Mars Reconnaissance Orbiter (MRO)
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PSP_010169_2650_RED_abrowse-01.jpgDunes and other Surface Features in Chasma Boreale (edm n. 1 - possible True Colors; credits: Lunexit)53 visiteThe sand dunes visible here are Barchan Dunes.
Barchan Dunes are also commonly found on Earth, and are crescent-shaped with a steep slip face bordered by horns oriented in the downwind direction. Barchan Dunes form by uni-directional winds and thus are good indicators of the dominant wind direction.
In this case, the dunes indicate that the direction of the strongest winds are parallel to the chasma walls, roughly East to West. The dark material composing the dunes could be volcanic ash or is possibly dark sand eroding out of the polar layered materials.MareKromium
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PSP_010169_2650_RED_abrowse-03.jpgDunes and other Surface Features in Chasma Boreale (edm n. 2 - natural colors; credits: Lunexit)53 visiteLe dune che vedete in questo dettaglio extramagnificato del panorama relativo alla Regione di Chasma Boreale SEMBRANO essere collegate da una frattura longitudinale, semi-irregolare ed a bordi frastagliati. Questa "frattura", se sovrasaturiamo l'immagine ed operiamo una ulteriore magnificazione, mostra delle leggere differenze di colore e di albedo e, alla fine, pare assomigliare davvero molto ad un canale di drenaggio (una sorta di fiumiciattolo, per dirla semplicemente).
Rilievi similari li abbiamo già incontrati su Titano e, se per i drainage channels della Luna Nebbiosa non paiono esserci più dubbi sul fatto che un qualche tipo di liquido scorra nel loro letto, per quanto attiene Marte ancora tutto tace.
In realtà, il fatto che questa specie di "frattura" superficiale possa essere un piccolo canale (che si inserisce in un ampio reticolo di canali - osservate il ctx frame per capire il contesto di riferimento) e che all'interno di esso scorra qualcosa, è pura speculazione; ma che la "frattura" (rectius: il network di fratture) sia oltremodo recente, è un fatto (basta osservare il dettaglio magnificato con una minima attenzione per capirlo).
La NASA, nel commentare questo frame, non si sofferma su queste "curiose" fratture del suolo e non ci offre alcuna idea/spiegazione delle stesse.
Peccato.MareKromium
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PSP_010169_2650_RED_abrowse-03~0.jpgDunes and other Surface Features in Chasma Boreale (edm n. 3 - false colors; credits: Lunexit)53 visiteAllora? Lo vedete il "possible North Polar drainage channel"? Notate come sia diverso dai soliti "cracks" e "fissures" del suolo? Osservatene bene i bordi e quindi provate a fare un confronto fra questo frame e qualche drainage channel Terrestre o di Titano: le somiglianze ci sono, e sono evidenti.
Verificare per credere!MareKromium
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PSP_010180_2645_RED_abrowse-00.jpgSmall and young Impact Crater in the NPLD (ctx frame - natural colors; credits: Lunexit)53 visiteThis image shows a small impact crater on the bright North Polar Perennial Ice Cap. Mars has Ice Caps at both its North and South Poles.
The Perennial, or Permanent, portion of the North Polar Cap consists almost entirely of water ice.MareKromium
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PSP_010180_2645_RED_abrowse-01.jpgSmall and young Impact Crater in the NPLD (edm - natural colors; credits: Lunexit)53 visiteThe Impact Crater is about 66 meters (215 feet) in diameter. Ejecta from this Crater can be seen extending primarily to the North-West.
The asymmetry in the crater ejecta can be an effect of atmospheric winds associated with the impact itself but, in this case, is most likely the result of an oblique impact (a low impact angle with respect to the horizontal).
As impact angles decrease, the ejecta blanket is increasingly offset downrange.
The impactor that formed this crater approached the surface from the South-East. The slightly elliptical shape of the crater is also a result of an oblique impact.MareKromium
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PSP_010183_2035_RED_abrowse-00.jpgColourful old Bedrock near Mawrth Vallis (possible True Colors; credits: Lunexit)53 visiteThis image covers part of a proposed Rover Landing Site in the Mawrth Vallis Region of Mars.
Polygonal fracture patterns (similar to a tiled floor) are visible on the surfaces of some of these rocks, and yellow/brown ridges protruding from the Surface may be composed of hard minerals or cemented sediments formed when water flowed through fractures in the ancient Bedrock. Dark gray-bluish dunes or ripples of wind-blown sand are also visible on the Surface here.
Elsewhere in the image, exposures of the light-toned rocks in the steep walls of impact craters reveal that these rocks are finely layered, similar to sedimentary rocks on Earth. The orbiting Infrared Spectrometers OMEGA and CRISM have demonstrated that these layered rocks contain Clay (---> argilla/minerali argillosi) minerals, which can only form in the presence of water.
The different colors of the rocks typically reflect differences in composition, suggesting that multiple styles or episodes of water activity may be recorded in the rock record here.
