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ngunn
That's fine for HTIF and HP, but going on Anderson and Bell's map there should be no LTIF at our current location. They have the LTIF mapped to the north of the HTIF while we are to the south of it, hence my query.

http://martianchronicles.files.wordpress.c.../09/figure7.jpg
JRehling
I've been thinking that the landing site was HP, having missed the fan, as you say, to the north. But our confusion is, I think, owing to the inherent complexity:

The distinctions we're talking about are not necessarily visible or even rigorously meaningful. Thermal inertia is a property that can vary from place to place on the basis of any combination of changes in composition or fine-scale morphology in potentially-wicked interaction between the visible surface and the near subsurface. Maybe MSL landed outside the area that Anderson and Bell colored as "fan" on their map, but is nonetheless in an area where the fan material is present, but in combination with other stuff so as to give it a different thermal inertial. In fact, there's no logical disconnect between these labels: "high thermal", "fan unit", "hummocky", and "plains" are potentially overlapping in any combination because they four different kinds of property.

I think MSL missed the region that A&B labeled as being the fan, but may in fact have some of that fan material all around, in some fraction, anyway.

On a very similar theme, I was surprised, having read A&B carefully, how difficult I find it to see the units on Mt. Sharp, which seem apparently in the B&W images taken from orbit, in the images from MSL. There are many possible reasons for this, including the viewing geometry, the image properties (such as gamma), my lack of field geography savvy, etc.

A&B did a good job of imposing some logic and order on Gale, but in both the MSL landing site and the distant views of Mt. Sharp, things seem a little more chaotic up-close.
elakdawalla
I was having the same issue you were in seeing the units on Mt. Sharp until I realized that most of the interesting stuff -- the clays and sulfates -- is actually in a trough at the base of Mt. Sharp and mostly not visible from where the rover landed.

Working out some comparisons of the A&B units to images from HiRISE and pointing out locations on the landing site panorama has been on my list of blog entries to write for a long time, but it's a big project and I haven't made much progress yet.
ngunn
(Replying to JR) All good points. I agree that the views from the ground are taking us into a post-A&B era. But the meeting of three distinct terrain types at Glenelg is most clearly seen in the orbital images so it didn't take Curiosity to show us that.

High thermal inertia is, I think, indicative mainly of a lack of loose cover over the bedrock. In Anderson and Bell that is identified with a particular rock unit, but why would one particular type of rock preferentially remain clear of debris? I think ithe HTI
disribution may be controlled more by the geographical context of the removal process and the ease of removability of whatever material used to cover the bedrock.

EDIT
Emily: good luck with that project - I look forward to seeing the results
stewjack
In the conclusion section of the abstact for Anderson and Bell III: Mars 5, 76-128, 2010 open access paper,
there is the following sentence -"Some layers in the mound are traceable for >10 km, suggesting that a
spring mound origin is unlikely."

My understanding of that would be that Mt Sharp was not cemented together by underground (upwelling) mineral water flows during,
I guess, - the period when Gale crater was buried in sediment. Because earlier it is said "The rim of Gale Crater is dissected by
fluvial channels, all of which flow into the crater with no obvious outlet." As well as, I guess, that hot springs would be variable in flow,
time and location? After doing some Googling apparently hot spring can create mounds using nothing but precipitated minerals. However;
I don't now how that would relate to the 10 km layers. Would be enough to say that a mound with many layers wasn't created by hot springs?
Or am I completely misunderstanding what the sentence is trying to communicate?



serpens
QUOTE (Stellingwerff @ Nov 30 2012, 01:04 PM) *
...... a very nice graph showing exactly why we don't see the basalt yet. It's close, but MSL will need to drive towards the mount to find an exposed trough all the way down to the basalt unit. (In many places the dark dunes are actually covering the basalt floor...)


