Mars Reconnaissance Orbiter (MRO)
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PSP_004311_1050_RED_abrowse-PCF-LXTT.jpgBasal Exposure of South Polar Layered Deposits - SPLD (Absolute Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)132 visitenessun commentoMareKromium
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PSP_004313_1760_RED_abrowse-00.jpgWinslow Crater - context frame n. 1 (MULTISPECTRUM; credits: Lunexit)60 visiteIn this first HiRISE image of Winslow Crater (PSP_004313_1760), distinct dark rays surrounding the crater and are consistent with the THEMIS data’s suggestion of rockier materials. V-shaped patterns in the rays — referred to as a “herringbone” pattern — are identical to those around fresh Lunar Craters.
These form when materials are ejected from the crater at a very low angle, which form clusters of secondary craters that preferentially eject materials down-range in a V-shaped pattern. (It‘s the same pattern that you would get when shooting a water pistol nearly parallel to a sidewalk.)
Also noteworthy are the large meter-to-decimeter-sized boulders on the steep rim that have not been buried or physically weathered to smaller sizes in this windy region, indicating that they have not been exposed long.
This is also reminiscent of Meteor Crater and examples of fresh simple craters on the Moon.
The ring of rocky, cliff-forming materials in the inner wall of the Crater represents original bedrock that was uplifted and exposed by the impact. The characteristic morphology is called “spur and gully” consisting of both the protruding bedrock inter-fingered with debris shoots feeding fans of sandy materials that extend down to the crater floor.
Throughout this Region, the present-day surface consists of a mix of global dust and volcanic sands from the Syrtis Major complex that typically cover the local bedrock. Winslow Crater is an excellent example of how craters can provide a window into the subsurface by exposing the local bedrock within the ejecta and crater wall.MareKromium
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PSP_004313_1760_RED_abrowse-01.jpgWinslow Crater - extra-detail mgnf from frame n. 1: the "Herringbone Pattern" (MULTISPECTRUM; credits: Lunexit)53 visitenessun commentoMareKromium
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PSP_004313_1760_RED_abrowse-02.gifWinslow Crater's Changing (GIF-Movie; credits: NASA)67 visitenessun commentoMareKromium
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PSP_004324_1060_RED_browse.jpgPolygons on South Polar Layered Deposits53 visiteThis image shows an exposure of south polar layered deposits, thought to record recent global climate changes on Mars.
The layers were probably laid down over the past few million years over a large area near the south pole, then eroded to show the layering visible in this image.
The layers appear brighter where their slopes are steeper and facing the Sun.
Within the brighter, steeper part of the layered deposits, a network of polygonal fractures is visible. The polygons outlined by the fractures are typically a few hundred meters (approx. 1000 feet) across, and traverse layer boundaries. Such polygonal fractures are seen on Earth in places where ground ice is present, and previous Mars orbiters have found evidence for abundant ground ice in the south polar region of Mars. So it is not surprising to see polygonal fractures here; what is unusual is that they cross layer boundaries, apparently unaffected by the changes in slope across them.
This suggests that the polygonal fractures formed after the scarp exposing the south polar layered deposits was formed by erosion. This indicates, possibly, that the scarp has been stable for some time, allowing the polygonal fractures to form.
MareKromium
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PSP_004353_0935_RED_browse.jpgThe "Global Dust Storm" over the South Polar Residual Cap55 visiteA dust storm has been raging on Mars, hampering the ability of the HiRISE team to carry out a seasonal monitoring campaign.
An area of the Southern Seasonal Polar Cap was selected in December 2006 for repeated imaging, to observe the sublimation (evaporation) of the seasonal Carbon Dioxide Polar Cap through Southern Spring.
Images collected as the season progressed show channels carved by escaping gas and fans of dust blown by the wind. This campaign has been stymied however by the arrival of a Martian dust storm. In this image the surface is completely obscured by the dust in the air.MareKromium
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PSP_004384_1705_RED_abrowse-PCF-LXTT.jpgN/W Melas Chasma (Absolute Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)80 visiteThis HiRISE image covers a portion of the Wallrock and Canyon Floor in South-Western Melas Chasma.
Along the Floor of Melas Chasma is an unusual Blocky Deposit composed of light-toned Blocks in a darker matrix. The HR provided by the HiRISE camera reveals Layers only a few meters thick in some of the light-toned Blocks. The Blocks vary in size but most fall between approx. 100 up to 500 mts in diameter. Although most Blocks appear rounded, others have angular edges and can be very elongate. The morphologies of the Blocks suggest ductile deformation, such as from a flow or by tectonic disruption after emplacement. Aeolian Ripples are interspersed between the Blocks in the darker Matrix.
Small valleys can be seen along the Wallrock. The Wallrock is a mixture of two geologic units that differ mainly in their reflectance. The light-toned unit appears to be thinner and only exposed in localized spots. Several of the light-toned Deposits are seen only in the Valleys, suggesting they were either deposited or are exposed by erosion.MareKromium
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PSP_004412_1715_RED_abrowse-PCF-LXTT.jpgArsia "Dusty" Layers (Absolute Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)68 visiteThis image covers a Pit in the lower West Flank of Arsia Mons, one of the 4 giant Volcanos of the Tharsis Region.