These characteristics have made Mawrth Vallis a prime candidate Landing Site for future Mars Rover Missions, including NASA’s Mars Science Laboratory due to launch in 2009.MareKromium
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PSP_010198_2645_RED.jpgStratigraphy of the NPLD (possible True Colors; credits: Lunexit)53 visiteThis image shows an example of layers in the Martian NPLD. These Deposits, part of the Planum Boreum dome, are composed mainly of water ice and small amounts of dust.
The layers within these Deposits are exposed by shallowly-sloping troughs that cut into them. This image is particularly interesting because it crosses complicated trough geometry, making the layers appear curved and exposing multiple stratigraphic levels.
Note that layers of different thicknesses are visible. Layer thickness is directly related to the accumulation rate of the layer; a higher accumulation rate will lead to a thicker layer.
However, a myriad of factors work together to influence accumulation rate, such as the amount of Sunlight reaching the Surface and the amount of water vapor existing in the contemporaneous Atmosphere.MareKromium
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PSP_010200_1805_RED_abrowse-00.jpgFresh Crater Cluster (CTX Frame - Natural Colors; credits: Dr Paolo C. Fienga - Lunexit Team)54 visiteAlthough most of the craters HiRISE usually images are ancient, impact cratering is an ongoing process on the Martian Surface.
While very large craters are rare, smaller ones with diameters of a few meters form on timescales rapid enough for Mars missions to confirm the presence of a new crater. Data from the Mars Orbiter Camera (MOC) on the (now defunct) Mars Global Surveyor, the Context Camera (CTX) on MRO, and HiRISE have dated craters to within a few years or even months, based on repeat images that show no craters in the earlier image and craters present in the later image.
Most of the new craters identified by CTX and HiRISE have been located in Mars' dustiest areas, where a new impact will scour dust from the Surface and reveal darker underlying rock. This color difference makes the craters easier to spot. Other, less dusty areas of Mars are certainly being bombarded as well, but the size of the craters makes them difficult to detect without stark color contrasts.
Once a new dark spot has been identified by CTX, HiRISE will take a follow-up image to confirm that the dark spots are in fact Impact Craters.MareKromium
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PSP_010200_1805_RED_abrowse-01.jpgFresh Crater Cluster (EDM - Natural Colors; credits: Dr Paolo C. Fienga - Lunexit Team)65 visiteMany of the newest craters are part of a crater cluster, like this one. This cluster is about 350 meters (almost a quarter mile) across at its longest, and the largest crater in the image is 5 meters (16 feet) in diameter.
These clusters likely result from breaking up of the impactor before it strikes the surface. How widely dispersed the craters are depends on the strength and density of the impactor. Scientists can study these clusters to learn more about the object that created them.MareKromium
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PSP_010206_1975_RED_abrowse-00.jpgAncient Bedrock and Megabreccia in Nili Fossae region (ctx frame - possible True Colors; credits: Lunexit)53 visiteThis image captures a record of changing environments on ancient Mars, as recorded in the rock record at Nili Fossae.
In addition to Megabreccia (see the edm that follows), the image shows layered rocks which have been shown by the orbiting spectrometers OMEGA and CRISM to contain Clay minerals. These minerals must have formed in the presence of water, and may have later been transported and deposited here in sedimentary layers.
Most of the layers appear to overlie the exposures of Megabreccia, but some Megabreccia blocks are themselves internally layered, suggesting that sedimentary processes were active here early in Martian History.
Above the clay-bearing layers is a dark, rough-textured rock unit that was emplaced later. Geologic mapping of the Nili Fossae Region has shown this deposit to be a Lava Flow from the Syrtis Major Volcano to the South. The minerals detected in the Lava Flow suggest that liquid water had become rare on the Martian Surface by the time the flow occurred.MareKromium
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PSP_010206_1975_RED_abrowse-01.jpgAncient Bedrock and Megabreccia in Nili Fossae region (edm - possible True Colors; credits: Lunexit)57 visiteThis edm shows a rock type known as Megabreccia, composed of numerous differently colored blocks, each up to 40 meters (130 feet) across, arranged in a seemingly disorganized array.
Megabreccia forms when an energetic event, such as formation of an impact crater, breaks up pre-existing rocks and jumbles their fragments. Megabreccia is found in some of the most ancient rocks exposed on the Martian Surface.MareKromium
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PSP_010219_2785_RED_abrowse-00.jpgDunes in Abalos Undae (ctx frame - possible True Colors; credits: Lunexit)53 visiteThe Abalos Undae Dunefield stretches westward, away from a portion (Abalos Colles) of the ice-rich North Polar Layered Deposits that is separated from the main Planum Boreum dome by two large chasms (---> abissi, crepacci).
These dunes are special because their sands may have been derived from erosion of the Rupes Tenuis unit (the lowest stratigraphic unit in Planum Boreum, beneath the icier layers) during formation of the chasms.
Some researchers have argued that these chasms were formed partially by melting of the polar ice.MareKromium
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