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PSP_010169_2650_RED_abrowse-00.jpgDunes and other Surface Features in Chasma Boreale (ctx frame - possible True Colors; credits: Lunexit)64 visiteThis image shows dark sand dunes in Chasma Boreale. Chasma Boreale is a giant trough that cuts into the North Polar Ice Cap for about 570 Km (approx. 350 miles) forming a broad valley bordered by stacked layers of ice.
A portion of the North Polar Ice Cap is visible at the northern edge of the trough in the left portion of the image.
Many dark toned sand dunes march down the trough under the winds’ direction.
Coord.: 84,9° North Lat. and 331,8° East Long.
Spacecraft altitude: about 319 Km
M.L.T.: 13:35 (early afternoon)
Solar Incidence Angle: 67°MareKromiumNov 20, 2008
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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)57 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.MareKromiumNov 20, 2008
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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)57 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.MareKromiumNov 20, 2008
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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)58 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.MareKromiumNov 20, 2008
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PSP_010206_1975_RED_abrowse-01.jpgAncient Bedrock and Megabreccia in Nili Fossae region (edm - possible True Colors; credits: Lunexit)60 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.MareKromiumNov 20, 2008
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PSP_010183_2035_RED_abrowse-00.jpgColourful old Bedrock near Mawrth Vallis (possible True Colors; credits: Lunexit)59 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.MareKromiumNov 20, 2008
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PSP_010198_2645_RED.jpgStratigraphy of the NPLD (possible True Colors; credits: Lunexit)57 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.MareKromiumNov 20, 2008
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PSP_007961_2530_RED.jpgWestern Rim Region of Korolev Crater (possible True Colors; credits: Lunexit)57 visiteThis image was originally suggested by Ehsan Sanaei’s high school astronomy club in Yazd, Iran. They write, “[We are interested in] exploring the impact region near the northern Martian Pole and observing the contrast between ice-covered and [non-ice covered] Regions.”
Mrs. Stoica’s 9th grade class, at Tudor Vianu High-School of Computer Science, in Bucharest, Romania, helped to analyze the image by writing that “we observe a major crater, a small mountain chain, dunes and a series of small valleys and crevasses which [contain] ice.”
Indeed, this image shows part of the western rim of Korolev Crater, a prominent 80-Km-diameter crater located in the Northern Polar Region. It was taken in Northern Spring and shows dark regions of dust and sediment and bright regions of ice and frost. At highest resolution both bright and dark areas of the surface are covered by polygonal fracture patterns.
Although much of the ice has likely started to sublimate (change from a solid to a gas) in the darker regions, ice fills the fractures.MareKromiumNov 20, 2008
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PSP_005632_1225_RED_abrowse~0.jpgPartially Exhumed Crater in Amphitrites Patera (MULTISPECTRUM; elab. Lunexit)57 visiteThe terrain in this image is located in Amphitrites Patera, South-West of Hellas Basin. This area constitutes the interior of an ancient impact crater that was filled by a layer of smooth material, possibly composed of ash and dust, mixed with interstitial ice (ice filling spaces between dust and ash grains).
The curved ridge toward the lower left of the image is a remnant of the crater rim that was exhumed by erosion of the filling material. The morphology (appearance and shape) of the small, scalloped depressions, which we observe within the smooth material, suggests that the erosion process was sublimation (the process of a material going directly from a solid state to a gaseous state).
Scalloped depressions are a typical feature of the Mid-Latitudes of Mars between 40 and 60°. They usually have a steep pole-facing scarp (cliff), displaying series of small pits and fractures and a gentler, smoother, equator-facing slope. This asymmetry is most likely due to differences in solar heating.
The large scalloped depressions appear to have formed from the coalescing of multiple, smaller scalloped depressions. Their formation may be an ongoing process, although no definitive evidence has been uncovered so far.MareKromiumNov 20, 2008
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PSP_010222_1815_RED.jpgLight-toned Bedrock in Terra Meridiani (possible True Colors; credits: Lunexit)57 visiteThis observation shows part of a broad expanse of bare rock in Terra Meridiani. This is a large area with abundant sedimentary rocks forming a stack hundreds of meters thick, and now being eroded into a landscape reminiscent of the South-Western United States.
The timescale involved in depositing and eroding these layers is evident from the remnant impact craters preserved here. The large arc in the image is the rim of one crater; the smaller, circular dark spots are traces of other impacts. Light sediments are found both inside and outside the large crater, indicating that this crater formed during the period of sediment deposition. It is likely that this depression, which was probably more than a kilometer deep when it formed, was completely filled and buried and is now being exhumed. Crater densities are often used to estimate the age of surfaces on Mars, but here the rate of erosion is enough to erase small craters, reducing the apparent age of the surface. These rocks probably date from an early era of Martian History, but no fresh, pristine craters are visible.
The smaller circular patches are also impact craters seen somewhere in a complex cycle of burial and erosion. They are filled with dark material which probably mantled the region at one point, most likely after all of the light material was deposited. In some places this appears to have been hardened into rock, as in the large dark circle in the north-central part of the image. Material eroded from this hardened mantle may now be forming the ripples seen in many places as it is blown by the wind; the color of the ripples is similar to the slabs of dark mantle.
At the finest scale, the light sediments are intricately textured. A diverse assortment of fine cracks called joints are visible. The scale and density of these joints varies across the image; this suggests variations in the properties of the rocks. Although the image as a whole is a relatively flat plain, at small scale the surface is intricately rough. The balance between erosion and rock strength has left a surface with many small knobs, mesas, cliffs, and bumpy textures.
Further evidence for the diversity of rocks here comes from the enhanced color. The dark mantling materials are generally blue in the RGB color image while the sediments are generally pale, but a diverse range of hues indicates variations in the composition (or in the amount of sand and dust trapped on the surface by textures of varying roughness). This helps to highlight layering and shows which rocks are most similar to each other.MareKromiumNov 20, 2008
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PSP_010219_2785_RED_abrowse-00.jpgDunes in Abalos Undae (ctx frame - possible True Colors; credits: Lunexit)57 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.MareKromiumNov 20, 2008
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PSP_010219_2785_RED_abrowse-01.jpgDunes in Abalos Undae (edm - possible True Colors; credits: Lunexit)57 visiteThis enhanced-color close-up (1,2 Km across) shows an example of dunes in Abalos Undae.
The enhanced color data illuminate differences in composition: the dunes appear of a green/bluish color because of their basaltic composition, while the reddish-white areas are probably covered in dust and residual ice. Upon close inspection, tiny ripples and grooves are visible on the surface of the dunes (both ripples and grooves are formed by wind action, as are the dunes themselves).
It is possible that these dunes are no longer migrating (the process of dune formation forces dunes to move in the direction of the main winds) and that the tiny ripples are the only active parts of the dunes today.MareKromiumNov 20, 2008
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