Tag Archives: geology

Exploring with Mars Reconnaissance Orbiter

Terrain sample
Click for full image.

In my never-ending rummaging through the images released each month from the high resolution camera on Mars Reconnaissance Orbiter (MRO), I have sometimes been puzzled by the titles they choose for some photographs. For example, many pictures each month are simply titled “Terrain Sample.” The image to the right, cropped and reduced to post here, is one example, and its content adds to the mystery.

The photograph itself shows a generally featureless surface. Other than the scattering of small craters, there are only very slight topographical changes, the most obvious of which is the meandering ridge to the east of the largest crater.

I wondered why this picture was taken, and why it was given such a nondescript name. To find out, I emailed Veronica Bray at the University of Arizona. She had requested this image as part of her job as a targeting specialist for MRO. Her answer:
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Strange Martian gullies

Gullies on Mars
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Cool image time! The image to the right, cropped and reduced to post here, was taken in 2010 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). Uncaptioned, the image page is simply entitled “Older Gullies and Channels in Slopes of Softened Large Crater.”

I stumbled upon it today while researching another image taken this year of the “valley networks” in the floor of that same crater. Those networks were intriguing, but the gullies on the right were much more fascinating, because they appear to be some form of erosion drainage coming down both sides of a high ridge near the northern rim of this large apparently unnamed crater in the southern cratered highlands of Mars, to the west of Hellas Basin.

On Earth my immediate explanation for this erosion would be a major monsoon-like storm, such as we get here in the southwest and call “gully-washers.” When a lot of water is quickly dumped onto a hill where there is not of vegetation to help bind the soil together, the water will quickly carve out gullies that looks almost exactly like these.

On Mars, who knows? It certainly wasn’t a monsoon thunderstorm that did this. And being in the Martian southern highlands it is unlikely it was from an ocean of any kind. Were there lakes here? Past research has found places where lakes might have existed on Mars, but these places are far north in the transitional zone into the northern lowlands.

Nor are these gullies the only interesting features in this one image.
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Mass wasting on Mars

Mass wasting in Martian crater
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Cool image time! Mass wasting is a term that geologists use to describe a specific kind of avalanche, where the material moves down slope suddenly in a single mass.

The image on the right, taken from the image archive of the high resolution camera on Mars Reconnaissance Orbiter (MRO) and cropped and reduced in resolution to post here, shows a dramatic example of this kind of avalanche. You can see two separate avalanches, each of which moved a significant blob of material down slope into the center of the crater floor.

Studying such events is important. Scientists know that Mars has an underground ice table at high latitudes. What they don’t know is how far south that ice table extends. This crater is located at 5 degrees north latitude, almost at the equator, so if this avalanche exposed any ice in newly exposed cliff wall that would be a significant discovery.

Based on the color image, there does not appear to be any obvious ice layers, as seen in higher latitude scarps in the southern hemisphere. This doesn’t prove they aren’t there, merely that this image was unable to see them. Maybe the resolution is not good enough. Maybe the ice is too well mixed in with the dust and dirt and it therefore isn’t visible. Maybe the ice table is deeper underground than the deepest part of this crater.

Or it could be that at the Martian equator the underground ice is mostly gone. For future colonists, knowing this fact will influence where they put those first colonies. Near the equator has some advantages, but if there is little easily accessible water those advantages mostly vanish.

At the moment we simply do not know, though much of the imagery now being taken from orbit are attempts to answer this question.

One final detail about the image. Note the slope streaks coming down the crater’s slopes. These remain their own Martian mystery.

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Wind and/or water erosion on the Martian northern lowlands

A mesa in the northern Martian lowlands
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Cool image time! The picture on the right, cropped and reduced in resolution to show here, was taken by the high resolution camera on Mars Reconnaissance Orbiter on April 21, 2019, and shows the erosion process produced by either wind or water as it flowed from the east to the west past one small mesa.

