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HiRISE Update 30 July 2008
Elian Gonzales
post Jul 30 2008, 08:36 PM
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New captioned images, including one of Spirit at Martian mid-winter.

http://hirise.lpl.arizona.edu/nea.php
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Stu
post Jul 30 2008, 08:54 PM
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Thanks for the prompt, Elian; I keep forgetting the updates. Love that Athabasca Valles image, one of my fave places on Mars! smile.gif


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dburt
post Aug 1 2008, 10:12 PM
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Thanks also. My favorite (naturally) has got to be the one called stair-stepped mounds in Meridiani Planum, here.
http://hirise.lpl.arizona.edu/PSP_008930_1880
At the highest resolution given for the index image (you can choose "wallpaper" 2560 x 1600 in the lower right of the web page), each stairstep seems to be separated from the one above it by a layer of dark boulders. Other possibilities might include repeated deposition of thin lava layers or repeated development of awfully strong layers of dark cement on top of each bright layer before the next one was deposited. If dark boulder layers, that would seem to rule out wind as the depositing agent, at least of the boulders. Note: A similar observation of apparent interlayer boulder beds was made by Emily in some other HiRISE images over a year ago, and that observation inspired me to start writing here.

As has been said before, too bad the best exposures on Mars are too steep for rovers. sad.gif

-- HDP Don
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djellison
post Aug 1 2008, 10:56 PM
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QUOTE (dburt @ Aug 1 2008, 11:12 PM) *
each stairstep seems to be separated from the one above it by a layer of dark boulders.


Really? Shading, dust deposition, and rockfall from each layer above seems to me, to be what we're seeing.

Doug
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dburt
post Aug 2 2008, 02:05 AM
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Hi Doug - Yes, a second inspection shows you're absolutely right, especially as regards the apparent darkness (shadows and small overhangs). Of course, that still leaves us with the question of why the flat-topped, heavily cracked, boulder-generating benches are so much more resistant to erosion than the intervening dust-covered layers (among many other questions). Anyway, thanks for straightening me out on the shadows (duhh!).

Lesson (that I often wish I could teach myself): beware the Rosenthal effect and always look at least twice, class.

-- HDP Don
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