HiRISE: New Spotlighted Captioned Images (2010 Dec 08)

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HiRISE: New Spotlighted Captioned Images (2010 Dec 08)

Post by bystander » Thu Dec 09, 2010 1:59 am

Crater in Light-Toned Layered Bedrock South of Oyama Crater (ESP_020086_2020)

Who wants color? My preferred HiRISE color product uses all three color bands (i.e, wavelengths) that HiRISE can image -- IRB, which refers to Infrared-Red-Blue/Green.

By substituting a wavelength that is normally invisible to the human eye for one that is, like infrared for red, we are able to create a "false"-color image. The infrared is useful because its sensitive to iron-bearing minerals and their oxidation state (degree of "rusting"). Ferrous iron, the more oxidized variety, is what makes Mars so reddish. Basically, most of the materials on Mars are pretty oxidized/rusted, and therefore altered from the more original ferric iron state (the less oxidized iron common to volcanic minerals such as olivine and pyroxene). So in general, the bluer the materials in our IRB images the less oxidized (altered) and the redder or yellower the materials, the more oxidized, or altered.
Layered Central Crater Mound (PSP_003655_1885)

This image shows a portion of a mound partly filling an impact crater. The impact crater is a little more than 60 kilometers (37 miles) across, and the central mound about half that, extending well beyond the area shown here.

Large impact craters typically have central peaks which surge upwards in the last stage of crater formation. However, mounds like this represent a different process: sedimentary infill of the crater after its formation.

At this site, the mound appears to be layered. Step-forming layers crop out throughout the center of the image. This indicates that the mound material was deposited in a series of events, likely the same process repeating many times. Many processes could form layers like this, including aeolian (wind) deposition, volcanic ash, or lake sedimentation.
Dune Field in Crater in the Hellespontus Region (PSP_004275_1275)

Hellespontus is one of the regions on Mars where dust storms have often been seen to start. Winds have picked up dust which has then become trapped on the broad crater floors of the region.

Large quantities of dark sand form beautiful features on the surface. This example is in a crater at 23 degrees East, 52 degrees South. At HiRISE resolution these features also show sinuous flows which are distinctly different in morphology from slope streaks. The latter are probably the result of gravity-induced slippage.

It is unknown whether these flows are currently active or what the material is that initiates the flow. Although the dune fields are at high Southern latitude, the very dark surface makes them strongly absorbant and therefore warm in the Martian summer. Hence, water is a possible candidate but this remains to be investigated.
Polar Pit Gullies (PSP_004988_1085)

This observation shows partial views of two high latitude pits. These polar pits contain gullies, small-scale slope features that are proposed to require some amount of liquid water to form.

Several of the gullies have multiple channels and debris aprons from numerous flows that occurred throughout time. Many of the gullies are seen to originate at a boulder layer at the pit edges. This layer is deteriorating and releasing boulders that can be seen rolling down the pit walls. The bright material near the pit edges is probably seasonal frost.

What is particularly interesting about these gullies is that some might be forming. The gullies on this wall have incised alcoves, but only a few have well-developed channels.
South Pole Residual Cap Swiss-Cheese Terrain Monitoring (PSP_005095_0935)

Like Earth, Mars has concentrations of water ice at both poles. Because Mars is so much colder however, carbon dioxide ice is deposited at high latitudes in the winter and is removed in the spring, analogous to winter-time water ice/snow on Earth.

Around the South Pole there are areas of this carbon dioxide ice that do not disappear every spring, but rather survive winter after winter; this persistent carbon dioxide ice is called the south pole residual cap. The retention of carbon dioxide ice throughout the year by the southern polar cap is one characteristic that distinguishes it significantly from Mars' North polar cap.

As can be seen in this HiRISE image of the South Pole residual cap, relatively high-standing smooth material is broken up by circular, oval, and blob-shaped depressions. This patterned terrain is called "swiss cheese" terrain.
Dust Devils Dancing on Dunes (PSP_005383_1255)

Dust devils make dark, diffuse scribble markings on the surface by kicking up dust, and are especially active in the summertime over dark surfaces, such as those with many deposits of sand-sized material.

The surface warms up in the sunlight, creating the right conditions to form dust devils. Mars also has larger dust storms that can deposit a thin layer of dust and eliminate the dust devil tracks.

These images show a small portion of the sand dunes in Russell Crater, which are of special interest due to the peculiar channels that formed on the steep slopes.
Credit: NASA/JPL/University of Arizona

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