The freaky floor of Mars’ Hellas Basin

The perplexing floor of Hellas Basin
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Today’s cool image takes us to the Death Valley of Mars, Hellas Basin, a place I like to call the basement of Mars. The photo to the right, cropped and reduced to post here, was taken by the high resolution camera on Mars Reconnaissance Orbiter (MRO) on September 28, 2020, and gives us another example of the very strange and inexplicable geological formations that are often found on the floor of Hellas.

The picture was taken not as part of any particular research project, but somewhat randomly for engineering reasons. In order to maintain the proper temperature of MRO’s high resolution camera, it must take images in a regular cadence. When large gaps in time occur between requested images, the camera team then picks locations to fill those gaps, sometimes randomly, sometimes based on a quick review of earlier wide angle images.

Sometimes these “terrain sample” images are quite uninteresting. More often they hold baffling surprises.

I think the photo to the right falls into the latter category. Though the terrain covered by the full image is largely flat and lacking in large features, the surface is strewn with perplexing small details.

The light streaks might be dust devil tracks, but why are they light here when such tracks are routinely dark everywhere else on Mars? What formed the many parallel small ridges? What caused the smooth solid patch near the photo’s center top? And why do the ridgelines at the western edge of that patch run in almost a perpendicular direction to the other ridges?

All a mystery, but then the floor of Hellas Basin is filled with such mysteries. Below is a list of some other cool images of the floor of Hellas, all weird and mystifying. Also below is an overview elevation map of Hellas Basin, with darker blue indicating the lowest elevations. The white cross marks the location of today’s photo.
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Back to Mars’ glacier country

Tongue-shaped glacial flow on Mars
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The cool image to the right, rotated, cropped, and reduced to post here, was taken on November 3, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows what the science team labels a “Possible Tongue-Shaped Flow Feature in Protonilus Mensae.” There is no caption, so I will try to provide.

Protonilus Mensae is part of the long string of chaos terrain that runs about 2,000 miles along the transition zone between the southern cratered highlands and the northern lowland plains at about 30 to 40 degrees north latitude, and includes the other mensae regions dubbed Deuteronilus to the west and Nilosyrtis to the east. This region of Mars I like to call glacier country, because almost every high resolution photograph appears to show glacial features. To get an idea what I mean, take a gander at these past posts, their locations indicated by number in the overview map of Protonilus Mensae below:
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The strange moated mesas of the Kasei Valley on Mars

Overview map

In showing my readers today’s cool image, I want to present it as it is seen by scientists, first from a far distance that with time increasingly zooms in to reveal mysteries on a very human scale.

The overview map to the right essentially gives us the view of Mars as seen by scientists following the Mariner 9 orbiter mission that began mapping the Martian surface in late 1971 after the conclusion of a global dust storm that had hidden its surface initially. As the first high resolution map of Mars, the orbiter revealed numerous puzzling and surprising features, including the largest volcanoes and canyons in the solar system. The orbiter also found that the red planet’s surface was comprised of two very different regions, the northern lowland plains and the southern cratered highlands.

The overview map, covering from about 13 degrees south latitude to about 34 degrees north latitude, shows us all but the southern cratered highlands. The white box in Kasei Valles is where today’s cool image is located. Both Kasai and Valles Marineris represent those giant canyons, all invoking to Earth eyes the possibility of catastrophic floods of liquid water sometime in the past.

Ascraeus Mons is the northernmost of the three giant volcanoes east of the biggest volcano of all, Olympus Mons. All sit on what scientists now call the Tharsis Bulge.

Chryse Planitia, where Viking-1 landed in 1976, is part of those northern lowlands that some scientists believe might have been once had an intermittent ocean sometime in the past. Today’s image is about 600 miles from the outlet into Chryse Planitia.

The geological mystery of all these features demands a closer look, something that scientists have been pursuing now for more than a half century.
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The pit caves of Mars: Can humans someday live in them?

