Tag: geology

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Today is the last part in our four part exploration of the cratered southern highlands of Mars, begun last week. (For the early parts, go here-Part #1, here-Part #2, and here-Part #3.) Though there is no need, new readers should read the first three parts first, in order to get the larger perspective of this final post.

The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on December 20, 2022 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows the eastern main gully descending down into a pit that sits in the north center of 52-mile-wide Asimov Crater, as shown in the inset on the overview map above. (For an MRO high resolution of the western gullies into this pit, see this January 2019 cool image post.)
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This is the third part of this week’s series taking a look at some of the strange features in the southern cratered highlands of Mars. In the first part I posted a beautiful image of what appears to be a crater filled to the brim with glacial ice, surrounded by an ice sheet plain. In part two we took a look at the interior of Rabe Crater, which though very nearby does not appear to have obvious glacial features within it at all. What it has instead are deep open air pits and a lot of sand dunes.

Today’s image to the right, cropped, reduced, and sharpened to post here, takes us to the interior of an unnamed 45-mile-wide crater only about 70 miles north of Rabe. The black dot in the inset on overview map above indicates the photo’s location. The picture was taken on January 1, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). Like Rabe, this crater also has many large open-air pits. In the picture one pit, near the lower center of the picture, is surrounded by soft-looking mounds and a strangely swirling textured and uneven terrain that makes up the majority of the crater’s floor.

This picture might help explain what we saw in Rabe. The textured terrain in this unnamed crater could easily be ice-impregnated and now hardened sand dunes. The pit could be where that impregnated ice has sublimated away, leaving behind the dust from those ancient dunes which then forms new sand dunes. In Rabe, the crater floor above its pits looks very similar to this swirling textured surface, suggesting the same process is going on there.

What strengthens this explanation is the many other craters nearby, all indicated by red dots in the overview map above, that also have pits or distorted crater floors. Their proximity suggests that there is an underground ice layer in this region, always at about the same elevation, and each crater impact exposed it. With time that exposed ice, no longer pure but filled with material from the impacts, sublimated partly away, producing the pits as well as ample sand to form sand dunes.

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Today and for the next three days the cool images that I will post from Mars will explore a region that I have not covered very much in depth, the cratered southern highlands between the giant basins Argyre and Hellas. The map above is an overview of this 7,000-mile-long region, all of which is inside the 30 to 60 degree south latitude band where scientists have found much evidence of buried glaciers. In this region the bulk of that evidence is most obvious inside craters.

The picture to the right, cropped, reduced, and sharpened to post here, was taken on December 21, 2022 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), and shows a typical example of the kind of glacial feature found. The white cross on the map marks its location, west of the Hellespontus Mountains that form the western rim of Hellas Basin.

Scientists have dubbed this feature concentric crater fill, a purposely vague term because — though it looks like glacial fill — until there is data to confirm it the scientists would quite properly rather not commit themselves. The concentric rings suggest multiple layers, each of which likely marks a different climate cycle in Mars’ geological history.

In this case the glacier features also appear to cover the entire plain surrounding the crater as well as its rim. The small crater to the west is similar, and both give the appearance that the ice sheet that covers them came after the impact, draping itself over everything, with the craters only visible because the ice sheet sags within their interiors.

More crazy features from the cratered highlands to come.

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Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on February 4, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows the terminating cliffs of the north pole ice cap of Mars, dubbed Rupes Tenius on this side of the icecap.

At this point the elevation difference of the icecap’s edge from top to bottom is not significant, only about 1,500 feet or so, though this is a very rough estimate. As with all other images of the ice cape’s edge, there are many many layers visible, all indicating a different cycle in the climate history of Mars as its rotational tilt swings from about 11 degrees to 60 degrees over eons.

Moreover, at this point there is likely not that much difference between the terrain on top and the terrain below. Both will be mixed ice and dust and coarse rocks, though the percentages will be shifting towards less ice as we go down.
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Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on January 11, 2023 by the high resolution camera on Mars Reconnaissnace Orbiter (MRO).

The scientists labeled this picture “Rocky Terrain.” Though this describes the overall sense of the full image, it fails to capture correctly the nature of this patch of ground at the center of the picture. As you can see, this patch of spongelike surface starts and ends abruptly. It appears that it is a layer on top of the surrounding terrain that has also been eroded aggressively since its placement.

The many craters on its surface seem to have come later, though as the crater size diminishes it becomes harder to separate the craters from the sponge holes. Moreover, some of the larger craters are distorted in shape, as if the impact hit material that was viscous and could flow somewhat.

The overview map below gives some context, but only some.
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Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on December 20, 2022 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows a strange terrain of craters and mounds, with all the mounds having pits within them like volcanic calderas. In between the surface has a two-toned stippled look, as if two different materials are in the process of mixing.

My immediate impression was that of the bubbly surface of a vat of tomato sauce simmering. Or maybe the vile mixture created by the witches in Shakespeare’s Macbeth, which as they mix they chant:

First witch:
Round about the cauldron go;
In the poison’d entrails throw.
Toad, that under cold stone
Days and nights has thirty-one
Swelter’d venom sleeping got,
Boil thou first i’ the charmed pot.

ALL:
Double, double toil and trouble;
Fire burn, and cauldron bubble.

Of course, this is not a vat of witch’s brew or tomato sauce. It is the surface of the planet Mars, but an alien surface nonetheless.
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Cool image time! The picture to the right, rotated, cropped, reduced, and enhanced to post here, was taken on January 27, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), and shows what the scientists label a “streak-spoke pattern” inside the crater. To my eye, the pattern more resembles hanging draperies, neatly tied near the top and then pulled apart as they descend to the ground.

