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Geomorphology of Gale Crater, Rock on!
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post Oct 1 2012, 01:47 AM
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QUOTE (dvandorn @ Sep 28 2012, 10:36 PM) *
Instead of harboring water in the past, these results tend to indicate that Hellas has never seen much water at all. I think that's likely why it has never been considered as an attractive landing site, even though it is such a low spot that the atmospheric pressure there is higher at the surface than just about anywhere else on Mars.


Hi Doug

Was Hellas was thought to have some glacial formations? Maybe the ice is covered so deep by rock debris and dust that it cannot be picked up by the spectrometer. However my source is Wikipedia so that may be wrong. http://en.wikipedia.org/wiki/Hellas_Planit...sible_glaciers/ Supposedly MROs radar sounder saw it.

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drz1111
post Oct 1 2012, 05:59 PM
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A question about redox and sedimentary paleoenvironments on Mars:

One of the things I've been thinking about the last few days is that my instincts w/r/t paleoenvironments is all wrong when it comes to Mars.

Take "hottah" - when I saw that, I immediately thought "oh, its cool as hell, but I see why they didn't stop there - fluvial conglomerates are notoriously poor environments to preserve organics".

But that's wrong, or rather, potentially wrong, on Mars, isn't it? It's true on earth in post-proterozoic rocks b/c the atmosphere is oxic and sediment deposited in well-mixed water will lead to oxidized organics, most likely through biologic activity.

But who-the-hell-knows what the Mars atmosphere was like when those conglomerates were deposited? Wouldn't it be more likely that the conglomerates were deposited in a reducing environment, like those auriferous precambrian conglomerates in south africa? Is that necessarily a bad environment for preservation of organics?

Which leads me to my next point, color. When you look at some of the finely-bedded outcrops that the pictures are showing, they're clearly darker and, more importantly, greyer than the overlying rocks (e.g. compared to the hottah, which seems to be a light tan). Earth-instincts; that's a shale or shale-like rock, deposited in an anoxic environment.

But why would that be so on Mars? I guess EVERY lacustrine-type depositional environment on Mars could be anoxic, but, that's not consistent with where Mars eventually evolves to and what MER observed. Redox is all a big mystery, right? We don't know the chemsistry, and one thing that seems likely is that the biologicially mediated redox chemistry that you see in sediments in Earth is unlikely to apply there. And do our usual Earth-honed instincts about color & redox state of the paleoenvironment hold true?

And, to sum it all up, to the extent we don't know much about any of the above, how the heck do we know where to look for preserved organics?
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elakdawalla
post Oct 1 2012, 07:03 PM
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Re: Hottah, that's a good question, and there were a lot of talks at landing site selection meetings about what kinds of rocks were good for preserving organics. Grotz's emphasis through the last three rounds of meetings was preservation, preservation, preservation. High-energy environments like mountain streams are not good places. Fine sediment settling in deltaic environments are good, which was why Eberswalde was the other favored landing site. So you're probably right, Hottah was cool but not the paleo-environment they were looking for. Glenelg has better potential.

Mars doesn't have an oxygen atmosphere but it does have strong oxidizers acting at the surface, so some of the chemistry is analagous. That goes out of my depth though. Check the landing site selection meeting website, there are probably some presentations addressing Martian aqueous chemistry.


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Eyesonmars
post Oct 1 2012, 08:50 PM
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The area Curiosity has been traversing has quite a few small, mostly ghostly, circular features ( looking at the route map). Assuming they are impact related - are they primary or secondary impacts ? Do they date from the time of creation of the deposit or have they been created after/during erosion exposed the surface. I'm surprised at how dense they area. Our eventual target area, the phyllosilicate area, also has these craters in abundance. They seem to have a maximum size cutoff.
What do they tell us ?
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drz1111
post Oct 1 2012, 09:11 PM
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QUOTE (elakdawalla @ Oct 1 2012, 03:03 PM) *
Re: Hottah, that's a good question, and there were a lot of talks at landing site selection meetings about what kinds of rocks were good for preserving organics. Grotz's emphasis through the last three rounds of meetings was preservation, preservation, preservation. High-energy environments like mountain streams are not good places. Fine sediment settling in deltaic environments are good, which was why Eberswalde was the other favored landing site. So you're probably right, Hottah was cool but not the paleo-environment they were looking for. Glenelg has better potential.