Four more pits in the Tharsis Bulge on Mars

It has been more than four months since my last report on the pits of Mars. Time to do another.

The collage to the right shows the four different pits photographed by the high resolution camera of Mars Reconnaissance Orbiter (MRO) since October. The links to each image are:

Like almost all the cave pits so far found on Mars, all are in the Tharsis Bulge of giant volcanoes to west of Valles Marineris. The overview map below shows these pits in the context of every other pit in this region that I have featured on Behind the Black.
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The slowly disappearing dry ice cap at Mars’ south pole

The Happy Face crater near Mars' south pole
Click for the 2020 full image.

Cool image time! The photo to the right of two images taken by the high resolution camera on Mars Reconnaissance Orbiter (MRO) was posted as a captioned image by the orbiter’s science team today.

This crater, dubbed the Happy Face Crater because of the shape of the blobby features within it, is located on the south pole ice cap of Mars, about 200 miles from the south pole itself.

Today’s caption noted how these pictures, taken nine years apart, illustrate the change going on at the Martian south pole.

The “blobby” features in the polar cap are due to the sun sublimating away the carbon dioxide into these round patterns. You can see how nine years of this thermal erosion have made the “mouth” of the face larger. The “nose” consisted of a two circular depressions in 2011, and in 2020, those two depressions have grown larger and merged.

While this caption noted the importance of studying these long term changes in order to understand the evolution of Mars’ climate and geology, it did not give the very specific discovery these changes suggest for Mars globally, a discovery that is actually very significant.

The two ice caps of Mars have some fundamental differences, all presently unexplained. The similarities are obvious. Both have permanent caps of water ice that are presently believed to be in a steady state, not shrinking or growing. Both each winter get covered by a thin mantle of dry ice that sublimates away completely with the coming of spring.

The differences are more puzzling, as shown by the maps of the two poles below.
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Mysterious colors on Mars, near the landing site of Europe’s rover

Mysterious colors on Mars
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Cool image time! Today the science team for the high resolution camera on Mars Reconnaissance Orbiter (MRO) released a new captioned image, which I have cropped and reduced to post here to the right.

The photo was taken October 12, 2020, and shows a small very colorful area on top of an isolated hill. To quote the caption, written by Sharon Wilson:

An isolated, elongated mound (about 1 mile wide and 3.75 miles long) rises above the smooth, surrounding plains. Horizontal layers are exposed at the northern end of the mound, and its surface is characterized by a very unusual quasi-circular pattern with varying colors that likely reflect diverse mineral compositions.

…The origin of this mound is unknown, but its formation may be related to the clay-bearing rocks in the nearby Oxia Planum region.

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Craters in slush on Mars

Dust devil steak across a slushy plain on Mars
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Cool image time! The photo to the right, cropped and reduced to post here, was taken on October 27, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It was taken not for any particular research project, but as one of the periodic images the camera team needs to take maintain the camera’s proper temperature. When they need to do this, they often will take a picture in an area not previously viewed at high resolution. Sometimes the image is boring. Sometimes they photograph some geology that is really fascinating, and begs for some young scientist to devote some effort to studying it.

In this case the photo was of the generally featureless northern lowland plains. What the image shows us is a scattering of impact craters that appear to have cut into a flat plain likely saturated with ice very close to the surface.

How can I conclude so confidently that these craters impacted into ice close to the surface? The location gives it away.
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The colorful and bright knobs of Ariadnes Colles on Mars

Colorful and bright knob in Ariadnes Colles
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Today’s cool image gives us a sample of the strange colorful hills in an even stranger knobby depression on Mars called Ariadnes Colles. The photo to the right, cropped and color enhanced to post here, was taken on September 10, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It focuses on just one of those colorful hills. The color strip only covers the western half, which is why that is the only part of the hill in color.

