Tag: geology

Cool image time! The photo to the right, cropped and reduced to post here, was taken on March 4, 2021 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows an eroded mound that appears to have flows coming off its north and south slopes that fill the surrounding low spots, including half-covering a nearby crater.

The science team for MRO’s high resolution camera chose this picture as their April 28th picture of the day, noting the following:

The objective of this observation is to examine a crater which seems to be in the process of getting covered by flow from a mound. This image, in Protonilus Mensae, may show us characteristics of the covering material: could it be debris-covered glaciers?

Below is a global map of Mars, with this mound’s location in Protonilus Mensae in the northern mid-latitudes indicated by a black cross.
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Today’s cool image to the right, cropped and reduced to post here, is of a crater in the mid-latitudes of Mars’s cratered southern highlands. The picture was taken on January 4, 2021 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), and is actually the only high resolution image ever taken of this crater.

The gullies in the north interior wall of this crater are the reason why this picture was snapped. These gullies are very typical on the pole-facing slopes of mid-latitude Martian craters, and have puzzled scientists since they were first discovered in the late 1990s in images taken by Mars Global Surveyor. Since then, thousands have been found, almost all of which in the 30 to 60 degree mid-latitude bands where glacial features are also found. Most occur on the more shadowed pole-facing interior slopes of the craters, though at higher latitudes they are also found facing the equator.

Since their discovery scientists have puzzled over their cause, which because of their locations favoring colder temperatures suggest some form of seasonal weather factor. The most preferred hypotheses propose some interaction with water ice or dry ice, or are simply dry flows of rocky granular material. None of these hypotheses have been confirmed. Some evidence suggests they are dry flows, no water involved. Other evidence points to the influence of an underground layer of water ice.

The mystery of these gullies is enhanced by by the wider view from MRO’s context camera below, rotated and cropped to post here.
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Cool image time! The photo to the right, cropped and reduced to post here, was taken on April 1, 2021 by the high resolution camera of Mars Reconnaissance Orbiter (MRO). It shows the central portion of the floor of an unnamed 5-mile-wide crater in northeast corner of Hellas Basin, the deepest large depression on Mars.

The latitude is 33 degrees south, where many glacier features have been identified, especially inside craters.

In this case, the cracked and flaked surface of this crater floor suggests what geologists call exfoliation, “the breaking off of thin concentric shells, sheets, scales, plates, and so on.” On Earth exfoliation generally refers to an erosion process seen on rock faces, though you can see it on other types of materials.

In this Martian crater we appear to be seeing the exfoliation of different ice layers, sublimating away at different rates as they are exposed to the Sun. The layers probably suggest different periods on Mars when snow was falling here, causing the glaciers to grow. The sublimation we see now suggest periods when this region was warmer and the ice was shrinking. Whether we are in such a period now is not yet determined by scientists.

Either way, the photo suggests at least two such cycles, though if we could drill down into this material we would likely find evidence of many more.

Below the fold is a global map of Mars, showing the location of this crater with a red cross in Hellas. The regions surrounded by white borders are areas where many glacial features have been found.
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For original images click here and here.

Today’s cool image provides us a glimpse at the carved canyons created when the mid-latitude glaciers on Mars were active in the past and slowly flowing downhill into the section of the northern lowland plains dubbed Acidalia Planitia.

The photo to the right is a mosaic of two images taken by the context camera on Mars Reconnaissance Orbiter and rotated, cropped, and reduced to post here. The mosaic shows a region at the very edge of Acidalia Planitia at latitude 43 degrees north.

Below is a close-up of the area in the white box, taken by MRO’s high resolution camera on February 28, 2021, as well as a global map marking the location of this image at the very edge of the glacier country found in the chaos terrain of Deuteronilus Mensae.
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Cool image time! The photo to the right, cropped and reduced to post here, was taken on April 5, 2021 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), and shows a particularly unusual crater in the southern mid-latitudes on the eastern edge of Hellas Basin.

This region east of Hellas is where scientists have spotted many features that suggest buried glaciers. The terraced material inside this crater, as well as the splattered material surrounding it on three sides, are examples of such glacial material. You can also see similar glacial features, though less pronounced, inside the crater to the north.

The global map of Mars below marks the general location of this crater by a blue cross.
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Cool image time! The photo to the right, rotated, cropped, and reduced to post here, was taken on April 1, 2021 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows the high cliff edge of the Martian north polar ice cap, and was taken as part of the springtime monitoring for the numerous avalanches that fall from the icecap’s steep edge every spring.

This particular cliff is probably about 1,000 feet high. I cannot tell if the image captured any avalanches on the very steep north-facing cliff. What struck me about this image however was the terraced layers so visible on the west-facing scarp. You can clearly count about eleven distinct and thick layers, each forming a wide ledge.

Each layer represents a different climate epoch on Mars when the ice cap was growing, with new snow being deposited.
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Cool image time! The photo to the right, rotated, cropped, and reduced to post here, was taken on January 6, 2021 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows a distinct conelike knob in an area of the northern lowland plains of Mars dubbed Acidalia Mensa.

According to this paper [pdf], this is possibly a mud volcano.

Bright pitted cones are common in the northern plains of Mars and have been documented to occur in numerous locations including Acidalia Planitia. Various interpretations of these features have been
proposed but growing consensus in recent literature has favored mud volcanism as the most likely formation mechanism. Mud volcanoes are provocative targets for exploration because they bring to the surface sedimentary materials otherwise inaccessible by normal surface exploration and can aid in reconstructing the sedimentary history of the northern plains. Also, by sampling fluids and sediments from deep in the Martian crust, mud volcanoes may be among the best places to search for ancient and extant life.

