火星的细节

译文是Rojer翻译的，引自:http://www.astronomy.com.cn/bbs/viewthread.php?tid=70259&;

     现在HiRISE已经拍了两千多张图像，本人打算从中筛选一些帖上来，但图片还是有不少，因此每页都帖有图片，大家记得翻页哦^_^。还有为了方便大家打开观看，故选择小尺寸的图像贴上来，如果家想看更清晰的大图，每张图都标有来源，大家可点击网址选择大图打开观看。^^至于有朋友对图片色彩的疑问，本人实在不清楚，只听闻过美国宇航局是有专门的美工加工美化图片的。还有第4页新增了黑白原图。


Anyone connected by Internet can now see planet Mars better than at any time in history, through the eye of HiRISE, the High Resolution Imaging Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter. The HiRISE team has just released more than 1,200 Mars images to the Planetary Data System.
通过安装在 NASA 火星勘测轨道器上的 HiRISE ——高清晰度成像实验相机，现在任何一个上网的人都能比历史上任何一个时期更好的观看火星。HiRISE 小组刚对行星数据系统公布了超过1200张火星图片。


Not only has the team released 1.7 Terabytes of HiRISE data -- the largest single dataset ever delivered to NASA's space mission data library -- but also a user-friendly way for the public to easily see HiRISE images.
小组不仅发布了1.7Tb的 HiRISE 数据——向 NASA 太空任务数据实验室提交的最大的一个数据集——而且以用户友好的方式使公众更容易看到 HiRISE 的图片。


Thanks to tools available on HiRISE's new webpage, any Internet user can quickly pull up and explore the same remarkable images that both thrill and confound scientists.
要感谢 HiRISE 新网页上的工具，任何一个因特网用户都能快速进入浏览那些令科学家颤抖、惊慌的非凡图片。


"These images must contain hundreds of important discoveries about Mars," said HiRISE Principal Investigator Alfred McEwen of the University of Arizona's Lunar and Planetary Laboratory. "We just need time to realize what they are."
HiRISE 的首席研究员、亚利桑那大学月球与行星实验室的 Alfred McEwen 说：“这些图片必定包含有关火星的上百个重要发现，我们需要时间来了解它们是什么。”


The HiRISE camera takes images of 6-kilometer- (3.5-mile-) wide swaths as the orbiter flies between 250 to 316 kilometers (155 to 196 miles) above Mars' surface. For at least the next 18 months, HiRISE will collect thousands of color, black-and-white, and stereo images of the Martian surface, resolving features as small as 40 inches across, covering about one percent of the planet.
HiRISE 相机在距火星表面250至316千米间的轨道上运行时获取6千米宽的一长溜图片。在接下来的至少18个月里，HiRISE 将采集数千幅火星表面彩色、黑白和立体图像，分辨率在40英寸之间，覆盖行星约1%的表面。


The team based at the University of Arizona's HiRISE Operations Center (HiROC) began releasing selected images on the Internet when science operations began in November 2006. In April, team members began reprocessing all the images taken up to March 25, 2007.
当2006年11月科学运作开始时，以亚利桑那大学 HiRISE 操作中心为基地的小组就开始在因特网上发布挑选出的图片。在4月，小组成员开始重新处理2007年3月25日之前采集到的所有图片。


With the first 1,200 images, HiRISE becomes a Planetary Data System (PDS) "data node." "A PDS data node is designed to provide access to a particular data set during an active mission, when the data are of greatest interest," said NASA's R. Stephen Saunders, the PDS program scientist. The PDS is online at http://pds.jpl.nasa.gov.
由于这1200张图片，HiRISE 成了行星数据系统（PDS）的一个数据节点。NASA PDS 计划科学家 R. Stephen Saunders 说：“一旦数据很重要，一个PDS数据节点是设计用于在一个现行任务期间提供对详细数据进行访问。”PDS 在线地址  http://pds.jpl.nasa.gov。


下图来源:http://hirise.lpl.arizona.edu/PSP_005424_1700

Aurorae Chaos  (PSP_005424_1700)

Credit: NASA/JPL/University of Arizona

This observation shows a portion of Aurorae Chaos, chaotic terrain east of the Vallis Marineris canyon system. Aurorae Chaos extends from Capri and Eos Chasmata on the west into Hydraotes and Aureum Chaos on the north and east.

