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Continuing into Glenelg, Leaving Rocknest behind, sols 102-166 (Nov 18 2012-Jan 23, 2013)
dburt
post Feb 2 2013, 05:30 PM
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QUOTE (Bill Harris @ Feb 1 2013, 08:38 PM) *
...RE: the LPSC paper cited: is NG Barlow a colleague of yours?
All in all, this LPSC is going to be very good!

No (she's at NAU; I'm at ASU), although she's certainly heard me give talks. She's been interested in martian impact phenomena, mainly rampart craters as seen from orbit, for far longer than I and she organizes an annual planetary cratering conference in Flagstaff that usually includes a field trip to Meteor Crater. Agree about LPSC; sorry I won't be going this year.
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CosmicRocker
post Feb 3 2013, 07:12 AM
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"dewatering via vibration"

I like that way of describing it. I was definitely thinking about vibration and ablation.


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serpens
post Feb 7 2013, 04:19 AM
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QUOTE (Bill Harris @ Feb 2 2013, 03:38 AM) *
.....Alien processes.
Though I do favor the "dewatering via vibration" process.....

Not alien Bill, although I guess that a lot would depend on whether there was a shallow lake here. Prodelta for this area? If the proposed coarse overlay covering the mud was thick enough the density difference alone could cause diapir effects. Alternatively as you and Tom prefer, seismic (impact) vibration could cause liquefaction, but the stimulus would be transient. Mud fill of cracks and diapir nodules should not be mutually exclusive events. Even munroes should be considered for the mounds. When they retrace the path in it will be interesting to see if Tom's dike material correlates to the mounds.
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360pano.eu
post Mar 28 2013, 03:54 PM
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http://www.360cities.net/image/mars-gigapi...ar-days-136-149

The images for panorama obtained by the two rover's Mast Cameras:
Narrow Angle Camera (NAC), which has a 100 mm focal length
Medium Angle Camera (MAC), which has a 34 mm focal length

The mosaic, which stretches 90000x45000 pixels, includes 295 images from NAC taken on Sols 136-149 and 112 images from MAC taken on Sol 137.
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CosmicRocker
post Apr 19 2013, 10:12 PM
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I have a question for anyone who attended the LPSC last month. Did anyone talk about Snake River? Was there any discussion of its origin and/or composition?


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elakdawalla
post Apr 19 2013, 11:03 PM
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Grotzinger mentioned it in his introductory overview talk. My notes say "snake, we think it's sedimentary dike, probably not igneous, associated with hydrostatic pressure during compaction."


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CosmicRocker
post Apr 21 2013, 05:58 AM
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Thanks, Em. If you have any info on the elemental or mineralogical composition, it would be interesting to know.

All of this apparent fracturing/dessication of early Martian sediments fascinates me. On various scales we see the boxwork features at Gale and Cape York. Earlier in the MSL mission we saw possible mud cracks and even larger polygonal fracturing in the distant slopes of Mt. Sharp. From orbit, HiRise reveals large-scale boxwork/polygons on the surface. I don't know if any of these are related, but it is tempting to guess.

I have to imagine that there is a whole new paradigm unfolding. It's fascinating... smile.gif


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marsophile
post Apr 28 2013, 03:34 AM
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QUOTE
"A determination about how much time passed between the emplacement of the water-formed rocks and then a second episode of water flowing through cracks in the rocks can not be determined with Curiosity's instrument suite," she said.


http://spaceref.com/mars/curiousmars-tripl...production.html

If APXS readings were obtained for the vein material, would not the relative amounts of deuterium give an estimate of the time intervening between the two events?
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dvandorn
post Apr 28 2013, 03:56 AM
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QUOTE (marsophile @ Apr 27 2013, 09:34 PM) *
If APXS readings were obtained for the vein material, would not the relative amounts of deuterium give an estimate of the time intervening between the two events?

Ummm... can the APXS detect deuterium at all, much less analyze its relative abundance? An Astronomy Online review of the MER APXSes (which, as I understand it, are quite similar to the one on Curiosity) says the following:

QUOTE
The x-ray mode is sensitive to major elements, such as Mg, Al, Si, K, Ca, and Fe, and to minor elements, including Na, P, S, Cl, Ti, Cr, and Mn. The alpha mode is sensitive to lighter elements, particularly C and O. The depth of analysis varies with atomic number, ranging from approximately 10 to 20 micrometers for sodium, to approximately 50 to 100 micrometers for iron. The detection limit is typically 0.5 to 1 weight percent, depending on the element. The APXS is insensitive to small variations of the geometry of the sample surface because all major and minor elements are determined, and can be summed to 100 weight percent.