Mars doesn't have an oxygen atmosphere but it does have strong oxidizers acting at the surface, so some of the chemistry is analagous. That goes out of my depth though. Check the landing site selection meeting website, there are probably some presentations addressing Martian aqueous chemistry.



Mars has strong oxidizers acting at the surface now. IIRC, however, the redox chemistry is thought to have been totally different back when clays may-or-may not have been being deposited. I would presume in a higher-Ph surface environment, most sedimentary settings would be reducing - like Precambrian earth.
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ngunn
post Oct 1 2012, 09:31 PM
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Eyesonmars: Interesting question. Here's an off-the shelf response based on the conventional story about impact crater counts and age of surfaces. No big craters means a spell of significant deposition or erosion since heavy bombardment ceased. Many small craters means little net deposition or erosion for a very long time after the reworking of the surface that erased the big ones.

This being Mars you'd have to add that these little craters must have formed into a relatively dry surface since the little impactors couldn't have penetrated a significant thickness of water or ice.

Like you, I think the peculiar density of craters here, just above the Glenelg boundary, is significant. It could signify the exposure of an ancient surface neither mantled (as at Bradbury Landing) nor scoured away (Glenelg high thermal inertia unit). I note its similarity to the third type of terrain to the SE of Glenelg.
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Eyesonmars
post Oct 2 2012, 07:41 PM
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QUOTE (ngunn @ Oct 1 2012, 09:31 PM) *
Like you, I think the peculiar density of craters here, just above the Glenelg boundary, is significant. It could signify the exposure of an ancient surface neither mantled (as at Bradbury Landing) nor scoured away (Glenelg high thermal inertia unit). I note its similarity to the third type of terrain to the SE of Glenelg.

Pure conjecture here: If this dense crater network is an ancient feature that has been exhumed recently can we infer that the atmosphere must have been quite thin at this time? As I understand it there is a relationship between minimum crater size and mass of an atmosphere. IF so, and ( another IF) the cratered surface dates to roughly the time of the next surface below - our alluvial fan/stream bed - does this fact influence our interpretation of what we assume (almost certainly) is the water carved/deposited features in front of us ??
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ngunn
post Oct 4 2012, 08:39 PM
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I've just come across this detailed thermal inertia map. Let's see if the link works:
http://www.nasa.gov/images/content/692124m...-43_946-710.jpg

EDIT Well it sort of worked, but it leaves out the caption and the link to the bigger version. I'll have another go . .
http://www.nasa.gov/mission_pages/msl/mult.../pia16159.html#

smile.gif
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djellison
post Oct 4 2012, 09:34 PM
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Yes - the full size is here : http://www.nasa.gov/images/content/692127m...9-full_full.jpg

I find the NASA HQ websites very hard to navigate so I tend to use the photojournal where you'll find it also

http://photojournal.jpl.nasa.gov/catalog/PIA16159

(PS Base map from Fred Calef, annotation by me )
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ngunn
post Oct 4 2012, 09:56 PM
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Brilliant! Thanks Doug. While you're on the line, can you point us to a contour map of this place (my quest in post 1)? We're in an enclosed basin and since ancient liquid water is in play I'd like to get a sense of which direction is down and where the bottom is.
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djellison
post Oct 4 2012, 10:10 PM
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Contour - no - but there is this - http://photojournal.jpl.nasa.gov/jpeg/PIA16158.jpg
You could have found it by going to the first page under 'Mars' on the photojournal.
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ngunn
post Oct 4 2012, 10:30 PM
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That's good, and there's also this:
http://blogs.esa.int/mex/2012/08/03/gale-crater-in-3d/

However they're not really at the level of detail required to help us 'on the ground'.
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Eyesonmars
post Oct 4 2012, 11:12 PM
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True. But even at 100 meters/pixel you can just make out the channel where it enters Gale crater and the upper portions of the alluvial fan.
(we are looking southwest so the channel enters from the far right)
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elakdawalla
post Oct 4 2012, 11:17 PM
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Peter Grindrod has a good blog entry on this topic.


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ngunn
post Oct 5 2012, 08:48 AM
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Just what I was looking for, thanks Emily.
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