaks and mounds as well as the strange wavy bands of light and dark had changed in eight years. As of 2017 however little had changed. The patches in the 2009 image seem darker, but that is almost certainly due to the lower sun angle causing longer shadows.

The slope goes downhill to the left. The wavy bands are thought to be geological layers exposed by erosion. The cause of the dark patches remain unknown.

I stumbled upon these two early images because of a third new image of this location, taken in February 2019 and spotted by me during my review of April 2019 images downloaded from MRO. That uncaptioned new image was titled “Change Detection in Olympus Maculae.” Had scientists spotted some new volcanic activity at this spot? To find out I dug into the MRO archive at this location and found both the 2009 and 2017 images.

The 2019 image is below. It is cropped, rotated, and reduced to match exactly with the image above in order to highlight any changes that might have occurred.
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Seasonal frost in a gully on Mars

Frost in a gully on Mars
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Cool image time! The photo on the right, cropped, reduced, and brightened slightly to post here, was part of the April image release from the high resolution camera on Mars Reconnaissance Orbiter (MRO). According to the titled of this release, it purports to show visible frost on what looks like an avalanche debris slope on the rim of a large crater. The frost is the bright streaks on the upper left of the slope.

I wonder. During last month’s 50th Lunar and Planetary Science Conference in Texas, there was one paper that I reported on that showed something very similar to this, and proposed that white streaks like this in a gully were actually exposed snow/ice. They proposed that the snow/ice was normally covered by dust, and the white streaks were where the dust had blown away to reveal the ice below. This in turn would then sublimate into gas, which in turn would cause the gully avalanches over time.

Below is a close-up of the white streaks on this rim.
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A dance of dust devils

A dance of dust devils on Mars

Many of my image posts about Mars have emphasized how slowly things change there. This post will highlight the exact opposite. When it comes to dust devils, it appears they can leave their trace frequently and often, and for some reason they seem to also favor specific locations.

June 2011
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The string of images above are all of the same location in the southern highlands of Mars. All were taken by the high resolution camera of Mars Reconnaissance Orbiter (MRO) and can be found in the camera’s archive. I have cropped them to show the same approximate matching area. The first image in that strip above, shown at higher resolution to the right, was taken in June 2011 and titled “Possible Gully Features” by the MRO science team. This is not surprising, as the rounded hills in this image are actually the southwest rim of a large crater, and the slopes of craters have been found one of the best places to find the gullies where seasonal changes occur, all possibly caused by underground water.

From the title, it appears that the science team might have first hoped to spot either slope streaks or recurring slope lineae, the two most intriguing of these changing features. Instead, that 2011 image showed them a very eroded crater rim with a small scattering of dust devil tracks.

November 2018
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This lack of gullies probably reduced interest in this location. It wasn’t until seven years later, in November 2018, that the MRO team decided to take another image of this location (the second image in the strip above and shown to the right at higher resolution). This time they found a significant increase in the number of dust devil tracks.

At this point the decision must have been made to take another image of this location a month later in December 2018. I assume the scientists were curious to see if they would spot any additional changes in that one month period. This was dust devil season, so the likelihood of seeing more tracks was not unreasonable.

How many tracks appeared, and whether they were concentrated in any particular place, such as the ridge lines, would help researchers better understand what generates them, which in turn will give them a better understanding of the Martian atmosphere.

The result was astonishing.
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Thumbprints on Mars!

Thumbprints terrain on Mars!
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Honestly, don’t ask me. I didn’t come up with the name. I found the image on the right, cropped and reduced to post here, as part of the April image dump from the high resolution camera of Mars Reconnaissance Orbiter. The uncaptioned release dubbed this “Thumbprint Terrain in Northern Mid-Latitudes,” and it is obvious to see why. The cropped image on the right focuses in on the oval white mounds that really do look like some giant child was touching a soft damp muddy surface randomly with his fingers, leaving behind raised fingerprints as the mud stuck to his fingers as he pulled them away.

Each white area seems to have a crater. I suspect these are not impact craters, but possibly mud volcanoes, as each is at the top of a mound. My hypothesis is further strengthened by the location, which is deep within the low northern plains of Mars, a place where some scientists believe an intermittent ocean once existed. These mounds could have easily formed at that ocean’s floor, or thereafter when the land here was drying out.

On the other hand, these could be from impact. Maybe they are scattered ejecta from a larger impact, landing here in a group on a wet muddy surface. The impacts might have concentrated the material around the crater, making it more resistant to erosion, which is why the craters now stand above the floor of the plain.

On the third hand, all these theories could be wrong. Have any of your own?

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Monitoring the ice scarps on Mars for changes

Scarp #1 in 2011
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Scarp #1 in 2018
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Back in January 2018 planetary scientists released a paper announcing the discovery of a number of Martian cliff faces, or scarps as they called them, that all appeared to expose an underground layer of ice.

Those cliffs were mostly located to the southeast of Hellas Basin, the basement of Mars that is also advantageous for human colonization because its lower elevation means its atmosphere is thicker. (For example, that thicker atmosphere would make air transportation more practical.)