Ariadnes Colles is a patch of chaotic terrain 110 by 100 miles in size, located in the southern cratered highlands due south of Mars’s volcano country, at latitude 34 degrees south. What makes this particular patch of chaos distinct from the many others on Mars is that the hills, knobs, and mesas within it are routinely bright and colorful, compared to the darker surrounding terrain. Moreover, as noted in this Mars Express press release for images of Ariadnes Colles from that orbiter,

In contrast to other chaotic terrains … Adrianes Colles is not a water-source region. It is still debated, therefore, whether Ariadnes Colles was formed by the action of water or wind.

The darker material in the southern areas is most likely sand or volcanic ash; some slopes of the flat-topped features have been covered by this dark material that was blown up on the slopes.

The sand or volcanic ash most likely come from the Medusae Fossae Formation several hundred miles to the north, the largest volcanic ash deposit on Mars. The colors on the hill likely come from a variety of minerals.

The overview map below shows the entire patch, with the location of the hill above indicated by the white dot in the red rectangle that shows the full image location.
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Draping moraines on Mars

Draping moraines on Mars
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Cool image time! The photo on the right, rotated, cropped, reduced, and annotated to post here, was taken by the high resolution camera on Mars Reconnaissance Orbiter on October 6, 2020. It shows the northern interior rim of 42-mile-wide Greg Crater in the southern cratered highlands of Mars.

What makes it interesting is the curving ridge that appears to drape itself around several larger hilltops. That ridge is a moraine, the debris or glacial till that accumulates at the foot of glaciers as push their way down hill. As the glacier had flowed those hills became obstacles, so that the glacier (and its moraine) were forced to go around.

The overview map and wider view from the context camera on MRO below give the setting.
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A glacier filled canyon on Mars?

Large glacial flow exiting Mamers Valles
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The photo to the right, rotated, cropped, and reduced to post here, was taken on September 9, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows the northern half of a 15-mile wide canyon on Mars whose floor appears to be completely filled by a glacier. The full picture shows both the north and south rims, and captures the canyon’s outlet from the southern cratered highlands into the chaotic terrain of Deuteronilus Mensae, the region of Mars I like to call glacier country. This region of canyons and mesas forms the transition zone down to the northern lowland plains, and is a region where almost every MRO image shows glacial-type features.

The size and age of this glacial feature is what makes it stand out. First, note the craters on its surface. The glacier has to be quite old and inactive for a long time for those craters to still exist as they appear. Any movement would have distorted them, and they show little distortion.

The overview map below gives a sense of this glacier’s size.
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A Martian “glacier” made of volcanic ash

A Martian
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Of the numerous cool images I’ve posted on Mars, many have documented the growing evidence that in the mid-latitudes of the Red Planet are many buried glaciers of ice.

Today’s cool image to the right, rotated, cropped and reduced to post here, shows something that at first might resemble the features one would expect from an ice glacier, but in reality is actually a flow of volcanic ash being blown almost like a river, with the prevailing winds blowing from the south to the north.

The photo was taken by the high resolution camera on Mars Reconnaissance Orbiter (MRO) on November 1, 2020. The location, very close to the equator and in the transition zone dubbed the Cerberus Plains, is also smack dab between Mars’s biggest volcanoes, a region I like to dub Mars’s volcano country. The overview map below gives the context.
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Summer at the Martian south pole

Overview of the Martian south pole

Today we have two cool images, both giving us a tiny glimpse at what it is like in the middle of summer on the fringes of Mars’ south pole ice cap. Their location is indicated by the blue crosses on the overview map on the right.

To review, the south pole on Mars is, like its north pole, mostly made up of a permanent icecap of water. In the south, this icecap is mostly mixed with dust and debris in the area outlined in black and dubbed the layered deposits. On top of this is a smaller thick water ice cap, indicated by light blue, which is in turn topped by a thin cap of frozen carbon dioxide, or dry ice, indicated by white. During the winter the entire pole, down to 60 degrees latitude also gets covered by a temporary mantle of dry ice, that sublimates away each spring.

