| Piú viste - Mars Reconnaissance Orbiter (MRO) |
ESP_012774_1080_RED_abrowse-00.jpgDefrosting Dunes in Richardson Crater (ctx frame - Natural Colors; credits: Lunar Explorer Italia)60 visiteThis image shows a portion of the Dunes that fill Richardson Crater, a 55-Km-diameter crater in the South Polar Region of Mars and a frequent repeat target for the HiRISE camera.
During Southern Fall and Winter, these Dunes are coated with seasonal CO2 frost, which then sublimates into the Atmosphere as the temperature rises in Spring and Summer.
This Natural Color shows a boundary between Dunes that are mostly covered with Seasonal Frost and Dunes that have mostly thawed. The color of many dunes on Mars can change dramatically depending on the Season. Frost tends to be very bright in HiRISE images, particularly in the blue-green filter, but the Dune sand itself is very dark.
The dark streaks and spots on the frost-covered regions represent areas that are in the process of thawing out. In some areas, the frost has sublimated away. In others, a small avalanche of sand or dust may have spilled on top of the frost. Some of them may also be patches of coarse-grained ice that are relatively clear so that we can see the sand below. As Spring advances toward Summer in the South on Mars, these Dunes continue to appear darker and more red to HiRISE.
Dunes near the Polar Regions of Mars are studied both by scientists who are interested in the effects of this seasonal cycle of thawing and frosting over, and by scientists who wait for the frost to disappear so that they can study the dunes themselves.MareKromium
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ESP_012774_1080_RED_abrowse-01.jpgDefrosting Dunes in Richardson Crater (edm - Natural Colors; credits: Lunar Explorer Italia60 visitenessun commentoMareKromium
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ESP_011633_1195_RED_abrowse.jpgDunes (Natural Colors; credits: Lunar Explorer Italia)60 visitenessun commentoMareKromium
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ESP_011610_0935_RED_abrowse.jpgSawtooth Pattern in Carbon Dioxide Ice (Natural Colors; credits: Lunar Explorer Italia)60 visitenessun commentoMareKromium
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ESP_012251_0935_RED_abrowse.jpgJust like Magnetic Fields (Natural Colors; credits: Lunar Explorer Italia)60 visitenessun commentoMareKromium
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ESP_012853_1480_RED_abrowse-00.jpgTerra Cimmeria (ctx frame - Natural Colors; credits: Lunar Explorer Italia)60 visiteThis image shows a network of small valleys in the Terra Cimmeria Region of the Martian Southern Highlands. This location is approx. 1000 Km (about 600 miles) South of Gusev Crater, the Landing Site of the Mars Exploration Rover Spirit.
The valleys in this image are carved into light-toned bedrock exhibiting a range of colors, which likely reflect a range of mineralogical compositions. The bedrock is pervasively fractured, and some of the fractures appear to be filled with material of a different color, possibly composed of minerals that crystallized or were cemented together when fluids (perhaps water) circulated through the fractures.MareKromium
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ESP_012271_0940_RED_abrowse.jpgSouth Polar "Swiss-Cheese Surface Features" (Natural Colors; credits: Lunar Explorer Italia)60 visiteThis image represents a Martian Terrain containing "Swiss Cheese" features. This Terrain is found only within the residue of the Southern Polar Cap, which comprises of mostly frozen CO2 and H2O.
These particular features are flat-floored, circular depressions that are believed to form from different rates in the seasonal changes of the CO2 and H2O ices. Varying rates in sublimation (when these ices change directly to vapors upon heat and back to deposited solids upon cooling) produces these rimmed depressions from the flat polar ice plane. It is hypothesized that the depression areas are made up of dry ice - such as Carbon Dioxide - and the material below consists of the water ice.
This Carbon Dioxide solid rises and slightly evaporates into the thin Atmosphere in the Summer while the water layer remains in place. As the South Pole cools with seasonal change, the "Swiss Cheese" formation is obtained with risen CO2 rimmed depressions and flat water mesas.
The Martian North Pole will evaporate all of its CO2 in the Summer; however the South Pole is colder and this may explain why this Terrain is only found in this area.
Some of the circular features in the full image show distinct cusps that point in the direction of the Pole. These cusps suggest insolation, a measure of solar radiation that is pushing the movement/formation of these depressions away from the Pole. There is also an observed lateral outward growth of the features at the rate of about 1-to-3 meters a year, indicating to scientists that the depressions must form in a CO2 medium.MareKromium
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ESP_013071_1365_RED_abrowse.jpgCentral Peak Gullies (Natural Colors; credits: Lunar Explorer Italia)60 visitenessun commentoMareKromium
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ESP_012926_1365_RED_abrowse.jpgLohse Crater (Natural Colors; credits: Lunar Explorer Italia)60 visiteThis image is of the Eastern half of the Central Peak of Lohse Crater located in the Southern Hemisphere.
The crater itself is highly degraded and is roughly 80 miles in diameter. Of specific interest are the pristine looking Gullies that appear to have sourced from layers below the top of this uplifted region.
Smaller Gullies appear to emanate in all directions from the uplifted region, but of special interest is the larger Gully located on the northern most slope of the Central Peak. This Gully has a larger alcove and a better developed debris apron than surrounding Gullies. This implies that either this gully formed over a longer time period or that more fluid was involved in its formation.
Gullies are present on many slopes on Mars, especially between the latitudes of 30 and 70° in both Hemispheres. Gullies are formed by fluids and have three distinct parts to them: an eroded “alcove” at the top, a sometimes sinuous “channel” section, and finally a large “debris apron” where the material eroded by the Gully is deposited.MareKromium
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ESP_013144_2075_RED_abrowse.jpgCollapse Features on the Flank of Elysium Mons (Natural Colors; credits: Lunar Explorer Italia)60 visiteThis image is of the Flanks of the "Shield Volcano" Elysium Mons. The volcano is considered to be the youngest within the Elysium Mons Province, which also contains the volcanoes Hecates Tholus and Albor Tholus.
Of course, "young" is a relative term. The last eruption of Elysium Mons could well have been a billion years or more ago.
This image shows a series of flat bottomed valleys along the flanks of Elysium Mons. There is considerable debate on exactly how these valleys form. In Hawaii, the classic example of Shield Volcanoes on Earth, similar valleys are carved by prodigious rainfall. While some rain may have fallen in the earliest epochs of Mars' Geologic History, the lack of small drainage networks shows that these Martian Channels were not carved by rain. However, Mudflows and Lava Flows could potentially erode the sides of the Volcano.
An important hint for the origin of the Valleys comes from the Chain of Pits visible in the Northern part of the image. These Pits form as the ground is pulled apart by Marsquakes. Thus it seems that many of these Valleys are first formed by movement along Faults. Then Mud and/or Lava Flows widen the sides of the Valley and give it a flat floor.MareKromium
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ESP_012506_0850_RED_abrowse.jpgDefrosting Spots over Polygonal Terrain (Natural Colors; credits: Lunar Explorer Italia)60 visitenessun commentoMareKromium
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ESP_011749_1000_RED_abrowse.jpgSpring View of Unnamed Crater with South Polar Layered Material (Natural Colors; credits: Lunar Explorer Italia)60 visitenessun commentoMareKromium
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