| Piú viste - Mars Reconnaissance Orbiter (MRO) |
PSP_005194_1070_RED_browse.jpgFaulting in the South Polar Layered Deposits54 visiteThe scarp shown in this image marks the edge of the Polar Layered Deposits. These layered deposits are a mixture of dust and water-ice. Each layer is thought to record information about the state of the Martian climate at the time of its deposition.
The polar layered deposits were once more extensive, but have been eroded back to their current size. Most of this erosion takes places at inclined scarps (such as this one) which retreat as icy material is ablated away.
Other processes are also operating on these deposits as exemplified by the fault that is visible on the left of the image. Layers appear offset from one side of the fault to another indicating that the layered deposits have been fractured into large blocks that have moved relative to each other. The source of the stress that caused this fracturing is unknown; some possible examples are subsidence of the underlying terrain or perhaps melting of a portion of the base of the ice-sheet.
This particular Region of the Layered Deposits (Ultimi Lingula) contains many examples of this brittle fracture (which is otherwise rare in these Deposits). Another less obvious fault lies near the center of the image at the base of the scarp. This fault does not break through, or even deform, the upper layers which may indicate that the fault occurred when only half the layered deposits had accumulated. These observations point to a history of faulting in this region that at least spans the age range of these Layered Deposits. MareKromium
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PSP_004959_0865_RED_browse.jpgPolygonal Fracturing of South Polar Layered Deposits54 visiteThis image shows the South Polar Layered Deposits, with curving layer outcrops caused by erosion of valleys into the Deposits.
On closer inspection, polygonal (mostly rectangular) fractures are visible, mostly near the center of the image. Polygonal fractures are also observed in the North Polar Layered Deposits, but typically on a much smaller scale.
Here in the South, the fractures cross layer boundaries, while in the North the fractures are usually confined to a single layer.
Therefore, the fractures in the South Polar Layered Deposits formed after the surface was eroded to the configuration seen here, probably due to expansion and contraction of water ice below the surface.MareKromium
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PSP_005419_1380_RED_browse-01.jpgFlow-like Features in Promethei Terra (extra-detail mgnf)54 visiteThe subimage (approx. 390 x 260 meters) shows in detail some of the ridges developed in the slope deposits. Numerous fissures cut through the surface, forming polygons 5 to 10 mt (5,5 to 11 yards) across.
Such well-preserved polygons indicate that the downhill flow had stopped before they formed. Polygonal features similar to these are common in terrestrial periglacial regions such as Antarctica, where ice is present at or near the surface. Antarctica's polygons formed by repeated expansion and contraction of the soil-ice mixture due to seasonal temperature oscillations.MareKromium
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PSP_005419_1380_RED_browse-00.jpgFlow-like Features in Promethei Terra (context frame)54 visiteThis image, part of the south-facing slopes of a massif in Promethei Terra in the Southern Highlands, shows flow-like features (tongue-shaped lobes, parallel ridges) that indicate movement of surface materials downhill and towards the South-West, following the regional slope.
The difference in elevation between the ridge (near the top or northern-most portion of the image) and the valley (to the South) is over 2200 meters (7,200 feet).
These flow-like features are reminiscent of those observed in terrestrial landslides and rock glaciers , in which the downhill movement of rocks and soils is facilitated by an agent (most commonly water in landslides, ice in glaciers) that acts as a lubricant and provides cohesion. Theoretical calculations predict that under current and recent Martian climate conditions, neither water nor ice would be stable near the surface for extended periods of time in this Region.
The temperatures are so low that water would freeze, and then quickly sublime, because the air is very thin and dry. Ice could, though, be stable at present approximately 1 meter (3 feet) or more below the surface.
MareKromium
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PSP_005346_1755_RED_abrowse-01.jpgLow-Order Inverted Streams near Juventae Chasma (extra-detail mgnf)54 visiteThis subimage (approx. 1120 meters across) shows a juncture of 2 of the "Inverted Channels".
It is likely that the water flowed from the left to the right of the scene, because channels usually join rather than divert unless there is an obvious obstacle in the way.
No such obstacle is seen here, but one might have been present when the stream originally flowed.
However, there is no way of knowing this.MareKromium
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PSP_005346_1755_RED_abrowse-00.jpgLow-Order Inverted Streams near Juventae Chasma (context frame - elab. Lunexit)54 visiteThis image shows plains North-West of Juventae Chasma, one of the Martian canyons that are part of the equatorial Valles Marineris System. The two most noticeable features in this scene are craters on mesas (plateaux) and raised, winding ridges. The raised ridges are "Inverted Channels". It is likely that liquid water, either pure or salt water, flowed through these channels. The channels are raised because streams transport sediment as they flow, deposit the heavier sediment on the stream floor, and, eventually fill in once their water supply dwindles. Over time, wind erosion modifies a landscape, and this has played an important role on these plains. It eroded the land around the channels leaving the remnant channels exposed and standing high. The channels did not erode as much since they were more resistant, possibly because the deposited sediment had cemented together.
The craters on mesas are also evidence of active wind erosion: when craters form, they eject material out onto the surrounding landscape.
It appears that several of the craters’ ejecta visible here cemented, making the ejecta more resistant to erosion and leaving them standing high as craters on plateaux.MareKromium
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PSP_005680_1525_RED_abrowse-00.jpgPossible ancient Salt Deposits in Terra Cimmeria (Extremely Saturated and ENhanced Natural Colors - credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)54 visiteThe ancient cratered highlands of the Southern Hemisphere of Mars has an intriguing and complex history as it has been riddled with impact craters and modified by volcanic processes and by the wind.