Most of what we see on Mars has a basaltic provenance but as implied by djellison I think that we could be a little more careful in our use of the word. The Anderson and Bell paper refers to the Basal Unit. Basal is by (USGS) definition located at the bottom of a geological unit which in this case I would think is the bottom of the post impact crater fill sequence. I am not sure why the reference to basalt crept in. The final crater floor would have been made up of allogenic breccias and impact melt and I guess this is the Basal Unit referred to by Anderson and Bell. At least that is what I assumed when I first read the paper, which on re-reading, only mentions basalt once in reference to the makeup of dunes. That final crater fill would be pretty deep and beneath that would be fractured pre impact material that, given the size of the impactor, would probably have been subject to a degree of impact metamorphism.
dvandorn
Yep, Mars' surface is primarily basaltic, no doubt. And like the Moon, much of the original crust has been highly brecciated by the Late Heavy Bombardment (the "event" which likely resulted in the Gale impact, among tens of thousands of other impacts of similar size).

Analysis of basalts, where they were emplaced, would give us a nice feel for what was happening in Mars' mantle while the majority of the basaltic eruptions occurred and the basalt was emplaced on the surface. Sort of a snapshot of the mantle during the period(s) of heavy volcanism. However, it is the alterations and re-depositions of that basaltic set of "building blocks" that tell us about the climate and conditions on the surface after the basalts were originally emplaced.

So... Gale is not a good place at all to survey variations in directly emplaced basalt flows. The occasional unaltered chunks of basalt lying on Gale's floor were likely transported from somewhere else (be it a few kilometers to hundreds of kilometers from where a rock might rest right now). It is, however, a wonderful place to look at the history of re-deposition and alteration of rock beds (and even deflation of covering beds), much of which (it seems to me) has to have happened when the alteration, deposition and deflation processes that went on were far more active than they are now.

Since one of the main purposes of Curiosity is to try and characterize those processes (because those processes, once understood, then highly constrain the climate and environment in which they occurred), Gale is a very good place. Precisely because this is a place where we can study the history of those processes and try to understand them.

-the other Doug
Zelenyikot
I think that rock high thermal inertia is a lava stream, from a volcano about which I wrote earlier. Ancient eruption caused a wave of a lava which became HTI. After eruption were weaker and began only water flows from the melted glaciers. So appeared the alluvial fan.
This hypothesis is hasty, but it seems to me logical.
Hope we discover soon.
JRehling
Replying to stewjack, re: 10 km layer seemingly disproving a spring origin:

I remember encountering this passage for the first time. My interpretation was that a layer which extends 10 km and remains roughly constant in altitude indicates, if sedimentary, a massive reservoir of water filling the crater like a lake, whereas a spring would have a small origin and would not supply adequate water to create a level surface across such a great area. In fact, that seems like a profound understatement, although I suppose that depends entirely on how large the volume of a "spring" may be.

Since we only see the edges, I suppose, also that you could have a level visible edge at some distance away from and below the source of the spring (as the edge of, say, Olympus Mons is far away from, but below, the vent, and is nonetheless relatively level), but then Olympus Mons is hardly a "spring."
stewjack
QUOTE (JRehling @ Dec 1 2012, 12:38 AM) *
Replying to stewjack, re: 10 km layer seemingly disproving a spring origin:
I remember encountering this passage for the first time. My interpretation was that a layer which extends 10 km and remains roughly constant in altitude indicates, if sedimentary, a massive reservoir of water filling the crater like a lake, whereas a spring would have a small origin and would not supply adequate water to create a level surface across such a great area.


Thanks! I bet that sentence took a while to construct. Leaving out "roughly constant in altitude," avoids discussion of sloped layers.
serpens
There are a couple of other reasons why attributing Mount Sharp as a spring mound will not hold water. The lower half of the mound transitions from phyllosillicates to sulphates but the upper half of the mound is a aeolian deposition. So a spring would not explain Mt Sharp. Further, if this was a spring mound then we are considering a huge volume of water - probably enough to fill the crater given the size of Mt Sharp, which would have almost certainly have resulted in a breach of the Northern crater wall. No such breach exists. Well that's my take anyway.
nprev
Is there any real evidence that Mt Sharp is anything but a typical central crater peak, albeit with modified surface units due to subsequent environmental variations?