It is almost certain that the erosion here was caused by wind, but as we don’t know when this happened, it could also be very old, and have occurred when this terrain was at the bottom of the theorized intermittent ocean that some believe once existed on these northern lowlands. The location itself, near the resurgences for Marineris Valles and the other drainages coming down from the giant volcanoes, might add weight to a water cause, except that the erosional flow went from east to west, and the resurgences were coming from the opposite direction, the west and the south.

The terrain has that same muddy wet look also seen in the more damp high latitudes near the poles. Here, at 43 degrees latitude, it is presently unknown however how much water remains below the surface.

When the craters to the right were created, however, it sure does appear that the ground was damp. Similarly, the material flow to the west of the mesa looks more like the kind of mud flow one would see underwater.

I must emphasize again that I am merely playing at being a geologist. No one should take my guesses here very seriously.

At the same time, I can’t help being endlessly fascinated by the mysterious nature of the Martian terrain.

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Ghost dunes on Mars

A ghost dune
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Cool image time! The Mars Reconnaissance (MRO) science team today released a captioned image of several ghost dunes on Mars. The image on the right is cropped and reduced to highlight one of those ghosts, which the scientists explain as follows.

Long ago, there were large crescent-shaped (barchan) dunes that moved across this area, and at some point, there was an eruption. The lava flowed out over the plain and around the dunes, but not over them. The lava solidified, but these dunes still stuck up like islands. However, they were still just dunes, and the wind continued to blow. Eventually, the sand piles that were the dunes migrated away, leaving these “footprints” in the lava plain.

The location of these ghost dunes is inside the southeast edge of Hellas Basin, what I call the bottom of Mars.

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The big water volcano on Ceres

Scientists have proposed a new detailed model to explain the formation of the large mountain Ahuna Mons on the asteroid Ceres.

The new theory doesn’t change the generally accepted idea that this mountain is a ice volcano, formed by the rise of a brine from below. It simply provides some details about the process.

A study involving scientists from the German Aerospace Centre (DLR) has now solved the mystery of how Ahuna Mons, as the mountain is called, was formed, using gravity measurements and investigations of the geometrical form of Ceres. A bubble made of a mixture of salt water, mud and rock rose from within the dwarf planet. The bubble pushed the ice-rich crust upwards, and at a structural weak point the muddy substance, comprising salts and hydrogenated silicates, was pushed to the surface, solidified in the cold of space, in the absence of any atmosphere, and piled up to form a mountain. Ahuna Mons is an enormous mud volcano.

The bubble would be the equivalent of a magma chamber of lava here on Earth.

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Crater? Pit? Volcano?

Crater? Pit? Volcano?
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Cool image time! The photograph on the right, cropped to post here, was taken by the high resolution camera of Mars Reconnaissance Orbiter (MRO) on April 16, 2019 of the slope of a mountain inside a region dubbed Eridania that is part of the planet’s southern highlands.

The photograph, released as part of the June image release from MRO, came with no caption. Furthermore, the image title, “Eridania Mons,” provided no additional information, which is why I clicked on it. The vagueness of the title made me curious.

The full image shows a generally featureless plain. Near the image’s bottom however was the geological feature shown in the cropped section to the right. At first glance one thinks it is a crater. This first impression can’t be the entire story, because the feature is raised above the surrounding terrain, and in that sense is more like a small volcano with a caldera. The irregular pit inside the caldera kind of confirms this conclusion.

I would not bet much money on this conclusion. The overall terrain of the Eridania quadrangle is filled with craters, large and small. There does not seem to be any obvious evidence of past volcanic activity, and if there had been it has not expressed itself in large volcanoes.

However, other images of this mountain show many circular features that at first glance appear to be craters like the featured image. They appear slightly raised above the surrounding terrain, though not in as pronounced a manner.

They all could be small volcanoes. Or maybe they are impacts that hit a dense surface which prevented them from drilling too deep down, and instead caused the crater to be raised above the surrounding terrain.

