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.

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.

Two distinctly different terrain types are visible in this image of the northern lowlands of Mars.

An older, heavily cratered landscape has been inundated by much younger flows. The valley floors are filled with flows that have relatively smooth surfaces and very few superposed impact craters.

In contrast, the mesas and hills making up the older terrain have blocky surfaces, perhaps fragmented by ancient impacts. The smooth surfaces of the flows are punctuated by curved, subparallel fractures oriented transverse to the flow direction. These cracks resemble crevasses in terrestrial glaciers and were formed when the brittle solid crust of the flow fractured as it was dragged downstream. Detailed images such as this will help determine the role ice may have played in these flows.

Named after a 19th century French astronomer, Henry Crater is a 165 kilometer (103 mile) diameter impact crater, located in Arabia Terra on a portion of the Martian highlands extending into the northern hemisphere. This observation shows multiple layers on the edge of a mound on the floor of the crater, which is distinct from others in the immediate vicinity.

The layers represent the eroded remains of sedimentary rocks that formed from sediments deposited within the crater sometime after its formation. The origin of the sediments on the crater floor in not known but may be windblown dust and sand. The layers exhibit differences in degrees of hardness and resistance to erosion with resistant layers forming cliffs and more easily eroded layers forming ledges.

Several dark streaks are visible on slopes (see subimage). Slope streak formation is among the few known processes currently active on Mars. Streaks are believed to form by downslope movement of dust in an almost fluid-like manner (analogous to a terrestrial snow avalanche) either exposing darker underlying material or creating a darker surface by increasing its roughness.

The THEMIS instrument onboard the Mars Odyssey spacecraft identified a possible salt deposit in this area, based on the infrared colors of the ground. Salt deposits typically form when water evaporates, suggesting that this might have once been an area favorable for life on Mars.

The possible salt deposit is the slightly lighter-colored area in the center of the image. The light-colored material is found peeking out from underneath sand dunes between small ridges and knobs of more tan colored material in the enhanced color data. This suggests that the (possibly) salty layer was buried by other materials and then exposed by erosion.

This layer also exhibits a fracture pattern similar to clay-rich materials visible elsewhere on Mars. It is interesting that this layer is also relatively devoid of boulders, suggesting that it is made up of some weak material.

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.

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.

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.

This observation shows part of the floor of a large impact crater in Arabia Terra. This crater formed in the distant past when a large asteroid or comet struck Mars, and has been heavily modified since formation. The crater was partially filled by sediments, forming the rock outcrops and layers visible in this image.

After this material was laid down, part of the deposits were eroded away. The central part of the image has been carved especially deeply, forming a distinct depression.

This depression has been a site of aeolian (wind) transport of sand in more recent times. A particularly interesting aspect of this site is that there appears to have been multiple styles of aeolian activity. Both large sand dunes (the dark hills, deep blue in the color image) and smaller ripples (sharp, light-toned narrow ridges) are visible. While ripples are often found in association with dunes, the different colors suggest that the material is not the same. (At full resolution, the surfaces of both the dunes and the large ripples are covered with much smaller ripples.)

Even where the ripples and dunes are in contact, there is a distinct contrast between the materials. In the subimage, dark sand appears to fill a trough between two large light ripples, suggesting that the dark sand has moved more recently. This could be due to different grain sizes, since certain sizes are most easily lifted by the wind