火星的细节

来源:http://hirise.lpl.arizona.edu/PSP_006234_1870



Cerberus Fossae and Surrounding Features  (PSP_006234_1870)

Credit: NASA/JPL/University of Arizona

This observation shows lightly cratered plains in Elysium Planitia, which is a low-lying area located in the equatorial region of Mars. Part of an extensional (normal) fault system known as the Cerberus Fossae runs through the center of this image.

Elsewhere in Elysium Planitia, the Cerberus Fossae acted as a fissure-vent for erupting flood lavas, but here the geological activity appears to have been predominantly tectonic. Nonetheless, the raised, lobate (tongue-shaped) margin of an ancient lava flow is faintly discernible in the southern part of the image.

Near the center of the image, a few relatively deep depressions, partly filled with dark sand, are visible in the Cerberus Fossae. These are pit craters formed by collapse as normal faulting progressed. The largest pit crater is about 110 meters (360 feet) wide and about 300 meters (980 feet) long. Steep scarps along the perimeters of the pit craters and the linear margins of the Cerberus Fossae provide a cross-sectional view of the near-surface strata. The exposed material is rocky and has the tendency to break into large boulders that tumble downhill as erosion widens the troughs and depressions. A few low hills appear in the northern half of the image; dark streaks etch their flanks. These “dark slope streaks” formed when small avalanches removed a surface layer of bright dust, exposing darker underlying materials.

The different shades of the streaks may reflect their relative ages, with darker slope streaks being fresher features.

                               
登录/注册后可看大图

来源:http://hirise.lpl.arizona.edu/PSP_005788_1035

Repeated Erosion and Deposition in the South Polar Layered Deposits  (PSP_005788_1035)

Credit: NASA/JPL/University of Arizona

This image of the south polar layered deposits (SPLD) shows evidence of multiple episodes of deposition and erosion near the base of those deposits.

The SPLD, like the north polar layered deposits, are thought to contain a record of global climate changes on Mars. The surface of the outcrop shown here slopes generally toward the right. The layering at the bottom of the image is cut off by deposits that partly fill two broad valleys that were previously cut into the SPLD, probably by wind erosion. These more recent deposits appear to cover the flatter, upper part of the SPLD at left, and have also been eroded to expose layering with them.

                               
登录/注册后可看大图

来源:http://hirise.lpl.arizona.edu/PSP_006270_0955

South Polar Layered Deposits and Residual Ice Cap  (PSP_006270_0955)

Credit: NASA/JPL/University of Arizona

A wide variety of south polar terrains are on display in this spectacular HiRISE color image. The reddish material in the upper two thirds of the image is the south polar layered deposits (SPLD). These deposits are a stack of layered, dusty water ice. Scientists believe that these layers record previous climatic conditions on Mars, much like terrestrial ice-sheets provide a record of climate change on the Earth.

This image shows the face of one of the many scarps or shallow cliffs that cut into the polar layered deposits. These scarps expose the internal layers within the SPLD. You can see these climate-recording layers in the upper two thirds of the image running from lower-left to upper-right.

The terrain in the lower third of the image is quite different in both appearance and composition. The bright, white-ish material is a thin covering of carbon dioxide ice draped over the flat areas of the SPLD. This covering of carbon dioxide is being eroded away by expanding flat-floored pits. Parts of the floors of these pits show the reddish brown coloring of the underlying polar layered deposits. These pits have eroded the carbon dioxide ice layer to such an extent that only isolated mesas remain today and even these shrink in extent by a few meters each year.

These mesas also have several layers within them, indicting that they likely contain a climatic record, albeit a much shorter one than preserved in the SPLD. Most of the isolated mesas have white-ish tops; however, some (near the foot of the SPLD scarp) have reddish tops. This may either be due to bright carbon dioxide ice thinning to reveal the older (and darker) carbon dioxide ice that makes up the main body of the mesa, or perhaps dust has settled out of the atmosphere to cover the brighter frost. There was a large Martian dust storm earlier this year which could have caused either effect.