‘Tis a puzzle. The irregular pit in this particular feature adds to the mystery. It does not look like the kind of pits one sees in calderas. Instead, its rough edge suggests wind erosion.

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Rover update: May 30, 2019

Summary: Curiosity confirms clay in the clay unit. Yutu-2 begins its sixth day on the far side of the Moon. Three other rovers move towards completion and launch.

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

Clouds over Gale Crater
Clouds over Gale Crater

Curiosity

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

Curiosity’s journey up the slopes of Mount Sharp in Gale Crater goes on! On the right is one of a number taken by the rover in the past week, showing water clouds drifting over Gale Crater.

These are likely water-ice clouds about 19 miles (31 kilometers) above the surface. They are also “noctilucent” clouds, meaning they are so high that they are still illuminated by the Sun, even when it’s night at Mars’ surface. Scientists can watch when light leaves the clouds and use this information to infer their altitude.

While these clouds teach us something about Martian weather, the big rover news this week was that the data obtained from the two drill holes taken in April show that the clay formation that Curiosity is presently traversing is definitely made of clay, and in fact the clay there has the highest concentration yet found by the rover.

This clay-enriched region, located on the side of lower Mount Sharp, stood out to NASA orbiters before Curiosity landed in 2012. Clay often forms in water, which is essential for life; Curiosity is exploring Mount Sharp to see if it had the conditions to support life billions of years ago. The rover’s mineralogy instrument, called CheMin (Chemistry and Mineralogy), provided the first analyses of rock samples drilled in the clay-bearing unit. CheMin also found very little hematite, an iron oxide mineral that was abundant just to the north, on Vera Rubin Ridge. [emphasis mine]

That two geological units adjacent to each other are so different is significant for geologists, because the difference points to two very different geological histories. The formation process for both the clay unit and Vera Rubin Ridge must have occurred at different times under very different conditions. Figuring out how that happened will be difficult, but once done it will tell us much about both Gale Crater and Mars itself.

With the success of their clay unit drilling campaign, the Curiosity science team has had the rover begin its trek back from the base of the cliff below Vera Rubin Ridge to its planned travel route up the mountain.

An updated description of that route was released by the Curiosity science team last week, while I was in Wales. Below is their image showing that route, with additional annotations by me and reduced to post here.
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The mysterious slope streaks of Mars

Massive flow on Mars
A typical Martian slope streak.

The uncertainty of science: In the past decade or so scientists have documented in detail a number of features on the Martian surface that evolve or change over time. From the constantly changing poles to the tracks of dust devils to landslides to the appearance of seasonal frost, we have learned that Mars is far from a dead world. Things are happening there, and while they are not happening as quickly or with as much energy as found on Earth, geological changes are still occurring with regular frequency, and in ways that we do not yet understand.

Of the known changing features on Mars, two are especially puzzling. These are the two types of changing streaks on the slopes of Martian cliffs, dubbed recurring slope lineae (referred as RSLs by scientists) and slope streaks.

Lineae are seasonal, first appearing during the Martian summer to grow hundreds of feet long, and then to fade away with the arrival of winter. Their seasonal nature and appearance with the coming of warm temperatures suggests that water plays a part in their initiation, either from a seep of briny water downhill or an avalanche of dust begun by. Or a combination of both. The data however does not entirely fit these theories, and in fact is downright contradictory. Some studies (such as this one and this one) say that the seasonal lineae are caused by water. Other studies (such as this one and this one) say little or no water is involved in their seasonal formation.

The answer remains elusive, and might only be answered, if at all, when Curiosity takes a close look at two lineae in the coming years.