Now for our cool images!
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Striped dunes in crater on Mars

Striped dunes in crater on Mars
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Cool image time! The photo on the right, rotated, cropped, and color-enhanced to post here, was taken by the high resolution camera on Mars Reconnaissance Orbiter (MRO) on October 1, 2020. It shows some large dunes with what appear to be black or dark features across their surface, reminiscent of tiger stripes.

The dunes are located on the floor of 42-mile-wide Kunowsky Crater, located in the northern lowland plains of Mars at the high mid-latitude of 57 degrees north.

What are the tiger stripes? The second image below, provided at the image link, zooms in at full resolution at the area in the white box, and shows that the stripes appear to actually be made up of spots strung together.
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A Martian polliwog

Three-mile-wide crater with exit breach
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Cool image time! The photo to the right, rotated, cropped, and reduced to post here, was taken on September 30, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO).

It shows one half of what scientists have dubbed a pollywog crater, in which there is a single breach in the crater wall, aligned with the low point in the crater’s floor. Such craters suggest that they were once water- or ice-filled, and that they drained out through the breach either quickly in a single event or slowly over multiple events.

The second image below was taken by the wide angle context camera on MRO, and not only shows this entire crater, but several other adjacent craters, all of which show evidence of glacial fill in their interiors. The latitude here is 34 degrees south, placing these craters within the mid-latitude bands where such glacial features have been found by scientists in great numbers.
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Terraced mesas in Martian crater

Terraced mesa in Martian crater
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The cool image to the right, reduced and annotated to post here, was a captioned photo released by the Mars Reconnaissance Orbiter (MRO) science team earlier this week. Taken by MRO’s high resolution camera, it shows in color a beautifully stair-stepped mesa located in an unnamed 22-mile-wide equatorial crater in Arabia Terra, the large transitional zone between the lowland northern plains and the southern cratered highlands. As the caption notes,

Several craters in Arabia Terra are filled with layered rock, often exposed in rounded mounds. The bright layers are roughly the same thickness, giving a stair-step appearance. The process that formed these sedimentary rocks is not yet well understood. They could have formed from sand or volcanic ash that was blown into the crater, or in water if the crater hosted a lake.

If volcanic ash, the layers are signalling a series of equal eruptions of equal duration, which seems unlikely. Water is also puzzling because of the equatorial location. Like yesterday’s mystery cool image, water is only likely here at a time when the red planet’s rotational tilt, its obliquity, was much higher, placing this at a higher latitude than it is today.

Regardless, make sure you look at the full image here. This crater floor is chock-full of more such terraced mesas, some of which are even more striking than the sample above.

I have also posted below the MRO context camera photo of the entire crater.
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A splat on Mars

A splat on Mars
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Cool image time! The photo to the right, cropped to post here, was taken on October 31, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). Labelled simply as a “Terrain Sample”, it was not taken as part of any specific science research but because the MRO science team need to regularly take pictures to maintain the camera’s temperature. When such engineering images are required they try to pick spots of some interest, but sometimes the resulting picture is somewhat bland.

If you look at the full image, you will see that blandness generally describes it. However, in the upper left corner was a most intriguing-looking crater, which I have focused on above. From all appearances, when this impact happened the ground was quite soft, almost like mud, and thus the ejecta splattered away not as individual rocks and debris but as a flow.

The map below gives a little context, but really doesn’t explain this crater fully.
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Cones on Mars!

Today’s cool image is actually a bunch, all found recently in the monthly image download from the high resolution camera on Mars Reconnaissance Orbiter (MRO).

All the photos I post below show pimple-like cones, all of which appear to be a type of small volcano. The cones are found in a wide range of locations, from the northern lowland plains to the cratered highlands to the mid-latitude transition zone between the two. They are also found at the bottom of deep canyons, in the floors of craters, and amidst mountains.

