by bystander » Wed Feb 01, 2012 8:50 pm
Alfred McEwen wrote:The Floor of Toro Crater (ESP_025067_1970)
Toro Crater may have experienced hydrothermal alteration, producing diverse minerals. The mineral diversity leads to diverse color in HiRISE, especially when enhanced
as in this subimage.
In general the blue and green colors indicate unaltered minerals like pyroxene and olivine, whereas the warmer colors indicate alteration into clays and other minerals. The linear north-south trending features are windblown dunes that are much younger than the bedrock.
This is a stereo pair with
ESP_025344_1970.
Ginny Gulick wrote:Crater with Gullies on a Central Structure (ESP_025082_2295)
The 40-kilometer diameter unnamed crater (49 degrees North, 21 degrees East) in this image is located west of Lyot Crater and north of Deuteronilus Mensae in the Northern Plains of Mars.
As seen in the subimage, gully systems in the central structure have eroded underlying layers (undercutting) that are less resistant to erosion than the surface rock of the central structure. Previous channelized water flows likely transported the eroded sediments toward the southeast and deposited them forming the expansive debris aprons.
The formation of channels on the debris aprons supports the hypothesis that these sediments were transported down the gullies and then deposited onto the aprons by flowing water. In the larger, northernmost system, sediments have partially filled in the channel segments and winds have remobilized these sediments forming the dunes that line the gullies.
This is a stereo pair with
PSP_009298_2295.
Paul Geissler wrote:Active Erosion in Pasteur Crater (ESP_025372_2000)
This image shows knobs and bluffs that are being actively eroded by the Martian wind. Fine, light-toned sedimentary layering is
exposed in the bedrock at the base of the cliffs.
Also in this scene are two types of unconsolidated aeolian sediments. The reddish ridges are relatively immobile, and are probably similar to granule ripples on Earth that are protected from the winds by a surface layer of coarse grains. The dark gray dunes are probably made up of fine (approximately 0.1 mm) basaltic sand.
Previous HiRISE images (
PSP_001756_1995,
PSP_010643_1995) showed that the sand in Pasteur Crater is currently mobile.
This sand is thought to be locally derived, from dark deposits within a small crater called Euphrates that is located within Pasteur, upwind of the sand dunes. The movement of this sand contributes to the erosion of the ancient bedrock, sandblasting the formation into the knobs seen today and exposing layers that were deposited in ages past.
Alfred McEwen wrote:Another Well-Preserved Impact Crater (ESP_025450_1595)
Shown here is a stereo pair (
see the anaglyph) of a well-preserved impact crater about 6 or 7 kilometers wide from rim to rim. By well-preserved we mean that the crater has a sharp rim, deep cavity, impact morphologies preserved down to scales of tens of meters, and little sign of infilling or degradation by a range of processes (other impacts, volcanism, tectonism, icy flow, aeolian erosion and infill, etc.).
When seen at full HiRISE resolution, almost all craters on Mars do show some modification such as subsequent smaller impacts, wind-blown deposition and/or erosion, and downslope movement of material on steep slopes.
We have imaged hundreds of well-preserved impact craters on Mars ranging from 1 meter to more than 100 kilometers wide. These targets are of great interest for multiple reasons: first, we want to better understand impact cratering, a fundamental surface process. Second, such craters often contain good exposures of bedrock in the steep walls and, if the crater is large enough, in the central uplift. Just like terrestrial geologists are attracted to good bedrock outcrops like road cuts, planetary geologists are attracted to well-preserved craters.
Third, the steep slopes often reveal active processes, such as formation of gullies, boulder falls, and slope streaks that could form in a variety of ways. Some of these active processes could be related to water, since the crater may expose lenses of ice or salty water, or create deep shadows that trap volatiles, or expose salts that can extract water from the air.
This is a stereo pair with
ESP_024738_1595.
Credit: NASA/JPL/University of Arizona
PDS Release: February 2012 (Orbit Ranges 25,000—25,399)
<< Previous HiRISE Update[quote="Alfred McEwen"][float=left][img3=""]http://www.uahirise.org/images/wallpaper/800/ESP_025067_1970.jpg[/img3][/float][url=http://www.uahirise.org/ESP_025067_1970][b][i]The Floor of Toro Crater (ESP_025067_1970)[/i][/b][/url]
Toro Crater may have experienced hydrothermal alteration, producing diverse minerals. The mineral diversity leads to diverse color in HiRISE, especially when enhanced [url=http://www.uahirise.org/images/2012/details/cut/ESP_025067_1970.jpg][b]as in this subimage[/b][/url].
In general the blue and green colors indicate unaltered minerals like pyroxene and olivine, whereas the warmer colors indicate alteration into clays and other minerals. The linear north-south trending features are windblown dunes that are much younger than the bedrock.