Slope streaks however are the focus of this post, as they are even more puzzling, and appear to possibly represent a phenomenon entirely unique to Mars. I became especially motivated to write about these mysterious ever newly appearing features when, in reviewing the May image release from the high resolution camera on Mars Reconnaissance Orbiter (MRO), I found four different uncaptioned images of slope streaks, all titled “Slope Stream Monitoring.” From this title it was clear that the MRO team was re-imaging each location to see if any change had occurred since an earlier image was taken. A quick look in the MRO archive found identical photographs for all four slope streak locations, taken from 2008 to 2012, and in all four cases, new streaks had appeared while older streaks had faded. You can see a side-by-side comparison of all four images below the fold.
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Fractured and collapsed Martian crater floor

Fractured and collapse Martian crater floor
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Time for some puzzling Martian geology. The image on the right, rotated, cropped, and reduced to post here, comes from the Mars Reconnaissance Orbiter (MRO) high resolution archive, and shows a strangely collapsed and fractured crater floor. In fact, like a number of other Martian craters, rather than having a central peak, the center of the crater floor, shown at the image’s center right, seems depressed.

The crater is located in a region dubbed the Cerberus Plains, in a hilly subregion called Tartarus Colles. Of the transition zone between the northern lowlands and the southern highlands these plains comprise the second largest region.

Being in the transition zone I would guess that the geology here is strongly influenced by the ebb and flow of the slowly retreating intermittent ocean that is thought to have once existed in the nearby lowlands. As water came and went, it created a variety of shoreline features scattered about, but not in a single sharp line as we would expect on Earth. Think more like tidal pools, where in some areas water gets trapped and left behind only to sublimate away at at later time.

We can see some hints of these processes in the images of the floors of two other craters that I have previously highlighted, here and here.

With this geological overview in mind, the broken plates here remind me of features I’ve seen in caves. Mud gets washed into a passage, partly filling it. Over time a gentle water flow over the surface of the mud deposits a crust of calcite flowstone on top of the mud. Should the water flow suddenly increase, it will wash out the mud below the crust. If the crust is not very strong or thick, it will crack into pieces as it falls, and thus resemble what we see here in this Martian crater.

There are cases where the crust becomes thick enough to remain standing, which produces some spectacular hanging calcite draperies that seem to defy explanation.

The collapse in the center of the crater is more puzzling, but suggests, based on comparable-looking Earth geology, that any perched water in this canyon might have actually drained out through underground drainage, accessed through the depression.

Be warned: All my explanations above are based on what exists on Earth, and Mars is very different from Earth. The lower gravity, colder temperatures, and different chemistry guarantee that the geological processes there will not be identical. We start by using what we know here, but recognize that we need to learn more about Mars to truly understand what goes on there.

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The many pits of Arsia Mons

The many pits of Arsia Mons

When it comes to Mars, it appears that if you want to find a pit that might be the entrance to an underground system, the place to look is on the slopes of Arsia Mons, the southernmost volcano in the chain of three giant volcanoes between Olympus Mons to the west and the vast canyon Marineris Valles to the east.

To the right is an overview map showing the pits that have been imaged since November by the high resolution camera of Mars Reconnaissance Orbiter (MRO). The black squares show the pits that I highlighted in previous posts on November 12, 2018, February 22, 2019, and April 2, 2019. The numbered white squares are the new pits found in March photograph release from MRO.

And this is only a tiny sampling. Scientists have identified more than a hundred such pits in this region. Dubbed atypical pit craters by scientists, they “generally have sharp and distinct rims, vertical or overhanging walls that extend down to their floors, surface diameters of ~50–350 m, and high depth to diameter (d/D) ratios” that are much greater than impact craters, facts that all suggest that these are skylights into more extensive lava tubes.

Below are the images of today’s four new pits.
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Curiosity second drill hole in clay formation a success

two drill holes in clay formation
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The Curiosity science team has confirmed that their second drill hole in the clay formation that the rover is presently exploring was a success.

They have confirmed that enough material from the drill hole has been deposited in their chemical analysis hopper.

The image to the right, cropped and reduced to post here, shows both drill holes on the two different flat sections of bedrock near the top.