                               
登录/注册后可看大图

来源:http://hirise.lpl.arizona.edu/PSP_006148_1820

Sand and Rock in Meridiani Planum  (PSP_006148_1820)

Credit: NASA/JPL/University of Arizona

This observation shows rock outcrops in Meridiani Planum, in the area of the landing site of the Mars Exploration Rover, Opportunity. The image is centered on a cluster of buttes, steep-sided erosional remnants protruding from a level plain. There are two broad categories of material in the image: light-toned sedimentary rock and dark-toned material, which is likely wind-blown sand.

The light-toned material was probably deposited as sediments transported by wind or water; Opportunity found outcrops of aeolian (wind-deposited) sandstone, and this may also be the case in the area of this image. The dark areas show ripples formed by material (probably grains of sand eroded from basaltic lava) blowing in the wind.

In the RGB enhanced-color image (which is not what the colors would like to the naked eye), the dark material is relatively blue, while the light rock ranges from pale blue to tan. The pale blue color in some cases may be due to small amounts of basaltic sand overlying relatively tan rock outcrops, but could also be a real difference due to varying composition or cementation of the rock.

The presence of buttes like those at the image center suggests rock layers of varying resistance. Relatively hard, resistant rock on top can armor a patch of weaker material below; this is commonly observed on Earth. Relations like this are found at many sites in the Colorado Plateau (the Four Corners area of the United States), which has been used as an analogue for this region on Mars.

                               
登录/注册后可看大图

真是太酷了，张张精品，再顶！

先去吃饭了回来再贴。

lz辛苦了。顶一下先，
我的望远镜要是能达到这个境界那就牛×。

来源:http://hirise.lpl.arizona.edu/PSP_006006_1715

Layering in Upper Walls of Valles Marineris  (PSP_006006_1715)

Credit: NASA/JPL/University of Arizona

This observation shows parts of the upper walls of Valles Marineris with layered rocks. These layers extend down to a smooth-appearing slope, that is likely material shed from the upper parts of the chasm walls; down-slope stripes are visible, indicating that material has fallen or slid downhill in a process termed "mass wasting."

The layers, exposed in most rock outcrops in this image, are most likely lava flows from flood lavas that once erupted across the region. These layers are located in the upper walls of most of Valles Marineris and are sometimes exposed at depths well below the surrounding plateau, recording extensive volcanism in the history of the region. Similar, thick successions of lava flows are found at some sites on Earth (for example, the Columbia River flood basalts in the northwest U.S.).

                               
登录/注册后可看大图

来源:http://hirise.lpl.arizona.edu/PSP_005456_1650


Color View of Spirit at ‘Home Plate’  (PSP_005456_1650)

Credit: NASA/JPL/University of Arizona

This image shows the feature dubbed “Home Plate” in Gusev Crater, the site of the Mars Exploration Rover Spirit's investigation of the surface.

Spirit is visible inside the perimeter of the bright “Home Plate” feature, near the 5:30 position. This color image was created using only the blue-green and red HiRISE channels, so the “B” in this RGB product was synthesized using data from the two available channels.

                               
登录/注册后可看大图

来源:http://hirise.lpl.arizona.edu/PSP_005799_1505


Mass Wasting in Southern Hemisphere Crater  (PSP_005799_1505)

Credit: NASA/JPL/University of Arizona

This image shows an impact crater in the southern hemisphere of Mars with striking mass wasting features on the northern wall. (Mass wasting is the general term for a variety of processes in which rock or soil moves downhill).

Several dark, nearly continuous layers of rock ring the upper part of the crater slope. In the northern part of the layer, dark downslope striations can be seen even at low resolution. At the full resolution of HiRISE, these are seen to be comprised mostly of boulders. In several cases the striations descend directly from rocky outcrops, and they form due to rocks breaking and falling from the outcrops near the rim. This demonstrates the relative instability of the steep slopes of young craters; this is an important process in crater degradation. The dark streaks in this case may indicate particularly steep slopes.

