| Piú votate - Mars Reconnaissance Orbiter (MRO) |
PSP_008244_2645_RED_abrowse.jpgNorth Polar Layered Deposits (MULTISPECTRUM; credits: Lunexit)53 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.MareKromium
(6 voti)
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PSP_007801_2610_RED_abrowse.jpgDefrosting Dunes in the North Polar Sand Sea (MULTISPECTRUM; credits: Lunexit)63 visiteThis image shows defrosting sand dunes near the North Polar Region of Mars.
Around Mars’ North Pole is a vast Region or “sea” of sand dunes that become covered with CO2 frost or ice in the Northern Hemisphere’s Winter. The light areas indicate that parts of the dunes are still covered in frost or ice.
As Mars’ Northern Hemisphere enters into Spring and begins to warm, the CO2 sublimates. The CO2 sublimates in surprising ways, with trapped gas bursting through the ice in jets that leave dark streaks when the wind is blowing
During the Summer, all the frost will have sublimed leaving dark sand dunes. The unfrosted dunes are dark because the sand is derived from dark volcanic rocks.MareKromium
(6 voti)
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PSP_007653_2010_RED_abrowse-00.jpgBright on Dark (MULTISPECTRUM; credits: Lunexit)53 visiteThis image reveals bright Slope Streaks in Bahram Vallis, a long sinuous valley that winds across North-Eastern Lunae Planum and Xanthe Terra to the circum-Chyrse basin.
Typically, dark and light-toned Slope Streaks appear together on light-toned slopes. This scene is a rare case in which only bright streaks are visible on a dark surface. Slope Streaks generally start at a point source and widen downslope as a single streak or branch into multiple streaks. Some of the Slope Streaks show evidence that downslope movement is being diverted around obstacles, such as large boulders, and a few appear to originate at boulders or clumps of rocky material.
Many hypotheses have been proposed for the formation of slope streaks including dry avalanching, geochemical weathering, liquid stains or flows, and moisture wickering. Recent observations from HiRISE images have revealed that the interior of Slope Streaks is lower in elevation than the surroundings indicating that material must have been removed and then deposited in the formation of the streak.
Slope Streak formation is among the few known processes currently active on Mars. Where they appear together, dark Slope Streaks cross cut and lie on top of the older and lighter-toned streaks leading to the belief that lighter-toned streaks are dark streaks that have lightened with time as new dust settled on their surface. Over the course of several years, MOC images from this Region did not reveal any new dark or light-toned Slope Streaks suggesting that streak formation is not currently active here.
HiRISE will continue to monitor this Region for new slope streaks and changes in tone of old streaks.MareKromium
(6 voti)
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PSP_007193_2640_RED_abrowse-01.jpgDefrosting Northern Dunes (extra-detail mgnf - MULTISPECTRUM; credits: Lunexit)53 visiteThis extra-detail mgnf shows a Region of the dunes that are just beginning to lose their seasonal ice cover. In most of the image the dunes are a muted red color. Where the sun is shining on the steep dune crests the frost is gone and dark dust is free to cascade down the sides. This thin layer of dust, like slope streaks found elsewhere on Mars, flows down around obstacles and may come to rest mid-slope.MareKromium
(6 voti)
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PSP_007338_2640_RED_abrowse-1.jpgCaught in Action: Avalanches on North Polar Scarps (natural colors; credits: Lunexit)53 visitenessun commentoMareKromium
(6 voti)
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PSP_006891_1970_RED_abrowse-01.jpgAt the base of the Olympus... (EDM - Saturated Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)53 visiteThe bottom right part of the cutout has a much flatter and smoother surface. These are younger lava flows that have buried the lower part of the volcano. When lava flows form vast smooth sheets, they are called "flood" lavas.
In the bottom of the cutout, the flood lavas have odd, wiggly looking plateaus. These are parts of the lava crust that were lifted up when more liquid lava was injected into the middle of the slowly solidifying lava flow.