Let us begin.
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Ancient and recent volcanoes on Mars

Volcanic vent on eastern flank of Olympus Mons
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Cool image time! The photo to the right, rotated, cropped, and reduced to post here, was taken by the high resolution camera on Mars Reconnaissance Orbiter (MRO) on October 25, 2020. It shows what it calls a “possible volcanic vent east of Olympus Mons”.

Is this active? If not, how old is it. Also, the elongated shape of the vent suggests the possibility of a lava tube, or at least some underground complexity to the release of its magma.

In order to get some clarity, I emailed Sarah Sutton of the Lunar and Planetary Laboratory of the University of Arizona, who requested this photograph. Her response:

The image is of a small shield volcano with an elongated vent at the summit. We don’t have complete stereo here yet, so we can’t tell exactly what the height is. This vent might have sourced tube-fed flows, but in this case, we can’t resolve such features in the image data. This and other small shield volcanoes in the vicinity are partially buried by plains-forming lava flows. The lava flows around the base overlap the flows that emanate radially from the summit vent. Therefore we infer that the shield is older than the surrounding lava flows.

The vent, which runs from the southwest to the northeast, sits on top of a sloping wide hill, which is that small shield volcano described by Sutton. The flat plains surrounding this hill are from later eruptions from other and possibly larger volcanoes. The wider overview map below might give us a clue as to the source.
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Confirmed: Martian glacial features are ice

Lobate glacial flows on Mars
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Scientists using the radar instrument on Mars Reconnaissance Orbiter (MRO) have now confirmed that the Martian glacial features that most resemble the glaciers seen on Earth are made of substantial amounts of ice, and were possibly active and growing only a few million years ago.

“Our radar analysis shows that at least one of these features is about 500 meters thick and nearly 100 percent ice, with a debris covering at most ten meters thick,” said Berman, lead author of “Ice-rich landforms of the southern mid-latitudes of Mars: A case study in Nereidum Montes” published online in Icarus at https://doi.org/10.1016/j.icarus.2020.114170. PSI scientists Frank C. Chuang, Isaac B. Smith and David A. Crown are co-authors on the paper.

Global mapping of Viscous Flow Features (VFFs), a general grouping of ice-rich flow features in the southern hemisphere of Mars shows a dense concentration in Nereidum Montes, along the northern rim of Argyre basin. Located within a northwestern subregion of Nereidum Montes is a large number of well-preserved VFFs and ice-rich mantling deposits, the paper says, potentially the largest concentrations of any non-polar region in the southern hemisphere.

…Processed data from the Shallow Radar (SHARAD) instrument aboard NASA’s Mars Reconnaissance Orbiter spacecraft were used to search for basal reflections across VFFs within the region. For one in particular, these observations and analysis indicate that it is composed of nearly pure water ice. Model ages obtained from crater counts and their associated size-frequency distributions (SFDs) on both ice-rich mantling deposits and small lobate VFFs suggest that the deposits stabilized several to tens of millions of years ago in the Late Amazonian Epoch, and that small lobate VFFs likely formed due to the mobilization of mantling deposits.

This data here reinforces the impressions from many other places within the 30-60 degree latitude bands on Mars where many such features are found.

Mars might be a desert, but it is a desert like Antarctica, not the Sahara. Any settlement there must use the Earth’s south pole as its guide for construction and design.

Strange crater in the basement of Mars

Strange crater in Hellas Basin
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Today’s cool image to the right, cropped and reduced to post here, is intriguing for a number of reasons. Taken on September 11, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), it shows a partially buried crater found in the middle of Hellas Basin, the lowest point on Mars and what I like to call the red planet’s basement.

What makes this crater intriguing is the layered pile of material filling its interior. If I didn’t know any better, I would think some construction crew has used a bulldozer to push debris from the crater’s right half in order to smooth the ground in preparation for building a strip mall, office building, or housing development.

This of course is not what happened. Then what did create those layered piles in the crater’s left half?
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Cryptic Terrain on Mars

Cryptic terrain near Mars' south polar ice cap
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Cool image time! The photo to the right, rotated and cropped to post here, was taken on September 27, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows what is likely a crater that is partly buried by ice and dust and sand near or on the edge of Mars’s south polar ice cap.

