by bystander » Wed Apr 25, 2012 8:25 pm
Alfred McEwen wrote:How Did Valles Marineris Form? (ESP_025415_1675)
This image (and its companion for stereo) crosses an impact crater about 50 kilometers (30 miles) wide. The crater was visible in Mariner 9 and Viking Orbiter images acquired decades ago, and was interpreted as evidence that the floor of Coprates Chasma was an old surface like that of the surrounding plateaus north and south of the canyon, and had dropped more than 10 kilometers (6 miles) as a huge intact block of crust.
However, this image and others acquired by MRO reveal a geologically young crater, with far fewer superimposed craters than the high plateaus, and
well-preserved primary impact morphologies. This crater must have formed after the opening of Valles Marineris, and is not evidence, by itself, that this portion of the canyon system formed from simple downdrop of a giant intact block.
The opening of Valles Marineris did involve crustal spreading and faulting, but may have had a more complex history. Many of the large landslides in Valles Marineris could have been triggered by this impact event.
Alfred McEwen wrote:Folded Layers in Melas Chasma, Central Valles Marineris (ESP_026312_1700)
There are folded layered deposits in the southern half of this image. How did this folding occur? On Earth, rocks are commonly folded when deeply buried and subject to high heat and pressure, which can make any rock flow. Such deep burial (and re-exposure or exhumation) is unlikely at this location.
In general Mars has experienced much less vertical motion of geologic strata than on Earth. Another possibility is that these layers were soft and deformable near the surface, such as wet or icy sediments. There are other folded layers in the giant Hellas impact basin, such as
ESP_025780_1415.
Please get out your 3D glasses for a look at the
stereo anaglyph here.
This is a stereo pair with
ESP_025811_1700.
Alfred McEwen wrote:Sedimentary Layers in West Candor Chasma (ESP_026378_1730)
West Candor Chasma in central Valles Marineris contains some of the thickest of the fine-grained layered deposits on Mars.
We can't see the grain sizes with HiRISE, but as the material erodes in the wind it disappears--apparently carried away by the wind--so the grains must be small. The layers may have been deposited from windblown materials, fall of volcanic sediments, or carried in by water, or all of the above.
Subsequently the layers may have been altered by groundwater, producing hydrated minerals such as sulfates.
The enhanced colors in the sub image are related to the minerals or to overlying dust or sand. The dark blue sharp-crested ridges are sand dunes.
Laszlo Kestay wrote:Terrain Near the MSL Landing Site (ESP_026568_1750)
This image is of a region slightly to the southwest of where the MSL rover, called Curiosity, will land in August 2012.
It shows three distinct terrains: (a) older plains, (b) an overlying unit with a distinct margin, and (c) recent sand dunes. The dunes indicate that the strongest winds tend to blow from the southwest toward the northeast and, like many dune fields on Mars, are probably moving slowly.
The second unit has a margin that, at low resolution, is similar to a lava flow. It also has a hard surface that retains impact craters better than the older plains beneath it.
At full HiRISE resolution it is evident that this deposit is not lava.It has thin layers and a dense network of fractures across its surface. The tops of some lava flows and lava lakes are also fractured. However, HiRISE has confirmed that the size and other characteristics of lava fractures are quite different from the ones visible here. Hence, this is some kind of sedimentary deposit, possibly consisting of largely of hardened mud.
It is likely that Curiosity will have an opportunity to investigate terrain like this soon after landing as it drives to the layered mound to the south.
Credit: NASA/JPL/University of Arizona
<< Previous HiRISE Update[quote="Alfred McEwen"][float=left][img3=""]http://www.uahirise.org/images/wallpaper/800/ESP_025415_1675.jpg[/img3][/float][url=http://www.uahirise.org/ESP_025415_1675][b][i]How Did Valles Marineris Form? (ESP_025415_1675)[/i][/b][/url]
This image (and its companion for stereo) crosses an impact crater about 50 kilometers (30 miles) wide. The crater was visible in Mariner 9 and Viking Orbiter images acquired decades ago, and was interpreted as evidence that the floor of Coprates Chasma was an old surface like that of the surrounding plateaus north and south of the canyon, and had dropped more than 10 kilometers (6 miles) as a huge intact block of crust.
