by bystander » Thu Nov 03, 2011 1:27 am
Nathan Bridges wrote:Diverse Layers and Mineralogy near Mawrth Vallis (ESP_024055_2045)
This HiRISE image shows diverse layers in a region near Mawrth Vallis, a channel that was probably carved by water in Mars' ancient past.
The color subimage shows details of layers exposed in a crater wall.
Tannish to white tones are apparent, which may be reflective of differences in mineralogy. CRISM, a spectrometer on MRO, has detected clays in Mawrth, so the layers here may be clay-rich.
Clays contain water, indicating that this region may have been wet in the past. The subimage also shows polygonal-like textures on some of the layered rock. These may be dessication polygons formed when the wet clays dried. The dark patches on the layers are sand dunes.
This is a stereo pair with
ESP_024200_2045.
Ingrid Daubar wrote:Rafting Rocks (ESP_023314_1440)
This image shows some interesting features where smoother, dark areas with straight sides are separated by narrow channels of higher material.
This is especially clear
in the southern portion of the image (rotated so north is at approximately 11 o'clock, 3.2 kilometers or 2 miles across). It looks as if a flat solid surface broke up, and then the individual pieces were rafted apart.
In other areas of Mars, similar features formed when a layer of lava solidified on top of still-molten rock. The solid layer at the surface broke apart either when it contracted as it cooled, or when the liquid below it flowed and dragged along the bottom of the top layer of solid rock.
However, this area of the Hellas basin is not expected to have any volcanic activity. Hellas is a huge, old impact crater, filled with sediments and heavily eroded. In addition, there are subtle differences in the textures here that make this look different from the plate-like lava we find in other areas of Mars. Instead, perhaps something similar happened, but with a mixture of ice and rock instead of lava.
It's possible that a freezing mudflow was pulled apart here, with a frozen upper layer breaking and rafting apart on top of slushy material. When the underlying slushy ice later froze, it would have expanded and been squeezed up between the plates, creating the raised ridges between them.
Ingrid Daubar wrote:Continuing Avalanches (ESP_016228_2650)
Since HiRISE first started
finding avalanches on Mars, we have continued searching for them in the most likely places: steep cliffs at the edges of the layered deposits at the North Pole.
These layers are exposed in the scarp face that cuts through them diagonally
across this subimage. The bright smoother material at the lower left is at the top of the cliff, and here we have caught another avalanche as it falls down the steep slope towards the upper right of the image.
A large (approximately 200 meters or 600 feet across) cloud of reddish dust has been kicked up at the base of the scarp. Fine tendrils of bright wisps are visible farther up the cliff face—these may be individual falls of material, before spreading out as the avalanche plummets downward.
This might allow scientists to figure out the exact location of the start of the avalanche; for example, which layer it originally came from and how far it fell. This information will help narrow down what triggers these falls: is it seasonal temperature changes in the ice layers, gusts of wind passing over loosened rocks in steep slopes, or something else entirely?
In the upcoming season of spring in the Northern hemisphere, HiRISE will be searching for even more of these events in order to better understand when and where they happen, and why.
Ginny Gulick wrote:Gullies on the South Wall of Dao Vallis near the Confluence with Niger Vallis (ESP_024315_1435)
Dao Vallis is an outflow channel that begins on the southeastern flank of the broad low-relief volcano Hadriaca Patera and extends in a southwestwardly direction across the Southern highlands for approximately 1000 kilometers ending near Hellas basin. Outflow channels are generally thought to result from the catastrophic release of enormous amounts of ground water that create floods that scour the surface over periods of days to several months.
This image shows the south wall of Dao Vallis just upstream of the confluence with Niger Vallis.
The gullies that flow into Dao Vallis begin just below the top of the valley wall and erode through the upper rock layers. Gully deposits appear to overlap the material that fills the valley floor. This valley fill material was likely ice-rich and flowed down the wall or valley similar to slow moving glacial material on Earth.
Located beyond the gullies on the valley floor is an intriguing crater-like feature
surrounded by concentric fractures. These fractures would allow ice to sublimate into the atmosphere from the subsurface materials causing progressive collapse of the crater walls and resulting in the formation of the interior hummocky terrain. Fine-grained sediments are trapped by the hummocky terrain and are reworked by local winds forming dunes on the central portion of the crater floor.
Credit: NASA/JPL/University of Arizona
<< Previous HiRISE thread[quote="Nathan Bridges"][float=left][img3=""]http://www.uahirise.org/images/wallpaper/800/ESP_024055_2045.jpg[/img3][/float][url=http://www.uahirise.org/ESP_024055_2045][b][i]Diverse Layers and Mineralogy near Mawrth Vallis (ESP_024055_2045)[/i][/b][/url]
This HiRISE image shows diverse layers in a region near Mawrth Vallis, a channel that was probably carved by water in Mars' ancient past. [url=http://www.uahirise.org/images/2011/details/cut/ESP_024055_2045.jpg][b]The color subimage shows details[/b][/url] of layers exposed in a crater wall.
Tannish to white tones are apparent, which may be reflective of differences in mineralogy. CRISM, a spectrometer on MRO, has detected clays in Mawrth, so the layers here may be clay-rich.
