Tag: geology

Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on January 27, 2025 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows the terraced layers descending down a 7,000-foot-high ridgeline within Hebes Chasma, one of several enclosed chasms that are found to the north of Mars’s largest canyon system, Valles Marineris.

The white dot on the overview map above marks this location, inside Hebes. The rectangle in the inset indicates the area covered by the picture, which only covers the lower 5,000 feet of this ridge’s southern flank.

The ridgeline might be 7,000 feet high and sixteen miles long, but it is dwarfed by the scale of the chasm within which it sits. From the rim to the floor of Hebes is a 23,000 foot drop, comparable to the general heights of the Himalaya Mountains. Furthermore, this ridge is not the highest peak within Hebes. To the west is the much larger mesa dubbed Hebes Mensa, 11,000 feet high and 55 miles long.

The terraces indicate the cyclical and complex geological history of Mars. Each probably represents a major volcanic eruption, laying down a new bed of flood lava. With time, something caused Hebes Chasm to get excavated, exposing this ridge and these layers.

The excavation process itself remains unclear. Some scientists think the entire Valles Marineris canyon was created by catastrophic floods of liquid water. Others posit the possibility of underground ice aquifers that sublimated away, causing the surface to sink, eroded further by wind. Neither theory is proven, though the former is generally favored by scientists.

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Cool image time! The picture to the right, cropped, reduced, and sharpened to post here, was taken on January 24, 2025 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). Labeled simply as a “terrain sample,” it was likely taken not as part of any specific research request but to fill a gap in the schedule in order to maintain the camera’s proper temperature.

In this case the camera team got something quite intriguing. The entire terrain is reminiscent of stucco found on the outside walls of southwest homes. What makes even more intriguing is that the stucco appears to be material that has covered the terrain, based on the two craters that appear half-buried by it. Moreover, this picture only captures a small portion of this landscape, which extends like this over an area approximately 40 miles squared.

What caused this strange terrain? As always, the overview map below provides a clue, though no firm answers.
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Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on January 27, 2025 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). Labeled simply as a “terrain sample,” it was likely taken not as part of any specific research project but to fill a gap in the schedule in order to maintain the camera’s proper temperature.

Whenever the camera team needs to do this, they try to find an interesting object to photograph, and often succeed. In this case they focused on the geology to the right. I suspect that at first glance my readers will have trouble deciphering what they are looking at. Let me elucidate: This this a 2.5-mile-wide canyon, about 1,000 feet deep, that is bisected by a ridge about 500 feet high.

On the sunlight walls of this canyon you can see boulders and debris, with material gathered on the canyon floor. The smoothness of the floor suggests also that a lot of Martian dust, likely volcanic ash, has become trapped there over the eons.
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Cool image time! The picture to the right cropped, reduced, and sharpened to post here, was taken on January 29, 2025 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). I have also rotated it so north is up. Labeled simply as a “terrain sample,” it was likely taken not as part of any specific research request but to fill a gap in the schedule in order to maintain the camera’s proper temperature.

In this case the timing allowed the camera team to capture this breath-taking picture of these graceful arching dunes sitting in what is likely the near-surface ice sheet that covers much of the red planet’s high latitudes. That sheet is not pure ice, but a complex mixture of ice, dirt, dust, and sand, covered during the winter by a thin mantle of dry ice.

The isolated dunes appear to be ridges sticking up from that flat terrain, but this impression is probably incorrect, based on the location.
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Cool picture time! The photo to the right, cropped, reduced, and sharpened to post here, was taken on September 30, 2024 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). Labeled simply as a “terrain sample,” it was most likely taken not as part of any specific research project but to fill a gap in the schedule in order to maintain the camera’s temperature.

The image is fascinating nonetheless, as the landscape is typically alien for Mars. What caused the many random ridges and knobs? Why are there oblong areas that are smooth and have no ridges? And why is there dark material inside that crater that appears to have been blown out to the northeast? If you click on the image to see the full image, not all the craters look this way. One has a similar dark feature, but others are as bland as the entire terrain.

