Mars Reconnaissance Orbiter (MRO)
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PSP_003639_1345_RED_browse-01.jpgDebris Apron South of Euripus Mons (extra-detail mgnf - possible natural colors; elab. Lunexit)53 visiteA closer view of the upper portion of the image (see here), reveals that rough sharp scalloped ridges are particularly prominent.
This scalloping may have resulted from sublimation of ice below the surface.MareKromium
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PSP_003639_1345_RED_browse-02.jpgDebris Apron South of Euripus Mons (extra-detail mgnf - possible natural colors; elab. NASA)53 visiteAt full resolution, Polygonal Features can be observed (see here), which are characteristic of Periglacial Terrains. These polygons form by the contraction and expansion of the ground due to freezing and thawing of ice just below the surface during seasonal changes.
All of these features provides evidence that ice was or is present just below the surface at this location. This apron is not pockmarked with craters, suggesting it is relatively young in age.MareKromium
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PSP_003647_1745_RED_browse-00.jpgCanditate Cavern Entrance (CTX Frame - Absolute Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)85 visiteThis image shows a very dark spot on an otherwise relatively bright dusty Lava Plain to the North-East of Arsia Mons, one of the four giant Tharsis volcanoes.
This is NOT an Impact Crater as it lacks a Raised Rim or Ejecta Blanket. What's amazing is that we cannot see any detail in the shadow. The HiRISE camera is very sensitive and we can see details in almost any shadow on Mars, but not here.
We also cannot see the deep walls of the Pit. The best interpretation is that this is a Collapse Pit into a Cavern or at least a pit with Overhanging Walls. We cannot see the Walls because they are either perfectly vertical and extremely dark or, more likely, overhanging.
The Pit must be very deep to prevent detection of the floor from skylight, which is quite bright on Mars.MareKromium
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PSP_003655_1885_RED_abrowse-00.jpgBeautiful Windworks (Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga)116 visiteThis image shows a portion of a Mound partly filling an Unnamed Impact Crater.
The Impact Crater is a little more than 60 Km (approx. 37 miles) across while the Central Mound is about half that figure (since it extends itself well beyond the area shown here).
Large Impact Craters typically have Central Peaks which surge upwards in the last stage of crater formation. However, Mounds like this represent a different process: Sedimentary Infill of the Crater AFTER its formation.
At this site, the Mound appears to be Layered. Step-forming Layers crop out throughout the center of the image. This indicates that the Mound material was deposited in a series of events, likely the same process repeating many times. Many processes could form Layers like this, including Aeolian Deposition, Volcanic Ash or Lake Sedimentation.
Unfortunately, fine details of the Layers are obscured by Dust which covers most of the Mound. Avalanches in this Dust Layer are responsible for the many small Dark Streaks that can be seen in the image.
Anyway, however the material in the Mound formed, it was once even more extensive, perhaps entirely filling the Crater. Wind Erosion has caused the formation of these elongated shapes (called "Yardangs").MareKromium
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PSP_003656_2015_RED_abrowse-PCF-LXTT.jpgLayering in Becquerel Crater (Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)80 visiteBecquerel Crater is one of several impact craters in Arabia Terra that have light-toned layered deposits along the crater floor. The light-toned deposits are particularly striking to look at in this HiRISE image because they are stacked together to produce a thick sequence of layered beds. The layers appear to be only a few meters thick and show little variations in thickness.
On Earth, layered beds with these characteristics are typically formed in water environments, although aeolian (wind blown) deposition on Mars through a cyclic process is also possible. Volcanic eruptions would not be expected to produce ash or volcanic flows of such regular thickness, and there are no nearby volcanic vents.
Some of the layering in the image appears dark, probably due to deposition of basalt sand along flatter surfaces rather than any compositional variations in the layer beds themselves. Faults can also be seen displacing portions of the layered beds. The surface of the light-toned deposit is not smooth but instead appears disrupted into polygonal cracks and blocks.
Relative to most surfaces on Mars, there are almost no impact craters seen in this image. This is not due to a young age but rather to the friable (easily eroded) nature of the light-toned layered deposits that enable wind easily to erode the unit, thereby removing any impact craters. Evidence of erosion by the wind is most apparent in the bottom of the image where linear ridges most likely formed by wind scouring away material in a North-South direction and creating the ridges.