It also shows an example of what planetary scientists have dubbed “cryptic terrain,” found generally on the margins of that ice cap. In this case, the location is on a plateau adjacent to the ice cap dubbed Promethei Planum. Despite a lot of searching, I could not locate any research papers describing Promethei Planum, though data outlined in one Mars Express press release from 2008 suggested it was part of the polar ice cap more than two miles thick that is covered by a thin mantle of dry ice each winter.

The strange curlicue cliffs and plateaus seen here are thought to form as part of the arrival and then sublimation away of that seasonal dry ice mantle, but how that process exactly works to create these particular geological features remains I think a mystery. North is to the top. The general grade is also downhill away from the icecap to the north.

Moreover, the overview map below, with the location of this image indicated by the blue cross, illustrates more mysteries.
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Landslides on the edge of Mars’ youngest lava field

Landslides on the edge of Mars' youngest lava field
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Cool image time! The photo to the right, cropped to post here, was taken by the high resolution camera on Mars Reconnaissance Orbiter (MRO) on September 28, 2020. It shows several indentations in a north-south cliff face, with debris apparently falling down into a flat plain to the east.

The scientific history of this picture is very interesting. The first photo of these landslides was taken in 2006 and was titled, “Landslides on Flat Topography in Elysium Planitia”. The second, taken a few months later in 2007 to produce a stereoscopic view, was labeled “Landslides Along Shoreline in Elysium Planitia.” This most recent 2020 image is merely labeled “Landslides in Elysium Planitia.”

Is the flat terrain to the west a seabed to an ancient ocean, as suggested by the title for the 2007 image, with these landslides erosion caused in the far past by water lapping up against these cliffs?
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Terby Crater and its drainages into Mars’ basement

Channels in Terby Crater on Mars
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Cool image time! Over the past few years, in my endless rummaging through the archive of high resolution images from Mars Reconnaissance Orbiter (MRO) I have posted a lot of photos of meandering channels of all kinds, most of which evoke to Earth eyes canyons eroded by flowing water. (This September 2020 cool image is just one of the more recent examples.)

Today’s cool image is another example, but in this case it is only a very small part of a very large drainage basin that is more than a hundred miles across and extends at least that far southward into the basement of Mars, Hellas Basin, the place on Mars with the lowest elevation.

The photo to the right, rotated and reduced to post here, was taken on September 12, 2020 by the high resolution camera on MRO. I normally wouldn’t post the whole image, but to crop it would mean you wouldn’t get the sense of extensive nature of this drainage. Downhill is to the south. The channel apparently passes through three or four stages. First, its northernmost section is in a wide canyon, the floor of which resembles glacial debris (though with a latitude of 27 degrees south this is a bit too close to the equator for ice). More likely we are looking at wind-blown sand and dunes being pulled downhill in the floor of the canyon.

This first canyon is also actually a gap in the rim of a 13-mile-wide unnamed crater. See this MRO context camera image for a wider view.

Next, the drainage becomes a series of meandering small interweaving channels, resembling the channels often seen in beach mud as the tide goes out.

Finally, the channels head into a gap to fall over a sloping cliff into lower terrain.

Nor these stages entirely linked. The first glacial-like stage exiting the gap in the crater appears to drain to the southeast, while the second seems to emanate from what appears to be a very faint small crater now partly buried. Both head south toward the gap, but the path of the eastward drainage appears less obvious. Some of it flowed westward to join the meandering channels but some also appears to work its way south more to the east.

This one image shows a lot of channels, but it is only a very small slice of this whole drainage system. In fact, we are looking here at only one strip of the interior slope of the northern rim of 108-mile-wide Terby Crater.

