Tag: Mars

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Cool image time! The picture to the right, cropped to post here, was taken on December 29, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows strange spidery formations on the rim of a 17-mile-wide crater about 500 miles from the south pole of Mars.

Scientists think these spider features are formed due to the seasonal cycle on Mars. In the winter at the poles the carbon dioxide in the atmosphere falls as snow in the polar regions, creating a thin dry ice mantle that covers everything. When spring arrives, sunlight goes through the clear mantle to heat its base, causing that dry ice to sublimate into gas that is trapped below the mantle. Eventually that mantle cracks at a weak point and the gas escapes, spewing dark dust on its top. By summer the mantle is entirely gone, and the black splotches disappear as they blend back into the same colored ground.

At the south pole the ground appears to be firmer and more structurally sound than at the north pole. The trapped gas appears to travel upward along the same tributary paths to the same escape points each year, thus carving these spidery features that are permanent features.
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Cool image time! The picture to the right, cropped to post here, was taken on December 20, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows what the science team labels as “Dunes with Blotches.”

The blotches, or as I call them splotches, are the round dark patches on dunes themselves. Though their darkness is reminiscent of the dark patches that appear as spider features in the south polar regions of Mars, there are problems linking the two. The spiders form when the winter mantle of dry ice that falls as snow begins to weaken when the Sun reappears in the spring. Sunlight travels through the clear dry ice to warm the base of the mantle, causing it to sublimate into carbon dioxide gas. That gas however is trapped at the base, and only escapes when the thin mantle cracks at weak points. As the gas puffs out it carries with it dust, which leaves dark patches on the surface that disappear when the mantle disappears entirely by summer.

In the southern hemisphere at the poles the ground is somewhat stable, so the trapped gas appears to travel along the same paths each year to the same weak spots. This in turn causes it to carve spidery patterns in the ground, like river tributaries, except here the tributaries of gas flow uphill to their escape point. At the north pole the ground is not as stable. Instead we have many dunes, so that the dry ice mantle sublimates away at different places each year. There is no chance to form such spider patterns over time.

Making these splotches more puzzling is the season. This picture was taken in the winter, at a time one would think no dry ice is sublimating away.
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Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on September 27, 2023 by the high resolution camera on Mars Reconniassance Orbiter (MRO). Dubbed a “terrain sample” by the science team, this picture was likely chosen not as part of any specific research project but to fill a gap in the camera schedule so as to maintain that camera’s proper temperature.

When the team needs to do this they try to pick interesting targets. In this case the location is the region of many many parallel north-south fissures that extend for more than 800 miles south of the giant but relative flat shield volcano Alba Mons. These fissures are grabens, cracks formed when underground pressure pushed the ground up and caused it to spread and crack.

What attracted me to this picture is the ridgeline. It struck me as a wonderful place to hike. I have even indicated in red the likely route any trail-maker would pick to go from the valley below up onto the ridge, and then along its knifelike edge to the south. The height of the cliff down to the east valley averages about six hundred feet, guaranteeing beautiful scenery the entire length.
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Cool image time! The picture to the right, cropped, reduced, and sharpened to post here, was taken on December 21, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). The science team labeled it a “fresh crater”, but that description I think is misleading, as it implies a recent impact.

The crater does not look like a fresh impact crater to me. Such things on Mars usually appear very dark, as the impact dredges up dark material. This crater is not dark. More significant is the crater itself. The small 300-foot-wide inner crater, surrounded by a circular plateau and all sitting inside the larger 1,200-foot-wide crater is completely unique compared to any impact crater I have ever seen. Impacts in soft material, such as ice-impregnated ground, can cause concentric ripple rings, but they don’t look like this.

Instead, this crater more resembles the caldera of a volcano, where subsequent eruptions can produce overlapping depressions at the volcano peak. (See for example this picture of Olympus Mons.)

Moreover, the crater sits on top of a peak approximately 300 feet high. While impacts in ice-impregnated ground on Mars can produce splash aprons as seen here, the crater usually sits at about the same elevation as the surrounding terrain, not at the top of a peak. This peak suggests the apron was forned not by a splash but repeated flows coming down from the top.
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Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on September 14, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows a small section of the Cerberus Fossae cracks, a parallel series of cracks that stretch more than 700 miles across the volcanic plains of Mars.