                               
登录/注册后可看大图

来源:http://hirise.lpl.arizona.edu/PSP_005965_1855

Landslide in Shalbatana Vallis  (PSP_005965_1855)

Credit: NASA/JPL/University of Arizona

Shalbatana Vallis is a large channel that may be the result of lake formation and subsequent drainage from Ganges Chasma.

The valley has steep walls and a flat floor. Recently, a section of the steep wall collapsed and produced a landslide into the valley floor. This HiRISE image appears to show the source of this landslide to be a collapsed spur. The newly exposed surface has little dust coverage and is more blue in color when compared to the surrounding surface. It therefore appears quite fresh.

The debris in the valley floor is also interesting; the edges of the debris flow appear to be quite steep and surrounded by dunes.

                               
登录/注册后可看大图

来源:http://hirise.lpl.arizona.edu/PSP_005709_1405

Gullies in the Eastern Hellas Region of Mars  (PSP_005709_1405)

Credit: NASA/JPL/University of Arizona

This image shows several gullies along the southern wall of unnamed crater in the eastern Hellas region of Mars. This particular crater has gullies on both the polar and equatorial-facing walls.

The gully floors appear to be filled with rough-textured, somewhat knobby-looking materials. As multiple gullies located upslope feed into a single gully reaching the crater floor, the materials have converged to form a large deposit. Lineations parallel to apparent flow direction are evident on the textured surface.

It's not clear if liquid flows carved the gullies at this location, but the eastern Hellas region is well known for its abundant ice-rich flow features, such as lobate debris aprons at the base of knobs and massifs. Thus, the gully floor materials may have also incorporated ice at some time in the recent past and moved downslope as possible glacial-like flows.

                               
登录/注册后可看大图

来源:http://hirise.lpl.arizona.edu/PSP_005370_1845

Plains in North Sinus Meridiani  (PSP_005370_1845)

Credit: NASA/JPL/University of Arizona

This observation shows plains speckled with craters in north Sinus Meridiani, a dark albedo feature.

Several of the craters have wind streaks off their southwest rims. This indicates that recently, the wind has been dominantly coming from the northeast in this region. As the wind blows, it erodes material off the crater rims, and this material can be deposited downwind, as seen here in the form of streaks. Eventually the craters' rims will be completely eroded and just faint circular features will remain.

There is a bright mesa at the top of the image that also has a very prominent wind streak. The subimage (approximately 1 kilometer across) shows the bright mesa located at the top right of the image. Part of the wind streak is visible in the lower left.

This streak can also be seen in color (see PSP_005370_1845_RGB), where the streak appears redder than its surroundings. Differences in color result from differences in composition and/or particle sizes. The western edge of the mesa appears in this color product to be tinted red, similar in tone to the mesa's wind streak.

                               
登录/注册后可看大图

来源:http://hirise.lpl.arizona.edu/PSP_005904_1725

Yardangs in Memnonia Sulci  (PSP_005904_1725)

Credit: NASA/JPL/University of Arizona

The Memnonia Sulci region is southeast of Elysium Planitia at the boundary between the smooth lowlands and cratered southern highlands.

This region is characterized by yardangs, which are ridges formed by wind erosion of the regional deposits. In the subimage, you can see the individual layers of these deposits. These are commonly believed to be fine ash layers but they could also be sedimentary in origin, deposited either by wind or water. Some isolated patches of dunes are also visible throughout the image, abutting the ridges of the yardangs.

                               
登录/注册后可看大图

来源:http://hirise.lpl.arizona.edu/PSP_005188_1765

Transected Wrinkle Ridge in Ophir Chasma  (PSP_005188_1765)

Credit: NASA/JPL/University of Arizona

The upper right corner of this observation shows a prominent ridge called a wrinkle ridge. The wrinkle ridge has been transected by the wall of the Ophir Chasma just south of the Martian equator.

