| Ultimi arrivi - Mars Reconnaissance Orbiter (MRO) |
PSP_008311_1835_RED_abrowse-01.jpgFeatures and Mineralogy of Aram Chaos (extra-detail mgnf - MULTISPECTRUM; credits: Lunexit)59 visiteIn this extra-detail mgnf, the lighter-toned area is a heavily fluted and pitted Capping Unit. This surface tends to trap dark sand in the lows.
The dark sand can also be seen to form dunes below the cliff.
Sulfates have been detected in the cliff walls in some areas within Aram Chaos, as well as Hematite. It has been suggested that these materials were deposited within a lake setting.MareKromiumGiu 12, 2008
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PSP_008100_1790_RED_abrowse.jpgLayered Rocks in Iani Chaos (MULTISPECTRUM; credits: Lunexit)73 visiteThis image shows rocks on the floor of Iani Chaos, a Region of collapsed and disorganized Terrain.
The Chaotic Terrains on Mars may have been the sources of floodwaters that carved the giant outflow channels. They typically contain irregular hills like the one in the center of this image. In some cases, they also have light-toned rocks exposed on the floors. The point of interest is to determine whether these rocks predate the chaos or formed after the collapse; however, the contacts may be obscured by later material mantling the ground.
The rocks here are light-toned, and have dark low patches which are likely a thin cover of wind-blown sand. At a coarse scale, linear features are also visible in the rock, likely reflecting aeolian (wind) erosion in a preferred direction. A variety of processes could have contributed to forming these rocks, from volcanic eruptions to lake deposition or accumulation of wind-blown sand.
Stepped layers occur in places, suggesting a repetitive process. This argues for an origin as aeolian or lake-bed sediments, since volcanic eruptions may be of variable strength.MareKromiumGiu 12, 2008
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PSP_008233_1920_RED_abrowse.jpgCrater Floor Fan (MULTISPECTRUM; credits: Lunexit)60 visiteThis image shows a Fan of material deposited on the floor of a large Impact Crater.
The material was transported into the Crater through a valley, likely by running water. The end of the valley is visible in the West (lower) part of the image. Arcuate steps visible in the East are probably due to layers of different strength or cohesion; these suggest variations in the flow conditions.
A faint Trough is carved into the upper surface of the Fan. This could have been cut by the last water to flow across the surface. If the channel was flowing into a lake, this might indicate a drop in lake level, leading to erosion.
The surface of the Fan has many small dark spots, particularly on the upper tier.
The largest spots, most commonly around impact craters, are big enough to show that these are boulders.
If these boulders are original and not due to the hardening of fan sediments into rock, it suggests that the flows which deposited the Fan were relatively energetic events able to carry rocks across several feet.MareKromiumGiu 12, 2008
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PSP_005620_1210_RED_abrowse.jpgSouthern Alcoves (MULTISPECTRUM; credits: Lunexit)58 visiteThis image shows the West Wall of a Southern Hemisphere Crater. The scene is covered in Dust Devil Tracks which appear as dark wispy features.
Dust Devils are small-scale funnels that move across the surface kicking up dust as they go, thus leaving trails. The Crater is covered in small polygons in many locations. These polygons are probably related to periglacial processes; for example, temperature cycling of ice-rich material or sublimation, when gases trapped under the surface escape causing the remaining terrain to collapse to form pits.
Also in this Crater are several Gullies on the Southern Wall. These Gullies have very wide alcoves/source regions. It is unknown what is responsible for different Gully Alcove shapes and morphologies.MareKromiumGiu 12, 2008
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PSP_005924_2210_RED_abrowse.jpgFeatures of Cydonia (MULTISPECTRUM; credits: Lunexit)56 visiteThe Cydonia Region on Mars is located in Arabia Terra at the boundary between the Northern Lowlands and Southern Highlands. This Region gained notoriety when Viking imaged a landform that looked like a face.
The “Face” has subsequently been imaged by many orbiters, including HiRISE ( PSP_003234_2210), showing that it is simply a rocky mound, and the face-like appearance was due to a trick of shadows. This observation was taken of a Region slightly to the South-West of that landform.