Chaotic terrain is thought to form from subsurface collapse following volatile release. It is possible that the Martian crust was at one time enriched in ices that became gases or liquid at relatively low temperatures upon encountering a heat source or was violently shaken. These ices existed in spaces between soil particles. If a large volume of volatiles is suddenly released, then there is a large portion of the soil volume missing. The soil cannot support itself, so it collapses.

Since chaotic terrain is often located at the head of the Martian outflow channels (giant flood plains), it is also possible that the chaotic regions are the source of the fluids that formed the outflow channels. Aurorae Chaos connects to outflow channels via other chaotic regions.

                               
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[ 本帖最后由 寻找拉玛 于 2008-2-1 14:58 编辑 ]

来源:http://hirise.lpl.arizona.edu/PSP_006528_1120

Sources of Basaltic Sand  (PSP_006528_1120)

Credit: NASA/JPL/University of Arizona

Sand dunes are among the most prominent wind-formed features found on Mars. Their morphologies depend on the winds and also on the local supply of sand grains, so they provide clues to the nature of both the Martian atmosphere and surface.

Dunes form through the accumulation of coarse sand grains carried by the wind by means of saltation, or bouncing along the surface. Monitoring the present day dune activity can help determine the timescale over which Martian rocks are eroded, as the impacting grains sandblast the surface over time. The sands of Mars must be continually replenished as the coarse grains are ground into fine dust by repeated impacts. Finding the hidden sources of fresh sand is a challenge for HiRISE.

This image was targeted at a point in Mitchell Crater in the southern highlands of Mars where sands abruptly appear and spread north. The sands seem to derive from the edge of an eroding mesa (shown here with an arrow; 8.66 kilometer, or 5.4 miles across). A close-up view of the terrain nearby suggests that boulders and sand have been excavated by erosion from beneath brighter, polygonally fractured ground (1.45 km, or 0.9 mi across).

This rocky layer may originally have been a lava flow; Martian lava flows are predominantly composed of basalt, which would account for the dark color of the sand. The polygonal pattern of the bright upper layer may be due to repeated freezing and thawing of the soil that buries the lava flow. The tracks of dust-devils are clearly visible on the smooth, sandy surface but largely vanish when they cross into the polygonally fractured terrain.

                               
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来源:http://hirise.lpl.arizona.edu/PSP_006610_2035

Potential Landing Site Near Mawrth Vallis  (PSP_006610_2035)
Credit: NASA/JPL/University of Arizona
Mawrth Vallis contains clay minerals that formed by chemical alteration of rocks by water. It is one of the short list of potential sites that the Mars Science Laboratory rover will land at, and the HiRISE team is working to find a safe place to land in this area.

This observation shows a wide variety of scientifically interesting terrains as well as some potential hazards for landing. The central part of the image is dominated by light-toned materials with curving fractures of many different sizes. These fractures do not have a preferred orientation, indicating that they did not form in response to some regional stress pattern.

Instead, they formed by some more uniform process, possibly the drying of a thick mud deposit or the gradual rebound of the area as the overlying material was eroded away. The scattered mounds and sand dunes may or may not prove to be a danger, but it is reassuring to see that many of the impact craters have been smoothed out with a filling of wind-blown sand.

                               
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来源:http://hirise.lpl.arizona.edu/PSP_006633_2010

Potential Landing Site in Nili Fossae  (PSP_006633_2010)

Credit: NASA/JPL/University of Arizona

The Nili Fossae are valleys that have cut into the ancient crust of Mars, exposing clay minerals. These minerals formed in the presence of water and may be the result of chemical reactions between hot water and rocks. If so, this could have been a favorable location for Martian life in ancient times.