However, this image and others acquired by MRO reveal a geologically young crater, with far fewer superimposed craters than the high plateaus, and [url=http://www.uahirise.org/images/2012/details/cut/ESP_025415_1675.jpg][b]well-preserved primary impact morphologies[/b][/url]. This crater must have formed after the opening of Valles Marineris, and is not evidence, by itself, that this portion of the canyon system formed from simple downdrop of a giant intact block.
The opening of Valles Marineris did involve crustal spreading and faulting, but may have had a more complex history. Many of the large landslides in Valles Marineris could have been triggered by this impact event. [/quote]
[quote="Alfred McEwen"][float=left][img3=""]http://www.uahirise.org/images/wallpaper/800/ESP_026312_1700.jpg[/img3][/float][url=http://www.uahirise.org/ESP_026312_1700][b][i]Folded Layers in Melas Chasma, Central Valles Marineris (ESP_026312_1700)[/i][/b][/url]
There are folded layered deposits in the southern half of this image. How did this folding occur? On Earth, rocks are commonly folded when deeply buried and subject to high heat and pressure, which can make any rock flow. Such deep burial (and re-exposure or exhumation) is unlikely at this location.
In general Mars has experienced much less vertical motion of geologic strata than on Earth. Another possibility is that these layers were soft and deformable near the surface, such as wet or icy sediments. There are other folded layers in the giant Hellas impact basin, such as [url=http://www.uahirise.org/ESP_025780_1415][b]ESP_025780_1415[/b][/url].
Please get out your 3D glasses for a look at the [url=http://www.uahirise.org/anaglyph/singula.php?ID=ESP_025811_1700][b]stereo anaglyph here[/b][/url].
This is a stereo pair with [url=http://www.uahirise.org/ESP_025811_1700][b]ESP_025811_1700[/b][/url]. [/quote]
[quote="Alfred McEwen"][float=left][img3=""]http://www.uahirise.org/images/wallpaper/800/ESP_026378_1730.jpg[/img3][/float][url=http://www.uahirise.org/ESP_026378_1730][b][i]Sedimentary Layers in West Candor Chasma (ESP_026378_1730)[/i][/b][/url]
West Candor Chasma in central Valles Marineris contains some of the thickest of the fine-grained layered deposits on Mars.
We can't see the grain sizes with HiRISE, but as the material erodes in the wind it disappears--apparently carried away by the wind--so the grains must be small. The layers may have been deposited from windblown materials, fall of volcanic sediments, or carried in by water, or all of the above.
Subsequently the layers may have been altered by groundwater, producing hydrated minerals such as sulfates. [url=http://www.uahirise.org/images/2012/details/cut/ESP_026378_1730.jpg][b]The enhanced colors in the sub image[/b][/url] are related to the minerals or to overlying dust or sand. The dark blue sharp-crested ridges are sand dunes. [/quote]
[quote="Laszlo Kestay"][float=left][img3=""]http://www.uahirise.org/images/wallpaper/800/ESP_026568_1750.jpg[/img3][/float][url=http://www.uahirise.org/ESP_026568_1750][b][i]Terrain Near the MSL Landing Site (ESP_026568_1750)[/i][/b][/url]
This image is of a region slightly to the southwest of where the MSL rover, called Curiosity, will land in August 2012.
It shows three distinct terrains: (a) older plains, (b) an overlying unit with a distinct margin, and (c) recent sand dunes. The dunes indicate that the strongest winds tend to blow from the southwest toward the northeast and, like many dune fields on Mars, are probably moving slowly.
The second unit has a margin that, at low resolution, is similar to a lava flow. It also has a hard surface that retains impact craters better than the older plains beneath it.
At full HiRISE resolution it is evident that this deposit is not lava.It has thin layers and a dense network of fractures across its surface. The tops of some lava flows and lava lakes are also fractured. However, HiRISE has confirmed that the size and other characteristics of lava fractures are quite different from the ones visible here. Hence, this is some kind of sedimentary deposit, possibly consisting of largely of hardened mud.
It is likely that Curiosity will have an opportunity to investigate terrain like this soon after landing as it drives to the layered mound to the south. [/quote]
[b][i]Credit: NASA/JPL/University of Arizona[/i][/b]
[url=http://asterisk.apod.com/viewtopic.php?f=29&t=28309][size=85][b][i]<< Previous HiRISE Update[/i][/b][/size][/url]