Additionally, it is one of the most heavily dissected terrains on Mars exhibiting the densest population of Valley Networks: old dried up channels and valleys that may have been formed by surface runoff, the seepage of ground water, or both.
Recently, the Thermal Emission Imaging System (THEMIS) aboard Mars Odyssey, in conjunction with spectral data from the Thermal Emission Spectrometer (TES) aboard the Mars Global Surveyor (MGS) have revealed the presence of a unique surface deposit that may be rich in chloride salts formed from the presence of liquid water. Three separate missions (MGS, MO and MRO) have come to reveal the composition and nature of these unique deposits, which, although they occur as relatively small deposits (less than 25 square Km) are widely distributed in Noachian (most ancient) terrains with fewer occurrences in the Hesperian (middle geologic time) terrains.
The deposit appears to be relatively thin and occurs in low-lying areas. It is also heavily pockmarked and discontinuous, possibly from removal of the material by erosion. Both of these aspects suggest that the deposit is indeed very old.
The presence of such salts is intriguing, and strongly suggests that conditions were favorable for water near or at the surface in the geologic past.
Polygonal cracks can be observed in this image and other images of these deposits elsewhere on Mars (see PSP_003160_1410) and are similar to desiccation cracks (formed from the rapid evaporation and drying of a wet surface) and indicate that these may were more likely deposited at the surface.
However, the volume and duration the water required for these deposits is still being investigated. MareKromium
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PSP_005381_0870_RED_abrowse.jpgSouth Polar Layered Deposits with Surface Modification (possible natural colors - elab. Lunexit)54 visiteThis image shows a scarp exposing the south polar layered deposits (SPLD). The polar layered deposits are thought to record recent climate variations on Mars, similar to ice ages on Earth.
Radar data indicate that the SPLD are ice-rich, with variations in dust contamination likely causing the layering visible here. HiRISE images of the SPLD will help to unravel Mars' climate history, but this image illustrates how this effort is complicated.
The development of surface features, by erosion, deposition, or modification of the surface, makes it difficult to determine the characteristics of the layers themselves. Some of the layers appear wavy, perhaps due to folding, flow, or uneven erosion since they were laid down. Short, branching, often radial channel systems are cut into the surface of the layers in places. These may be related to "spiders," thought to be formed as carbon dioxide gas flows along the surface when the seasonal polar cap sublimates in the spring. Pits and polygonal fractures are visible on the layers as well.
Apparently this exposure of SPLD is relatively old, as these features probably take many years to form. While these features are interesting in their own right, they disturb the SPLD outcrops and make it more difficult to measure the thickness of layers and compare them to other outcrops of SPLD.
MareKromium
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PSP_005343_2170_RED_abrowse-01.jpgScarp with Landslides and Boulder Tracks (extra-detail mgnf)54 visiteThis subimage - or extra-detail mgnf - (approx. 480 meters across) shows boulder tracks from the landslide scar on the left side of the image.
Some boulders can be seen forming trails along the slope at the top part of the subimage, while others can be seen at the end of their trails (...).MareKromium
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PSP_005813_2150_RED_abrowse.jpgUnusual Depression near Elysium Mons (MULTISPECTRUM; elab. Lunexit)54 visiteThis unusual depression and the associated concentric rings are situated within an area thought to have been deposited as a mud flow. Due to the lack of a distinctive, raised rim or other impact-related features, this crater is thought to have formed by the loss of material below the surface and subsequent collapse, rather than by an impact from space.
The exact mechanism for the loss of material is not fully understood, although the missing material was likely water in some form. This feature is near a large volcano, so perhaps there were explosive magma-water interactions that violently removed the water and some magma, followed by surface collapse. Or, less violently, there could have been simple melting of subsurface ice and then collapse of the surface into the resulting void. The rays emanating from the depression suggest some amount of violence before the surface collapse that sprayed material far from the depression.
Some aspects of this and other, nearby features are similar to the collapse pits associated with Grímsvötn volcano in Iceland, which erupts beneath an ice-cap. However, there are no rays formed during the eruptions at Grímsvötn.
MareKromium
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PSP_005788_1035_RED_abrowse.jpgRepeated Erosion and Deposition in the SPLD (MULTISPECTRUM; credits: Lunexit)54 visiteThis image of the SPLD shows evidence of multiple episodes of deposition and erosion near their base.
The SPLD, like the North Polar Layered Deposits (NPLD), are thought to contain a record of global climate changes on Mars. The surface of the outcrop shown here slopes generally toward the right. The layering is cut off by deposits that partly fill two broad valleys that were previously cut into the SPLD, probably by wind erosion. These more recent deposits appear to cover the flatter, upper part of the SPLD, and have also been eroded to expose layering with them.MareKromium
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PSP_006477_1745_RED_abrowse-01.jpgDD Tracks in Southern Schiaparelli Basin (extra-detail mgnf - False Colors; credits: Lunexit)54 visiteThis observation shows a Region near the Martian Equator that is a perfect tablet for the scribblings of Dust-Devils. This Region is made up of dark bedrock that is thinly blanketed by bright dust.
Dark tracks form when Dust-Devils scour the surface, exposing the darker substrate. The tracks tend to cluster together, as Dust-Devils repeatedly form over terrain that has been previously scoured and is consequently darker and warmer than the surrounding surface.
Once lofted by a Dust-Devil, the fine dust can be transported great distances before it settles again onto the surface.MareKromium
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