I don't see H mentioned anywhere in the list of elements to which the APXS is sensitive. Obviously, it's not a definitive list, but... just sayin', I thought APXS only gave relative atomic abundances and only for a selected set of elements to which the detectors are sensitive. I didn't think it actually gave molecular abundance information.

-the other Doug


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DFortes
post Apr 28 2013, 12:07 PM
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QUOTE (dvandorn @ Apr 28 2013, 04:56 AM) *
Ummm... can the APXS detect deuterium at all, much less analyze its relative abundance? An Astronomy Online review of the MER APXSes (which, as I understand it, are quite similar to the one on Curiosity) says the following:

I don't see H mentioned anywhere in the list of elements to which the APXS is sensitive. Obviously, it's not a definitive list, but... just sayin', I thought APXS only gave relative atomic abundances and only for a selected set of elements to which the detectors are sensitive. I didn't think it actually gave molecular abundance information.

-the other Doug


There are two answers to the question of this instrument's ability to detect light element. Firstly, hydrogen (and deuterium) do not fluoresce in the X-ray portion of the spectrum - their most energetic emissions unpon excitation are in the UV.
Secondly, progressively lighter elements emit lower energy X-ray (from 525 eV for oxygen, down to 54 eV for lithium), and these are more readily absorbed by any 'air' between the sample and detector. I haven't sat down to do the calculations, but I suspect that even the relatively thin martian atmosphere will substantially block these low-energy emissions along path lengths of mm to cm in air (to say nothing of through solid rock!)
And this is before you even begin to worry about what the detector is sensitive to....
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marsophile
post Apr 28 2013, 05:31 PM
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Ok, maybe the APXS instrument would not be the one to use. But perhaps a Chemin or SAM run with a vein sample could give the deuterium/hydrogen ratio. The question is whether this information could be used to estimate the time between the two water-related events, whichever instrument is used to obtain the data.
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Gerald
post Apr 29 2013, 12:05 PM
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I'd think, it will be very hard for CheMin, because water contents is low, and differences between HDO and H2O containing crystals will be tiny.
SAM should be well-suited for D/H ratio estimation, as described e.g. in this LPSC 2013 paper for atmospheric runs.
Two questions remain:
1. H2O tends to evaporate faster than HDO. But is the rate the same for clay minerals and sulfates?
2. How can D/H ratio be scaled to absolute time?

So, for simplified assumptions within a given model of Martian history, it should be possible to retrieve a model-dependent time estimate.
May be, over time an assignment of D/H ratios to sediment layers becomes available.
But ground water may have lower D/H ratio than the atmosphere.

To reduce those uncertaintes it will help to look also to other isotope ratios.
But still, one will get the age of the material that built the rocks, in terms of when it was part of the atmosphere for the last time.

To obtain the time of the precipitation event, one needs to look at isotopic ratios of decay products of radio isotopes, e.g. at Ar-40.
SAM is able to measure the Ar40/Ar36 ratio, see e.g. in this LSPC 2013 poster.
This Ar40 has to be compared with the potassium 40 concentration, which can be estimated by the overall potassium concentration obtained by APXS.

I've no idea, whether accuracies will be acceptable.
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Gerald
post Jun 10 2013, 09:51 PM
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QUOTE (CosmicRocker @ Apr 21 2013, 07:58 AM) *
... If you have any info on the elemental or mineralogical composition, it would be interesting to know. ...

There have been released APXS and ChemCam data about Snake River to the PDS today.

ChemCam investigated Snake River on Sol 147 with a 1x5 raster, 30 laser shots at each raster point. Annotated spectra can be found in this PDS subdirectory. The target name and other metadata can be found in file msl_ccam_obs.csv of this PDS subdirectory.

APXS investigated Snake River on Sol 149. Calculated elemental composition can be found in the rwp-csv-file in this PDS subdirectory (easy to read with a text editor after download). The target name is documented in the first line of the rsp-csv-file of the same directory.
APXS measurement may have included some dust.

Excerpt of the APXS rwp-file, sorted by abundancy ("computed weight percent of the oxide", see associated lbl-file):
QUOTE
"oxide", "APXS analysis ver 1","statistical uncertainty (precision)"
SiO2 , 43.71 , 0.96
FeO , 23.64 , 0.51
Al2O3 , 7.41 , 0.38
CaO , 6.94 , 0.35
MgO , 6.42 , 0.33
SO3 , 5.40 , 0.27
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CosmicRocker
post Jun 12 2013, 05:08 AM
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Many thanks for posting that information, Gerald. smile.gif smile.gif smile.gif
Ever since some of us speculated here that Snake River might be a clastic dike and we later learned that the science team held a similar opinion, I have been very interested to see the supporting data from the analytical instruments.


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