by bystander » Thu Oct 03, 2013 5:31 am
HIRISE Science Team wrote:Differential Compaction around a Crater Peak (ESP_033108_1800) (HiClip)
This image shows a central peak that is surrounded by a ring-like graben feature and relatively flat terrain. Does the graben show evidence of what geologists call "differential compaction"?
Compaction refers to sediment that is originally porous and is covered up by other sediment (called "loading") that reduces that porousness. In other words, sand particles are pushed closer and closer together. Differential compaction is when there is variation in the thickness of a given area that creates uneven surface and has different degrees of porosity. The presence of the graben might be a clue to the formation of such unevenness.
This is a stereo pair with
ESP_033253_1800.
HIRISE Science Team wrote:Aligned Scallops (ESP_033111_2300) (HiClip)
This observation shows what we call "scalloped terrain," that appears here to merge in a linear depression.
How do these scallops form? Possibly from the collapse of the terrain due to sublimation (when a solid transforms directly into a gaseous state) of subsurface ice. There is also a large number of rocks on the surface.
HiRISE resolution can help us examine the surface much more closely to see if there are any differences between the surrounding plains and the floor of these scalloped depressions.
James Secosky wrote:Colorful Dunes (ESP_033272_1400) (HiClip)
This field of dunes lies on the floor of an old crater in Noachis Terra, one of the oldest places on Mars.
When there are perfect conditions for producing sand dunes--steady wind in one direction and just enough sand--barchan sand dunes form. The word "barchan" is a Russian term because this type of dune was first described in the desert regions of Turkistan.
Barchans have a gentle slope on the upwind side and a much steeper slope on the lee side where horns or a notch often forms. The wind in this case came from the southwest. Observing dunes on Mars can tell us how strong the winds are, as well as their direction. If pictures are taken at regular intervals, one may see changes in the dunes and in ripples on the dunes' surface.
The color in the photograph is not the same as we would see with our eyes because an extra color (infrared) is added. Our eyes cannot detect infrared, but it is used because it can give us clues to the composition of the surface. On Mars dunes are often dark in color because they were formed from the common, volcanic rock basalt. In the dry environment, dark minerals in basalt, like olivine and pyroxene, do not break down as quickly as they do on Earth. Although rare, some dark sand is found on Earth, for example in Hawaii which also has many volcanoes discharging basalt.
Credit: NASA/JPL/University of Arizona
HiRISE PDS Release: October 2013 (Orbit ranges 32,900—33,299)
<< Previous HiRISE Update[quote="HIRISE Science Team"][float=left][img3=""]http://www.uahirise.org/images/wallpaper/800/ESP_033108_1800.jpg[/img3][/float][size=110][url=http://www.uahirise.org/ESP_033108_1800][b][i]Differential Compaction around a Crater Peak (ESP_033108_1800)[/i][/b][/url] [b][i]([url=http://www.youtube.com/watch?v=K-KRZNhoiG4]HiClip[/url])[/i][/b][/size]
This image shows a central peak that is surrounded by a ring-like graben feature and relatively flat terrain. Does the graben show evidence of what geologists call "differential compaction"?
Compaction refers to sediment that is originally porous and is covered up by other sediment (called "loading") that reduces that porousness. In other words, sand particles are pushed closer and closer together. Differential compaction is when there is variation in the thickness of a given area that creates uneven surface and has different degrees of porosity. The presence of the graben might be a clue to the formation of such unevenness.
This is a stereo pair with [url=http://www.uahirise.org/ESP_033253_1800][b]ESP_033253_1800[/b][/url]. [/quote]
[quote="HIRISE Science Team"][float=left][img3=""]http://www.uahirise.org/images/wallpaper/800/ESP_033111_2300.jpg[/img3][/float][size=110][url=http://www.uahirise.org/ESP_033111_2300][b][i]Aligned Scallops (ESP_033111_2300)[/i][/b][/url] [b][i]([url=http://www.youtube.com/watch?v=Njz9FJ8VeTE]HiClip[/url])[/i][/b][/size]
This observation shows what we call "scalloped terrain," that appears here to merge in a linear depression.
How do these scallops form? Possibly from the collapse of the terrain due to sublimation (when a solid transforms directly into a gaseous state) of subsurface ice. There is also a large number of rocks on the surface.
HiRISE resolution can help us examine the surface much more closely to see if there are any differences between the surrounding plains and the floor of these scalloped depressions. [/quote]
[quote="James Secosky"][float=left][img3=""]http://www.uahirise.org/images/wallpaper/800/ESP_033272_1400.jpg[/img3][/float][size=110][url=http://www.uahirise.org/ESP_033272_1400][b][i]Colorful Dunes (ESP_033272_1400)[/i][/b][/url] [b][i]([url=http://www.youtube.com/watch?v=UnFuFe3BEus]HiClip[/url])[/i][/b][/size]
This field of dunes lies on the floor of an old crater in Noachis Terra, one of the oldest places on Mars.
When there are perfect conditions for producing sand dunes--steady wind in one direction and just enough sand--barchan sand dunes form. The word "barchan" is a Russian term because this type of dune was first described in the desert regions of Turkistan.
Barchans have a gentle slope on the upwind side and a much steeper slope on the lee side where horns or a notch often forms. The wind in this case came from the southwest. Observing dunes on Mars can tell us how strong the winds are, as well as their direction. If pictures are taken at regular intervals, one may see changes in the dunes and in ripples on the dunes' surface.
[url=http://uahirise.org/images/2013/details/cut/ESP_033272_1400.jpg][b]The color in the photograph[/b][/url] is not the same as we would see with our eyes because an extra color (infrared) is added. Our eyes cannot detect infrared, but it is used because it can give us clues to the composition of the surface. On Mars dunes are often dark in color because they were formed from the common, volcanic rock basalt. In the dry environment, dark minerals in basalt, like olivine and pyroxene, do not break down as quickly as they do on Earth. Although rare, some dark sand is found on Earth, for example in Hawaii which also has many volcanoes discharging basalt. [/quote]
[b][i]Credit: NASA/JPL/University of Arizona[/i][/b]
[url=http://www.uahirise.org/releases/oct_13.php][size=110][b][i]HiRISE PDS Release: October 2013 (Orbit ranges 32,900—33,299)[/i][/b][/size][/url]
[url=http://asterisk.apod.com/viewtopic.php?t=32166][size=85][b][i]<< Previous HiRISE Update[/i][/b][/size][/url]