This HiRISE image is part of a series in search for a safe place the Mars Science Laboratory rover can land. In the central part of the image, the terrain is a mix of sand dunes and relatively smooth rock exposures. There are some small knobs but very few large rocks in the area. Instead, the multi-colored rock exposures seem to be mostly a mosaic of flat fractured rock.

On the southern edge of the image, an impact crater is a potential hazard. In the northern part of the image, the scarp marking the boundary of the valley is visible.

                               
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来源:http://hirise.lpl.arizona.edu/PSP_006625_1405


Clay Minerals in the Northwestern Bosporos Montes  (PSP_006625_1405)

Credit: NASA/JPL/University of Arizona

The Bosporos Montes make up part of the rim of the giant Argyre impact basin on Mars. The Compact Reconnaissance Imaging Spectrometer (CRISM) identified this as a location with clay minerals. Such minerals contain water and may have formed under conditions favorable for life.

This HiRISE image was taken to support the CRISM Team’s investigation of this area. While HiRISE does not have the ability to identify minerals the way CRISM can, the enhanced colors in this image are similar to those seen in other clay-containing parts of Mars.

The light-toned mesas and plains are crisscrossed with small fractures that could have formed as a muddy clay deposit dried. However, this material is strong enough to form boulders where it has been hit by impact craters.

                               
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来源:http://hirise.lpl.arizona.edu/PSP_006538_1035

Southern Dunes and Spiders  (PSP_006538_1035)

Credit: NASA/JPL/University of Arizona

This image gives a rare glimpse of an area in the far south of Mars that is frequently obscured by clouds or covered by surface frosts.

Crescent-shaped sand dunes can be seen scattered across patterned ground. The surface patterns are made up of channels carved by carbon dioxide gas as it escapes from under the seasonal frost. The dunes were still partially frozen when this picture was taken during the vernal equinox, as the Sun moved into the northern hemisphere at the end of the southern summer. Bluish ice is visible on the steep faces of the dunes and along their bases.

Typical sand dunes on Earth and Mars gradually move downwind as sand accumulates on the upwind (convex) side and then avalanches down the steeper down-wind side, called the “slip face”. Here, the sand motion appears to be around the dunes instead. Clean patches of ground downwind of the dunes show that the surface is sheltered by the dunes, which prevent dark sand from being deposited in their lees.

                               
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极地窖集水沟

来源:http://hirise.lpl.arizona.edu/PSP_005410_1115

Polar Pit Gullies  (PSP_005410_1115)

Credit: NASA/JPL/University of Arizona

This image shows polar pit gullies in a depression. The gullies do not appear to have been active recently, as their channels and alcoves are covered with polygonal fractures and ripples that have formed over time. The alcoves contain boulders from eroding layers up-slope. Several of the alcoves extend to the slope rim, suggesting head-ward erosion.

The rest of the scene contains abundant polygonal ground, thought to have formed by processes involving ground ice. This image is at a high latitude where polygonal terrain is common. This feature is not found in equatorial regions, which supports a relationship with ground ice because ground ice is not stable near the equator today.

There are several muted circles on the plains in the lower half of the image; these are possibly relaxed craters. If a crater forms in ice-rich ground, the ice enhances the degradation of the crater and gives the crater a “softened” appearance.

                               
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来源:http://hirise.lpl.arizona.edu/PSP_005684_1890


Sand Dunes in Nili Patera Caldera  (PSP_005684_1890)

Credit: NASA/JPL/University of Arizona

A set of dark sand dunes within the northeastern edge of a dune field in Nili Patera, a volcanic caldera in the Syrtis Major region of Mars is the focus of this HiRISE observation.