The overview map below only increases these mysteries, even if it does provide some further data.
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Cool image time! The picture above, rotated, reduced, and sharpened to post here, was taken on September 2, 2024 by the high resolution camera on Mars Reconnaissance Orbiter (MRO).

The tiny white dot near the lower center of the overview map below marks the location, on the northern wall of the smaller parallel canyon to the much larger part of Valles Marineris dubbed Coprates Canyon.

The scientists label this a “slope deposit.” What I see is a dust glacier flowing down hill in that long hollow (indicated by the arrows), with the ripple dunes actually acting almost like waves. Nor is this description unreasonable. On Mars the dust will gather in the hollows of these slopes and over time, with no rain and little wind to disturb them, will begin to flow down much like a glacier.

In this case, the descent is gigantic, considering the size of Valles Marineris. From the top to bottom of this image the elevation drop is about 14,000 feet over a distance of 11 miles.

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Cool image time! The picture above, reduced and rotated to place north to the left, was taken on November 5, 2024 by the high resolution camera on Mars Reconnaissance Orbiter (MRO).

The science team labeled it “Stepped Features in Tartarus Skopulus”. The white dot on the overview map to the right marks the location, right at the equator on the northern edge of the Medusae Fossae Formation, the largest volcanic ash field on Mars, about the size of the subcontinent of India. As I wrote in a post in 2024:

It is believed that most of the planet’s dust comes from this ash field. It is also evident that the ash is a leftover from the time period more than a billion years ago when the giant volcanoes that surround this field were erupting regularly. The eruptions laid down vast flood lava plains that coat the surface for thousands of miles.

The ash either came from the eruptions themselves, or was created as the thin Martian wind eroded those flood lava plains, slowly stripping ash from the top. The ash then gathered within the black-outlined regions on the map.

In that 2024 post the cool image showed another location on the north edge of Medusae. In that case the prevailing wind had carved long parallel ridges as it pulled ash from the field.

Here, the wind appears to play no part, or if it did, it produced a very different terrain. At first glance it appears the stepped terraces formed as the ash field began to slide downhill to the north, spreading to crack along the curved lines. The inset especially suggests this explanation.

A closer look instead suggests these terraces each represent a different layer of ash placed down by a sequence of eruptions. Over time the prevailing winds, which here appear to generally blow to the south, stripped off the top of each layer, creating this stair-step landscape.

I however have no guess as to why the terraces are curved. Regardless, it is all strange, but quite beautiful in its own way.

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Cool image time! The picture to the right, cropped, reduced, and sharpened to post here, was taken on October 25, 2024 by the high resolution camera on Mars Reconnaissance Orbiter (MRO).

The science team labels this a “layered feature,” which is appropriately vague in order to not prematurely push a conclusion that is not yet proven. Extensive orbital imagery and data however strongly suggests the layers inside this crater are glacial in nature, each layer laid down during Mars’ many thousands of climate cycles as the planet’s rotational tilt swung back and forth from 11 degrees to 60 degrees. According to the most popular theory today, when that tilt was high, the mid-latitudes (where this 3,000-foot-wide unnamed crater is located) were actually colder than the planet’s poles. The water ice at the icecaps would then migrate from the poles to the mid-latitudes, causing the glaciers to grow.

When the tilt was low the process would reverse, with the mid-latitudes now warmer than the poles, causing the glaciers to shrink. The wedding cake nature of these layers is likely because, over time, Mars has steadily lost its total budget of water to space, so with each cycle the glacier could not grow as much.

Though many such glacial-filled craters have been found in the mid-latitudes, reinforcing these theories, the location of this crater is even more interesting.
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Cool image time! The picture to the right, cropped, reduced, and sharpened to post here, was taken on October 31, 2024 by the high resolution camera on Mars Reconnaissance Orbiter (MRO).

The science team labels this “Impact Ejecta with Marginal Pits,” though even on the full image I am not sure what the impact ejecta is. The pits themselves appear to have formed when near-surface ice sublimated away during the summer months. The location is at 59 degrees north latitude, deep within the Martian northern lowland plains. Since orbital data suggests much of those plains at this latitude has an ice table of some thickness near the surface, it is very reasonable to assume these pits formed when summer sunlight heated that ice, turning it to gas which eventually pushed out to form the pits.