The two images to the right show what they listed as scarp #1 in their paper, rotated, cropped, and reduced to post here. The first image was taken in May 2011, with the second taken in December 2018, and was part of the March image release from the high resolution camera of Mars Reconnaissance Orbiter (MRO).

The December 2018 image was taken almost a year after the paper release, and was titled “Scarp Monitoring.” I therefore wondered whether the scientists had identified any changes. They theorize that these scarps form when the exposed ice slowly sublimates to gas into the atmosphere, causing the cliff face to collapse and retreat, which in the case of scarp #1 would be a retreat to the north. The terraces below the scarp suggest previous cliff locations. In their paper they noted evidence of some changes in the studied scarps, including some fallen boulders, as well as color changes that suggest some evolution.

The rate of that retreat is not known with precision, but based on the facts presently at hand, the scientists have estimated that it took about a million years to form this scarp. Whether any evidence of this retreat would be visible in only seven years is the purpose of these scarp monitoring images.

Do you see any difference? I don’t, but because I also don’t trust my expertise I decided to email the paper’s lead author, Colin Dundas of the U.S. Geological Survey’s Astrogeology Science Center. His emailed comments are most interesting.
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A decade of changes at the Martian south pole

A decade of changes at the Martian south pole
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The image above, cropped, reduced, and annotated to post here, was released this week by the Mars Reconnaissance Orbiter (MRO) team. It shows the changes that have occurred at one location at the Martian south polar cap in the past decade. As planetary geologist Alfred McEwen wrote,

The south polar residual cap of carbon dioxide ice rapidly changes. This image was planned as an almost exact match to the illumination and viewing angles of a previous one we took in August 2009.

The pits have all expanded and merged, and we can just barely see the patterns in the 2009 image compared to this January 2019 picture. The 2009 image is also brighter and bluer, with more seasonal frost and/or less dust over the surface. These images were both taken in late southern summer, but our 2019 picture is slightly later in the Martian season by about two weeks.

You can get a better idea how much is changed by seeing the full image from which the above small area was cropped.
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More Martian Pits!

More pits on Mars!

As I said in my last post in February showing recent pit discoveries on Mars, I could almost make this a monthly series. In the March image download from the high resolution camera of Mars Reconnaissance Orbiter (MRO) were three (maybe four) more pits, all likely skylights above lava tubes and all located near the giant volcano Arsia Mons in the region dubbed the Tharsis Bulge. The image to the right shows all three, with a possible fourth just northwest of pit #2 and visible in its full image. For the full images of the other two pits go here (#1) and here (#3). In all three cases, click on the “black & white map projected” link to see the full image with scale.

Overview map

The overview map on right shows where these three pits are located. If you compare this map with my previous overview maps from November 12, 2018 and February 22, 2019 you can see that while these pits are all found on the volcanic slopes surrounding Arsia Mons, they are all different pits. Moreover, the ten pits listed in these three posts are only a small sampling of the more than hundred already found.

Whether these pits are deadend sinks or skylights into underground lava tubes that connect is at this point unknown. It would be a reasonable speculation to assume that some are deadends, and some link to extensive tubes of varying lengths. It would also be dangerous. Mars is alien. While the geology will be based on the same physical laws found on Earth, the lighter gravity is going to produce things differently.

The three images above however do show some intriguing details.
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Circular feature on Mars?

A circular feature on Mars?
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Today’s cool image is cool for two reasons. First and foremost, the image, found in the archive of the high resolution camera of Mars Reconnaissance Orbiter (MRO), is titled “Circular Feature.” On the right is the full image, reduced to post here. I have searched it high and low, at low resolution as well as full resolution, and can find nothing, nothing at all, that invokes a circular feature to me.

This strange terrain is located very close to the southern icecap. If anything, the knobs and features that fill this image remind me of brain terrain, partly obscured by a layer of partly melted snow or frost. Nothing however seems circular in the slightest.

The second reason this image is cool is that it is very representative of its very large surrounding region. For what appears to be several hundred miles in all directions this is all that one can see, in a variety of MRO images, here, here, here, here, here, and here, to show only a few. Ever so often a craterlike feature pops out, like in the last example, but generally the surface continues in this undulating bland manner, endlessly. The only changing aspect is the dark streaks that cut across, likely dust devil tracks made over a long period of time.

Below the fold is a section of the full resolution image, at full resolution. It doesn’t really matter where I took the crop, as anywhere in the full image everything looks pretty much the same. The only slow change that I can perceive is that the surface seems to be descending to the north, with the lighter areas implying the existence of terraces.

Take a look, and try to figure out for yourself what is going on here.
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How fast do things change on Mars?

Looking for dune changes on Mars

On Earth, it is assumed that in a period of a dozen years a sand dune would change significantly. Wind and rain and the yearly cycle of the seasons would work their will, reshaping and moving the dune steadily from one place to another.