This Region is characterized by Knobs and Buttes. Knobs are rounded hills and Buttes are hills with steep vertical sides and a flat top. A butte is similar to a plateau, but smaller in scale. These are features that are resistant to erosion, and there are several ways that such features may become more resistant than the surrounding areas. They can be plutonic intrusions or volcanic rocks that are more resistant rock types than the surrounding sedimentary rock. Alternatively, these Regions may be resistant because they have been cemented by water carrying dissolved ions that precipitate as minerals binding the sediment together.
Either way, they provide important information about the geologic history of the Region.
Of note in this image is the interesting pitted and patterned ground. This pitting may have resulted from the sublimation of interstitial ice. Patterned ground is common throughout the Northern Mid-Latitude Plains.MareKromiumGiu 12, 2008
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Psp_001736_2605_red.jpgThe Dunes of Olympia Undae (MULTISPECTRUM; credits: Lunexit)56 visiteThis HiRISE image shows dark dunes and light polygonal terrain in Olympia Undae, also known as the North Polar Erg.
Two sets of dunes are obvious. The major set trends ~North-South, indicating winds from the East or West. Between the crests of these dunes is a second set oriented mostly East-West.
Zooming in on the dunes, a rippled texture is apparent, probably due to redistribution of sand at the scale of meters and less. Near the crests of some dunes are channel-like features, with some branching downslope.
The origin of these channels is unknown, but they may result from the flow and displacement of sand that was fluidized by sublimating CO2 or water frost.
Bright patches of ground are found in some inter-dune areas, with many having a polygonal texture. Polygons on Earth form from contraction induced by stresses from dehydration, cooling, and other processes, so these features may have a similar origin.
The CRISM instrument on MRO and OMEGA on Mars Express indicates that many dunes in Olympia Undae are rich in the mineral gypsum. MareKromiumGiu 10, 2008
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PSP_006769_1595_RED_abrowse.jpgSouthern Highlands Panorama (Enhanced Natural Colors; credits: Lunexit)56 visiteThis image shows a portion of the Southern Highlands cut by Arda Valles, an ancient Valley Network.
The Valley Network is degraded as seen by the lack of obvious walls and a V-shaped bottom. The valley networks are thought to have formed by running liquid water on the surface of Mars billions of years ago, with a few being active more recently.
Arda Valles has many dunes within it and craters on top of it, which show that is has been around for long enough for craters to form. The surface that Arda Valles cuts is more cratered than the valley surface because wind has moved material into the valley throughout time such that the surface in the valley gets covered and past craters might be buried there.MareKromiumGiu 08, 2008
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PSP_008324_2050_RED_abrowse.jpgProposed MSL Landing Site in Mawrth Vallis - ellipse 4 (MULTISPECTRUM; credits: Lunexit)56 visiteMawrth Vallis has a rich mineral diversity, including clay minerals that formed by the chemical alteration of rocks by water. The CRISM instrument detects a variety of clay minerals here, which could signify different processes of formation. The high resolution of the HiRISE camera helps us to see and trace out layers, polygonal fractures, and with CRISM, examine the distribution of various minerals across the surface.
This surface is scientifically compelling for the MSL Rover, although some of the terrain can be somewhat rough. Scientists use HiRISE images to find the safest possible Landing Site for the Rover.MareKromiumGiu 05, 2008
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PSP_008390_2050_RED_abrowse.jpgProposed MSL Landing Site in Mawrth Vallis - ellipse 4 (MULTISPECTRUM; credits: Lunexit)59 visiteMawrth Vallis has a rich mineral diversity, including clay minerals that formed by the chemical alteration of rocks by water. The CRISM instrument detects a variety of clay minerals here, which could signify different processes of formation. The high resolution of the HiRISE camera helps us to see and trace out layers, polygonal fractures, and with CRISM, examine the distribution of various minerals across the surface.
This surface is scientifically compelling for the MSL Rover, although some of the terrain can be somewhat rough. Scientists use HiRISE images to find the safest possible Landing Site for the Rover.
