Dan Harlow

Crater in Western Arabia Terra with Stair-Stepped Hills and Dark Dunes

The HiRISE (High Resolution Imaging Science Experiment) which is one of the marque scientific platforms aboard the Mars Reconnaissance Orbiter has been busy snapping pictures of potential landing sites for the Mars Science Laboratory. Unique to the images which have already been sent back is the fact all of these are in full, high resolution enhanced color.

While most people think of Mars as a boring dusty desert, the topography of Mars is actually quite varied and spectacular. By examining these images NASA planners will now be able to better determine future landing sites for the next batch of robotic missions. Previously scientists had to depend on lower resolution and fuzzy black and white images to pick interesting targets on our neighbor planet. With these new photos not only will interesting features become more readily apparent but they also make for some spectacular images.

The following text and images are credit NASA and JPL.

Dunes in Wirtz Crater

Volatiles and Gullies

Inverted Channels Near Juventae Chasma

This image shows several long, sinuous features on the plains near Juventae Chasma. These features have been explained as former stream channels now preserved in inverted relief.

Inverted relief occurs when a formerly low-lying area becomes high-standing. For instance, depressions may become filled with lava that is more resistant to erosion. In the case of stream channels, there are several possible reasons why the channel might stand out in inverted relief. The streambed may contain larger rocks, which remain while fine material is blown away by the wind, or it could be cemented by some chemical precipitating from flowing water.

These features are old, since several impact craters cut the ridges. They provide important information about past processes on Mars. Understanding how streams could have formed is an important issue in understanding the history of water on Mars.

West Candor Layering

Section Through Largest of Holden Crater Fans

Layers Exposed in Crater Near Mawrth Vallis

This above image covers an impact crater roughly 4 kilometers (2.5 miles) in diameter. The portion highlighted above shows a 1 kilometer segment of the crater wall and rim.

The surface outside the crater (top) is relatively dark, while the interior wall of the crater exposes lighter, layered bedrock of diverse colors. A few dark patches on the crater wall have small dunes or ripples on their surfaces, and are likely pits filled with dark sand. The crater provides a window into the subsurface of Mars, revealing layered sedimentary deposits.

Just 30 kilometers (20 miles) to the east of this crater lies Mawrth Vallis, an ancient channel that may have been carved by catastrophic floods. In layered deposits surrounding Mawrth Vallis, the orbiting spectrometers OMEGA (on Mars Express) and CRISM (on MRO) have detected phyllosilicate (clay) minerals, which must have formed in the presence of water. In this region on Mars, the colors of layers seen by HiRISE often correlate with distinct water-bearing minerals observed by CRISM, so the color diversity seen here may reflect a dynamic environment at this location on early Mars.

Note: the color in these images is enhanced; it is not as it would normally appear to the human eye.

Light-toned Layering on Plains South of the West Candor Region

Layered Terrain Near Putative Phyllosilicates in Mawrth Valles

Southern Layered Mound and Floor in Gale Crater

This HiRISE image shows the interior of Gale Crater, a region being considered as a landing site for the 2009 Mars Science Laboratory.

Gale is distinguished from many other craters on Mars by a large interior layered mound that extends to the height of the crater rim. The top part of this image contains portions of the southeast part of the mound, with the bottom part showing details of the crater floor.

The mound material here is exposed as several distinct smaller hills. Close up, the hills show abundant rocks and debris aprons on their flanks, lacking distinct bedrock layers seen elsewhere on Mars. This suggests that the mound material is friable and easily eroded by the wind over time.

Other evidence of wind activity includes bright bedforms near the top of the image and dark bedforms and sand sheets at bottom. Between the hills and dark sand are a series of stacked stratigraphic units. Polygons are seen in some of the units, indicating contraction due to water loss, cooling, or some other process. Many of the polygons seem highly fractured.

Possible crossbeds are seen in some of the rock exposures near the bottom of the image. This and other images of Gale will be studied over the coming months and years in order to better understand the geology and further assess the potential as a future landing site.

Fan Delta and Layers in Holden Crater

Layers in Terby Crater

Layers in Becquerel Crater

The layers shown in the above image are formed by loose sediment accumulating within Becquerel Crater.

The layers are interesting in that there are repeated cycles of thick and thin layers. These cyclic changes in layer thickness shows that some environmental conditions varied in a repeated way as each subsequent layer was deposited.

These variations may be due to annual climate cycles and/or a cyclic variability in the source of the sediment. Most layers are parallel to each other, indicating that deposition occurred by material settling onto the surface. A few layers are cross-bedded, meaning that they are not parallel to the older or younger layers.

Cross-bedding indicates that at the time that the layers were deposited, the sediment was transported along the ground surface by wind or water.

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