by bystander » Wed Oct 10, 2012 7:20 pm
Alfred McEwen wrote:Double Depressions or Expanded Craters on the Northern Plains (ESP_028688_2330)
This image covers part of the vast northern plains of Mars, in a region called Utopia Planitia.
In the color subimage, we see a bunch of shallow depressions, that are really double depressions. There is an inner low area that is quite circular, surrounded by shallower semi-circular depressions. The sun is to the lower left (southwest)--if you see domes instead or craters then your brain has inverted the topography.
How did these double depressions form? Once idea is that the inner depressions correspond to impact craters, or the floor deposits of impact craters. These are likely secondary craters that all formed at the same time from the ejecta of a much larger primary crater. The high latitude regions of Mars are known to be rich in water ice below a shallow dry layer. The dry layer protects the ice, which would otherwise sublimate (going directly from a solid to a gas) into the air and disappear.
What happens after an impact event disturbs the dry layer and exposes ice? The ice would sublimate, and if the ice isn't just filling pore space between non-ice materials, collapse of the surface must follow. Maybe that sublimation gradually eats away a shallow subsurface layer of this ice surrounding each impact crater to create these double depressions, or "expanded craters".
This is a stereo pair with
ESP_028411_2330.
Alfred McEwen wrote:What Is This? (ESP_028689_1180)
What are we looking at here? There are long linear ridges or elevated terrains covered by regular patterns of dark spots. Viewed at full resolution and in color we can see that the surface is covered by ripples and that some of the dark spots have bright halos around them.
Give up? These are sand dunes covered by carbon dioxide frost as seen in late winter when the carbon dioxide is starting to sublimate (change from solid to vapor). However, the way this sublimation happens is quite complex, leading to the spots, fans, streaks and so forth described in previous HiRISE image captions. We've imaged this spot 3 times in past years:
ESP_020276_1180,
ESP_019854_1180, and
ESP_019287_1180.
The scene looks very similar in
ESP_019854_1180 because that was almost exactly one Mars year ago, at the same season, but it looks different in the other two images. Sometimes such seasonal monitoring shows more differences in appearance in subsequent years at almost the exact same time of year, just as seasonal changes on Earth vary from year to year.
Alfred McEwen wrote:Where Curiosity May Roam (ESP_028823_1755)
This image is part of a series of color strips being acquired by HiRISE to support future traverse planning by the Curiosity rover.
The enhanced-color subimage shows an interesting portion of this scene, on the low slopes at the base of "Mount Sharp", where the rover could study deposits with diverse lithologies (rock types). The darkest areas mark deposits of loose, windblown sand. In general the bluer colors mark unaltered igneous minerals whereas the warm colors are due to altered minerals.
The experiments carried by the rover can provide much more detailed information about the compositions and implications for the geologic history of Mars.
Alfred McEwen wrote:The Top of Coprates Chasma (ESP_028962_1645)
This image covers a small portion of gigantic Coprates Chasma, part of Valles Marineris.
With enhanced IR colors, we see a portion of the very top of the south wall of the canyon, looking down onto the steep upper slopes. The colors indicate that diverse rock types are present.
Credit: NASA/JPL/University of Arizona
<< Previous HiRISE Update[quote="Alfred McEwen"][float=left][img3=""]http://www.uahirise.org/images/wallpaper/800/ESP_028688_2330.jpg[/img3][/float][url=http://www.uahirise.org/ESP_028688_2330][b][i]Double Depressions or Expanded Craters on the Northern Plains (ESP_028688_2330)[/i][/b][/url]
This image covers part of the vast northern plains of Mars, in a region called Utopia Planitia.
[url=http://www.uahirise.org/images/2012/details/cut/ESP_028688_2330.jpg][b]In the color subimage[/b][/url], we see a bunch of shallow depressions, that are really double depressions. There is an inner low area that is quite circular, surrounded by shallower semi-circular depressions. The sun is to the lower left (southwest)--if you see domes instead or craters then your brain has inverted the topography.
