火星的细节

来源:http://hirise.lpl.arizona.edu/PSP_001984_1735

Swirls of Rock in Candor Chasma  (PSP_001984_1735)

Credit: NASA/JPL/University of Arizona

This image shows spectacular layers exposed on the bottom of Candor Chasma, which is a large canyon in the Valles Marineris system.

The floor here is approximately 4 kilometers below the canyon rim. The layers are made of sand- and dust-sized particles that were transported here by either wind or water. This canyon may have been filled to its rim by these sedimentary layers, subsequently eroded away, most likely by the wind. The elongate hills may represent areas of rock that are stronger due to differences in the size of the sedimentary particles, chemical alteration, or both.

One of the most eye-catching aspects of this scene are the intricate swirls that these layers form. Sedimentary rock generally accumulates in horizontal layers. These layers, however, have been folded into the patterns that we see today. Folding of the layers that are exposed here may have occurred due to the weight of overlying sediments.

Understanding the geologic history of this region may provide clues into the history of water on Mars, because these layers may have accumulated in shallow lakes and may have undergone chemical reactions with this water. The presence of certain kinds of chemical reactions between water and rock can release energy that could have sustained habitable oases in these areas.

                               
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来源:http://hirise.lpl.arizona.edu/PSP_001546_2015

Layers in Becquerel Crater  (PSP_001546_2015)

Credit: NASA/JPL/University of Arizona

The layers shown in this image formed by loose sediment accumulating within Becquerel Crater.

The layers are interesting in that there are repeated cycles of thick and thin layers. These cyclic changes in layer thickness shows that some environmental conditions varied in a repeated way as each subsequent layer was deposited.

These variations may be due to annual climate cycles and/or a cyclic variability in the source of the sediment. Most layers are parallel to each other, indicating that deposition occurred by material settling onto the surface. A few layers are cross-bedded, meaning that they are not parallel to the older or younger layers.

Cross-bedding indicates that at the time that the layers were deposited, the sediment was transported along the ground surface by wind or water.

来源:http://hirise.lpl.arizona.edu/PSP_001488_1750

Edge along Gale Crater Interior Mound  (PSP_001488_1750)

Credit: NASA/JPL/University of Arizona

Gale Crater is one of several craters around the equator that have deposits of light-toned layered deposits. This HiRISE image covers the northern edge of the light-toned layered deposit in the center mound of Gale Crater, as well as a small portion of the crater floor.

The top of the image shows a relatively flat surface with lots of impact craters. Moving southward, there is a large canyon where dark sands have accumulated and formed ripples and dunes.

As one moves further to the south, the light-toned layered deposit rises upward in topography. Layering can be seen in some locations. The surface of the light-toned deposit is very fractured, producing meter-size blocks. The fact that we don't see many loose rocks along the surface suggests that the rocks are quickly being destroyed by winds due to their fragile nature.



Resistant hills tend to be elongated from the upper left to the lower right, consistent with upslope or downslope winds eroding the rocks.

来源:http://hirise.lpl.arizona.edu/PSP_001534_1560

Stereo Anaglyphs of River Meanders in Eberswalde Delta  (PSP_001534_1560)

Credit: NASA/JPL/University of Arizona

Eberswalde Delta contains river meanders, which indicate that flowing water was present for an extended period of time, not just the weeks required to explain the catastrophic flood channels.

Available here are two red-blue color anaglyphs in which you can view the topography with red-blue glasses (blue filter over your right eye). The first of these anaglyphs shows a relatively large area but with 3x reduction of spatial scale (75 cm/pixel), and the second is a sample at full resolution (25 cm/pixel, 10 MB).

The former river channels are high rather than low, which is called inverted relief. Coarse gravel was deposited in the stream channel, which later proved more resistant to erosion than the materials outside the channel, creating this inverted relief.

Meanders are formed when a river channel gradually erodes the outer banks, increasing the curvature of the channel. Eventually the river decides to take a short cut, cutting off a meander, as shown here. This produces what are called oxbow lakes.

(We previously released image PSP_001334_1560, including color, but acquired a later image (PSP_001534_1560) over this same area but from a different viewing angle to provide stereo coverage.)

来源:http://hirise.lpl.arizona.edu/PSP_001662_1520

Layered Deposits in Terby  (PSP_001662_1520)

Credit: NASA/JPL/University of Arizona

Terby Crater is a large (diameter ~165 km), Noachian-aged crater located on the northern rim of the Hellas impact basin (28ºS, 74.1ºE).

Terby hosts a very impressive sequence of predominantly light-toned layered deposits, up to 2.5 km thick that are banked along its northern rim and extend toward the center of the crater.

HiRISE image PSP_001662_1520 (1.4 MB) shows this stack of layered rocks as they are exposed westward facing scarp. The layered sequence consists of many beds that are repetitive, relatively horizontal and laterally continuous on a kilometer scale. Many beds are strongly jointed and fractured and exhibit evidence of small-scale wind scour.

The light-toned layers are typically at least partially covered with dark mantling material that obscures the layers as well as debris and numerous, meter-scale boulders that have cascaded down slope. The processes responsible for formation of these layers remain a mystery, but could include deposition in water, by the wind, or even volcanic activity.

This HiRISE image is a proposed landing site for the Mars Science Laboratory (MSL) in Terby Crater.

                               
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来源:http://hirise.lpl.arizona.edu/PSP_001440_1820

Northeast Sinus Meridiani Landforms  (PSP_001440_1820)

Credit: NASA/JPL/University of Arizona

来源:http://hirise.lpl.arizona.edu/PSP_002464_1745

Southern Layered Mound and Floor in Gale Crater  (PSP_002464_1745)

Credit: NASA/JPL/University of Arizona

This HiRISE image shows the interior of Gale Crater, a region being considered as a landing site for the 2009 Mars Science Laboratory.