It seems that the science team wants to spend a lot of time in this location, as described in my last rover update. It is therefore unclear when they will move south to follow their long term travel plans.

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Another spectacular landslide found on Mars

Landslide in Hydraotes Chaos
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Cool image time! In perusing the April image release from the high resolution camera of Mars Reconnaissance Orbiter (MRO), I came across the image above, cropped and reduced to post here, of the discovery of another landslide within Hydraotes Chaos, one of the largest regions of chaos terrain on Mars. The image above was taken on February 9, 2019, and has since been followed up with a second image to create a stereo pair.

This is not the first landslide found in Hydraotes Chaos. I highlighted a similar slide on March 11. Both today’s landslide as well as the previous one likely represent examples of gravitational collapses as shown in this science paper about Martian ground water. Some scientists have proposed that Hydraotes Chaos was once an inland sea, and as the water drained away the loss of its buoyancy is thought to cause this kind of landslide at the base of cliffs and crater rims.

The past presence of water also helps explain the soft muddy look of this landslide. When this collapse occurred the material was likely saturated with water. Today it is most likely quite dry and hardened, but when it flowed it flowed like wet mud. Its size, almost a mile long and a quarter mile across, speaks to Mars’s low gravity, which would allow for large singular collapses like this.

Hydraotes Chaos itself is probably one of the more spectacular places on Mars. It sits at the outlet to Marineris Valles, shown in the image below. This gigantic canyon, which would easily cover the entire U.S. if placed on Earth, was the largest drainage from the large volcanic Tharsis Bulge to the west, where Mars’s largest volcanoes are located.
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First Marsquake recorded by InSight?

The InSight science team has announced that they think they have detected their first Mars quake, though it was too small to provide much information about the Martian interior.

The Martian surface is extremely quiet, allowing SEIS, InSight’s specially designed seismometer, to pick up faint rumbles. In contrast, Earth’s surface is quivering constantly from seismic noise created by oceans and weather. An event of this size in Southern California would be lost among dozens of tiny crackles that occur every day.

“The Martian Sol 128 event is exciting because its size and longer duration fit the profile of moonquakes detected on the lunar surface during the Apollo missions,” said Lori Glaze, Planetary Science Division director at NASA Headquarters.

…Three other seismic signals occurred on March 14 (Sol 105), April 10 (Sol 132) and April 11 (Sol 133). Detected by SEIS’ more sensitive Very Broad Band sensors, these signals were even smaller than the Sol 128 event and more ambiguous in origin. The team will continue to study these events to try to determine their cause.

The data so far suggests is that Mars is far quieter than Earth geologically, but any conclusions at this point would be premature.

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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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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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Bennu’s cobbled equatorial ridge

Bennu as seen by OSIRIS-REx
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The OSIRIS-REx science team has released a new close-up image of Bennu, this time showing the asteroid’s equatorial ridge. The image on the right is that photograph, reduced to post here.

When the image was taken, the spacecraft was positioned over Bennu’s northern hemisphere, looking southward over the asteroid’s equatorial bulge. The field of view shown is 168 ft (51.2 m) wide. For scale, the bright, rectangular rock above the dark region is 8 ft (2.4 m) wide, about the size of a long bed on a pickup truck

Like Ryugu, the scientists for OSIRIS-REx are going to be challenged in finding a location smooth enough for their touchdown sample grab. That surface reminds me of some avalanche scree slopes I’ve hike across, where you’ve got nothing but rough rocks to walk on.

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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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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?
Click for full resolution image.

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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Strange craters in the Martian northern lowlands

Strange crater in the northern lowlands
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Cool image time! The image on the right, cropped and rotated to post here, was taken by the high resolution camera on Mars Reconnaissance Orbiter (MRO) and released in the monthly image dump provided by the science team. The release had no caption. It merely described this as a “Layered mound in crater.”