The overview map below gives the larger context. Terby Crater sits on the northern border of Hellas Basin, which in itself extends another 1,500 miles to the south. From this point the drop in elevation into Hellas is almost four miles.
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Aram Chaos: Illustrating the puzzle of Mars

Aram Chaos
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The geological history of Mars is incredibly complex, and we really don’t know much about it. What we do know right now is based on a limited number of tiny fragments of a much larger story, with those fragments allowing scientists to only make educated guesses on how they fit together.

Many of those guesses will certainly turn out right. Just as many will turn out wrong. At this moment in our exploration of the Red Planet we can only grasp at straws while always keeping an open mind, as later data is surely going to change any conclusions we presently have.

The photo to the right is a good illustration of this struggle. Rotated, cropped, and reduced to post here, it was taken on September 27, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), and shows what at first glance looks like a stream of white frost or ice descending down a canyon to the south.

That first impression however is entirely wrong. When I asked Chris Okubo of the U.S. Geological Survey, who requested this image from MRO, what it was, he explained,

The white material is not frost. Instead, these are sedimentary rocks comprised primarily of sulfates. The texture to me suggests these are lithified dunes.

Lithified merely means that the dunes have hardened into rock. Sulfates are a salt formed from sulfuric acid, and are on Mars often linked to some complex mineralogy. If you stood there the colors would be white and red, quite beautiful. As Okubo explained,

The sulfates are white to tan in color, but there would also be a lot of red/brown Mars dust on top of it. It would be similar to walking around some of the playas in the desert southwest.

Though these white sulfate deposits have their root in sulfuric acid, Okubo added that they “are in the form of minerals similar to gypsum and so they would be safe to touch.”

What is going on here? As is usually the case, we need to first take a wider view to get some context.
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Sagging cliffs on Mars

Sagging escarpment on Mars
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Cool image time! On Mars things change, but not like on Earth because the atmosphere is not as thick and there is no flowing water. The photo to the right, rotated, cropped, reduced, and annotated to post here, gives a good example of that slow change. The image was taken on August 29, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), and shows the high escarpment that in this one place separates the planet’s southern cratered highlands from the transition zone down to northern lowland plains.

In this spot that escarpment, approximately 4,000 feet high, shows signs of avalanches and sagging. In the upper steep section, I point to what looks like a dust avalanche that wiped the slope clear of rough terrain as it rolled downhill. At the bottom of the cliff a large section has separated away. Since this cliff is located at 28 degrees north latitude and is in the midst of the chaos terrain regions I like to dub glacier country, it is very possible that this large section is actually buried glacial ice that in shifting down slope cracked, separating the lower section from the upper.

This particular location is east of an area dubbed Nilosyrtis Mensae (where there is a lot of evidence of glaciers and frozen ice), and about 650 miles north of Jezero Crater, where the rover Perseverance will land on February 18, 2021.

A spray of Martian meteorites

A spray of small secondary impacts
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Cool image time! The photo to the right, cropped and reduced to post here, was taken on October 26, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It is what the camera team calls a “terrain sample,” meaning it was not specifically requested by a researcher but was instead chosen by the camera team because they need to regularly take images to maintain the camera’s temperature. When they do this, they try to pick a location that hasn’t been photographed in high resolution previously, and that might have some interesting features. Sometimes the photo is boring. Sometimes they hit pay dirt.

In this case, the photo captured an small impact crater, about 1,300 feet across, surrounded by a spray of secondary impacts. The color portion of the image shows what I suspect are dust devil tracks cutting across a surface that, because of its blue tint, is either rough or has frost or ice within it. At 48 degrees north latitude, the possibility of the latter is high, especially because this location is northwest of the Erebus mountains, where SpaceX has its prime Starship candidate landing zone and where scientists suspect ice is readily available very close to the surface. The overview map below shows this context.
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A place on Mars where lakes, snowfall, and rivers once existed

Inverted channels near Juventae Chasma
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Cool image time! The photo to the right, cropped and enhanced to post here, attracted my immediate interest when I was going through the November image dump from Mars Reconnaissance Orbiter (MRO) because of its meandering sharp ridges, estimated to be about sixty feet high on average. While I have previously posted MRO images of inverted channels such as these, their particular sharpness, plus their large number in this localized single image, aroused my curiosity. What is their history? Does this illustrate an particularly interesting place on Mars?

