| Piú viste - Mars Reconnaissance Orbiter (MRO) |
PSP_002202_2250_RED_browse-01.jpgPits, Cracks, and Polygons in Western Utopia Planitia (extra-detail mgnf) - elab. NASA56 visitenessun commentoMareKromium
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PSP_004030_1855_RED_browse.jpgBlast from the (Very Recent) Past56 visiteIn the center of this image is a very sharp-rimmed impact crater just 35 mt wide.
It lies in a bright, dust-covered region, but is surrounded by a slightly darker spot about 3 Km wide. The impact event created a blast of high winds that disturbed the dust and darkened the spot.
Since dust is constantly settling over the Region, the fact that we can still see the dark region means the impact event occurred of late, perhaps in recent decades. There are many dark streaks on topographic slopes over an even wider region surrounding the dark spot - these could be due to dust avalanches triggered by the impact, either from the air blast or from seismic shaking of the ground.
There are also rays of very small (approx. 1 mt in diameter) secondary craters extending radially outward from the 35-mt crater, created by the impact of rocks ejected from the main crater.
Thus a small impact crater has modified the surface over an area more then 10.000 times greater than that of the crater's interior.MareKromium
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PSP_004820_0940_RED_browse.jpgFingerprint Terrain with Sawtooth Patterns in the South Polar Ice Cap (Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)56 visiteThis image shows a portion of the South Polar Ice Cap. The ice you see here is frozen CO2 rather than the frozen water you are used to here on Earth.
Even on Mars, where the temperatures are much lower than on Earth, CO2 ice is a volatile substance. As it is so unstable, large amounts can sublimate very quickly when heated. In this ice cap we can see icy features shrink in size by several meters per year as the ice that makes them up is removed by solar heating. Usually these icy features are almost circular as you get equal amounts of Sunlight from every direction when you are at the Pole.
However, in this location something strange has happened. Instead of the usual circular features we see features that are decidedly linear in shape. These sets of linear features have been dubbed "fingerprint terrain" by Planetary Scientists. They are seen in several locations in this ice cap and usually have a wavelength close to 90 mt (295 feet). It's hard to understand why linear features would form in this sort of environment by sublimation of ice alone.
It is possible that these features are formed instead by atmospheric processes. Either the features are sand dunes covered by a thin covering of frost or they might be made up of loose ice crystals that saltate like sand grains and have collected into ripples.
It would be a huge surprise to find sand dunes in this location, just as you wouldn't expect to see sand dunes on top of the Greenland ice sheet on Earth. To confirm that they are made of CO2 ice, HiRISE will image this location again at the end of the year and compare it to this image to look for changes.
Icy features should show large changes, but sand dunes move much more slowly. MareKromium
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PSP_004847_1745_RED_browse-00.jpgThe "Martian Black Hole"...Again! (context frame)56 visiteVi invitiamo a leggere l'ultimo articolo sull'argomento (pubblicato su TruePlanets) dal titolo "Velvet Underground".MareKromium
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PSP_004917_1080_RED_browse-00.jpgComplex Geology in the South Polar Layered Deposits (context image)56 visiteThis section of the HiRISE image shows a scarp exposing the South Polar Layered Deposits, with illumination from the upper right (scarp slopes toward bottom). The Polar Layered Deposits probably contain a record of relatively recent climate changes on Mars, similar to ice ages on Earth.
The Deposits appear to be composed mostly of water ice, with variations in dust content controlling the erosion of the layers. This image shows that the history of the South Polar Layered Deposits has not been simple accumulation of horizontal layers.MareKromium
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PSP_005419_1380_RED_browse-01.jpgFlow-like Features in Promethei Terra (extra-detail mgnf)56 visiteThe subimage (approx. 390 x 260 meters) shows in detail some of the ridges developed in the slope deposits. Numerous fissures cut through the surface, forming polygons 5 to 10 mt (5,5 to 11 yards) across.
Such well-preserved polygons indicate that the downhill flow had stopped before they formed. Polygonal features similar to these are common in terrestrial periglacial regions such as Antarctica, where ice is present at or near the surface. Antarctica's polygons formed by repeated expansion and contraction of the soil-ice mixture due to seasonal temperature oscillations.MareKromium
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PSP_005346_1755_RED_abrowse-01.jpgLow-Order Inverted Streams near Juventae Chasma (extra-detail mgnf)56 visiteThis subimage (approx. 1120 meters across) shows a juncture of 2 of the "Inverted Channels".