This is a stereo pair with [url=http://www.uahirise.org/ESP_025344_1970][b]ESP_025344_1970[/b][/url]. [/quote]
[quote="Ginny Gulick"][float=left][img3=""]http://www.uahirise.org/images/wallpaper/800/ESP_025082_2295.jpg[/img3][/float][url=http://www.uahirise.org/ESP_025082_2295][b][i]Crater with Gullies on a Central Structure (ESP_025082_2295)[/i][/b][/url]
The 40-kilometer diameter unnamed crater (49 degrees North, 21 degrees East) in this image is located west of Lyot Crater and north of Deuteronilus Mensae in the Northern Plains of Mars.
[url=http://www.uahirise.org/images/2012/details/cut/ESP_025082_2295.jpg][b]As seen in the subimage[/b][/url], gully systems in the central structure have eroded underlying layers (undercutting) that are less resistant to erosion than the surface rock of the central structure. Previous channelized water flows likely transported the eroded sediments toward the southeast and deposited them forming the expansive debris aprons.
The formation of channels on the debris aprons supports the hypothesis that these sediments were transported down the gullies and then deposited onto the aprons by flowing water. In the larger, northernmost system, sediments have partially filled in the channel segments and winds have remobilized these sediments forming the dunes that line the gullies.
This is a stereo pair with [url=http://www.uahirise.org/PSP_009298_2295][b]PSP_009298_2295[/b][/url]. [/quote]
[quote="Paul Geissler"][float=left][img3=""]http://www.uahirise.org/images/wallpaper/800/ESP_025372_2000.jpg[/img3][/float][url=http://www.uahirise.org/ESP_025372_2000][b][i]Active Erosion in Pasteur Crater (ESP_025372_2000)[/i][/b][/url]
This image shows knobs and bluffs that are being actively eroded by the Martian wind. Fine, light-toned sedimentary layering is [url=http://www.uahirise.org/images/2012/details/cut/ESP_025372_2000_1.jpg][b]exposed in the bedrock at the base of the cliffs[/b][/url].
Also in this scene are two types of unconsolidated aeolian sediments. The reddish ridges are relatively immobile, and are probably similar to granule ripples on Earth that are protected from the winds by a surface layer of coarse grains. The dark gray dunes are probably made up of fine (approximately 0.1 mm) basaltic sand. [url=http://www.uahirise.org/images/2012/details/cut/ESP_025372_2000_2.jpg][b]Previous HiRISE images[/b][/url] ([url=http://www.uahirise.org/PSP_001756_1995][b]PSP_001756_1995[/b][/url], [url=http://www.uahirise.org/PSP_010643_1995][b]PSP_010643_1995[/b][/url]) showed that the sand in Pasteur Crater is currently mobile.
This sand is thought to be locally derived, from dark deposits within a small crater called Euphrates that is located within Pasteur, upwind of the sand dunes. The movement of this sand contributes to the erosion of the ancient bedrock, sandblasting the formation into the knobs seen today and exposing layers that were deposited in ages past. [/quote]
[quote="Alfred McEwen"][float=left][img3=""]http://www.uahirise.org/images/wallpaper/800/ESP_025450_1595.jpg[/img3][/float][url=http://www.uahirise.org/ESP_025450_1595][b][i]Another Well-Preserved Impact Crater (ESP_025450_1595)[/i][/b][/url]
Shown here is a stereo pair ([url=http://www.uahirise.org/images/2012/details/cut/ESP_025450_1595.jpg][b]see the anaglyph[/b][/url]) of a well-preserved impact crater about 6 or 7 kilometers wide from rim to rim. By well-preserved we mean that the crater has a sharp rim, deep cavity, impact morphologies preserved down to scales of tens of meters, and little sign of infilling or degradation by a range of processes (other impacts, volcanism, tectonism, icy flow, aeolian erosion and infill, etc.).
When seen at full HiRISE resolution, almost all craters on Mars do show some modification such as subsequent smaller impacts, wind-blown deposition and/or erosion, and downslope movement of material on steep slopes.
We have imaged hundreds of well-preserved impact craters on Mars ranging from 1 meter to more than 100 kilometers wide. These targets are of great interest for multiple reasons: first, we want to better understand impact cratering, a fundamental surface process. Second, such craters often contain good exposures of bedrock in the steep walls and, if the crater is large enough, in the central uplift. Just like terrestrial geologists are attracted to good bedrock outcrops like road cuts, planetary geologists are attracted to well-preserved craters.
Third, the steep slopes often reveal active processes, such as formation of gullies, boulder falls, and slope streaks that could form in a variety of ways. Some of these active processes could be related to water, since the crater may expose lenses of ice or salty water, or create deep shadows that trap volatiles, or expose salts that can extract water from the air.
This is a stereo pair with [url=http://www.uahirise.org/ESP_024738_1595][b]ESP_024738_1595[/b][/url]. [/quote]
[b][i]Credit: NASA/JPL/University of Arizona[/i][/b]
[url=http://www.uahirise.org/releases/feb_12.php][b][i]PDS Release: February 2012 (Orbit Ranges 25,000—25,399)[/i][/b][/url]
[url=http://asterisk.apod.com/viewtopic.php?f=29&t=26861][size=85][b][i]<< Previous HiRISE Update[/i][/b][/size][/url]