But what about the impact ejecta? Where is it? And where is the crater from that impact?
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Glacier country in the northern mid-latitudes of Mars

Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on November 4, 2024 by the high resolution camera on Mars Reconnaissance Orbiter (MRO).

The science team labels the features in the lowland below the mesas “ribbed terrain.” To me it looks like peeling paint. What it is however is glacial material, a lot of it. The white dot on the overview map above marks the location, in the middle of the 2,000-mile-long mid-latitude strip in the northern hemisphere I label glacier country, because practically every high resolution image of this region shows glacial features like those on the right.

The mesa with the crater on top gives a clue on the geological history. This is chaos terrain, a region of random mesas cross-crossed with canyons and wide low plains, as shown in the inset. The entire surface was probably once at the same height as the top of that mesa with the crater. Over time glacial ice eroded away along fault lines. As that sublimation process continued, the fault lines widened to became canyons, then the flat plains, with the isolated mesas remaining between.

The “peeling paint” terrain is likely a layer of ice that is in the process of sublimating away.

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Cool image time! The picture to the right, cropped to post here, was taken on September 26, 2024 by the high resolution camera on Mars Reconnaissance Orbiter (MRO).

I picked this image out of the MRO archive because of the many dust devil tracts that cut across the entire image, traveling in all directions with no apparent pattern. I also picked it because those tracks also cut across the many parallel small ridges that appear to be ancient ripple dunes that have since hardened into rock. What makes this landscape puzzling is how those dust devil tracks leave no evidence on those ridges. It is as if the ancient ripple dunes were laid down after the very recent dust devil tracks, even though that is chronologically entirely backwards.

Apparently, the dust devil tracks form because the devil only disturbs the dust that coats the flat low ground between the ridges. The ridges themselves are hard, and thus the devils, produced in Mars’ extremely thin atmosphere, can leave no mark.
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Cool image time! The picture to the right, cropped, reduced, and sharpened to post here, was taken on August 8, 2024 by the high resolution camera on Mars Reconnaissance Orbiter (MRO).

The picture’s research focus is the gullies, which the scientists’ describe as “perched pole-facing gullies on ancient crater wall.” Perched means the start and end of each gully is on that crater wall, linked neither to the top or bottom of the wall itself. That the gully starts below the top means whatever caused it came from within the wall itself, not from the plateau above. That it ends before the crater floor means the process that cut the gully out was not powerful enough to reach the bottom.

That the gullies are on the interior north wall of this unnamed 25-mile-wide crater means they get less sunlight year round, something that must play a part in causing the gullies.
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Cool image time! The picture to the right, cropped, reduced, and sharpened to post here, was taken on August 4, 2024 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It is labeled as a “terrain sample,” so it likely was taken not as part of any specific research project but to fill a gap in the schedule in order to maintain the camera’s proper temperature.

The picture shows a flat rippled plain with a handful of very small thin ridges, oriented 90 degrees from the smaller ripples and sticking up a few feet above them.

The rough surface of the small ripples suggest these are dunes of sand that have hardened into rock. The thin larger ridges suggest an underlying topography buried by the sand. The dunes however might not be dunes at all, as indicated by their location.
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Cool image time! The picture to the right, cropped, reduced, and sharpened to post here, was taken on September 1, 2024 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows what the scientists label “a fracture with clays.”

This canyon is about a mile and a half wide, with the floor ranging from 800 to 1,100 feet to the rim. It was not formed initially by any ice or water flow, but by a spreading of the crust, forcing cracks to form that might have later been modified by wind, ice, or water. The presence of clays in this canyon strengthens that later ice/water modification, as clays require water to form.

The streaks on the northern wall are slope streaks, an unexplained phenomenon unique to Mars. While at first glance they look like avalanches, they have no debris piles at their base, and do nothing to change the topography. In fact, streaks can sometimes go uphill for short distances, following the surface. They happen randomly throughout the year, and fade with time.

It is believed their cause is related to dust avalanches, but this is only one of a number of theories that attempt to explain them. None is entirely satisfactory.
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