On Mars, we would be reasonable to expect the same. Yet, this might be a mistake, as illustrated by the two images on the right, taken by cameras on Mars Reconnaissance Orbiter (MRO) a dozen years apart of the same large dune located in a crater far to the south in the planet’s southern highlands. Both images have been cropped and reduced in resolution to show here. For the full images, go here for 2007 and here for 2019.

The top image was taken October 31, 2007 by MRO’s context camera. The bottom image was taken on January 29, 2019 by MRO’s high resolution camera. Though the context camera does not have the resolution of the high resolution camera, the difference is of less significance in this context.

Have things changed? Putting aside lighting differences, it does appear that the white patches have changed slightly in a variety of places. There also might be changes in the small dunes on the left of the image, at the base of the large central dune.

The white patches are probably what interests the scientists who requested the second image. Could this be snow or frost, as is thought to exist in other places? There are studies [pdf] that expect ice to exist inside craters near the south pole. Identifying changes here would help answer this question.

Overall, however, not much is different. Though dunes definitely change on Mars, they do so much more slowly than on Earth. And in some cases what look like dunes are not really dunes at all, but a form of cemented sandstone, exhibiting even fewer changes over long time spans.

I do not know if these dunes are of sand or sandstone. What the two images reveal is that in either case, things do not change on Mars at the same pace as they do on Earth. Even after three Martian years, the thin Martian atmosphere simply doesn’t have the same energy as on Earth, even though it can move things easier in the weak gravity.

While the pole caps of Mars change a lot seasonally, the rest of the planet evolves very slowly. Mars is no longer an active planet like the Earth. It is, in many ways, a dead planet, once alive with activity but now silent and relatively quiet.

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Fresh crater in Martian northern lowlands

Fresh impact crater in northern lowlands
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Today’s cool image could be a sequel to yesterday’s. The image on the right, cropped to post here, was one of the many images released from Mars Reconnaissance Orbiter’s (MRO) high resolution camera in March. The release, uncaptioned, calls this a “fresh impact crater.”

In many ways it resembles the craters I posted yesterday, with a splashed look and a crater floor with features that favor the north. Why that divot exists in the northern half of the floor is to me a mystery. The crater floor looks like a sinkhole to me, with material slowly leaking downward at that divot to cause this surface depression. Yet the rim screams impact. And yet, why the double rim? Was this caused by ripples in wet mud when the bolide hit?

Location of fresh impact crater

The crater itself is all by itself deep in those northern plains. You can see its location as the tiny white rectangle slightly to the left of the center in the overview image to the right. The giant Martian volcanoes can be seen at the image’s right edge, almost a quarter of a planet away. This is at a very low elevation on Mars, almost as deep as Hellas Basin.

For some fun context, this location is very close to where Viking 2 landed in 1976. The Mars 2020 rover meanwhile will land at this overview image’s left edge, on the western shore of the oval cut into southern highlands at about the same latitude as Olympus Mons, the largest volcano on the right. And InSight and Curiosity sit almost due south, with Curiosity in the yellow in the transition from green to orange, and InSight to the north in the green.

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The layering at the Martian poles

Layering in the east side of Burroughs Crater
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Layering in the west side of Burroughs Crater
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In the past month the science teams of both Mars Reconnaissance Orbiter (MRO) and Trace Gas Orbiter (TGO) have released images showing the strange layering found in Burroughs Crater, located near the Martian south pole.

The top image above is the MRO image, rotated and cropped to post here. To the right is a cropped and reduced section of the TGO image.

Though both images look at the inside rim of the crater, they cover sections at opposite ends of the crater. The MRO image of the crater’s east interior rim, with the lowest areas to the right, while the TGO image shows the crater’s northwest interior rim, with the lowest areas on the bottom. As noted at the TGO image site:
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A gathering of dust devils

Dust devil tracks
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A bunch of cool images! The European Space Agency (ESA) today released more than a dozen Martian images taken by the camera on its Trace Gas Orbiter spacecraft.

In addition to a snapshot of InSight and its landing area, “The images selected include detailed views of layered deposits in the polar regions, the dynamic nature of Mars dunes, and the surface effects of converging dust devils.” The release also included images showing details of two of Mars’ giant volcanoes, Olympus Mons and Ascraeus Mons.

The image I have highlighted to the right, reduced to post here, shows a spot on Mars where for some unknown reason dust devils love to congregate.

This mysterious pattern sits on the crest of a ridge, and is thought to be the result of dust devil activity – essentially the convergence of hundreds or maybe even thousands of smaller martian tornadoes.

Below is a side-by-side comparison of this image (on the right) with a Mars Reconnaissance Orbiter (MRO) image taken in 2009 (on the left).
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Martian massive landslides

Though scientists have found some evidence of slow erosion and change on the Martian surface, it is today generally inactive. While the weak wind of Mars’ thin atmosphere continues to work its will, and the likely presence of underground frozen water acts to shift the surface shape as the seasons come and go, none of this happens quickly.

Essentially, Mars is a quiet place.