This photo was a follow-up to a previous picture by MRO on February 4, 2008, more than seven Martian years ago, to see if there had been any identifiable changes in that time. Both images were taken in springtime, and despite the passage of time, the 2023 image shows no obvious changes from the 2008 photo.

What caused this distinct pattern? The first guess would be the wind, except if so shouldn’t there have been some change over seven Martian years?
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Today’s cool image illustrates once again the importance of looking not simply at the picture but at the surrounding larger context in order to understand the Martian features within the photograph.

The photo to the left, cropped, reduced, and sharpened to post here, was taken on January 31, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). The location is at 26 north latitude, so it is in the dry equatorial regions. It shows what appears to be a large Martian flood lava plain, with at least two different flood lava events appearing to flow to the northeast, with the second only partly covering the first.

From this high resolution image it seemed probable that the source of the flow was from the southwest, an assumption that at first glance is strengthened by the overview map below.
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Cool image time. The picture to the right, cropped to post here, was taken on February 2, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), and shows a strangely blobby crater in the northern mid-latitudes where glacial features are frequently found inside craters.

In this case however the glacier seems very confused. As this is in the northern hemisphere, you would expect glacial material to survive on the north-facing southern interior slopes of the crater, where there is year-round less sunlight. The mottled eroded terrain in the south part of the crater floor suggests this. However, the crater also clearly has a terraced glacier on its south-facing northern interior slopes.

Why has the glacial material survived in both places, but not in the center of the crater?

In addition, there is that strange roughly circular feature attached to the south side of the crater. What formed it? Is it a glacier on the plains surrounding the crater? Or are we looking at volcanic material?

This crater is also unique. The crater just to its southwest (partly seen in the cropped image above), is a much more typical glacial-filled mid-latitude crater, its interior material more evenly distributed and its circular rim only slightly distorted.
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Cool image time! The picture to the right, cropped and reduced to post here, was taken on December 24, 2022 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows erosion gullies coming down off a mountain side, just north of a massive cliff that I estimate to be around 2,000 to 3,000 feet high.

Note the north-south-trending cracks. These suggest that this entire half-mile-high cliff face is slumping downward, cracking as it does so. The cracks at the start of the high flat-topped thumb-shaped mesa near the image bottom are especially intriguing. They suggest that this entire mesa might eventually separate and give way.

There is a specific reason this cliff face is slumping, as shown in the overview map below.
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Cool image time! The picture to the right, rotated, cropped, rotated, and sharpened to post here, was taken on November 28, 2022 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). Labeled merely as a “crater with mesa”, it gives us another example of the presence of glacial ice in the mid-latitudes of Mars.

That mesa is what planetary scientists have labeled “concentric crater fill,” a glacial feature found in numerous craters throughout the mid-latitude bands from 30 to 60 degrees latitude. The ground in the terrain surrounding the crater could be also be impregnated with ice, but based on the location as shown in the overview map below, it is just as likely to be lava.

In fact, the location of this particular crater illustrates why concentric crater fill might become the best source of ice for future colonists.
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Scientists have uncovered geological evidence of a past glacier in westernmost end of the giant Martian canyon Valles Marineris, right at the point where it transitions into the complex chaos region dubbed Noctis Labyrinthus. The white dot on the map to the right indicates the location.

The surface feature identified as a “relict glacier” is one of many light-toned deposits (LTDs) found in the region. Typically, LTDs consist mainly of light-colored sulfate salts, but this deposit also shows many of the features of a glacier, including crevasse fields and moraine bands. The glacier is estimated to be 6 kilometers long and up to 4 kilometers wide, with a surface elevation ranging from +1.3 to +1.7 kilometers. This discovery suggests that Mars’ recent history may have been more watery than previously thought, which could have implications for understanding the planet’s habitability.

“What we’ve found is not ice, but a salt deposit with the detailed morphologic features of a glacier. What we think happened here is that salt formed on top of a glacier while preserving the shape of the ice below, down to details like crevasse fields and moraine bands,” said Dr. Pascal Lee, a planetary scientist with the SETI Institute and the Mars Institute, and the lead author of the study. [emphasis mine]

You can read the paper here [pdf]. The research specifically suggests that near surface water ice in the dry equatorial regions of Mars could have been there much more recently that previously believed. It also suggests, by the rarity of this discovery, that there is likely almost no near surface ice in the equatorial regions, at present.

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Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on January 2, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It is once again a terrain sample image, taken not for any specific research but to fill a gap in the schedule so as to maintain the camera’s proper temperature.

What this picture shows is that even though Mars has a thin atmosphere that produces dust devils, the propagation of dust devils is not uniform across the red planet’s surface. In this picture there are a lot of devil tracks, going in many different directions. Yet few of the many cool images I post from MRO show this number of tracks. In many cases the ground might not be agreeable to leaving tracks, but that cannot be the entire explanation.
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Cool image time! The picture to the right, cropped and sharpened to post here, was taken on February 3, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows a number of crater splats of varying sizes. If you look at the full image, you will find several even bigger splats to the north of the one in the picture to the right. You will also see many more similar-sized crater splats to the south.

I cannot provide any confident explanation about what caused these splats, other than to assume that most here are secondary impacts from ejecta thrown out by a larger impact somewhere nearby. I also assume all these small impacts occurred at the same time because they all appear to have hit the ground when it had the same thick liquid consistency, a condition that was probably temporary. Note for example how many of the other craters in the full image do not have this same splattered look.
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