The lighter surface beneath the dunes is an ancient lava flow. The cracks in the flow probably formed when the lava cooled. Many of the cracks are dark and probably contain sand; the dark color of the dunes suggests that the sand is basaltic in composition and therefore originally derived from volcanic rock.

However, whether the sand formed from Nili Patera is not known, as it is possible the dunes have blown in from a more distal location. With two horns on one end and a rounded edge on the other, the dunes have a distinctive shape. The side of the dunes with the horns has a steeper slope — called the slip face &mdash and the rounded side exhibits a more shallow slope. These types of dunes are called “barchans” and, in analogy with similar dunes on Earth, form in areas with limited sand supply.

The horns of the barchans point in the downwind direction, indicating that the predominant surface winds in this region blew from the east-northeast (slightly upper right in the image). Zooming into the image, one can see landslides on many dune slip faces, indicating fairy recent slope failure. Very small ripples are visible on the dunes” surfaces, showing that the winds in this region have not only blown the barchans across the lava plain, but also modified the dunes themselves. Another HiRISE image, PSP_004339_1890, shows more barchan dunes in Nili Patera, south of this area.

                               
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来源:http://hirise.lpl.arizona.edu/PSP_006250_2200

Intra-Crater Deposits in Nilosyrtis  (PSP_006250_2200)
Credit: NASA/JPL/University of Arizona
Both ancient and modern deposits within craters in the northern lowlands area of Nilosyrtis are visible in this HiRISE observation. This crater and its neighbors are partially filled with sediments that display unusual morphologies, having patterned interiors and radial filaments.

The crater centers are occupied by heavily eroded mounds of material that probably once buried the craters in this region. Horizontal layering is visible in similar mounds elsewhere in this image, and close inspection shows that these mounds are covered by rocks, presumably ejecta from distant impacts.

The accumulation of ejecta on their surfaces indicates that the mounds are not recent deposits of dust or sand, but rather are ancient sediments perhaps deposited in a primordial sea. The radial filaments are much more recent deposits, as shown by the lack of ejecta on their surfaces, and are likely made up of dust and sand that is trapped between the older mounds and the crater walls.

                               
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来源:http://hirise.lpl.arizona.edu/PSP_006672_1420

Outcrops in the Hellas Montes  (PSP_006672_1420)

Credit: NASA/JPL/University of Arizona

The Hellas Montes are a group of mountains along the western rim of the giant Hellas Basin on Mars.

The Hellas Basin is the largest of the obvious impact craters on the Red Planet. It is very ancient and has been partially filled by sediments. The Hellas Montes are part of the eroded crater rim.

In the central part of this HiRISE image, we can see steep slopes where landslides have exposed a variety of rocks. The jumble of blocks, rather than stacks of layered sediments or lavas, is consistent with impact crater ejecta. On flatter slopes, the ground is covered with a mantling deposit that is generally considered to be ice-rich dust.

In the southern part of the image, a large circular depression—rimmed by a zone with many large boulders—is visible. This is an impact crater with a relatively thin mantling deposit on its rim.

                               
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lz辛苦啊，好图一定要顶的！

来源:http://hirise.lpl.arizona.edu/PSP_006477_1745

Dust-Devil Tracks in Southern Schiaparelli Basin   (PSP_006477_1745)

Credit: NASA/JPL/University of Arizona

Dust-devils are vortices of wind that form when air rising from a warm surface encounters shear in the above atmosphere. Martian dust devils can attain gargantuan proportions, reaching the size of terrestrial tornadoes with plumes that tower up to 9 kilometers above the surface. Dust-devils play an important role in sustaining the aerosols that make up Mars’ red sky and in cleaning the Martian surface after a dust storm.

This observation shows a region near the Martian equator that is a perfect tablet for the scribblings of dust-devils. This region is made up of dark bedrock that is thinly blanketed by bright dust. Dark tracks form when dust-devils scour the surface, exposing the darker substrate. The tracks tend to cluster together, as dust-devils repeatedly form over terrain that has been previously scoured and is consequently darker and warmer than the surrounding surface.

