Mars Reconnaissance Orbiter (MRO)
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TRA_000827_1875_IRB.jpgCerberus' River62 visiteThe prominent trough in this sub-image (of HiRISE image TRA_000827_1875_IRB ) 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 ridgesÑremnants of the former surfaceÑcast jagged shadows on the floor of the graben that reveal the rugged nature of the landscape in this region of Mars.
Image TRA_000827_1875 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on September 29, 2006. The complete image is shown below, centered at 7.4 degrees latitude, 168.5 degrees East longitude. The range to the target site was 275 km (171 miles). At this distance the image scale is 55 cm/pixel (with 2 x 2 binning) so objects ~165 cm across are resolved. The image shown below has been map-projected to 50 cm/pixel and north is up. The image was taken at a local Mars time of 3:26 PM and the scene is illuminated from the west with a solar incidence angle of 51.9 degrees, thus the sun was about 38.1 degrees above the horizon. At a solar longitude of 113.7 degrees, the season on Mars is Northern Summer / Southern Winter.
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TRA_000827_1875_RED_browse-2.jpgCerberus' River (Extremely Saturated Natural Colors; credits for the additional process. and color.: Dr Gianluigi Barca - Lunexit Team)55 visitenessun commentoMareKromium
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TRA_000828_1805_IRB-01.jpgYardangs in Medusae Fossae (1)53 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)53 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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TRA_000828_1805_IRB-03.jpgYardangs in Medusae Fossae (3)59 visitenessun commento
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TRA_000828_1805_IRB-04.jpgYardangs in Medusae Fossae (4)53 visitenessun commento
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TRA_000828_2495_IRB-1.jpgPolygonal Terrain (1)53 visiteA network of shallow surface troughs and fissures coalesce into polygonal patterns that are ubiquitous throughout this image. Polygonal patterned ground of this nature is quite common in permafrost regions of Earth, where seasonal thermal contraction of ice-cemented soil produces a honeycomb network of subsurface cracks. Cracks of this nature can also be produced by desiccation (mud cracks) or lava cooling (columnar joints), though typically on a smaller scale. The diameter of these martian polygons are dominantly 10-20 meters, analogous to terrestrial permafrost. The individual troughs are frequently only a couple of meters or less wide, and easily resolved at HiRISE resolution. Other characteristics, such as small ridges on either side of the troughs and the distribution of rocks in and around each polygon is also readily apparent. Small rocks and occasional larger boulders are also seen scattered throughout the image. Rocks protruding above the surface soil can be seen to cast shadows (solar illumination is from the lower left), which can aid in the determination of the rock's size and height. This image is located near an area under consideration as a landing site for the Mars Scout mission, Phoenix, planned for 2008. Examination of many factors including surface texture (roughness and morphology) and the size distribution of rocks will aid in final landing site selection.
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TRA_000828_2495_IRB-2.jpgPolygonal Terrain (2)54 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_000830_1440_IRB-1.jpgNiger Vallis (1)53 visiteThis image shows a portion of the floor of Niger Vallis, an ancient Martian outflow channel. Niger Vallis originates on the flanks of the volcano Hadriaca Patera, and empties into the Hellas impact basin. Outflow channels are observed in many regions of the planet, and may have been carved by brief eruptions of liquid water from beneath the surface. Since Niger Vallis formed, impacts have cratered the channel floor, and fine-grained wind-blown debris has been transported across the surface, eroding and burying all but the freshest craters. The curved ridge in the scene may be the remnant of a large crater rim. At the high resolution of this image, a pattern of parallel dunes and ripples can be seen, as well as individual boulders as large as two meters across.
Image TRA_000830_1440 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on September 30, 2006. The full image shown below is centered at -35.5 degrees latitude, 92.1 degrees East longitude. The range to the target site was 255 km (159 miles). At this distance the image scale is 51 cm/pixel (with 2 x 2 binning) so objects ~153 cm across are resolved. The image shown here has been map-projected to 50 cm/pixel and north is up. The image was taken at a local Mars time of 3:35 PM and the scene is illuminated from the west with a solar incidence angle of 77.5 degrees, thus the sun was about 12.5 degrees above the horizon. At a solar longitude of 113.8 degrees, the season on Mars is Northern Summer / Southern Winter.
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TRA_000830_1440_IRB-2.jpgNiger Vallis (2)53 visitenessun commento
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TRA_000840_2750_IRB-001.jpgChasma Boreale (1)53 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_000840_2750_IRB-002.jpgChasma Boreale (2)53 visiteDifferent layers show very different degrees of roughness and pitting, although the texture within a layer is quite consistent. One of the layers even displays a texture of polygons 3 up to 10 mt across, normally associated with periglacial freeze-thaw processes on Earth. Layers of different texture, brightness, and appearance indicate differing physical properties, composition and exposure to surface environmental conditions at time of emplacement and/or erosion.
In this way, polar layers on Mars record a history of climate conditions as sequences of layers on Earth often do.
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