Many Layers are exposed in the Pit, probably marking individual Lava Flows that overlapped (meaning: ONE Layer - ONE Flow), and provide information about the nature of the volcanic eruptions. This image was acquired in the middle of large regional Dust Storms on Mars, but the Atmosphere over this image is only moderately dusty because the altitude is 6,5 Km higher than the Planetary Mean (-----> media altitudine planetaria), so the air is quite thin and cannot hold as much Dust.
Although the Atmosphere is not too dusty, the Surface is buried by a Dust Layer that might be meters thick. These high-altitude locations on Mars have thick Dust Deposits because the thin air cannot blow away the Dust, or at least not as fast as it accumulates. On Earth the Oceans serve as "Dust Traps", while on Mars such Traps are the highest Volcanoes. MareKromium
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PSP_004423_1755_RED_abrowse-PCF-LXTT.jpgInverted Channels and Layers near Juventae Chasma (an Image-Mosaic in Absolute Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team:)96 visitePSP_004423_1755 shows Plains North of the South-Western Juventae Chasma, a Canyon belonging to the gigantic Valles Marineris Canyon System.
There are 3 distinct type of Terrains in this image:
1) Plains with possible Inverted Channels,
2) Plains with exposed Layers and
3) Layers on a wall of Juventae Chasma.
The right half of the image contains Plains with Craters and Sinuous Ridge Features that are possibly Inverted Stream Channels.
Inverted relief occurs when a formerly low-lying area becomes high-standing. There are several possible reasons why Channels might stand out in inverted relief. The streambed material may become cemented by precipating minerals, contain larger rocks, or become filled with lava, all which are more resistant to erosion.
Finer-grained, more erodable material surrounding the channel is blown away by the wind or carried away by water, leaving the resistant channel bed high and dry around its environs.
Another example of erosion can be seen in the next Terrain which covers about 2/3 of the left half of the image. Erosion has exposed a beautiful series of light and dark tone Layers (approximately 1 Km across). In the inset, the smallest of the rings is the deepest exposed Layer.
Layers are common in the Martian Canyons, but it is unknown what process formed them. It is likely, though, that the Layers in the Plains here are made of the same material as the Layers in the Canyons. MareKromium
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PSP_004650_0975_RED_abrowse.jpgExposure of South Polar Layered Deposits (Natural Colors; credits: Lunexit)54 visiteExtensive Layered Deposits are found in both Polar Regions of Mars and are thought to contain evidence of recent climate changes like ice ages on Earth.
Radar observations suggest that the NPLD - as well as the SPLD - are composed mostly of water ice, but many layered exposures, including this one, appear to be covered by a layer of dust that protects the underlying water ice from further erosion. The SPLD are more extensive than the NPLD, and have generally been less active recently.
The greater age of the SPLD is indicated by the higher density of craters on its Surface; as a matter of fact, a cluster of small craters is visible above center in this image. Also visible are widespread polygonal fractures, evidence of water ice expansion/contraction below the Surface.MareKromium
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PSP_004664_0955_RED_browse.jpgOutcrops of Layers in the South Polar Layered Deposits53 visiteThis image spans a section of the South Polar Layered Deposits (SPLD). The SPLD are composed of layers of water ice mixed with impurities (probably mostly dust). The most similar terrestrial analog to the SPLD are ice sheets, like those covering most of Greenland and Antarctica.
The materials of ice sheets are deposited by freezing of atmospheric water vapor on dust particles and precipitation of those water/dust particles (snow), by direct condensation (freezing) of atmospheric water vapor onto the surface, and by fallout of dust. Together, these processes cause an ice sheet to undergo accumulation (build-up). Ablation (removal of material, also called erosion) of an ice sheet can also occur. If more accumulation happens than ablation, the ice sheet grows; if reversed, the ice sheet shrinks, as is the case for many of Earth’s glaciers due to global warming. Each year, the amount of accumulation and ablation varies, so layers of different thicknesses and different amounts of impurities (dust) will be deposited onto the ice sheet.
Volcanic eruptions anywhere on the planet can also potentially spew ash high into the atmosphere, where it can travel great distances and fall onto an ice sheet surface. Later accumulations of water ice can then trap this volcanic ash as a layer within the ice sheet. Thus, layers in an ice sheet can originate through a variety of means and occur at a variety of scales (thicknesses).
This particular image is interesting because many layers are exposed and because more than one outcrop (exposure of layering) is visible—at the top of the image and at the bottom. You can imagine the outcrops at the top and bottom of the image as if you are looking down on a staircase. The approximately horizontal lines are the edges of the layers (the risers), and the flat areas between them are the layer surfaces (the flat parts of the steps). The middle of the image is the top of the staircase. At the bottom, the staircase of layers goes down again.
The layers in this image are on the scale of meters (several to tens of feet) in thickness and are much thicker than one might expect from annual accumulation (which might be about 0.5 millimeters per year, or 0.02 inch per year). So the layers we see in this image may be packages of thinner, annual layers. The reason that we can distinguish between different packages of annual layers (in other words, the reason that we can see layering at this scale) is because the rates of accumulation and ablation change not only yearly, but also on much longer time scales. Imagine drilling into the SPLD and looking at the walls of the hole with a microscope. Within the large-scale layering we see in this image, we might see annual accumulation layers, dusty layers created during large dust storms, and maybe even volcanic ash layers.MareKromium
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PSP_004673_0935_RED_browse.jpgSouth Pole Residual Cap - Swiss-Cheese Terrain Monitoring (Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)53 visitenessun commentoMareKromium
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