Once however catastrophic events took place, gigantic floods flowing down to the east from the planet’s huge volcanoes to carve out Marineris Valles, the solar system’s largest known canyon. As that water rushed eastward it ripped the terrain apart quickly, creating deep side canyons, drainage valleys, and chopped up regions now dubbed as chaos terrain, multiple mesas separated by numerous fissure-like canyons.

Overview of Marineris Valles and landslide

The overview map on the right shows Valles Marineris and its drainage to the east and north into the vast northern plains of Mars. It also shows the location of one of the largest regions on Mars of chaos terrain, dubbed Hydraotes Chaos, located close to the mouth of this gigantic drainage system more than 2,500 miles long.

Massive Martian landslide
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Recently scientists have used the high resolution camera on Mars Reconnaissance Orbiter (MRO) to begin taking images of the massive landslides on the face of the mesa north of Hydraotes Chaos that was hit directly by these floods. The location of the most immediately interesting of these landslide images is also indicated on this overview image.

To the right is that image, rotated, cropped, reduced, and annotated to post here. The white boxes indicate two full resolution sections that I highlight below at full resolution.

This image shows that full cliff. The total drop from the plateau at the top to the floor where Hydraotes Chaos is located to the south is approximately 8,200 feet, almost exactly comparable to the depth of the north rim of the Grand Canyon.

The image shows numerous evidence of avalanches and erosion, both at its base and at its rim. None of these avalanches likely occurred during those catastrophic floods, but long afterward.
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Brain Terrain on Mars

Brain terrain on Mars
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Cool image time! This week the Mars Reconnaissance Orbiter (MRO) science team featured four new captioned images taken by the spacecraft and released as part of the March image dump. The first, dubbed “The Slow Charm of Brain Terrain,” deserves an immediate post on Behind the Black. To the right is only a small section cropped from the full image. From the caption:

You are staring at one of the unsolved mysteries on Mars. This surface texture of interconnected ridges and troughs, referred to as “brain terrain” is found throughout the mid-latitude regions of Mars. (This image is in Protonilus Mensae.)

This bizarrely textured terrain may be directly related to the water-ice that lies beneath the surface. One hypothesis is that when the buried water-ice sublimates (changes from a solid to a gas), it forms the troughs in the ice. The formation of these features might be an active process that is slowly occurring since HiRISE [MRO’s high resolution camera] has yet to detect significant changes in these terrains.

Below is a cropped section of the full image, rotated and reduced to post here.
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Waterlike Martian lava flows

Flowing like water
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Each month the Mars Reconnaissance Orbiter (MRO) science team highlights with captions about four out of the 300-500 new images released that month.

Of the four captioned images in February, the first was entitled “Almost Like Water,” and focused on the waterlike nature of the lava flow. The image on the right is a cropped and annotated section of that featured photograph, with the yellow arrows indicating the flow directions.

The lava appears to have flowed smoothly around obstructions, almost like water, forming streamlined islands. In the southern part of this image, a branch of the flow diverts around a small crater, and eventually rejoins the main part of the flow. [Visible in the full photograph] Irregular-shaped ring structures appear on the northern end and are related to the volcanic activity that formed the flows.

You can see an example of one of those islands near the top of the above image.

This is hardly the only MRO image showing such flows. In fact, the February image release included a bunch, some of the more intriguing of which I highlight below. These lava flows are seen in many different places on Mars, in a wide variety of geological settings, facts that suggest that volcanic activity was once very widespread and ubiquitous on Mars.
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Another batch of caves/pits found on Mars

Four new pits on Mars

Overview of February 2019 pits

In the past year the monthly image releases from the high resolution camera on Mars Reconnaissance Orbiter (MRO) archive have frequently included newly discovered pit entrances. Each time I have written posts highlighting these new pits, in June, July, November 2018 and January 2019. In fact, this is happening so frequently I could almost label it a monthly update!

The November release imaged three pits found on the southern flanks of Arsia Mons. The January 2019 release found several north of the volcano, two of which are very close to the two middle new pits highlighted above. The February release, which is the focus of this post, included four more pits, shown above, all located north and west of Arsia Mons, as shown in the overview map to the right.

Pits 2 and 3 above appear to belong to a cluster of pits all located in the general area between Arsia and Pavonis Mons. (You can see their uncaptioned releases here and here.) Most sit alone on a flat somewhat featureless plain. Sometimes there are flow features nearby, but each pit usually seems to sit unique and unrelated to these other faint features.

Pit 1 is very intriguing in that it sits amid a very long chain of pits and canyons, all aligned, as shown in the image below and to the right.
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Rover update: February 20, 2019

Summary: Curiosity in the clay unit valley. Opportunity’s long journey is over. Yutu-2 creeps to the northwest on the Moon’s far side.

For the overall context of Curiosity’s travels, see my March 2016 post, Pinpointing Curiosity’s location in Gale Crater.

For the updates in the past year go here. For a full list of updates before February 8, 2018, go here.