That is certainly what is is. However, layering suggests a regionwide process. The crater to the immediate northeast (the rim of which can be seen in the upper corner of this image), does not have the same kind of layering. (Be sure to click on the image to see that other crater.) Its crater floor is instead a blob of chaotic knobs, with the only layering scattered in spots along its north interior rim.

That the layering of both craters favors the north suggests a relationship, but what that is is beyond me. Prevailing winds? Maybe, but I don’t have the knowledge to explain how that process would work.

It is not even certain that these two craters were formed by impact. They are located in the northern lowlands where an intermittent ocean is believed to have once existed, and thus might be remnants of that ocean’s floor. That they both have a muddy appearance reinforces this hypothesis, but once again, I would not bet much money on this theory. The features here could also be expressing the effect of an impact on a muddy seafloor.

In either case the craters imply that the ocean that might have once been here existed a long enough time ago for these craters to form (either by impact or some other process) and then evolve. This has been a relatively dry place for a very long time.

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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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Jezero Crater: The landing site for the Mars 2020 rover

Jezero Crater delta
Jezero Crater delta

At this week’s 50th Lunar and Planetary Science Conference in Texas, there were many papers detailing the geological, topographical, chemical, meteorology and biological circumstances at the landing sites for the 2020 Martian rovers, Jezero Crater for the U.S.’s Mars 2020 and Oxia Planum for Europe’s Rosalind Franklin.

Most of these papers are a bit too esoteric for the general public (though if you like to delve into this stuff like I do, go to the conference program and search for “Jezero” and “Oxia” and you can delve to your heart’s content).

Oxia Planum drainages

These papers do make it possible to understand why each site was chosen. I have already done this analysis for Rosalind Franklin, which you can read here and here. Oxia Planum is in the transition between the southern highlands and the northern lowlands (where an intermittent ocean might have once existed). Here can be found many shoreline features. In fact, one of the papers at this week’s conference mapped [pdf] the drainage patterns surrounding the landing ellipse, including the water catchment areas, as shown by the figure from that paper on the right.

With this post I want to focus on Jezero Crater, the Mars 2020 landing site. The image above shows the crater’s most interesting feature, an impressive delta of material that apparently flowed out of the break in the western wall of the crater.

This image however does not tell us much about where exactly the rover will land, or go. To do that, we must zoom out a bit.
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Lava tubes on Alba Mons

Lava tubes on the western slope of Alba Mons

During oral presentations today at this week’s 50th Lunar and Planetary Science Conference in Texas, scientists revealed [pdf] a map showing what they believe are numerous lava tubes flowing down the western slope of the giant Martian volcano Alba Mons.

The image on the right is taken from their paper. The red lines indicate collapsed tube sections, maroon collapsed sections on a ridge, and yellow volcanic ridges, which I assume are external surface flows. From their paper:

Lava tube systems … occur throughout the western flank, are concentrated in some locations, and are generally radial in orientation to Alba Mons’ summit. Lava tubes are typically discontinuous and delineated by sinuous chains of elongate depressions, which in many cases are located along the crests of prominent sinuous ridges. Lava tube systems occur as both these ridged forms with lateral flow textures and more subtle features denoted by a central distributary feature within the flat-lying flow field surface. Significant parts of the sinuous volcanic ridges show no collapse features, indicating a distinctive topographic signature for Alba Mons’ lava tubes.

Alba Mons is in some ways the forgotten giant volcano on Mars.
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Streaky Mars: Slope streaks and recurring slope lineae

New recurring lineae on Mars
Click for source paper [pdf].

Numerous presentations at this week’s 50th Lunar and Planetary Science Conference in Texas have focused on two different changing features on the Martian surface, dubbed slope streaks and recurring slope lineae (or RSLs, an example of an unnecessary and unwieldy acronym that I avoid like the plague).

