Mars Reconnaissance Orbiter (MRO)
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PSP_002804_0930_RED_abrowse.jpgSouth Polar Trough (Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)54 visiteThis image is taken in one of the Troughs that are typical within the stack of Martian South Polar Layered Deposits (SPLD).
Viewed at low resolution, sequences of layers of different albedos, or brightnesses, and/or textures can be seen. At full resolution, the different tones and textures can be seen to be due to different shapes and sizes of polygonal fractures, surface knobiness, and surface cover and concentration of frost, often within polygonal fractures.
Faint criss-crossing Troughs and Dimples can be discerned on even the smoothest surfaces. Perhaps the most notable features in the image are the distinct round to heart-shaped to blob-shaped depressions scattered throughout the smooth areas, dubbed "Swiss-Cheese Terrain".
The smooth material is solid CO2 ice representing the uppermost layer of the South Polar Residual Cap. The retention of CO2 ice throughout the year by the Southern Polar Cap is one characteristic that distinguishes it significantly from Mars' North Polar Cap. The Swiss-Cheese depressions are areas in which sublimation of the CO2 ice was initiated at a particular location and spread laterally from that point, creating rounded depressions typically several to 10 meters deep.
In HiRISE images, it is evident that this CO2-rich material is actually comprised of several individual horizontal layers. In this particular location, several images had been acquired over the previous decade by the Mars Orbiter Camera (MOC) at slightly lower resolutions. In a series of those MOC images, the Swiss-Cheese depressions were seen to enlarge radially, or grow over a time period of several years.
Part of the HiRISE imaging campaign includes continued monitoring of these features (at higher resolution) to understand their growth rates and patterns. In turn, we can better comprehend the role of CO2 — the main component of the Martian Atmosphere — in the current Martian Climate Regime.MareKromium
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PSP_002824_1355_RED_abrowse-00.jpgDunefield inside Rabe Crater (CTX Frame - Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)99 visiteMareKromium
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PSP_002824_1355_RED_abrowse-01.jpgDunefield inside Rabe Crater (EDM - Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)75 visiteMareKromium
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PSP_002839_1825_RED_abrowse-1.jpgAram Chaos (Absolute Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)54 visiteAram Chaos appears to be a former impact crater. The terrain is disrupted, giving it a chaotic appearance (hence the name "chaos"). Scientists have postulated that a lake may have once existed inside the crater and sediments were laid down within the lake. The mineral Hematite (rich in Iron) has been detected by orbiting spacecraft within Aram Chaos. Hematite has been identified in several other locations on Mars, including at the Mars Exploration Rover Landing Site in Meridiani Planum. The Hematite at both Meridiani and Aram Chaos most likely formed by precipitation in water.
This HiRISE image shows the light-toned sediments inside Aram Chaos that could have formed in a former lake. Unfortunately, dark debris now obscures much of this sediment, making it difficult to view and interpret the rocks. The light-toned Layered Deposit in the South (left) of the image is higher standing and has a peculiarly-looking pitted surface.
Circular structures with dark centers are likely to be impact craters that have been partly filled with dark debris, including sand. More irregular depressions appear to result from erosion of layered beds within the sediments. Wind could erode materials that are slightly weaker more quickly and produce the irregular topography seen along the surface of the deposit.MareKromium
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PSP_002840_1855_RED_abrowse-00.jpgMeanders in Nanedi Valles (Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)54 visiteThis observation shows a portion of Nanedi Valles, an equatorial Martian valley network.
Valley networks are thought to have formed by groundwater sapping either in conjunction with an ice layer to cover the running water or during a past warmer, wetter climate regime on Mars. Glacial activity has also been proposed to form the valley networks.
Groundwater sapping is the leading theory because of the morphology of the valleys. They commonly have approximately constant width along their reaches, as seen here, as well as theater shaped heads, as seen in the tributary valley in the bottom right of the scene. The meandering nature of valleys suggests persistent or repeated flow as required to form meanders in streams on Earth.
The subimage shows a potential remnant channel seen on the floor of Nanedi Valles just below the center of the image. If this is a remnant channel, it suggests that there was either repeated or waning flows in this valley. Winding dunes and abundant impact craters are found throughout the valley, as well as within this putative channel.
Dunes are thought to be transient features on Mars, although no movement has been detected to date. It is interesting to note that some of the dunes are superposed by craters indicating that the dunes were stable long enough for craters to form and not be erased.