MareKromium
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PSP_003695_1250_RED_abrowse-00.jpgUnnamed Southern Crater with Large Dunefield and DD Streaks (CTX Frame - Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)61 visitePSP_003695_1250 shows a Southern Hemisphere crater with gullies, dunes, periglacial modification, bright rock deposits and Dust Devil Tracks.
Although these features are all common on Mars, there are not many places that have all of them together as viewed here.
The gullies seen at the top of the image are likely caused by wet debris flows. They have deposits of multiple ages. The gully on the left has bright deposits that have been modified by periglacial processes overlain by slightly darker deposits that have not been modified. Periglacial processes, such as seasonal freezing and thawing, are responsible for the polygonal fractures seen near the gullies and around the image.
The dark material in the center of the image is a dune field.
There are several different sizes and orientations of dunes — these different orientations indicate that the dominant winds in the area have changed throughout time.
The dark streaks that criss-cross on the outskirts of the dune field are DDT.
DDs are spinning cells of dust that travel across the Martian Surface. As they move, they pick up and redeposit particles, as well as disturbing dust on the surface.
They are responsible elsewhere on Mars for removing dust from the solar panels of the Mars Exploration Rovers Spirit and Opportunity, which has helped to extend their missions way beyond the 90-day primary mission.
Note that the black rectangular feature near the top right of the image is a data gap resulting from data transmission problems; it is not a real feature. MareKromium
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PSP_003695_1250_RED_abrowse-01.jpgUnnamed Southern Crater with Large Dunefield and DD Streaks (EDM - Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)62 visiteThis EDM, approx. 750 mt across, shows Dust Devil Tracks near the South-West edge of the Dunefield. The bright protruding rocks on the lower side of the image are either being exposed or being buried, as the Dunes migrate. MareKromium
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PSP_003710_1530_RED_browse~0.jpgHolden Crater's Rim (Natural Colors; credits: Lunexit)54 visiteThe formation of the approximately 150 Km diameter Holden Crater interrupted the Northward flowing Uzboi Vallis Channel System. Relief associated with the Rim of Holden effectively blocked the Channel.
HiRISE image PSP_003710_1530 covers the portion of Holden Crater's Rim where it was overtopped by water that had backed up in Uzboi Vallis to the South. Water flowing over the Rim in multiple locations eventually focused on a single Channel that then cut deeply into the Rim.
After the impounded water drained into the Crater, the steep Wall on the East side of the main Channel collapsed in a Landslide that remains visible along the Floor.
Several Outcroppings of variably bright material are visible in the scar produced by the Slide. MareKromium
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PSP_003734_0950_RED_abrowse-00.jpgSouthern Spring's Features (CTX Frame - Absolute Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)82 visitenessun commentoMareKromium
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PSP_003734_0950_RED_abrowse-01.jpgSouthern Spring's Features (EDM - Absolute Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)79 visitenessun commentoMareKromium
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PSP_003830_1740_RED_abrowse-00.jpgLayered Bedrock in Candor Chasma (CTX Frame - Absolute Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)115 visiteThis image shows an area of Layered Deposits in Candor Chasma. Here, Sheets and Dunes of dark-toned Sand cover the light-toned, Layered Bedrock. Accumulations of dark Sand accentuate bedding within the light-toned Bedrock, giving some areas a sort of "zebra-striped" pattern.
In the left side of the scene, the Bedrock has been eroded into steep, craggy Cliffs. Some sections of these Cliffs are covered by triangular-shaped Debris Fans that are intermediate in color between the dark-toned Sand and light-toned Bedrock. These Fans may contain a mix of light-toned Bedrock that has crumbled away from the surrounding Cliffs as well as wind-blown Sand and Dust.
The Surfaces of some Fans are dissected by Gullies, which most likely formed through Dry Avalanching. The bottoms of the Gully Channels are often darker in tone than the surrounding Fan Surface. This may be due to accumulations of wind-blown Sand in the Gully Floor.MareKromium
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PSP_003830_1740_RED_abrowse-01.jpgLayered Bedrock in Candor Chasma (EDM n.1 - Absolute and Enhanced Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)122 visiteThis EDM shows a clear example of a "Gullied Fan", taken from the left (Northern) portion of the whole scene.MareKromium
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