Clays contain water, indicating that this region may have been wet in the past. The subimage also shows polygonal-like textures on some of the layered rock. These may be dessication polygons formed when the wet clays dried. The dark patches on the layers are sand dunes.
This is a stereo pair with [url=http://www.uahirise.org/ESP_024200_2045][b]ESP_024200_2045[/b][/url]. [/quote]
[quote="Ingrid Daubar"][float=left][img3=""]http://www.uahirise.org/images/wallpaper/800/ESP_023314_1440.jpg[/img3][/float][url=http://www.uahirise.org/ESP_023314_1440][b][i]Rafting Rocks (ESP_023314_1440)[/i][/b][/url]
This image shows some interesting features where smoother, dark areas with straight sides are separated by narrow channels of higher material.
This is especially clear [url=http://www.uahirise.org/images/2011/details/cut/ESP_023314_1440.jpg][b]in the southern portion of the image[/b][/url] (rotated so north is at approximately 11 o'clock, 3.2 kilometers or 2 miles across). It looks as if a flat solid surface broke up, and then the individual pieces were rafted apart.
In other areas of Mars, similar features formed when a layer of lava solidified on top of still-molten rock. The solid layer at the surface broke apart either when it contracted as it cooled, or when the liquid below it flowed and dragged along the bottom of the top layer of solid rock.
However, this area of the Hellas basin is not expected to have any volcanic activity. Hellas is a huge, old impact crater, filled with sediments and heavily eroded. In addition, there are subtle differences in the textures here that make this look different from the plate-like lava we find in other areas of Mars. Instead, perhaps something similar happened, but with a mixture of ice and rock instead of lava.
It's possible that a freezing mudflow was pulled apart here, with a frozen upper layer breaking and rafting apart on top of slushy material. When the underlying slushy ice later froze, it would have expanded and been squeezed up between the plates, creating the raised ridges between them. [/quote]
[quote="Ingrid Daubar"][float=left][img3=""]http://www.uahirise.org/images/wallpaper/800/ESP_016228_2650.jpg[/img3][/float][url=http://www.uahirise.org/ESP_016228_2650][b][i]Continuing Avalanches (ESP_016228_2650)[/i][/b][/url]
Since HiRISE first started [url=http://www.uahirise.org/PSP_007338_2640][b]finding avalanches on Mars[/b][/url], we have continued searching for them in the most likely places: steep cliffs at the edges of the layered deposits at the North Pole.
These layers are exposed in the scarp face that cuts through them diagonally [url=http://www.uahirise.org/images/2011/details/cut/ESP_016228_2650.jpg][b]across this subimage[/b][/url]. The bright smoother material at the lower left is at the top of the cliff, and here we have caught another avalanche as it falls down the steep slope towards the upper right of the image.
A large (approximately 200 meters or 600 feet across) cloud of reddish dust has been kicked up at the base of the scarp. Fine tendrils of bright wisps are visible farther up the cliff face—these may be individual falls of material, before spreading out as the avalanche plummets downward.
This might allow scientists to figure out the exact location of the start of the avalanche; for example, which layer it originally came from and how far it fell. This information will help narrow down what triggers these falls: is it seasonal temperature changes in the ice layers, gusts of wind passing over loosened rocks in steep slopes, or something else entirely?
In the upcoming season of spring in the Northern hemisphere, HiRISE will be searching for even more of these events in order to better understand when and where they happen, and why. [/quote]
[quote="Ginny Gulick"][float=left][img3=""]http://www.uahirise.org/images/wallpaper/800/ESP_024315_1435.jpg[/img3][/float][url=http://www.uahirise.org/ESP_024315_1435][b][i]Gullies on the South Wall of Dao Vallis near the Confluence with Niger Vallis (ESP_024315_1435)[/i][/b][/url]
Dao Vallis is an outflow channel that begins on the southeastern flank of the broad low-relief volcano Hadriaca Patera and extends in a southwestwardly direction across the Southern highlands for approximately 1000 kilometers ending near Hellas basin. Outflow channels are generally thought to result from the catastrophic release of enormous amounts of ground water that create floods that scour the surface over periods of days to several months.
This image shows the south wall of Dao Vallis just upstream of the confluence with Niger Vallis. [url=http://www.uahirise.org/images/2011/details/cut/ESP_024315_1435_1.jpg][b]The gullies that flow into Dao Vallis[/b][/url] begin just below the top of the valley wall and erode through the upper rock layers. Gully deposits appear to overlap the material that fills the valley floor. This valley fill material was likely ice-rich and flowed down the wall or valley similar to slow moving glacial material on Earth.
Located beyond the gullies on the valley floor is an intriguing crater-like feature [url=http://www.uahirise.org/images/2011/details/cut/ESP_024315_1435_2.jpg][b]surrounded by concentric fractures[/b][/url]. These fractures would allow ice to sublimate into the atmosphere from the subsurface materials causing progressive collapse of the crater walls and resulting in the formation of the interior hummocky terrain. Fine-grained sediments are trapped by the hummocky terrain and are reworked by local winds forming dunes on the central portion of the crater floor. [/quote]
[b][i]Credit: NASA/JPL/University of Arizona[/i][/b]
[url=http://asterisk.apod.com/viewtopic.php?f=29&t=25626][size=85][b][i]<< Previous HiRISE thread[/i][/b][/size][/url]