Gale is distinguished from many other craters on Mars by a large interior layered mound that extends to the height of the crater rim. The top part of this image contains portions of the southeast part of the mound, with the bottom part showing details of the crater floor.

The mound material here is exposed as several distinct smaller hills. Close up, the hills show abundant rocks and debris aprons on their flanks, lacking distinct bedrock layers seen elsewhere on Mars. This suggests that the mound material is friable and easily eroded by the wind over time.

Other evidence of wind activity includes bright bedforms near the top of the image and dark bedforms and sand sheets at bottom. Between the hills and dark sand are a series of stacked stratigraphic units. Polygons are seen in some of the units, indicating contraction due to water loss, cooling, or some other process. Many of the polygons seem highly fractured.

Possible crossbeds are seen in some of the rock exposures near the bottom of the image. This and other images of Gale will be studied over the coming months and years in order to better understand the geology and further assess the potential as a future landing site.

                               
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来源:http://hirise.lpl.arizona.edu/PSP_002743_1985

Proposed MSL Site in Nili Fossae Crater  (PSP_002743_1985)

Credit: NASA/JPL/University of Arizona

HiRISE image of proposed landing site for the Mars Science Laboratory (MSL) in Nili Fossae Crater.

                               
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来源:http://hirise.lpl.arizona.edu/PSP_001480_2015

Proposed MSL Site in Becquerel Crater  (PSP_001480_2015)

Credit: NASA/JPL/University of Arizona

HiRISE image of proposed landing site for the Mars Science Laboratory (MSL) in Becquerel Crater.

来源:http://hirise.lpl.arizona.edu/PSP_002809_1965

Proposed MSL Site in NE Syrtis Major  (PSP_002809_1965)

Credit: NASA/JPL/University of Arizona

HiRISE image of proposed landing site for the Mars Science Laboratory (MSL) in Northeast Syrtis Major.

                               
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强贴，顶

来源:http://hirise.lpl.arizona.edu/PSP_002832_1770

Proposed MSL Site in Elysium/Avernus Colles  (PSP_002832_1770)

Credit: NASA/JPL/University of Arizona

HiRISE image of proposed landing site for the Mars Science Laboratory (MSL) in Elysium/Avernus Colles.

来源:http://hirise.lpl.arizona.edu/PSP_002812_1855

Proposed MSL Site in Southwest Arabia Terra  (PSP_002812_1855)

Credit: NASA/JPL/University of Arizona

HiRISE image of proposed landing site for the Mars Science Laboratory (MSL) in Southwest Arabia Terra.

来源:http://hirise.lpl.arizona.edu/PSP_001596_1525

Layers in Terby Crater  (PSP_001596_1525)

Credit: NASA/JPL/University of Arizona

Image PSP_001596_1525 shows a sequence of predominantly light-toned, layered, sedimentary rocks exposed by erosion on the floor of Terby Crater. Terby Crater is ~165 kilometers (~100 miles) in diameter. It's located on the northern rim of the Hellas impact basin in the southern hemisphere of Mars.

The layered sequence is ~2 kilometers (~1.2 miles) thick and consists of many repetitive, relatively horizontal beds. The beds appear to be laterally continuous, which means you can identify a given layer in many locations across the area.

Details in the layering seen in this HiRISE image reveal variations in the brightness of the layers and may indicate differing mineralogies. Based on the ease with which wind appears to erode these layers, they are believed to be composed mostly of fine-grained sediments. However, one or more of the beds is weathering to form meter(yard)-scale boulders that have accumulated downslope in fans of debris (see subimage, full resolution, approx. 200 m [218 yards] across; 880x1062, 3 MB). These larger boulders indicate the material in the layers may be stronger than just fine-grained sediments.

It's not clear how these layers formed, but it may have involved deposition by wind or volcanic activity. Another theory involves all or part of the Hellas basin being filled with ice-covered lakes at one time in the past. The layers we see may have formed as material that was suspended in the water dropped down to the bottom of the lake.

来源:http://hirise.lpl.arizona.edu/PSP_003063_2050

Proposed MSL Site in Mawrth Vallis  (PSP_003063_2050)

Credit: NASA/JPL/University of Arizona

HiRISE image of a proposed landing site for the Mars Science Laboratory (MSL) in Mawrth Vallis.

来源:http://hirise.lpl.arizona.edu/PSP_003249_1510

Layered Deposits in Ritchey Crater  (PSP_003249_1510)

Credit: NASA/JPL/University of Arizona

This HiRISE image shows eroding layered deposits in Ritchey Crater, a large impact crater in the southern highlands.

Three general units can be seen: a relatively dark upper layer, a light middle unit, and the floor material, which may be mostly obscured by dust. The dark cap layer appears to be relatively hard and resistant, while the light material is weak. Once the upper layer is removed, the light layer does not last long.

The cutout from the top center part of the image shows this stack (2196x1442; 3 MB). The dark unit is thin and breaking into boulders. The light material is actually divided into smaller layers, and is pervasively fractured. However, the boulders falling from the edge are mostly small and rarely remain intact if they move more than a few meters. The cracking of the layer could be due to water loss from the layer, or to regional tectonic effects such as stresses from burial and erosion. The base unit is partially covered by wind-blown ripples.

It is unclear how each of these layers formed. Volcanic ash layers, lake or stream deposits, or sandstone deposited by dunes can all produce horizontal layers. Unraveling the origin would provide important clues to Mars' past.

                               
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