| Ultimi arrivi - Mars Reconnaissance Orbiter (MRO) |
PSP_003639_1345_RED_browse-02.jpgDebris Apron South of Euripus Mons (extra-detail mgnf - possible natural colors; elab. NASA)55 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.MareKromiumSet 27, 2007
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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.MareKromiumSet 20, 2007
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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. MareKromiumSet 20, 2007
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PSP_005155_1030_RED_browse.jpgExposure of South Polar Layered Deposits54 visiteA complex geologic history is on display in this image of the South 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 original stack of layered ice has eroded to produce a scarp that exposes the internal layers. Smooth material was then deposited to cover this scarp before being in turn eroded. Deposition on top of an eroded surface like this produces what geologists call an "unconformity in the stratigraphic record". Remnants of this smooth material can be seen on the left of the image and draping the layered scarp near the image center.
Although it looks, at first glance, like this material has flowed down the scarp, that is unlikely to have happened. The extremely cold temperatures at the Martian Poles mean that ice in general does not flow like we see it do here on Earth. There are also no indications of some of the geomorphologic features that flowing ice typically acquires (such as crevasses, compressional ridges or moraines).
MareKromiumSet 20, 2007
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PSP_004765_0940_RED_browse.jpgSouth Pole Residual Cap - Swiss-Cheese Terrain Monitoring (Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)54 visiteLike Earth, Mars has concentrations of water ice at both Poles. Because Mars is so much colder however, CO2 ice is deposited at high latitudes in the Winter and is removed in the Spring, analogous to winter-time water ice/snow on Earth.
Around the South Pole there are areas of this CO2 ice that do not disappear every Spring, but rather survive Winter after Winter; this persistent CO2 ice is called the "South Pole Residual Cap". The retention of CO2 ice throughout the year by the Southern Polar Cap is one characteristic that distinguishes it significantly from Mars' North Polar Cap.
As can be seen in this HiRISE image of the South Pole Residual Cap, relatively high-standing smooth material is broken up by circular, oval, and blob-shaped depressions. This patterned terrain is called "Swiss Cheese" terrain.MareKromiumSet 20, 2007
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PSP_004778_0945_RED_browse.jpgSouth Pole Residual Cap - Swiss-Cheese Terrain Monitoring (Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)54 visitenessun commentoMareKromiumSet 20, 2007
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PSP_004917_1080_RED_browse-00.jpgComplex Geology in the South Polar Layered Deposits (context image)54 visiteThis section of the HiRISE image shows a scarp exposing the South Polar Layered Deposits, with illumination from the upper right (scarp slopes toward bottom). The Polar Layered Deposits probably contain a record of relatively recent climate changes on Mars, similar to ice ages on Earth.
The Deposits appear to be composed mostly of water ice, with variations in dust content controlling the erosion of the layers. This image shows that the history of the South Polar Layered Deposits has not been simple accumulation of horizontal layers.MareKromiumSet 20, 2007
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PSP_004917_1080_RED_browse-01.jpgComplex Geology in the South Polar Layered Deposits (extra-detail mgnf)54 visiteAbove and right of center, the layers appear wavy and in places, layers are cut off by other layers. Such structures may be formed by flow or faulting, but in this case they are more likely to be due to erosion of the lower part of the layered deposits before the upper part was laid down over it. For example, deposition may have halted long enough for channels to be eroded into the layered deposits.
When deposition resumes, new layers deposited in the channels could form the structures visible here. However, without more precise topographic information than is currently available, other hypotheses cannot be excluded.MareKromiumSet 20, 2007
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PSP_004673_0935_RED_browse.jpgSouth Pole Residual Cap - Swiss-Cheese Terrain Monitoring (Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)54 visitenessun commentoMareKromiumSet 13, 2007
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PSP_004739_0935_RED_browse.jpgSouth Pole Residual Cap - Swiss-Cheese Terrain Monitoring (Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)54 visitenessun commentoMareKromiumSet 13, 2007
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PSP_004742_0990_RED_browse.jpgGeologic History Recorded in the South Polar Layered Deposits (Extremely Enhanced Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)54 visiteThe Polar Layered Deposits on Mars are thought to be composed of varying amounts of water ice and dust. The variations in the relative amounts of ice and dust are probably caused by recent climate changes on Mars, similar to ice ages on Earth.
