| Piú votate - Mars Reconnaissance Orbiter (MRO) |
TRA_000828_1805_IRB-04.jpgYardangs in Medusae Fossae (4)60 visitenessun commento
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TRA_000828_1805_IRB-03.jpgYardangs in Medusae Fossae (3)64 visitenessun commento
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TRA_000828_1805_IRB-01.jpgYardangs in Medusae Fossae (1)57 visiteThis series of 4 images covers a portion of an outcrop of the Medusae Fossae Formation, a series of light-toned terrains in the Martian Mid-Latitudes. The Medusae Fossae has been and remains one of the most enigmatic features on Mars. The unit is characterized by wind-sculpted landforms, most notably eroded ridges known as yardangs. The composition of the Medusae Fossae is not known, but candidates include indurated (hardened) volcanic ash or remnants of dust-ice mixtures that formed in a different Martian climate. This HiRISE image reveals new details of the Medusae Fossae.
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TRA_000828_1805_IRB-02.jpgYardangs in Medusae Fossae (2)59 visiteImage TRA_000828_1805 (here broken in 4 sub-images) was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on September 30, 2006. The full image is centered at 0,5° North Latitude and 142,1° East Longitude.
The images are oriented such that North is towards the top. The range to the target site was 270 Km (about 169 miles). At this distance the image scale is 27 cm/pixel (with 1 x 1 binning) so objects ~81 cm across are resolved. The image was taken at a local Mars time of 03:27 PM and the scene is illuminated from the west with a solar incidence angle of 55,2°, thus the Sun was about 34,8° above the horizon.
At a Solar Longitude of 113,6° the season on Mars is Northern Summer.
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North_Polar_Regions-Chasma_Boreale-PIA01926-det.jpgThe Walls of Chasma Boreale80 visiteThe Martian terrain in this remarkable image is at the head of a large chasm, named Chasma Boreale, which cuts through Mars' North Polar Layered Deposits (MNPLD). These ice-rich layered deposits are about 3000 mt (about 9.800 feet) thick and 1000 Km (1.600 miles) across, much like the Greenland ice-sheet on Earth. The head of Chasma Boreale ends in a steep icy cliff more than 1000 mt (about 3300 feet) high. The cliff has both light- and dark-toned layers, seen at right in this image. The image was taken by the HiRISE camera on NASA's MRO. The internal layers of the ice-sheet are visible in the cliff walls. The dark-toned flat area in the center and left of the image is the floor of this chasm, which contains many craters.
Scientists have proposed that Chasma Boreale was formed by a catastrophic flood that began under the ice-sheet and was later widened by wind erosion. However, the large number of craters on the chasm's floor implies that the floor is much older than the ice sheet. These craters should have been removed by the suggested flood; their presence has caused some Mars researchers to instead speculate that no large flood occurred and that Chasma Boreale was not covered with very much ice.
In addition to layered ice, there is also some material within the north polar layered deposits that appears to be composed of sand. The dark material near the base of the cliff wall is thought to be aprons of debris being eroded from sand-rich layers. Zooming in on this dark material with HiRISE reveals ripples, which are diagnostic of moving sand.
Some bright spots of material visible on the cliff wall were not present in previous years. These are likely patches of water frost. Each year layers of carbon dioxide and water frost coat this terrain before being removed during the summer. The water frost lasts longer, and patches that are shaded by nearby steep topography (such as this one) can persist even into late summer.
An unexpected surprise, not visible with previous camera resolutions, is the fragmentation of the exposed surfaces of these icy layers into polygonal blocks. These blocks appear to be breaking away from the layer margins and forming boulder-sized debris, which then rolls down slope (a process called mass-wasting). These boulders are likely to be large blocks of dusty water ice; once separated from the main ice-sheet they can be eroded away by sunlight. More boulder-sized objects are visible out in the floor of the chasm. Polygons are also visible throughout the chasm floor, indicating that water-ice is just below the surface.
Image TRA_000845_2645 was taken by the HiRISE camera on Oct. 1, 2006. The complete image is centered at 84.6 degrees latitude, 3.4 degrees east longitude. The range to the target site was 316 kilometers (198 miles). At this distance the image scale is 63 centimeters (25 inches) per pixel (with 2 x 2 binning), so objects about 186 centimeters (73 inches) across are resolved. The image shown here has been map-projected to 50 centimeters (20 inches) per pixel. North is up. The image was taken at a local Mars time of 3:34 p.m. and the scene is illuminated from the west with a solar incidence angle of 62.3 degrees, thus the sun was about 27.7 degrees above the horizon. At a solar longitude of 114.3 degrees, the season on Mars is northern summer.
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TRA_000840_2750_IRB-008.jpgChasma Boreale (7)60 visitenessun commento
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TRA_000840_2750_IRB-001.jpgChasma Boreale (1)60 visiteThis is an image of the North Polar Layered Deposits (NPLD) near the source Region of Chasma Boreale. Chasma Boreale is the largest re-entrant trough in the NPLD, with its head region located roughly 300 Km from the North Pole and its mouth opening into the Northern Plains at the perimeter of the NPLD. Chasma Boreale is thought to have formed due to outflow of water from underneath the Polar Cap, or due to winds blowing off the Polar Cap, or a combination of both.
Investigation of the currently visible layers around the source region may tell us if they have been deformed and down-dropped, perhaps by melting and flow of water beneath, or if they remain undisturbed. Layers here do not appear as fine as elsewhere in polar trough exposures, although this may be due to the relatively gently sloping exposure here.