Once lofted by a dust-devil, the fine dust can be transported great distances before it settles again onto the surface.

                               
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来源:http://hirise.lpl.arizona.edu/PSP_006248_1235

Dust Devil Tracks and Barchan Dunes in Terra Cimmeria  (PSP_006248_1235)

Credit: NASA/JPL/University of Arizona

This image shows a set of dark sand dunes within the northern part of an unnamed crater in the Terra Cimmeria region.

The dunes have a distinctive shape, with two horns on one end and a rounded edge on the other. The side of the dunes with the horns has a steeper slope and the rounded side a more shallow slope. These types of dunes are called “barchans” and, by analogy with similar dunes on Earth, form in areas with limited sand supply.

The horns of the barchans point in the downwind direction, thereby indicating that the predominant surface winds in this region blew from the east (right side of image). Further evidence of this wind regime is apparent when one zooms into the image. “Wind tails” are visible on the western (left) side of many rocks (many of these rocks may be ejecta from the degraded crater in the northern part of the image). Wind tails are formed by the accumulation of dust and sand in the lee of rocks, which act as wind shadows. Very small light ripples at a scale of a few meters (yards) are also apparent.

The dark, sinuous forms in the image are tracks left by dust devils, which lift bright dust off the surface, revealing the darker surface. Where dust devils cross the dunes, the fine texture on the dunes is undisturbed, indicating that the particles making up the dunes are coarse and fairly immobile.

                               
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清晰又漂亮!!!!!!!!!!!!!!!

来源:http://hirise.lpl.arizona.edu/PSP_006254_1885

Colliding Dunes in Meridiani Planum  (PSP_006254_1885)

Credit: NASA/JPL/University of Arizona

This observation shows a variety of wind-related features near the equator of Mars in northern Meridiani Planum.

Two distinct types of dark sand dunes are visible in this picture. The isolated dunes near the edge of the dune field are called barchans, and their shapes can be used to determine the wind direction. These barchans are about 200 meters (656 feet) across and display steep edges on their southwest sides, indicating that they are driven by northeasterly winds. This agrees with the orientation of the bright wind streak issuing from the crater at the top right of the picture, formed from bright dust eroding from the crater interior.

Towards the middle of the dune field, the shape of the dunes alters to the second type of dunes, known as “transverse” dunes. These are long ridges of sand that are oriented perpendicular to the prevailing wind direction, and tend to form where there is an abundant supply of sand. A closeup of the transition zone suggests that the individual barchans first merge into groups of two or three before the groups merge to form ridges.

Several indications suggest that the sand here is on the move. Sand fills small pits and polygonal fractures in the bedrock, indicating recent sand movement between the dunes. The transitioning dune types and the presence of outliers (dunes that form away from the main dune field) both suggest possible dune migration.

HiRISE will continue to monitor areas such as this over time, in order to quantify the rate of sand movement on Mars.

                               
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好图啊   要是中文的图文解说就好了  

来源:http://hirise.lpl.arizona.edu/PSP_006246_1910

Contact between the Medusae Fossae Formation and Amazonis Planitia  (PSP_006246_1910)

Credit: NASA/JPL/University of Arizona

Amazonis Planitia (seen in the northern half of this image) is one of the very flattest places on Mars. It is covered by vast floods of lava that have left a smooth lava plain.

The Medusae Fossae formation (seen in the southern half of this image) is a series of young wind-eroded deposits whose origin continues to be debated. It is generally thought to be composed of volcanic ash, perhaps like pumice on Earth. However, some scientists hypothesize that it is an equatorial ice-rich deposit.

In this image, it can be clearly seen that the Medusae Fossae formation is being eroded off of the Amazonis lavas. Pristine lava features can be seen emerging on either side of the ridges of wind eroding material. The thin wiggly ridges on the lava plains are “pressure ridges” formed by bucking of the lava crust while it flowed. The small cones, a few hundred meters or yards in diameter, that dot the lava plains formed when water underneath the lava turned to steam and exploded through the lava flow.