The picture itself was taken was on September 29, 2020 by MRO’s high resolution camera. The blue areas in the color strip probably indicate coarser-grained surface. This makes sense, as these ridges are believed to have been initially carved as channels by flowing water or ice, which compressed their riverbed and thus made it resistant to erosion. Over time, the surrounding terrain eroded away, leaving that channel behind now as a upstanding ridge. The surrounding eroded terrain should thus be expected to be rougher.

Where did the water for these rivers come from, however? As always, the overview maps below give the context, and a possible explanation.
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Eroded and possibly wet Lohse Crater

Gully flow near central peak of Lohse Crater on Mars
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Cool image time! Today we take a look at one particular 100-mile-wide crater, Lohse Crater, located in the southern cratered highlands on Mars. The photo to the right, cropped and reduced to post here, focuses in on one of the many eroding gullies found in the mountainous region surrounding the crater’s central peak. Taken on August 20, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), the full image is centered on that central peak, just off the south edge of this cropped section. This new image is part of a long monitoring campaign, begun in 2007, of this central peak region. For more than six Martian years, scientists have been tracking the numerous gullies found throughout the central peak region to see if there have been any changes.

I focused on this specific gully because I think it illustrates well why planetary scientists are monitoring these gullies. Whatever flowed down from the cliff on the left hit the material on the right hard enough and fast enough to imprint a curve into the material on the crater floor. Moreover, it does not appear to have simply been a landslide, for several reasons. First, the cliff does not appear cut back at the flow’s head, as you would expect if a section had broken off. Second, the material in the flow does not look like debris from an avalanche. In fact, there does not appear to be very much debris in the gully at all.

Third, and most important, the flow appears to originate at the cliff base, kind of what you’d expect if there was seepage coming out of a layer in that cliff face. Kind of what you’d expect on Earth, at a spring!

Was that flow water? This is the big question. Lohse Crater is significant in that it was one of the first locations on Mars [pdf] spotted by Mars Global Surveyor in the late 1990s where gullies were found suggesting some form of regular erosion possibly caused by flowing water. As this 2005 paper then concluded,
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Giant wind eddies in the sands of Mars

Wind eddies on Mars
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Cool image time! The image to the right, cropped and reduced to post here, was photographed by the high resolution camera on Mars Reconnaissance Orbiter (MRO) on August 5, 2020. It shows a cluster of the crescent-shaped gullies, apparently carved from desert sand by the prevailing winds.

Those prevailing winds here are from the southwest to the northeast. As the wind blows the sand to the east, it hits a more solid object, such as a mountain buried in the sand, which forces the wind and the blown sand to go around, much as water passes a boulder in river rapids. That solid object also causes an eddy to form at its face, the wind forced downward and then around and up, carving out the gullies by lifting the sand at the base of that solid object. The result are these crescent gullies, dubbed blow-outs.

The overview map helps explain why there is so much sand here, enough apparently to bury whole mountains.
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Glacial eddies on Mars?

Glacial eddies on Mars?
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Cool image time! The photo to the right, cropped and reduced to post here, was taken on August 15, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows a truly strange bunch of blocks beside a clean flow neatly organized in almost straight parallel lines.

What is going on? This location is at 38 degrees south latitude, a latitude where scientists have found a lot of features that resemble water ice glaciers, generally protected from sublimating away by a thin layer of dust and debris.

A first guess is that the smooth glacial flow at the lower right is disturbing the glacial material next to it, causing it to rip apart and break up. At the same time, the hollowed look of these glacial blocks suggests that the ice below that protective debris layer is also slowly sublimating away, causing the surface to sink.

The wider shot below helps confirm this impression.
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