Curiosity

Curiosity's view to the east on Sol 2316
Click image for full resolution version

Overview of Curiosity's future travels
Click image for original image

Since my January 22, 2019 update, Curiosity finally drove down off of Vera Rubin Ridge into a valley between the ridge and the lower slopes of Mt Sharp. The Mars Reconnaissance Orbiter (MRO) overview on the right has been annotated by me to show the rover’s travels (shown by the yellow dotted line), with its proposed route indicated by the red dotted line. The yellow lines indicate approximately the terrain seen in the panorama above. The panorama was created from images taken on Sol 2016.

The valley that Curiosity is presently traversing is dubbed “the clay unit” or “the clay-bearing unit” by the geologists, based on its make-up determined from orbital data. So far they have found this terrain to be “some of the best driving terrain we’ve encountered in Gale Crater, with just some occasional sandy patches in the lee of small ridges.” Initially they had problems finding any rocks or pebbles large enough for the instruments to use for gathering geological data. For the past week or so, however, they have stopped at “bright exposure of rock” where some bedrock was visible, giving them much better material to work with.
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A river valley floor on Mars

Overview of Reull Valles region

Today’s cool image focuses in on a Mars Reconnaissance Orbiter (MRO) uncaptioned photograph taken of the valley floor of Reull Vallis, a meandering canyon that drains into Hellas Basin, the bottom of Mars.

The image on the right is not that photograph. Instead, it is an overview of the area surrounding it. The image location is indicated by the black cross, dead center within the floor of Reull Vallis itself. This valley, as well as Dao and Niger to the northwest but lower in elevation are all thought to have been formed from flowing water, all of which apparently drained from the east and to the west into Hellas Basin.

This last detail is very important and bears repeating before looking at today’s subject image. The river that formed Reull Vallis flowed from the east to the west. Now for that picture.
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Monitoring a fresh-looking Martian landslide

2012 image of Martian landslide
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2018 image of Martian landslide
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Time for two cool images! To the right are two images taken by the high resolution camera on Mars Reconnaissance Orbiter (MRO), the top one taken in April 2012, and the bottom taken in December 2018. Both have been cropped and reduced slightly in resolution to post here.

The second image is trying to answer, in only a small way, one of the most fundamental questions of the Martian environment: How fast does it change? The images from orbit have periodically seen evidence of new impacts. MRO images have tracked dust devil tracks. And we know that somehow water, ice, wind and volcanic activity have eroded and reshaped the surface over eons.

What we don’t know truly and with detail is the pace of these changes, with any accuracy. The pace of some things over time seems obvious. For example, Mars’s inactive but gigantic volcanoes suggest that once volcanism was very active, but over time has ceased so that today it is unclear if any is occurring. Similarly, the geological evidence suggests that in the far past water flowed on the surface, producing catastrophic floods. Now that liquid water is all but gone, and this erosion process as ceased.
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Strange crescent-shaped pit near Martian south pole

crescent-shaped pit near Martian south pole

Cool image time! The south polar cap of Mars is a strange place. It is largely ice, with a seasonal cap of frozen carbon dioxide, or dry ice. Because the dry ice sublimates away during the summer months, the cap undergoes regular changes that reshape it, producing alien features that are not seen on Earth.

The image on the right is another example of these alien features. I found it in the February image release from the high resolution camera on Mars Reconnaissance Orbiter. I have merely cropped the full image to focus at full resolution on its primary feature, a region of stippled-like surface surrounding an area of black striping that in turn surrounds a crescent-shaped pit outlined by whiter material.

Why is there a pit here? Why is it crescent-shaped? Why is it surrounded by that whiter material? I could guess and say that the pit is a vent from which water vapor from the lower cap of water sprays out onto the upper cap of frozen carbon dioxide, staining it with white ice, but I am most likely wrong.

Moreover, what causes the black striping, as well as the stippled material surrounding it? The black stripes are probably related to a similar process that forms the spider formations found in the polar regions, except that these are not spiders. Why the parallel straight lines?

A lot of questions with no answers. While many features on Mars are strange, the features near the poles are probably stranger still, as they form in a place with chemistry, temperatures, gravity, and materials in a combination and scale that we on Earth have no experience with.

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Mysterious dark-toned Martian terrain

Dark toned ridge in Martian southern highlands
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Cool image time! The picture on the right, cropped and reduced to post here, was part of the January image release from the high resolution camera of Mars Reconnaissance Orbiter (MRO). It shows an area in the Martian southern highlands where the surface suddenly gets darker, for no obvious reason.

The uncaptioned release image is titled “Dark-Toned Ridge at Junction with Dark-Toned Plain.” From the image itself it is hard to understand this title. In the full image the darkest terrain is a strip in the center, with slightly lighter dark terrain on either side, and the lightest terrain to the north or south. The photograph however does not show us how far this dark terrain extends to the west or east.

Two Mars Odyssey image strips of less resolution, here and here, show that this region is filled with several large patches of dark-tone surface. With this particular patch the center dark ridge is surrounded by that slightly lighter dark area.

MRO itself has not taken many images of this region, as shown in the overview image below. The red rectangles indicate MRO’s high resolution photographs, with this image indicated by the cross. At this low resolution this region seems somewhat nondescript. The Mars Odyssey image strips show that there many features here, but with little significant relief.