These cracks formed when the ground spread apart, creating a void in which the surface collapsed. You can see this process illustrated quite clearly by the crater in the lower right, as indicated by the arrow. The crater had existed prior to the crack. When the ground split and collapsed, only the northeast quadrant of the crater was destroyed.

These cracks might also have been the source of Mars’ most recent large volcanic event, as shown by the overview map below.
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Cool image time! The two pictures above, both rotated, cropped, reduced, and enhanced to match and to post here, were taken by the high resolution camera on Mars Reconnaissance Orbiter (MRO) sixteen years apart. The first, on the left, was taken on February 23, 2007, while the second, on the right, was taken on November 1, 2023.

What drew me to both images was the label for the second: “Dune Change in Arabia Region Crater.” To find out if this image had revealed any changes in the dunes I went back and found the earliest MRO picture of this location, and sized and enhanced the dunes in both to match.

Do you see any changes? I don’t. However, that really means nothing. These are not the highest resolution versions that MRO obtains, and a very careful comparison of those best images might detect more subtle changes than our eyes can perceive in the versions above. Also, there might be brightness changes that require careful software analysis.

The white dot on the overview map to the right marks the location, in Arabia Terra, the largest transition region on Mars between the northern lowland plains and the southern cratered highlands. The inset shows the half filled crater in which these dunes sit. The grayed area on the floor of the crater marks the entire dune field, extending eastward to the crater rim from this one spot, indicated by the black dot.

It is likely that the dust is blown into this crater and gets trapped there. Whether the dunes move or change is not clear, though if they do the changes are small, even after almost two decades. Instead, the two pictures suggest these dunes have hardened into a form of sandstone, that can be eroded over time by the wind, but only very very slowly.

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Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on September 13, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO).

The science team labels this “Friable Outcrops in Aeolis Dorsa.” What we are looking at is the northeasternmost tip of a 30-mile long plateau that marks the northern edge of Mars southern cratered highlands. For most of its length the top of that plateau is relatively smooth, broken by some vague surface features and a few scattered craters (suggesting it is relatively young). However, as you approach the plateau’s edges and especially that northeastern tip the surface begins to break up into the rough terrain shown to the right. It appears that the prevailing winds from the north are scouring the soft topsoil here and causing it to wear away, leaving behind those innumerable small ridges, almost all of which are oriented from north-to-south.

But why is the topsoil here soft and so easily scoured?
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Cool image time! The picture to the right, cropped and reduced to post here, was taken on August 27, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It was featured by MRO’s science team yesterday, in which Shane Byrne of the Lunar and Planetary Lab University of Arizona wrote the following:

River beds often get filled with gravel and the surrounding terrain is often built up of fine-grained mud from river overflows. The gravely river bottom and the fine-grained surroundings can lead to a strange phenomenon that geologists call inverted channels. After the river disappears, the fine-grained surroundings can be easily eroded away leaving the gravely river bed as a high-standing ridge.

These ridges show the location of the old river beds in Mars’ distant past. The angle at which the ridges join together indicate that these rivers flowed from top-right to bottom-left (i.e. southwest).

The picture above is a mosaic produced from the global survey taken by MRO’s lower resolution context camera. It gives us a fuller picture of this river system, with the rectangle showing the small area covered by the photo on the right. Overall this ancient and extinct river of ridges travels more than thirty miles downhill from the northeast to the southwest.
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This cool image poses a mystery that might be important for future colonists. The picture to the right, cropped, reduced, and sharpened to post here, was taken on October 23, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO).

The science team merely labels this vaguely as simply “landforms.” What it appears to be is an ancient flow of mudlike material or a delta that moved from the west to the east. Its nature is even more evident in the full picture. The top of the delta however appears corroded and old, with a number of craters on top suggesting it has been here for a long time.