It is possible that the craters on top of the dunes are secondary craters that formed as a product of a larger impact. Secondary craters from a single impact are clustered in space and form almost simultaneously, implying that the dunes were stable for a time period—long enough for a single crater, rather than multiple craters, to form.
MareKromium
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PSP_002856_0875_red-PCF-LXTT.jpgSouth Polar Layered Deposits and Scarp (Absolute Natural Colors; credits: Dr Paolo C. Fienga - Lunexit Team)120 visitenessun commentoMareKromium
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PSP_002882_0940_RED_abrowse-00.jpgSouth Polar Layered Deposits (CTX Frame - Absolute Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)82 visitenessun commentoMareKromium
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PSP_002882_0940_RED_abrowse-02.jpgSouth Polar Layered Deposits (EDM - Absolute Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)75 visitenessun commentoMareKromium
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PSP_002882_0940_RED_browse~0.jpgFresh Craters on the South Polar Layered Deposits (Natural Colors; credits: Lunar Explorer Italia)54 visiteThis image was taken in the Southern Spring, when the surface was completely covered by Carbon Dioxide frost. Therefore, most of the brightness variations in this scene are caused by topography.
The Polar Layered Deposits are broken into blocks by fractures in two directions. Neither set of fractures is parallel to the current scarp face, suggesting that they were not formed as the scarp was eroded, but instead are due to pre-existing weaknesses in the Polar Layered Deposits.
The (small?) craters that can be seen at about 23:00 - approx. in the central portion of the frame - appear to have formed at the same time by an impactor that broke up as it entered the Martian Atmosphere.
The presence of many craters such as these on the South Polar Layered Deposits indicates that they are not as young as the North Polar Layered Deposits, which have very few craters on them.MareKromium
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PSP_002884_1395_RED_abrowse-00.jpgUnnamed Southern Crater with deep Gullies (CTX Frame - Absolute Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)95 visiteThis observation shows gullies in a Southern HemisphereUnnamed Crater whose Floor has large Mounds of material that are likely "Slump Blocks" that fell off the Crater Walls during a late stage of formation (---> this is a Gravity Wasting Event). There are also a large number of Dunes of different sizes and facing different directions on the Crater Floor.
A lot of Polygonal Fractures can also be seen on the Walls, inside the Gullies (see the following EDM). In addition, some of the Gullies facing the East were active more recently. They do not have Polygonal Fractures or they have fractures that are less well-developed.
A narrow, primarily unmodified Channel is also visible.
It is unknown over what period of time Gullies formed in individual settings and globally. It is possible that Gully formation continues today.MareKromium
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PSP_002884_1395_RED_abrowse-01.jpgUnnamed Southern Crater with deep Gullies (EDM - Absolute Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)83 visitenessun commentoMareKromium
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PSP_002892_1760_RED_abrowse-00.jpgLayered Deposits in Aureum Chaos (CTX Frame - Absolute Natural Colors; credits: Dr Paolo C. Fienga - Lunexit Team)55 visiteThis observation shows an Outcrop of a large slab of Layered Deposits in Aureum Chaos.
Chaotic Terrains on Mars are disorganized regions of Blocks and Large Mounds which appear to have been produced by the collapse of pre-existing terrain. They are often associated with giant Outflow Channels, and they may have been the source of the water that carved the Channels.
This link is an important part of understanding the history of water on Mars. One way to address this is to study the rocks left behind in the Chaotic Terrains.
The Outcrop shown in the following EDM is several kilometers across and light-toned. It has a slab-like appearance, with relatively steep edges and a flat top, although the top has many small Knobs and Spires. In places, particularly along the West edge of the main slab, it is clear that the light material is composed of many fine layers, which are eroding in a stepped fashion due to the variable resistance of the layers. The flat surface of the Outcrop is partially coated with Dark Dust, obscuring its light tone.
Along the edges, the Outcrop is breaking into boulders and eroding away, but it is strong enough that it preserves steep Slopes, particularly on the Eastern Edge.
Away from the large slab, the image consists of Hills and Mounds characteristic of Chaotic Terrain. Little detail is visible on the Mounds. The low areas have been partially covered by wind-blown Sand or Dust, forming the pervasive Ripples seen in the image. Light material can be seen under the Ripples in a few places, indicating that the light layered deposits extend farther than just the slab.MareKromium
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