Location of dark toned ridge

At high resolution there does not appear to be much difference between the darker and lighter areas. The lighter areas in general seem less rough and at a slightly lower elevation, but both areas are dominated by ridges and dunes trending southwest-to-northeast.

Why is this slightly higher region darker? Let’s assume that this darker material was a lava flow overlaying the surface. Over eons wind erosion, trending southwest-to-northwest, roughly eroded both it and the lower layers around it, leaving behind this rough corroded terrain. The different make-up of the darker material allows it to erode in a rougher manner.

While possibly correct, I would not bet much money on this guess. It is not clear it is lava. It is not clear that it is a flow. It does not explain why there are two areas of different darkness. And it certainly not clear what the make-up of any of this stuff is.

This is simply another cool mystery on the Martian surface.

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Strange fernlike ridges on Mars

Fernlike ridges on Mars

Cool image time! The two images on the right, cropped, rotated, and reduced in resolution to post here, were both taken by the high resolution camera on Mars Reconnaissance Orbiter (MRO). To see the full resolution version of each, go to the 2009 and 2018 releases.

The 2009 release was a captioned release, whereby scientist Alfred McEwen of the science team provided his explanation of these strange features.

The dark branched features in the floor of Antoniadi Crater look like giant ferns, or fern casts. However, these ferns would be several miles in size and are composed of rough rocky materials.

A more likely hypothesis is that this represents a channel network that now stands in inverted relief. The channels may have been lined or filled by indurated materials, making the channel fill more resistant to erosion by the wind than surrounding materials. After probably billions of years of wind erosion the resistant channels are now relatively high-standing. The material between the branched ridges has a fracture pattern and color similar to deposits elsewhere on Mars that are known to be rich in hydrated minerals such as clays.

These strange fernlike features do not appear to be very common on Mars. In fact, I suspect that while Mars does have many inverted channels like this, the fernlike nature of these particular channels is unique on Mars. They are located on the floor of Antoniadi Crater, a large 240-mile-wide very ancient and eroded crater located in the Martian southern highlands but near the edge down to the northern lowlands.

In seeing the new 2018 image, I was immediately compelled to place it side by side with 2009 image to see if anything had changed in the ensuring near-decade. There are color differences, but I suspect these are mostly caused by different lighting conditions or post-processing differences. Still, the dark center to the crater in the upper left of both images suggests a change in the dust dunes there, with the possibility that some of the dust has been blown from the crater over time. Also, you can see two horizontal tracks cutting across the center of the 2018 image, which I would guess are dust devil tracks, with one more pronounced.

I can imagine some planetary geologists have spent the last few months, since the second image was taken, pouring over both photographs, and have might even located other interesting changes. And if they find no significant changes, that in itself is revealing, as it gives us a sense of the pace at which the Martian surfaces evolves.

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The many pits/caves of Mars

Sinkhole in Martian northern lowlands with dark seep

Time for many cool images! Over the years I have written frequently about the pits/caves on Mars, in both magazine articles and the many posts here at Behind the Black. The following posts are the most significant, with the June 9, 2015 providing the best geological background to many of these pits, especially the many located near the giant volcanoes of Mars.

As I wrote in that June 9, 2015 post:
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Weird Martian fracture feature

Fractured collapse feature on Mars

Cool image time! When I first looked at the high resolution Mars Reconnaissance Orbiter (MRO) image on the right, my immediate reaction was, “What the heck is that?” The image to the right is cropped and reduced, but if you click on it you can see the full image at high resolution.

The fractured terrain appears to be all within a collapse. To my eye it appears that while the overall surface has sunk, the fractures indicate an area where there has been an eruption upward, which after the eruption collapsed again, so that the fractured area remains at the apparent bottom of the collapse sink. I was immediately reminded of Upheaval Dome in Yellowstone National Park, which some geologists believe was formed by a “salt bubble” rising upward to create a salt dome.

A thick layer of salt, formed by the evaporation of ancient landlocked seas, underlies much of southeastern Utah and Canyonlands National Park. When under pressure from thousands of feet of overlying rock, the salt can flow plastically, like ice moving at the bottom of a glacier. In addition, salt is less dense than sandstone. As a result, over millions of years salt can flow up through rock layers as a “salt bubble”, rising to the surface and creating salt domes that deform the surrounding rock.

Context image for fracture feature

The process and materials involved were certainly different on Mars. Nonetheless, it does appear we are looking at an eruptive feature unrelated to molten lava. The context image to the right, showing this feature’s location in Mars’ vast northern lowlands, also shows that it has occurred on terrain that has bulged upwards relative to the surrounding lowlands. Nearby MRO images also show similar bulge/collapse features.

To decipher the geological mystery here, we would also need to know when this happened and whether there ever was a liquid ocean residing on top of it, before, during, or after the eruption. We also do not know well the make-up of the underground materials, including whether any frozen water and salt is present.