Today, these cones are still partly filled with Medusae Fossae formation materials. At least in this location, HiRISE finds no evidence for ice at or near the surface of the Medusae Fossae formation. Instead, the wind carved slopes are covered with dark streaks that formed as dry avalanches of dust.

                               
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来源:http://hirise.lpl.arizona.edu/PSP_003492_1405

Gullies with Sharp Color Contrasts  (PSP_003492_1405)

Credit: NASA/JPL/University of Arizona

This image shows a southern mid-latitude crater: it has bright landslides on its southeast and west walls, some of which have noticeable boulder tracks where boulders rolled down the slopes.

The most noticeable features of this crater are the gullies on the north wall. A couple of small gullies appear to emanate from an overhang. The others originate at or near layers up-slope. The layers are sturdy and resistant from erosion: the layers that appear to be decaying into resolvable boulders, instead of particles easily moved by the wind, are evidence of this.

The color portion of this observation is spectacular. Note the distinct, blue layers lining the south rim of the crater and the white-blue rocks poking through. Wind erosion will likely expose them as time continues.

The top part of the image captures the complex floor of a larger crater upon which the featured crater is superposed. There are a large number of dunes as well as prominent ridges. The color contrast of the gullies to their surroundings is quite distinct. The gullies have blue channels; however, their down-slope debris aprons are redder. This probably indicates a change in particle size, or that the debris aprons have been covered with dust to blend into their surroundings.

Please note that this image is false color; it is not as it would appear naturally to the human eye.

                               
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来源:http://hirise.lpl.arizona.edu/PSP_005409_1530

Central Pit Crater  (PSP_005409_1530)

Credit: NASA/JPL/University of Arizona

This observation shows an unnamed central pit crater in the southern mid-latitudes. Impact craters have different morphologies depending on the size of the impactor and the properties of the target material.

Smaller impactors generate bowl-shaped craters, while very large impactors create craters with central peaks or central rings. It is currently unknown what causes central pits to form.

This central pit crater is not very fresh, as evidenced by a number of craters occurring within it. Recently, HiRISE had identified ponded and pitted material in several fresh craters around Mars that is undetectable in lower resolution images. The pits are thought to form from escaping volatiles (gases) that were caused by boiling ices present at the time of impact.

Although the central pit, located near the bottom of the image, has degraded over time, there are still some remnant pits that appear to have coalesced (joined, see subimage, approximately 1.5 kilometers across). It is possible that all central pit craters on Mars consist of coalesced, smaller pits.

                               
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来源:http://hirise.lpl.arizona.edu/PSP_006494_1535

Wrinkle Ridge in Solis Planum  (PSP_006494_1535)

Credit: NASA/JPL/University of Arizona

This observation shows a wrinkle ridge in the Solis Planum, a region of Mars that is a high-elevation volcanic plain located south of the Valles Marineris canyon system and east of the Tharsis volcanic complex. In the Solis Planum, wrinkle ridges are typically spaced apart roughly 40 kilometers (25 miles).

Wrinkle ridges are linear to arcuate positive relief features and are often characterized by a broad arch topped with a crenulated ridge. These features have been identified on many bodies such as the Moon, Mercury, and Venus. On Mars, they are many tens-to- hundreds of kilometers long, tens of kilometers wide, and have a relief of a few hundred meters. 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.

Wrinkle ridges commonly have asymmetrical cross sectional profiles and an offset in elevation on either side of the ridge. The ridge in this image (see subimage) appears to have a steeper southeast facing slope and a more gentle northwest facing slope. Some layering is also apparent in the ridge. Large dunes border the ridge to the north.

The reddish colors visible in the color image most likely indicate the presence of dust (or indurated dust).

                               
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