These apparently are considered two different phenomenon (with some overlap), something I had not recognized previously. For example, one presentation [pdf] this week described slope streaks as:

…gravity-driven dark or light-toned features that form throughout the martian year in high-albedo and low-thermal-inertia equatorial regions of Mars. The distinctive features originate from point sources on slopes steeper than ~20°, follow the topographic gradient, extend or divert around small obstacles, and propagate up to maximum lengths of a few kilometers. The streaks brighten with time, sometimes become brighter than their surroundings, and fade away over timescales of decades. [emphasis mine]

An example can be seen here. This is in contrast to the recurring slope lineae, shown in the image above, which another paper [pdf] described as:

…dark linear features that occur on the surface of steep slopes in the mid-latitudes of Mars. These areas are warm, occasionally exceeding temperatures of 273-320 K. [Lineae] recur over multiple years, growing during warm seasons and fading away during colder seasons. Their apparent temperature dependency raises the possibility that liquid water is involved in their formation. [emphasis mine]

I have highlighted the key differences. While slope streaks are long lived and change slowly, lineae change with the Martian seasons. And the slope streaks appear to exist at lower latitudes. These difference means that the formation process of each must be also different.

The problem is that scientists still don’t know what causes either, though they have many theories, involving both wet and dry processes.

Most of the presentations at the conference this week focused on the recurring lineae, which I suspect is because of their seasonal aspect. This feature strongly suggests a water-related source for the lineae, and everyone who studies Mars is always focused on finding sources on Mars where liquid water might be found. Also, slope streaks appear more often in dunes, which also strongly suggests a dry process. One paper, however, did a comparison study of lineae with one specific kind of dune slope streak to see if the freatures might be related.

The most interesting result [pdf] for all these papers documented the apparent increase in recurring lineae following the global dust storm last year. The image at the top of that post is from this paper, and shows a fresh lineae where none had been prior to the storm. From the paper’s abstract:
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Land of mesas

Ariadnes Colles
Click for full image.

Cool image time! The Mars Odyssey science team today released the image on the right, cropped and rotated to show here, of a region on Mars named “Ariadnes Colles.”

The term colles means hills or knobs. The hills appear brighter than the surrounding lowlands, likely due to relatively less dust cover.

This is certainly a place with lots of hills, or to be more precise, mesas, as many of them seem to be flat topped.

The lack of dust cover on the tops is probably because, like on Earth, the winds blow much better once you get a bit above the surface. (This is why sailing ship builders kept adding higher and higher sails to their ships, until the top sails of clipper ships rose a hundred-plus feet above the deck.) These better winds clean off the mesa tops, just as they did to the solar panels on the rovers Opportunity and Spirit several times during their long missions.

Ariadnes Colles is another example of Martian chaotic terrain. Since this region is located deep in the cratered and rough southern highlands of Mars, the erosion that created these mesas was likely not water-flows. Was it wind? Ice?

Your guess is as good as anyone’s.

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Mars likely has many large and extensive cave systems

Mamers Valles

More caves on Mars! This week the Lunar and Planetary Institute and the Johnson Space Center are jointly holding the 50th Lunar and Planetary Science Conference in Texas. I have been going over the program, and will be posting reviews of some of the more interesting results all this week.

We begin with caves, which should not be surprising to my regular readers. As a caver who also knows their value for future space colonists, I am always attracted to new discoveries of cave passages on other worlds. Today’s however is a doozy.

The image to the right is of Mamers Valles on Mars, what scientists have dubbed a fretted valley, a common feature in the transition zone between the low altitude northern plains and the southern highlands. It comes from a paper [pdf] with the typically unexciting scientific title, “Fretted channels and closed depressions in northern Arabia Terra, Mars: Origins and implications for subsurface hydrologic activity.”

What the scientists really means here is that their research strongly suggests that Mars has a very large and very extensive number of underground drainage systems, which have caused collapses on the surface that often resemble meandering river canyons, such as seen above. As they explain:
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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
Click for full image.

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
Click for full image.

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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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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