This process is called "inflation" and is seen on many lava flows on Earth. These younger lava flows are cut by two different sets of faults. One makes the branching valley in the flood lavas and the other creates the sinuous ridge and valley along the edge of the Olympus Mons lava flows.
Lower resolution images that cover a broader area suggest that the sinuous fault is an old buried structure that has been more recently reactivated.MareKromium
(6 voti)
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PSP_005418_1075_RED_abrowse-01.jpgDistorted Layers in the SPLD (extra-detail mgnf - MULTISPECTRUM; credits: Lunexit)53 visiteThis enhanced image (1,2 Km or 0.7 miles across) shows a section of the South Polar Layered Deposits, which are an accumulation of layers consisting mostly of water ice and dust. Perhaps their closest analog on Earth would be the Ice Caps of Greenland and Antarctica.
This image is particularly interesting because the layers are not flat-lying but rather appear "wavy" (---> ondeggianti).
This appearance could partly be an “illusion” due to erosion after the flat-lying layers were deposited. In that case, the wavy appearance is due to the fact that the layer edges are wavy, going into and out of the plane of the outcrop exposing the layers.
Alternatively, this waviness could be due to deformation of the layers folding caused by flow of the ice.
Here, the flow probably occurred long ago since current temperatures are too low to allow the ice to flow at a significant rate.MareKromium
(6 voti)
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PSP_005682_1035_RED_abrowse-01.jpgBasal Exposure of South Polar Layered Deposits (extra-detail mgnf; possible natural colors - elab. Lunexit)54 visiteSome layers have an irregular wavy appearance that may have been caused by flow of the ice in the past when the now-exposed ice was still buried.
It is currently too cold at the surface in the South Polar Region of Mars for significant flow to be occurring today.
Other layers appear to be converging and some are truncated and may represent the so-called "unconformities" (see here).
Unconformities form when a previous episode of erosion removes all or part of a layer and is later followed by more deposition.MareKromium
(6 voti)
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PSP_003639_1345_RED_browse-00.jpgDebris Apron South of Euripus Mons (context image - possible natural colors; elab. Lunexit)53 visiteEuripus Mons is located to the east of Hellas impact basin in the southern mid-latitudes of Mars.
The overall wavy, curved surface pattern of this debris apron suggests that material flowed out from the isolated flat-top ridge. This mass movement of debris probably involved ice flow (possibly forming rock glaciers) and potentially liquid water.MareKromium
(6 voti)
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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
(6 voti)
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PSP_005155_1030_RED_browse.jpgExposure of South Polar Layered Deposits53 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).
MareKromium
(6 voti)
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PSP_003368_1755_RED_browse.jpgProposed MSL Site in Juventae Chasma (detail of the so-called "Martian Handwriting")109 visiteForse qualche Lettore avrà già riconosciuto il luogo e l'oggetto di questa ripresa e forse no.
Nel dubbio, Vi diciamo che si dovrebbe trattare (il condizionale è d'obbligo, poichè non abbiamo le coordinate esatte al centesimo di grado e quindi potremmo anche sbagliarci - ma di poco...) di una porzione della famosa - si fa per dire, naturalmente - "Scritta Marziana" di cui si è parlato sia nel Forum di SpazioUfo.com, sia nella nostra Rubrica TruePlanets.
Nostra opinione?
Se si tratta effettivamente di una porzione della "Scritta", allora pensiamo che adesso risulterà evidente a tutti come il parlare di artificialità del rilievo sia stato non solo azzardato e fuori luogo, ma addirittura ridicolo.
In caso contrario (e cioè qualora questo dettaglio fosse semplicemente relativo ad una zona promiscua alla "Scritta"), un simile e spettacolare frame MRO ci deve comunque essere di aiuto per capire, una volta che esso sia stato posto a confronto con il frame ESA-Mars Express relativo alla medesima zona, che l'operare congetture usando le orrende ed extra-piallate pseudo-immagini ESA è più che periglioso: è - semplicemente - assurdo.
E con questo, almeno per noi, la querelle sulla "Calligrafia Marziana"...è chiusa.MareKromium
(6 voti)
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