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TRA_000828_2495_IRB-2.jpgPolygonal Terrain (2)59 visiteImage TRA_000828_2495 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on September 30, 2006. The complete image is centered at 69,3° North Latitude and 130,2° East Longitude. The range to the target site was 315 Km (199 miles). At this distance the image scale is 32 cm/pixel (with 1 x 1 binning) so objects ~96 cm across are resolved. The images shown here has been map-projected to 75 cm/pixel and North is up. The image was taken at a local Mars time of 3:01 PM and the scene is illuminated from the West with a solar incidence angle of 53,4°, thus the Sun was about 35,1° above the horizon. At a Solar Longitude of 113,7°, the season on Mars is Northern Summer / Southern Winter.
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TRA_000825_2665_IRB-00.jpgNorth Polar Layers (1)73 visiteThis image of the north polar layered deposits was taken during the summer season (solar longitude of 113.6 degrees), when carbon dioxide frost had evaporated from the surface. The bright spots seen here are most likely patches of water frost, but the location of the frost patches does not appear to controlled by topography. Layers are visible at the bottom of the image, mostly due to difference in slope between them. The variations in slope are probably caused by differences in the physical properties of the layers. Thinner layers that have previously been observed in these deposits are visible, and may represent annual deposition of water ice and dust that is thought to form the polar layered deposits. These deposits are thought to record global climate variations on Mars, similar to ice ages on Earth. HiRISE images such as this should allow Mars' climate record to be inferred and compared with climate changes on Earth.
Image TRA_000825_2665 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on September 29, 2006. Shown here is the full image, centered at 86.5 degree latitude, 172.0 degrees East longitude. The image is oriented such that north is to the top. The range to the target site was 298.9 km (186.8 miles). At this distance the image scale is 59.8 cm/pixel {with 2 x 2 binning} so objects ~1.79 m across are resolved. In total the original image was 12.2 km (10024 pixels) wide and 6.1 km (5000 pixels) long. The image was taken at a local Mars time of 3:30 PM and the scene is illuminated from the southwest with a solar incidence angle of 63.5 degrees, thus the sun was about 26.5 degrees above the horizon.
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TRA_000823_1720_RED_fault.jpgFault of Jus57 visiteThe sharpness and quality of HiRISE images allows geologists to work out the detailed geometry and sequence of events that have shaped the landscape. For example, this area shows exposures of light- and dark-toned layers of rock that have been faulted and folded. These rocks formed out of sedimentary deposits that originally accumulated in thick horizontal sequences, like a layer cake.
These layers have since been tilted on-end and eroded, exposing the sequence of layers that we now see at the surface. A prominent dark layer extends through the center of the scene from the upper right to the lower left of the image. This dark layer is discontinuous and offset along a fault.
The thin grey zone that extends from the upper left to the lower right of the image delineates the fault plane. This fault was originally a thrust, or compressional fault, that formed prior to the aforementioned tilting event. Tilting of this fault and the surrounding rock reveals a series of drag folds adjacent to the fault plane. These drag folds formed as the layered rock bent in response to friction along the fault plane as the thrust fault formed, prior to the tilting event. This fault offsets the dark layer by a maximum of 70-75 m. Smaller secondary folds and faults are also visible in this scene. The smallest resolved fault offset of an individual rock layer is 1-1.5 m. Also visible in this image are numerous small 4-10-m-diameter impact craters that are surrounded by ejecta of meter-scale boulders.
(3 voti)
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T-TRA_000853_1900_RED_MarteValles_01.jpgSeeps in Marte Vallis58 visiteMarte Vallis is a relatively young channel system on Mars that was carved by catastrophic floods of water. The HiRISE image samples just a small part of the valley system, but captures a variety of different landforms. The mesa in the eastern half of the image is a remnant of the pre-flood surface while the valley floor is covered by a surface with plates and ridges.
We highlight a piece from the southeastern portion of this HiRISE image, along the edge of the mesa. Some of the most striking features in this area are the dark streaks streaming down the cliff face. These mark locations where the layer of dust has been removed, exposing the darker surface underneath. The details of this cleaning process are not well-understood, but are thought to be driven by avalanches of dust. These avalanches appear to be more capricious than typical landslides or mudslides—they are sometimes able to surmount some large obstacles but in other cases are deflected by relatively small boulders. The darkness of the streaks vary, which suggests that they formed at different times. These streaks are expected to gradually fade as more dust will be deposited in the future. However, such fading has yet to be observed.
The role of dust is also clearly evident on the floor of the valley. The fluted mounds are characteristic of a thick dust deposit that is being gradually stripped away by wind. This extensive dust cover complicates any attempt to understand the details of the floods that carved the valley and the processes that formed the plates and ridges on the floor.
(3 voti)
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T-TRA_000827_1875_RED.jpgA long trough in Cerberus Fossae59 visiteThe prominent trough in this image is a segment of the Cerberus Fossae rift system. In geological terminology the trough is known as a graben, or down-dropped region bounded by faults. In this location the graben is about 300 m wide and 90 m deep. Bright, dust-covered, cratered plains surround the graben, and darker sediments blanket much of its floor. Dunes that vary in size and spacing occur within the darker sediments, and their shapes suggest that the wind typically blows from east to west. Light-toned, angular boulders pepper the darker sediments. They have broken away from the rocky walls of the graben and tumbled downhill. Over time this mass wasting has caused the cliffs to retreat, widening the trough. The somewhat lighter patches of cratered terrain on the graben floor were once level with the surrounding plains, but have since been lowered by faulting. Over time they may become obscured or buried by the darker sediments. High-standing ridges - remnants of the former surface - cast jagged shadows on the floor of the graben that reveal the rugged nature of the landscape in this region of Mars.
(3 voti)
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