Its mudlike appearances suggests water was involved, possibly as ice impregnated within the soil. However, the location says no, unless this occurred so long ago that the entire climate of Mars and this region was vastly different. And in fact, it might have been.
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Cool image time! The picture to the right, cropped, reduced, and sharpened to post here, was taken on September 17, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows two significant features, both of which suggest the action of near-surface water ice to change to surface of Mars.

First are the gullies on the cliff wall, which also happens to be the interior slope of a 30-mile-wide crater. Since the first discovery of gullies on Mars, scientists have pondered their origin, with all their hypothesises always pointing to some form of water process. One popular theory [pdf] points to some form of intermittent water flow linked to long term climate cycles caused by the extreme shifts in the red planet’s rotational tilt, from 11 to 60 degrees. Another theory suggests the gullies form from the winter-summer freeze-thaw cycle and the accumulation of frost during winter.

The second feature are the three avalanche debris piles at the base of these gullies. The long extent of each suggests the avalanches flowed more like wet mud than falling rocks. If the ground here was impregnated with ice, than this look makes sense.
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Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on October 21, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO).

The science team labels this “patterned ground.” I see instead a whole range of inexplicable Martian geological features that, while each has been documented previously, each remains puzzling as to its formation process.

First there is the stucco-like peaks of all sizes on the upper left. This surface really looks like it had been wet plaster covered with Saran Wrap that had its peaks pulled up when that wrap was pulled off quickly.

Then there is brain terrain on the right. Always associated with glacier features on Mars, these convolutions are unique to Mars and as yet not entirely understood.

Next there is the circular arc on the middle left. It appears to be the remains of an impact crater now filled partly, but if so why has its northern rim disappeared so completely?

If you look close at the image above as well as the full image, you will find other mysterious features as well.

The location is the white dot on the overview map above. The rectangle in the inset shows the area covered by this picture, part of the floor of an unnamed eighteen-mile-wide and one-mile deep crater. The glacial material that appears to fill its interior as well as the splash apron that surrounds it all suggest the ground here is impregnated with water ice. Located as it is on the western end of the 2,000-mile-long north mid-latitude strip I dub glacier country — where practically every image shows glacial features — this conclusion is not surprising.

In fact, this photo illustrates well the alieness of Mars. We understand glaciers and ice, but on Mars, with its very cold temperatures, one-third Earth gravity, and thin atmosphere, those glaciers and ice are able to do things that we don’t yet understand. Untangling these geological processes will take decades of work, and likely will not be completed until people can walk the Martian surface and study it up close.

And won’t that be fun?

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Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on September 10, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows what the scientists label simply as a “double-rim crater.”

If you look close you might not be unreasonable to call this instead a triple-rim crater, as there appear to be two rings on each side of the highest crater rim.

Multple rings in craters are not rare. We see many on the Moon. Most however are associated with very large impacts, and are an expression of the ripples formed at impact, not unlike the ripples seen when you drop a pebble in water. Unlike water ripples, the ripples formed in rock are impact melt that quickly refreezes, thus capturing those ripples as concentric rings.

In this case, these rings likely signal not freezing rock but freezing ice.
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Cool image time! The picture to the right, cropped, reduced, and sharpened to post here, was taken on September 18, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO).

It shows the very typical surface on a high plateau in Mars’ dry tropical regions. The dunes you see here, in this very small slice, cover a region about 80 miles square, with the prevailing winds appearing to consistently blow from the northeast to the southwest and forming these endless striations.

The dunes are made of volcanic ash, and the size of this particular ash field gives us a sense of the past volcanic activity that once dominated the red planet. Once, the atmosphere was filled with ash, which covered the ground across large regions. In the subsequent eons the thin Martian atmosphere has reshaped and piled that ash into giant mounds hundreds of miles across, with the surface striated as we see here.
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Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on August 31, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), and shows what the science team labels as a “vent near Olympica Fossae.”

The grade within the fissure is downhill to its center. Outside the vent the grade is downhill to the north and south, with the overall grade sloping to the west as well. Note the layers on each side of the depression. Each indicates another volcanic flood event that laid down another layer of lava. At some point this vent either blew up through those layers, or it had remained opened during all those many events, the lava flowing out and acting like water to erode the layers on the north and the south.

As always, the scale of Martian geology is daunting, as shown by the overview map below.
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