HiRISE Science Team wrote:Light-Toned and Possible Hydrated Materials in Gullied Crater (ESP_025472_1405)
This observation shows a gullied crater in the Southern mid-latitudes with light-toned deposits near the center of its floor, and two areas of collapsed terrain at the northern and southern edges of the crater floor.
Data from the CRISM instrument--also onboard the Mars Reconnaissance Orbiter--tentatively show a minerals containing chemically-bound water in the "chaotic" areas.
HiRISE Science Team wrote:Well-Preserved Impact Crater with Ridges (ESP_025557_1705)
Although the rim of this well-preserved crater and its smooth walls are very impressive, note also the spectacular collection of ridges draping the underlying topography on the floor of this crater.
What can account for the formation of the terrain at the crater floor? One possible reason might the former icy flows at this latitude. High resolution images like this can give us better insight into features like this.
This subimage also shows the faint tracks of material that has rolled down from near the top of the crater rim to the floor.
This is a stereo pair with ESP_017975_1705.
Ginny Gulick wrote:Northern Polar Dune Field (ESP_027378_2540)
This field of crescent-shaped dunes (lat.73.62, lon. 328.215) is located just south of the North Polar layered terrain.
These dunes, known as barchan dunes, usually form where there is a moderate supply of sand and a prevailing wind direction. The "arms" or "horns" of barchan dunes point in the downwind direction and in this case indicate that the prevailing winds blow towards the east.
The dunes in the close-up image are approximately 100 meters across and are traversing a bumpy, hard terrain. Polygonal patterns are evident in some areas while numerous meter-scale boulders are strewn throughout the region. The boulders are more numerous in areas where the polygonal patterns are less pronounced. Repeat imaging of this dune field could reveal whether these dunes are presently moving.
Shane Byrne wrote:Polar Cliffs and Falling Blocks (ESP_027451_2635)
There is an ice sheet at the North Pole of Mars that is a few miles thick at its center. At some places (like in this image) it ends in steep cliffs that can be about 800 meters (2600 feet) high.
The slopes of these cliffs are almost vertical which causes slab-like blocks of ice to break off and crash down to the surrounding plains. Dense networks of cracks cover these icy cliff faces making it easier for these blocks to break free. We've seen new debris at the base of many of these cliffs appearing between successive HiRISE images, so we regularly monitor sites like this to check for new blocks that have fallen. Understanding how these cliffs are formed helps us understand the climatic record stored in the ice sheet itself.
Have any new blockfalls occurred here? Try and compare this image with ESP_018959_2635 (taken almost exactly one Martian year ago) and check for yourself!
Credit: NASA/JPL/University of Arizona
PDS Release: July 2012 - Orbit ranges 27,000—27,399 (30 Apr–31 May 2012)
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