Wrinkle ridges are linear to arcuate topographic highs typically consisting of a broad arch topped by a crenulated ridge. They have been identified on the Moon, Mars, Mercury, and Venus. On Mars, they are many tens to hundreds of kilometers long, tens of kilometers wide, and may be several hundred meters high. They are characterized by asymmetrical cross sectional profiles and an offset in elevation on either side of the ridge.

Wrinkle ridges are most commonly believed to form from horizontal compression or shortening of the crust due to faulting and are often found in volcanic plains.

                               
登录/注册后可看大图

来源:http://hirise.lpl.arizona.edu/PSP_004867_1220

Crater Modified by Ice Processes  (PSP_004867_1220)

Credit: NASA/JPL/University of Arizona

This image captures an impact crater on the surface of Amphitrites Patera, an ancient volcano on the southern margin of the giant Hellas Basin. The Hellas Basin was formed by a very large impact into the southern highlands early in the geologic history of Mars. The basin has a number of volcanoes along its margin, perhaps because magma could take advantage of the deep cracks in the crust that resulted from the impact.

Amphitrites Patera is far enough south to approach the Martian "antarctic" and there is evidence for large amounts of ice in the ground. As in the polar regions of Earth, the icy ground (permafrost) is able to move and be modified by a variety of processes. In this case, the rim of the small impact crater is filled with a honeycomb of cracks. These are likely to have formed where dust- and soil-covered ice or ice cemented soil was cracked by thermal contraction in the winter. Subsequently, the underlying ice was able to escape into the atmosphere (sublimate) allowing the ground along the cracks to collapse. The only place where large boulders are visible is along the rim of the crater; this is probably where the boulders were not so deeply buried by the icy layer.

The Martian atmosphere was dusty at the time this image was acquired, so small imperfections in the processing are very visible in the standard image products. The cutout was specially processed to remove these artifacts.

                               
登录/注册后可看大图

来源:http://hirise.lpl.arizona.edu/PSP_005571_0950

South Polar Residual Cap Margin in Enhanced Color  (PSP_005571_0950)

Credit: NASA/JPL/University of Arizona

This scene is about 2.7 kilometers (approximately 1.7 miles) long and shows part of the edge of the south polar residual cap in enhanced color. Illumination is from the lower right.

The relatively bright, grayish areas are the residual cap, and the darker, reddish areas are mostly likely covered by dust. The south polar residual cap is made, for the most part, of carbon dioxide ice (commonly called "dry ice") and dust, with a little water ice in some places.

In the subimage, one can see fractures in the residual cap ice near the margin and, farther in, circular depressions that, in some places, appear to have coalesced. These depressions constitute what is called "Swiss cheese terrain." and it's fairly easy to see why. The Swiss cheese terrain is created when the carbon dioxide goes directly from the solid state (ice) to a gaseous state (the more familiar carbon dioxide gas) as temperatures warm during south polar summer. Swiss cheese formation may also be linked in a complicated way to the behavior of major Martian dust storms.

Images like these, taken before and after dust storm events, can aid our understanding of that complicated relationship.

                               
登录/注册后可看大图

来源:http://hirise.lpl.arizona.edu/PSP_005514_1360

Thumbprint Texture on Dark Dunes in Rabe Crater  (PSP_005514_1360)

Credit: NASA/JPL/University of Arizona

This image shows part of the floor of Rabe Crater, a large (108 kilometers, or 67 miles in diameter) impact crater in the Southern Highlands.

Dark dunes—accumulations of wind blown sand—cover part of crater's floor, and contrast with the surrounding bright-colored outcrops. The extreme close-up view reveals a thumbprint-like texture of smaller ridges and troughs covering the surfaces of the larger dunes. These smaller ripples are also formed and shaped by blowing wind in the thin atmosphere of Mars.

One puzzling question is why the dunes are dark compared with the relative bright layered material contained within the crater. The probable answer is that the source of the dark sand is not local to this crater; rather, this topographic depression has acted as a sand trap that has collected material being transported by winds blowing across the plains outside the crater.

                               
登录/注册后可看大图