This image of the South Polar Layered Deposits shows many layers, some of which are cut off or truncated against other layers (near the center of the image). These truncations are probably due to periods of erosion separating periods of deposition.
After nearly horizontal layers are deposited, they can be partly eroded (perhaps by winds) before more layers are deposited over them. In this image, there is evidence for at least two such episodes of erosion and burial. These types of observations are useful to Mars scientists as they try to unravel the climate history of Mars. MareKromiumSet 13, 2007
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PSP_003948_0935_RED_browse.jpgSouth Pole Residual Cap (Swiss-Cheese Terrain Monitoring)54 visiteLike Earth, Mars has concentrations of water ice at both Poles. Because Mars is so much colder however, Carbon Dioxide (CO2) ice is deposited at high latitudes in the Winter and is removed in the Spring, analogous to winter-time water ice/snow on Earth.
Around the South Pole there are areas of this CO2 ice that do not disappear every Spring, but rather survive Winter after Winter; this persistent CO2 ice is called the "South Pole Residual Cap".
The retention of CO2 ice throughout the year by the Southern Polar Cap is one characteristic that distinguishes it significantly from Mars' North Polar Cap.
As can be seen in this HiRISE image of the south pole residual cap, relatively high-standing smooth material is broken up by circular, oval, and blob-shaped depressions. This patterned terrain is called "swiss cheese" terrain. The high-standing areas are carbon dioxide ice with thicknesses of several to approximately 10 meters. The depressions are thought to be caused by the removal of this carbon dioxide ice by sublimation (the change of a material from solid directly to gas). As most depressions seem to have relatively flat floors, there is likely some layer below, possibly made of water ice, that cannot be as easily removed by sublimation. Complicated shapes arise when neighboring growing depressions intersect.
A previous Mars imaging system, the Mars Orbiter Camera (MOC), took images of the same places on the south pole residual cap every year for many years, and showed that there are annual changes taking place within it. By looking at different sizes and shapes of depressions in an image such as this, and by comparing images of the same place from year to year, the development of "swiss cheese" terrain can be described. The sublimation process may begin as a small, shallow depression in a smooth surface. This depression then deepens until reaching the resistant layer below, and continues to expand laterally in all directions, creating the generally round depressions we see today. Different heights and thicknesses of smooth areas, and different depths of depressions, may indicate that multiple episodes of accumulation and sublimation have occurred.
This is one of the locations previously monitored at lower resolution by MOC. With the high resolution and repeat-imaging capability of HiRISE, we intend to continue monitoring and better measure the amount of expansion of the depressions over one or more Mars years. This is one of the locations specifically targeted by HiRISE for this purpose.
Knowing the amount and rate of carbon dioxide removal can give us a better idea of the role of carbon dioxide (the main component of the Martian atmosphere) in polar and atmospheric processes, of current environmental and climatic conditions, and of how Mars climate may be changing.
In HiRISE images such as this one, it is evident on the slopes of the large, especially high mesa just above the center of the image that the carbon dioxide-rich material may be constructed of several individual horizontal layers. However, it also appears that as erosion eats into the mesa, pieces of a stronger mesa surface layer break off and are left strewn on the mesa slopes, where they may give the appearance of layering.
An interesting feature in this HiRISE image is the crisscrossing network of faint ridges and troughs on the upper smooth terrain. These may also be complexly involved in the sublimation and deposition of carbon dioxide ice. MareKromiumSet 13, 2007
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