Back At Larry's Lookout |
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May 18 2005, 06:29 PM
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#1
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Some pretty complex driving by the look of it:
http://qt.exploratorium.edu/mars/spirit/fo...E0P1214R0M1.JPG Now this is odd: http://qt.exploratorium.edu/mars/spirit/na...E0P0617R0M1.JPG It looks like some of the rocks have slid down the dune |
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May 22 2005, 07:29 AM
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#2
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Senior Member Group: Members Posts: 2228 Joined: 1-December 04 From: Marble Falls, Texas, USA Member No.: 116 |
Sorry this is long, but I found myself on a roll...
It definitely seems to be a "crusty unit," but going so far as to call it a "duricrust" seems unwarranted. I really haven't yet seen anything I'd call a true duricrust on Mars. I really prefer the "weakly cemented by salts" hypothesis. Water ice is a second choice for me. There were a few images from around sol 110 taken near Endurance that keep popping up as examples of duricrust, but taken in the context of the surroundings, they appear to me to be soil/dust covered slabs of fractured bedrock that were disturbed by Oppy's wheels. Purported examples of duricrust: http://marsrovers.jpl.nasa.gov/gallery/all...03P2584L7M1.JPG http://www.lyle.org/~markoff/pds/234567/1P...87L234567C1.JPG Context images showing the dust/soil covered plates of broken-up bedrock surrounding Endurance crater: http://marsrovers.jpl.nasa.gov/gallery/all...3P2366L7M1.HTML http://marsrovers.jpl.nasa.gov/gallery/all...3P2366L7M1.HTML http://www.lyle.org/~markoff/pds/257/1P137...P2361L257C1.JPG These are some that have been partially exhumed: http://www.lyle.org/~markoff/pds/257/1P138...P2295L257C1.JPG http://www.lyle.org/~markoff/pds/257/1P138...P2295L257C1.JPG -------------------- ...Tom
I'm not a Space Fan, I'm a Space Exploration Enthusiast. |
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May 22 2005, 06:39 PM
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#3
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Senior Member Group: Members Posts: 3419 Joined: 9-February 04 From: Minneapolis, MN, USA Member No.: 15 |
QUOTE (CosmicRocker @ May 22 2005, 02:29 AM) It definitely seems to be a "crusty unit," but going so far as to call it a "duricrust" seems unwarranted. I really haven't yet seen anything I'd call a true duricrust on Mars. I really prefer the "weakly cemented by salts" hypothesis. Water ice is a second choice for me. "Duricrust" is a term that was applied to some Viking soils back in the 1970s, to describe the cohesive properties of the upper few mm of some of the soils. As far as I've ever been able to tell, it's used in a descriptive, not a diagnostic, manner -- it describes the cohesive qualities of some top layers of Martian soils. It doesn't pre-suppose a reason for the cohesiveness, i.e., it doesn't assume that the duricrust is created by a permafrost layer or anything like that. (So the idea of an absolute "true duricrust" doesn't really enter the discussion, I don't think.) In fact, the conclusion of the original Viking team was that the duricrust is likely a weakly cemented unit resulting from evaporation of salts from groundwater. Since no evidence of current groundwater was returned, they didn't state that assumption as certain, but I know it was the preferred theory for the observed phenomenon. -the other Doug -------------------- “The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
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May 23 2005, 03:36 AM
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#4
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Senior Member Group: Members Posts: 2228 Joined: 1-December 04 From: Marble Falls, Texas, USA Member No.: 116 |
QUOTE (dvandorn @ May 22 2005, 12:39 PM) "Duricrust" is a term that was applied to some Viking soils back in the 1970s, to describe the cohesive properties of the upper few mm of some of the soils. As far as I've ever been able to tell, it's used in a descriptive, not a diagnostic, manner -- it describes the cohesive qualities of some top layers of Martian soils. It doesn't pre-suppose a reason for the cohesiveness, i.e., it doesn't assume that the duricrust is created by a permafrost layer or anything like that. (So the idea of an absolute "true duricrust" doesn't really enter the discussion, I don't think.) In fact, the conclusion of the original Viking team was that the duricrust is likely a weakly cemented unit resulting from evaporation of salts from groundwater. Since no evidence of current groundwater was returned, they didn't state that assumption as certain, but I know it was the preferred theory for the observed phenomenon. -the other Doug I know that the term had been used for similarly caked soils observed by a Viking misssion, and even by many other scientists studying other parts of Mars over the years. All I am saying is, it that it's a misuse of the term. Duricrust is a useful geologic term which has a much longer history than that of the space program. While the definition is fairly broad and open to some interpretation, it has always implied an indurated, strongly to moderately cemented soil or regolithic material. Ie, it is literally as hard as a rock, and therefore has the ability to control the later geomorphic evolution of the landscape. Laterites, bauxites,ferricretes, silcretes, even caliches are classic duricrusts. Apparently most of us agree that whatever we call it, this looks like some kind of a salt-caked crust. I don't want to debate semantics. It's just that I hate definition-creep, especially when it erodes the value of a time-worn and useful term. -------------------- ...Tom
I'm not a Space Fan, I'm a Space Exploration Enthusiast. |
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