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PSP_008681_2550_RED.jpgTransverse Dunes in Vastitas Borealis (natural colors; credits: Lunexit)58 visiteThe Vastitas Borealis Region, or Northern Lowlands, is a large area of low-lying surface that surrounds Mars’ North Pole.
On average, the Region is 4-5 Km lower in elevation than the mean radius of the Planet. How this basin formed is not known, although researchers have postulated that it could have been the result of a very large-scale impact sometime in Mars’ distant past. As of this writing, it is Summer in the Martian Northern Hemisphere, allowing the HiRISE camera to image this Region in full sunlight.
The sinuous landforms are dunes composed of sand that is made of basalt (a volcanic rock) or gypsum (a hydrous sulfate). There is a transition of modified barchanoid (crescent shaped dunes, generally wider than they are long) and transverse chains into star dunes; the winds change a lot in this area. The orientation of the barchanoid and transverse dunes indicate that the winds that formed them blow from the East (right side of image).
In some areas there are a few linear dunes. The light-toned, smaller bedforms are designated Transverse Aeolian Ridges (TARs).
MareKromium
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OPP-SOL1613-1N271377483EFF90DCP1935L0M2.jpgFrom inside Victoria - Sol 1613 (trichromatic version; credits: Lunexit)58 visitenessun commentoMareKromium
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OPP-SOL1613-1N271377429EFF90DCP1935L0M2.jpgFrom inside Victoria - Sol 1613 (trichromatic version; credits: Lunexit)58 visitenessun commentoMareKromium
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PSP_009039_1660_RED.jpgCraters in South-Eastern Syria Planum (natural colors; credits: Lunexit)58 visiteThis image shows two landforms that appear similar, but are the result of two very different geologic processes.
These two depressions are craters. The smaller, rounder crater formed when an asteroid collided with Mars. This impact blasted out the pre-existing rocks, forming this quasi-circular crater.
The larger, more irregular-shaped crater is a Pit Crater. These types of craters form through collapse of the ground surface into large underground voids. In this Region of Mars, these underground voids are likely caused by the movement of magma (molten rock) through the subsurface. As the magma moves underground, it forces the rock apart and forms large “caverns.” These voids are structurally unstable and can lead to collapse of the overlying rock, forming pit craters at the surface.
Impact Craters are distinguished from Pit Craters by the presence of a raised rim. Rock blasted out during the impact falls back to the ground and accumulates near the crater, forming this raised rim. Upward warping of the ground during the impact process also contributes to the raised appearance of the crater rim. Since Pit Craters form through collapse, their rims are at the same level, or perhaps slightly lower, than surrounding ground surface.
The Impact Crater has a bright streak extending South-East (toward the upper right). The bright material is dust, deposited downwind of the crater by prevailing winds. Zooming into the streak, small bedforms, presumably composed of dust or dust aggregates, are visible. Similar features are seen in other dusty regions of Mars.MareKromium
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OPP-SOL1619-1N271912729EFF90GBP1997R0M1.jpgFrom inside Victoria - Sol 1619 (trichromatic version; credits: Lunexit)58 visitenessun commentoMareKromium
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PSP_005410_1115_RED_abrowse.jpgPolar Pit Gullies (MULTISPECTRUM; credits: Lunexit)58 visiteThis image shows Polar Pit Gullies in a depression. The gullies do not appear to have been active recently, as their channels and alcoves are covered with polygonal fractures and ripples that have formed over time. The alcoves contain boulders from eroding layers up-slope. Several of the alcoves extend to the slope rim, suggesting head-ward erosion.
The rest of the scene contains abundant polygonal ground, thought to have formed by processes involving ground ice. This image is at a High Latitude where polygonal terrain is common. This feature is not found in Equatorial Regions, which supports a relationship with ground ice because ground ice is not stable near the equator today.
There are several muted circles on the plains in the lower half of the image; these are possibly relaxed craters. If a crater forms in ice-rich ground, the ice enhances the degradation of the crater and gives the crater a “softened” appearance.MareKromium
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OPP-SOL1605-1.jpgFrom inside Victoria - Sol 1605 (True Colors; credits: Dr G. Barca)58 visitenessun commentoMareKromium
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OPP-SOL750-1.jpgMartian Paving - Sol 750 (natural colors; credits: Dr G. Barca)58 visitenessun commentoMareKromium
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NGC-6960-4.jpgNGC 6960 - The "Witch's Broom Nebula"58 visite"...Assumete il controllo del petrolio ed avrete il controllo delle Nazioni; assumete il controllo del cibo, ed avrete il controllo delle Popolazioni..."
Henry KissingerMareKromium
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OPP-SOL1601-1.jpgExtremely unusual Surface Feature - Sol 1601 (True Colors; credits: Dr G. Barca)58 visitenessun commentoMareKromium
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OPP-SOL1600-1.jpgFrom inside Victoria - Sol 1600 (True Colors; credits: Dr G. Barca)58 visitenessun commentoMareKromium
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PSP_009114_2645_RED.jpgEroding Dunes in Chasma Boreale (natural colors; credits: Lunexit)58 visiteSand moves along a planetary surface by a process scientists call “saltation”, whereby the individual grains are driven by the wind and bounce forward in short hops. In a process that is not yet completely understood, sheets of saltating sand grains organize themselves into sand dunes, visible in this image as the dark features.
Sand dunes move by having the wind push sand grains up and over the top of the dune where they then slide down to the base. The steep side of the dune that the sand grains slide down is called "slip-face" and it is the constant transport of sand from the downwind side of the dune to the "slip-face" that makes the dune move forward in this direction. HiRISE data allow us to see which side of these dunes has the steeper slope (such as the aforementioned "slip-face"), telling us what direction the dune — and strong near surface winds — are moving.
Yet something else is also happening to these particular dunes. Dark streaks lead away from the dunes toward the lower left of the image. These streaks are caused by sand grains being blown off the dunes and saltating away. This is not ordinarily a cause for concern because in a stable dune, individual grains are constantly added and removed; however, there does not appear to be any influx of sand upwind of these dunes, so they are probably being eroded.
It is also interesting that these streaks do not point in the same direction as the "slip-face". One possible scenario is that the dunes migrated Westward when sand supply was more plentiful. Today, the wind direction has shifted, blowing more toward the South-West, and the influx of new sand has ceased, such that in the future, the dunes will completely erode away. Repeated HiRISE observations will be able to look for changes in the shape and size of these dunes.MareKromium
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