It is likely that the water flowed from the left to the right of the scene, because channels usually join rather than divert unless there is an obvious obstacle in the way.
No such obstacle is seen here, but one might have been present when the stream originally flowed.
However, there is no way of knowing this.MareKromium
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PSP_005680_1525_RED_abrowse-00.jpgPossible ancient Salt Deposits in Terra Cimmeria (Extremely Saturated and ENhanced Natural Colors - credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)56 visiteThe ancient cratered highlands of the Southern Hemisphere of Mars has an intriguing and complex history as it has been riddled with impact craters and modified by volcanic processes and by the wind.
Additionally, it is one of the most heavily dissected terrains on Mars exhibiting the densest population of Valley Networks: old dried up channels and valleys that may have been formed by surface runoff, the seepage of ground water, or both.
Recently, the Thermal Emission Imaging System (THEMIS) aboard Mars Odyssey, in conjunction with spectral data from the Thermal Emission Spectrometer (TES) aboard the Mars Global Surveyor (MGS) have revealed the presence of a unique surface deposit that may be rich in chloride salts formed from the presence of liquid water. Three separate missions (MGS, MO and MRO) have come to reveal the composition and nature of these unique deposits, which, although they occur as relatively small deposits (less than 25 square Km) are widely distributed in Noachian (most ancient) terrains with fewer occurrences in the Hesperian (middle geologic time) terrains.
The deposit appears to be relatively thin and occurs in low-lying areas. It is also heavily pockmarked and discontinuous, possibly from removal of the material by erosion. Both of these aspects suggest that the deposit is indeed very old.
The presence of such salts is intriguing, and strongly suggests that conditions were favorable for water near or at the surface in the geologic past.
Polygonal cracks can be observed in this image and other images of these deposits elsewhere on Mars (see PSP_003160_1410) and are similar to desiccation cracks (formed from the rapid evaporation and drying of a wet surface) and indicate that these may were more likely deposited at the surface.
However, the volume and duration the water required for these deposits is still being investigated. MareKromium
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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)56 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
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PSP_005813_2150_RED_abrowse.jpgUnusual Depression near Elysium Mons (MULTISPECTRUM; elab. Lunexit)56 visiteThis unusual depression and the associated concentric rings are situated within an area thought to have been deposited as a mud flow. Due to the lack of a distinctive, raised rim or other impact-related features, this crater is thought to have formed by the loss of material below the surface and subsequent collapse, rather than by an impact from space.
The exact mechanism for the loss of material is not fully understood, although the missing material was likely water in some form. This feature is near a large volcano, so perhaps there were explosive magma-water interactions that violently removed the water and some magma, followed by surface collapse. Or, less violently, there could have been simple melting of subsurface ice and then collapse of the surface into the resulting void. The rays emanating from the depression suggest some amount of violence before the surface collapse that sprayed material far from the depression.
Some aspects of this and other, nearby features are similar to the collapse pits associated with Grímsvötn volcano in Iceland, which erupts beneath an ice-cap. However, there are no rays formed during the eruptions at Grímsvötn.
MareKromium
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PSP_001374_1805_RED_browse-00~0.jpgLayering in Exhumed Crater at Meridiani Planum Region (context image - MULTISPECTRUM; credits: Lunexit)56 visite...Noi, detto senza falsa modestia, sfidiamo la NASA a fare di meglio...MareKromium
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PSP_005388_1975_RED_abrowse-01.jpgPang Boche Crater (EDM; False Colors; credits for the additional process.: Dr Paolo C. Fienga - Lunexit Team)56 visiteThe interior of Pang Boche Crater contains material that likely slumped off the walls during late stages of its formation. The north wall of the crater has material that has not slumped to the floor, instead forming a terrace.
Also noteworthy is the abundance of small craters that surround, but do not occur within, Pang Boche. These are mostly Secondary Craters that formed when ejecta from an impact hit the surface. If the small craters were Primary Craters (formed from an impactor from space), then they would be expected to be within Pang Boche as well. Secondaries commonly occur in clumps as seen in this extra-detail mgnf (which is approx. 2 km across).
The strong clustering indicates that these craters are Secondaries.MareKromium
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