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#1 dickbill

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Posted 16 October 2012 - 04:18 PM

We need this thread.
http://www.nasa.gov/.../msl/index.html

what are the bright particles, metal, silicates, salt crystals?

#2 llanitedave

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Posted 16 October 2012 - 08:13 PM

The photo caption calls them "light-toned" as well as "bright" particles. That seems to me the better description.

I'm going to go out on a limb and make a guess...

Hydrated silica, or "opal".

There are a lot of other possibilities, so I'm not going to stand on it. But looking at the fact that some of these lighter particles have a nodular structure, some kind of fluid-based concretion seems plausible to me.

#3 Rick Woods

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Posted 17 October 2012 - 01:05 AM

The photo caption calls them "light-toned" as well as "bright" particles. That seems to me the better description.

I'm going to go out on a limb and make a guess...

Hydrated silica, or "opal".

There are a lot of other possibilities, so I'm not going to stand on it. But looking at the fact that some of these lighter particles have a nodular structure, some kind of fluid-based concretion seems plausible to me.


That's a pretty sturdy limb you're on; I know I've read an article fairly recently about opal fields being discovered on Mars from orbit. I can't find it in my stuff, though.

In any case, I like the title of this thread. :D

#4 dickbill

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Posted 17 October 2012 - 12:59 PM

Doesn't the sand in the trench look a bit 'hydrated'? it makes clums, like if it was possible to make a sand castle.

#5 FeynmanFan

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Posted 17 October 2012 - 03:07 PM

Opals? Cool, maybe Mars is going to be the next Coober Pedy. :jump:

#6 dickbill

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Posted 19 October 2012 - 08:27 AM

A better view of a bright particle, very pretty and indeed it has like an opalescent luster.
http://www.nasa.gov/...a/pia16233.html

#7 Jay_Bird

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Posted 19 October 2012 - 10:16 AM

I recall that a lot of previous indications from Spirit and Opportunity, either the 'blueberries' & gypsum veins, or just the salt content at many locations based on x-ray spectrum, were interpreted to indicate acidic groundwater conditions in Mar's past.

Isn't silica soluble at high pH, so opal would indicate more basic groundwater chemistry? If that's the case, this is an interesting finding that adds more to the Mars water story, aside from the future jewelry potential.

#8 llanitedave

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Posted 19 October 2012 - 11:16 AM

I could be wrong, but my impression was that the solubility of silica minerals is influenced much more strongly by temperature than pH in most conditions. It's a complex area that I'm not completely comfortable with, but the presence of other minerals also seems to influence it.

So I don't think acidic conditions, at least mild ones, are an impediment to opal deposition, but it's not going to be a simple determination.

Then again, I'm still not completely convinced it's opal we're looking at.

#9 scopethis

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Posted 19 October 2012 - 02:35 PM

tis some kind of seed pod...

#10 dickbill

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Posted 20 October 2012 - 08:39 AM

Low iron content spherules from Opportunity at Gusev. Those are not hematites.
http://www.nasa.gov/...er20120914.html

#11 dickbill

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Posted 21 October 2012 - 03:46 PM

Regarding acidity of early Mars, from the abstract of "Early geochemical environment of Mars as determined from thermodynamics of phyllosilicates.
Chevrier V, Poulet F, Bibring JP", it was not always acidic:

"...we investigate the geochemical conditions prevailing on the surface of Mars during the Noachian period using calculations of the aqueous equilibria of phyllosilicates. Our results show that Fe3+-rich phyllosilicates probably precipitated under weakly acidic to alkaline pH, an environment different from that of the following period, which was dominated by strongly acid weathering that led to the sulphate deposits identified on Mars..."

"...We suggest that the possible absence of Noachian carbonates more probably resulted from low levels of atmospheric carbon dioxide, rather than primary acidic conditions. Other greenhouse gases may therefore have played a part in sustaining a warm and wet climate on the early Mars."

Other gases, maybe Methane, or what else?

#12 dickbill

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Posted 15 November 2012 - 03:32 PM

Curiosity web site updated.
They have plotted the measured radiations against the pressure and found out radiations are weaker at night when pressure is higher because of the shielded effect of a thicker atmosphere. Makes sense.
http://www.nasa.gov/.../pia16479b.html

However they say:"...At each of the pressure maximums, the radiation level drops between 3 to 5 percent..."
But if the pressure maximum is reached at night, the solar radiations are completely shielded and cannot reach the ground, by definition, so i would have expected a more important daily variation than just 5%, that is, unless the solar radiation is a minor component of the total radiations reaching Mars (for example cosmic rays), which i don't think is the case.
Any idea why it's only a 5% variation?

#13 dickbill

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Posted 16 November 2012 - 09:43 AM

http://www.nasa.gov/.../pia16479b.html

Hmmm, not many bite on the question.
Again, I am very surprised because i expected that at night,( on the dark side of the planet), no solar radiation reach the surface and therefore the radiations fall to zero or near that, irrespective of the shielding effect of the atmosphere.
Against the naysayers who say Mars is too irradiated, one answer was that human on Mars could work at night safely.
The rest of radiative background that come from cosmic rays and that can hit the planet in any orientation, should be much less than solar particles.
Instead of that, Curiosity's measurement show a small decrease at night, from 210 to 195 the first day, for example (no units are given).
So, where do the radiations come from, at night?

#14 Jay_Bird

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Posted 16 November 2012 - 11:51 AM

The band of radiation that is being measured and plotted must not include solar UV or other solar components that have diurnal change independent of air density. I think the main point is that cooler night air is denser and offers more shielding. The radiation band measured and plotted may be only a small portion of the total radiation reaching Curiousity from sun, cosmic rays and maybe even low level emission from Mars rocks at landing site.

#15 dickbill

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Posted 16 November 2012 - 12:38 PM

The band of radiation that is being measured and plotted must not include solar UV or other solar components that have diurnal change independent of air density. I think the main point is that cooler night air is denser and offers more shielding. The radiation band measured and plotted may be only a small portion of the total radiation reaching Curiousity from sun, cosmic rays and maybe even low level emission from Mars rocks at landing site.


So, not even mentioning UV, all solar wind, alpha, protons, electrons are excluded at daytime? I understand the point of doing that if they wanted to see the effect of the atmospheric pressure only, but that's misleading.
That would mean the real radiation in daytime couldbe hundreds of times higher than plotted in the graph.






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