To be honest, we really don’t know much. I am sure a planetary scientist studying this feature could fill us in on some of these details, such as information provided by the colors in the color image. Even so, I am sure any good scientist would also admit to unknowns.

To get some real answers, we need to be there. It is as simple as that.

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Martian glacier with moraine?

Glacier flow on Mars, with moraine

Cool image time! In the past two decades numerous images and studies of the Martian terrain produced by orbiters have shown us landslides, lava flows, water and ice produced flows, and many glacial features, all vaguely familiar but often having components reminding us of the alien nature of the Martian landscape. I have posted many here at Behind the Black. (Just do a search here for the words “Mars flow” and you will have a wealth of cool images and alien geological features to explore.)

The image on the right, rotated, cropped, and reduced to post here, shows another such feature, but this time it is less alien and more resembling a typical Earth glacier, flowing downhill slowly and pushing a moraine of debris before it. The picture was taken by the high resolution camera on Mars Reconnaissance Orbiter (MRO) and was part of the January image release. If you click on the image you can see the complete photograph at full resolution.

The release has no caption, but is titled “Tongue-Shaped Glacier in Centauri Montes,” referring to the largest tongue-shaped flow on the left. This feature, more than any other in the image, resembles closely many glaciers on Earth. It even has an obvious moraine at its head. As the glacial flow pushed downward slowly it gathered a pile of material that eventually began to act almost like a dam.

The location of this feature is intriguing in its own right.
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New impact on the Martian south polar cap

New impact on Mars' south pole

Cool image time! The image to the right, cropped to post here, was taken on October 5, 2018 by the high resolution camera on Mars Reconnaissance Orbiter (MRO) and shows a recent meteorite impact that occurred sometime between July and September of 2018 on the Martian polar cap . If you click on the image you can see the entire photograph. As noted in the captioned press release,

It’s notable because it occurred in the seasonal southern ice cap, and has apparently punched through it, creating a two-toned blast pattern.

The impact hit on the ice layer, and the tones of the blast pattern tell us the sequence. When an impactor hits the ground, there is a tremendous amount of force like an explosion. The larger, lighter-colored blast pattern could be the result of scouring by winds from the impact shockwave. The darker-colored inner blast pattern is because the impactor penetrated the thin ice layer, excavated the dark sand underneath, and threw it out in all directions on top of the layer.

Location on edge of south polar cap

It is not known yet the size of this meteorite. The location is shown in the overview image to the right, with the impact indicated by the white dot. The black circle in the middle of the image is the south pole itself, an area where MRO’s orbit does not allow imagery. This location, on the edge of the Martian polar cap, is helpful to scientists because it has excavated material from below the cap, providing them a peek into previously unseen the geology there. Had the impact been farther south, on the thicker cap, that hidden material below the cap would likely not have been exposed.

The cap itself is made up of both ice and frozen carbon dioxide, though the CO2 is mostly seen as frost during winter months that evaporates during the summer.

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Volcanic vent between Arsia and Pavonis Monsa

volcanic vent on Mars

Cool image time. The photo on the right, rotated, cropped, and reduced to post here, was taken in September by the high resolution camera of Mars Reconnaissance Orbiter (MRO) and was part of the November image release. Click on the image to see the entire photograph at full resolution.

The uncaptioned release dubs this feature as “Small Eruptive Vents South of Pavonis Mons.” In truth, these vent pits are located almost exactly the same distance from both Pavonis Mons, the middle volcano in the line of three giant Martian volcanoes, and Arsia Mons, the southernmost of the three.

The image is interesting for several reasons. First, note the bulge surrounding the vent, making this look almost like a miniature volcano all its own. In fact, that is probably what it is. When it was active that bulge was likely caused by that activity, though it is hard to say whether the bulge was caused by flow coming from out of the vent, or by pressure from below pushing upward to cause the ground to rise. It could even have been a combination of both.

To my eye, most of the bulge was probably caused from pressure from below pushing upward. The edge of the bulge does not look like the leading edge of a lava flow. Still, this probably happened so long ago that Martian wind erosion and dust could have obscured that leading edge.

That this is old is indicated by the dunelike ripples inside the large pit, and the pond of trapped dust in the smaller pit. Because of the thinness of the Martian atmosphere it takes time to gather that much dust, during which time no eruptions have occurred.

One more interesting detail: If you look at the pits in full resolution, you will see that, based on the asymmetrical wind patterns between the west and east rims, the prevailing winds here are from the west. Located as it is just to the east of the gigantic saddle between Arsia and Pavonis Mons, this wind orientation makes sense, as a saddle between mountains tends to concentrate the wind, much like a narrowed section in a river produces faster water flow and rapids. As for why the wind blows mostly from the west, my guess (which should not be taken very seriously) is that it is probably caused by the same meteorological phenomenon that causes this generally on Earth, the planet’s rotation.

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Weird erosion in large Martian craters

Central pit in Asimov Crater

Cool image time! In reviewing the images in the December image release from the high resolution camera on Mars Reconnaissance Orbiter (MRO, I came across the image to the right, cropped, rotated and reduced to post here, showing the western half of the central pit of Asimov Crater. (Click on the link for the entire photograph.) The eastern half can be seen here.