MareKromiumGiu 05, 2008
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PSP_008244_2645_RED_abrowse.jpgNorth Polar Layered Deposits (MULTISPECTRUM; credits: Lunexit)57 visiteThe North Polar Layered Deposits of Mars form a layered stack of dusty ice up to 3 Km (about 2 miles) thick. The differences from layer to layer are thought to reflect differences in the climate of Mars that existed when the layers were formed.
We can see these internal layers exposed on the faces of the many troughs and scarps that cut through these deposits.
One of these scarp faces is shown here; it is situated at the head of a large canyon (named Chasma Boreale) that cuts through these Polar Layered Deposits.
The terrain on the upper side of the picture is higher and consists of the upper surface of the icy layered deposits in this area while the terrain on the lower side of the frame consists of the rocky ground that underlies the layered deposits. The cliff that separates these two areas runs down the center of the image with a relief of about 700 meters (about 2300 feet).
The section of the Layered Deposits that is exposed on this cliff face is unusual in that, as well layers of dusty ice, there are also layers of sand present. Small structures, called cross-beds, visible in the sandy layers indicate that each layer was originally a dune field that only later became covered with ice. Some of this sandy material is being removed from the cliff face and is forming new dunes at the foot of the cliff.MareKromiumGiu 05, 2008
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PSP_008208_2600_RED_abrowse-00.jpgAwakening Dunes... (MULTISPECTRUM; credits: Lunexit)56 visiteThis image captures unusual arrow-shaped sand dunes in the north polar Olympia Undae region that may have been formed by changing winds. The dark patches and streaks show sand that has begun escaping from a blanket of seasonal frost.
Many of the typical types of Martian dunes are similar to common dunes on Earth. Transverse dunes have gentle upwind slopes and steep lee sides that are perpendicular to the wind direction. Barchans are crescent-shaped dunes with a gentle upwind slope and steep lee with horns. Other common dunes on Earth and Mars are seif dunes that form sinuous parallel ridges with bi-directional winds forming the slip-faces.
The dune types in this image transition from transverse in the south through tight chains of barchans, to the strange, elongated dunes in the north. These elongated dunes appear to be modified barchans with two slip-faces and asymmetric horns. The drawn out limbs and remnant slip-faces were apparently produced by variations in the wind direction. The winds that created the transverse dunes blow from a single easterly direction, while the modified barchans are shaped by winds from an easterly-northeasterly direction. The elongated horns align parallel to northeasterly winds. These wind variations could be caused by local topography.
Two factors likely contribute to the unique morphology of these dunes. First, the southern horns defrost sooner than the northern horns because they receive sunlight more directly. This enables material to move more easily on their southern side. Second, the changing wind directions may be reorienting the dunes. One idea is that the barchans’ southern horns are being blown downwind into linear (seif-like) dunes, with sinuous crests and steep flanks. Another possible explanation is that they are drifts of sand (lee dunes) that form in the lee of an obstacle. The frozen barchans might act as obstacles to the wind, allowing loose sand to accumulate in their lee. In either case, the interaction between the sand, wind, and seasonal frost sculpts the dunes to their unusual, arrow-like appearance.
MareKromiumGiu 05, 2008
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PSP_006760_1370_RED_abrowse.jpgGullies in Terra Sirenum (MULTISPECTRUM; credits: Lunexit)73 visiteThis image shows Pole-Facing Gullies in a Southern Hemisphere Crater. Gullies are young features that are widely thought to form from fluvial processes involving liquid water. These particular gullies have very fine channels, including some that intersect and overlap. This is evidence that multiple flow events occurred within the Gullies.
The wavy, arcuate ridges at the bottom of the slope may have formed by gravity moving ice-rich material off the crater wall.
The pitted texture of the crater floor suggests that volatiles (ices that easily turn into gas) escaped from the subsurface, causing the surrounding material to collapse and form small pits.
Coord.: 42,6° South Lat. and 214,8° East Long.
Spacecraft altitude: about 254 Km
M.L.T.: 14:38 (early afternoon)MareKromiumGiu 02, 2008
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