How did these double depressions form? Once idea is that the inner depressions correspond to impact craters, or the floor deposits of impact craters. These are likely secondary craters that all formed at the same time from the ejecta of a much larger primary crater. The high latitude regions of Mars are known to be rich in water ice below a shallow dry layer. The dry layer protects the ice, which would otherwise sublimate (going directly from a solid to a gas) into the air and disappear.
What happens after an impact event disturbs the dry layer and exposes ice? The ice would sublimate, and if the ice isn't just filling pore space between non-ice materials, collapse of the surface must follow. Maybe that sublimation gradually eats away a shallow subsurface layer of this ice surrounding each impact crater to create these double depressions, or "expanded craters".
This is a stereo pair with [url=http://www.uahirise.org/ESP_028411_2330][b]ESP_028411_2330[/b][/url]. [/quote]
[quote="Alfred McEwen"][float=left][img3=""]http://www.uahirise.org/images/wallpaper/800/ESP_028689_1180.jpg[/img3][/float][url=http://www.uahirise.org/ESP_028689_1180][b][i]What Is This? (ESP_028689_1180)[/i][/b][/url]
What are we looking at here? There are long linear ridges or elevated terrains covered by regular patterns of dark spots. Viewed at full resolution and in color we can see that the surface is covered by ripples and that some of the dark spots have bright halos around them.
Give up? These are sand dunes covered by carbon dioxide frost as seen in late winter when the carbon dioxide is starting to sublimate (change from solid to vapor). However, the way this sublimation happens is quite complex, leading to the spots, fans, streaks and so forth described in previous HiRISE image captions. We've imaged this spot 3 times in past years: [url=http://www.uahirise.org/ESP_020276_1180][b]ESP_020276_1180[/b][/url], [url=http://www.uahirise.org/ESP_019854_1180][b]ESP_019854_1180[/b][/url], and [url=http://www.uahirise.org/ESP_019287_1180][b]ESP_019287_1180[/b][/url].
The scene looks very similar in [url=http://www.uahirise.org/ESP_019854_1180][b]ESP_019854_1180[/b][/url] because that was almost exactly one Mars year ago, at the same season, but it looks different in the other two images. Sometimes such seasonal monitoring shows more differences in appearance in subsequent years at almost the exact same time of year, just as seasonal changes on Earth vary from year to year. [/quote]
[quote="Alfred McEwen"][float=left][img3=""]http://www.uahirise.org/images/wallpaper/800/ESP_028823_1755.jpg[/img3][/float][url=http://www.uahirise.org/ESP_028823_1755][b][i]Where Curiosity May Roam (ESP_028823_1755)[/i][/b][/url]
This image is part of a series of color strips being acquired by HiRISE to support future traverse planning by the Curiosity rover.
[url=http://www.uahirise.org/images/2012/details/cut/ESP_028823_1755.jpg][b]The enhanced-color subimage[/b][/url] shows an interesting portion of this scene, on the low slopes at the base of "Mount Sharp", where the rover could study deposits with diverse lithologies (rock types). The darkest areas mark deposits of loose, windblown sand. In general the bluer colors mark unaltered igneous minerals whereas the warm colors are due to altered minerals.
The experiments carried by the rover can provide much more detailed information about the compositions and implications for the geologic history of Mars. [/quote]
[quote="Alfred McEwen"][float=left][img3=""]http://www.uahirise.org/images/wallpaper/800/ESP_028962_1645.jpg[/img3][/float][url=http://www.uahirise.org/ESP_028962_1645][b][i]The Top of Coprates Chasma (ESP_028962_1645)[/i][/b][/url]
This image covers a small portion of gigantic Coprates Chasma, part of Valles Marineris.
[url=http://www.uahirise.org/images/2012/details/cut/ESP_028962_1645.jpg][b]With enhanced IR colors[/b][/url], we see a portion of the very top of the south wall of the canyon, looking down onto the steep upper slopes. The colors indicate that diverse rock types are present. [/quote]
[b][i]Credit: NASA/JPL/University of Arizona[/i][/b]
[url=http://asterisk.apod.com/viewtopic.php?t=29675][size=85][b][i]<< Previous HiRISE Update[/i][/b][/size][/url]