It is unusual to see central pits in craters. One instead expects to see central peaks. The pit itself is intriguing because of its sinkhole appearance. In both the northwest and southwest corners you can clearly see drainages flowing down into the pit, including recent faint darkened streaks indicative of past seep avalanches. The same can been seen for the pit’s eastern half. Along the pit’s western rim are parallel cracks suggesting that the plateau itself is slowly shifting downward into the pit.

Furthermore, the rim cliff has multiple drainage gullies, all beginning just below the initial top layers. The look of those cliffs is very similar to what sees on the walls of the Grand Canyon, where the top of the cliffs show layers with the bottom of the cliffs buried under a slope of alluvial fill, material that has fallen to slowly form those slopes. The drainage gullies however would have come later, and suggest that some form of seepage is coming out of the contact between the layers at the top of the slope.

A look at the context image below and to the right reveals the greater mystery of this crater, as well as nearby Maunder Crater, the subject of a recent captioned image release from Mars Odyssey.

context map showing Asimov and Maunder Craters

In both cases a circular interior gully separates the crater floor from the crater’s rim. In fact, the crater floor almost appears raised. This is especially striking with Asimov Crater, where the central floor appears like a very flat plateau, except for that central pit and the surrounding gully.

The MRO team has taken a lot of images of the gullies, which you can see if you zoom in to latitude -46.843° longitude 4.831° on the map image at this website. It is clear that they want to know more about the origins of this geology. It suggests water flow, even though these craters are located in the Martian southern highlands, a place that is more reminiscent of the Moon, with many ancient craters and far less evidence of significant change.

What the geology in these two craters suggest is that some erosion process is eating away at the crater floors, beginning at its edges as well where there are voids below that allow the surface to sink. While that erosion is certainly helped by wind, it also implies the presence of underground water, either as ice or liquid, in the past and even possibly today.

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Lopsided ejecta from Martian crater

Crater with unequal ejecta

Cool image time! The image on the right, reduced and cropped to post here, comes from the December image release from the high resolution camera of Mars Reconnaissance Orbiter (MRO). (If you click on the image you can see the full resolution uncropped photograph.) Released without a caption, the release itself is intriguingly entitled, “Crater with Preferential Ejecta Distribution on Possible Glacial Unit.

The uneven distribution of ejecta material around the crater is obvious. For some reason, the ground was preferentially disturbed to the north by the impact. Moreover, the entire crater and its surrounding terrain look like the impact occurred in a place that was saturated somewhat with liquid, making the ground soft like mud.

That there might have been liquid or damp material here when this impact occurred is reinforced by the fact that this crater is located in the middle of Amazonis Planitia, one of the larger regions of Mars’ vast northern lowland plains, where there is evidence of the past existence of an intermittent ocean.

This however really does not answer the question of why most of the impact’s ejecta fell to the north of the crater. From the release title is appears the planetary geologists think that this uneven distribution occurred because the impact occurred on a glacier. As the ground has a lighter appearance just to the south of the crater, I suspect their reasoning is that this light ground was hard bedrock while the darker material to the north was that glacial unit where the ground was more easily disturbed.

This is a guess however (a common requirement by anyone trying to explain the strange features so often found on the Martian surface). Other theories are welcome of course, and could easily be correct as well.

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Flowing cracked mud on Mars?

mud cracks in crater?

Cool image time! The image on the right, rotated, cropped, and reduced to post here, comes from the December image release of the high resolution camera of Mars Reconnaissance Orbiter (MRO. Uncaptioned, the release titles this image “Cracks in Crater Deposit in Acheron Fossae.” If you click on the image you can see the entire photograph at full resolution.

Clearly the cracks appear to be caused by a downward slumping to the north, almost like a glacier made of mud. We can also see places on the image’s right edge where the mud appears to have flowed off a north-south trending ridge, then flowed downhill to the north. All of this flow is away from the crater’s central peak, which is only partly seen in the photograph near the bottom. That section is the central peak’s southwestern end, with the whole peak a ridge curving to the northeast beyond the edge of the image.

At the north edge of this mud flow the cracks become wider canyons, as if long term erosion is slowing washing the mud away. The flow then stair steps downward in a series of parallel benches. Meanwhile, in the flat central area of the mud flow above can be seen oblong depressions suggesting sinks that also flow to the north.

crater context overview

You can get a better idea of the crater’s overall floor and central peak by the low resolution context image to the right. The white rectangular box indicates the area covered by the full image above. A close look at this part of the crater floor suggests to me a circular feature like a faint eroded smaller crater that includes as its eastern rim the larger crater’s central peak. This impression suggests that the flows seen in the full resolution image are heading downhill into the lowest point of this smaller crater, that upon impact had reshaped the larger crater’s floor.

This impression however is far from conclusive. The features in the large crater could simply be the random geology that often occurs in the floors of impact craters.

What makes this particular mud slide most interesting, as is usually the case for most Martian terrain, is its location.
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