A previous cool image post, “Baby volcanoes on Mars”, showed another example in the same general area of Mars.

Though this conclusion is not yet confirmed, the multi-layered apron that surrounds the cone certainly suggests repeated eruptions of muddy water over time.

Scientists have taken many images of this area and cone using MRO’s context camera. (See this image as and example.) All show a very rough terrain, with cracks, fissures, and many smaller cones and knobs. This particular knob however dominates the landscape as one of the largest features. The aprons around it are darker, and appear to have been overlain on top of the nearby rough ground.

If such cones are mud volcanoes, they represent a geological process that is pretty much unique to Mars. There are some comparable features on Earth, but they are rare and do not match exactly.

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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 on March 6, 2021, and shows a mid-latitude crater in the northern lowland plains of Mars with what appear to be layered glacial features filling its interior.

The theory that scientists presently favor for explaining many of the features we see on Mars is based on many climate cycles caused by the wide swings the planet routinely experiences in its obliquity, or rotational tilt. When that tilt is high, more than 45 degrees, the mid-latitudes are colder than the poles, and water ice sublimates southward to those mid-latitudes to fall as snow and cause active glaciers to form. When that obliquity is low, less than 20 degrees, the mid-latitudes are warmer than the poles and that ice then migrates back north.

Such cycles, which are believed to have occurred many thousands of times in the last few million years, will place many layers on the ground in both the mid-latitudes and at the poles. The layers in this crater hint at this.

The overview map below gives some further context.
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Cool image time! The photo to the right, cropped and reduced to post here, was taken on February 2, 2021 by the high resolution camera on Mars Reconnaissance Orbiter (MRO) and was labeled as “Exhumed Craters Exhibiting Concentric Fill”.

The term “Concentric Fill” is used by planetary scientists to mark glacial-type features frequently found inside craters at latitudes greater than 30 degrees latitude. This crater however is at 22 degrees north latitude, too close normally to the equator to expect a buried glacier inside it. Any ice at such a latitude is expected to be underground and well protected. A debris covered glacier would likely sublimate away, which I think is why the scientists labeled this “exhumed.” Though there are the concentric features near its inside rim as well as covered by the sand dunes on the crater’s floor, they are assuming this is only evidence of past ice, no longer there. This assumption is strengthened by the splattered but eroded nature of the surrounding terrain. Such splats are typical of high latitude impacts in regions with ample buried ice. The eroded nature of this splat however suggests it is very old and has likely lost its ice.

Then again, this is an assumption.
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Every spring for the last seven Martian years scientists have eagerly aimed the high resolution camera on Mars Reconnaissance Orbiter (MRO) at the steep 1,500 to 3,000 foot high scarp at the edge of northern polar ice cap in order to capture images of what is Mars’s most spectacular annual event, the occurrence of tens of thousands springtime avalanches along that scarp.

Well, spring has returned to the northern hemisphere on Mars, and the scientists have begun another monitoring campaign. The photo to the right, cropped to post here, was taken on March 7, 2021 by MRO. It shows a particularly dramatic part of that scarp, a place where the scarp separates two curved alcoves and is thus narrowed down to a ridge about 1,000 feet high.

The nose of the ridge is sloping downward to the northwest, so the horizontal bands on its crest are actually evidence of older and older layers exposed as the elevation drops. The blue and black markings on the left slope are likely evidence of this season’s first avalanches, or might even be avalanches occurring as the picture was snapped! As explained to me by Shane Byrne of the Lunar and Planetary Lab University of Arizona during the last Martian avalanche season,

On Mars half of the images we take in the right season contain an avalanche. There’s one image that has four avalanches going off simultaneously at different parts of the scarp. There must be hundreds to thousands of these events each day.”

The overview map below shows the location of this picture, as well as all the other places the scientists have routinely monitored in the fourteen-plus Earth years since MRO reached Mars orbit.
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Today’s cool image to the right, rotated, cropped, and reduced to post here, was taken in January 2012 by the context camera of Mars Reconnaissance Orbiter (MRO). The location is a small section of the Tartarus mountain range that is cut by the Cerberus Fossae fissures, all located in Elysium Planitia, the large volcanic lava plain that lies between Mars’ big volcanoes. The white cross on the overview map below marks the location of the photo.

I picked this photo because it quickly shows us in one picture many of the typical features one finds in that lava plain.

For example, the distinct fissure that cuts across the mountains near the top of the picture is the northernmost large fissure of Cerberus Fossae. In my initial post on Cerberus I mistaken thought its large and many hundreds of miles-long fissures might be evidence of underground lava tubes. Since then I have learned while the depressions may signal underground voids, they are not a lava tubes but graben, cracks formed by the movement of the terrain on each side. The cracks opened when past volcanic activity caused the ground to swell upward, stretching and splitting it.

The dark splotch in the flat area just south of the fissure remains me of the maculae found in these lava plains to the west of Olympus Mons, splotches that for still undetermined reasons dust devils like to congregate, blowing off the red dust so that the dark basalt lava becomes visible. No high resolution image of this spot has yet been taken, so this is a pure guess on my part.

The mountains near the bottom of the photo illustrate the ancient lava flood that inundated these mountain peaks. The white box shows the area covered by the recent MRO high resolution image that I include below.
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