If that's true then the areas of interest are these modifications and the processes that made them, not the mountain's origin.
ngunn
The peak is too big and other similar size craters nearby don't have them so it's definitely atypical, probably the most extreme example of its kind on Mars.

I'm thinking about the possibility that Gale crater once had a much higher northern rim, at least as high as the top of the horizontal beds on Mt Sharp. If it formed at the edge of a frozen ocean maybe the north rim was largely composed of ice which has gone now.


serpens
nprev. I'm with you in that Mount Sharp probably has a central uplift core, but the bulk of the mountain is sedimentary. Have a look at a couple of the complex Lunar craters such as Maunder to get an idea of the relative size of a pretty much pristine central uplift.

The puzzle (and I deliberately avoid the word mystery) is why the sediment ended up as a central mound. I have difficulty accepting the explanation that the crater was overfilled to the height of (or greater than) Mt Sharp and then excavated, despite the credentials and credibility of the proposers. That hypothesis requires that the sediment that must have covered the rest of the crater and the surrounding area was totally removed while that on Mount Sharp was significantly more resistant. I'm backing a shallow crater lake for the phyllosilicates and a vortexing effect for the remainder. I don't have the smarts to model something so complex so take the last as being accompanied by wild guestures from the depths of an armchair.
dvandorn
If I don't say this as smoothly as I might otherwise, please forgive me. The thought racing around my brain delves into areas of physics about which I'm not completely confident.

First, it has struck me that dust devils form more easily on Mars than they do here on Earth. Considering how thin the air is and how cold the overall environment is, you would think there would be more energy available on Earth for such vortex formation than on Mars.

But, I says to myself -- Mars spins around its axis at roughly the same speed as Earth spins about her own axis. But Mars is significantly smaller. Its surface is rather closer to the center of rotation than is ours.

Would this not, based on conservation of angular momentum, mean that the coriolis force would be noticeably stronger on Mars? The spinning skater spins faster and faster as her arms are drawn towards her, and on Mars the difference in rotational speed between me and the spot 10 meters to the north or south is greater than at the same distance on Earth. And, if I understand the coriolis force correctly, it is this difference in rotational speed that drives everything from typhoons to dust devils to the swirl of water running down the drain.

So -- if I'm reading this right and the coriolis force on Mars is noticeably greater than on Earth, encouraging a lot more atmospheric vortex formation, how would this affect simple aeolian erosion patterns on an early Mars with a much thicker atmosphere than now?

Consider that in 6mb air pressure a modern Martian dust devil can pick up and entrain a pretty impressive mass of dust and pebbles. This process keeps much of the Martian surface swept clean of the ubiquitous orange-brown-yellow dust, the darker gray rock beds thus exposed forming the dark markings visible in telescopic images of Mars for more than a century.

How much more erosive would a thicker atmosphere be, if an increased coriolis force makes it tend to form vorteces at every opportunity?

This relates to the previous posts thus -- imagine Gale crater nearly filled with some form of fill. Then imagine a racetrack wind pattern running around inside the crater walls, breaking up into hordes of large dust devils which, due to the thicker air, are able to pick up tons of material and toss it high into the air?

You'd have a pretty dusty atmosphere all the time (which would tend to cool the surface, I imagine), but such a wind pattern might be able to deflate an *awful* lot of material out of a crater in a pretty short time, at least in geologic terms.

Maybe it was such a dust devil breakout phase that deflated a lot of crater fill on Mars?

-the other Doug
stevesliva
^ I tend to wonder if there was a relatively long timescale (like Milankovitch, not seasonal) dust cycle, in which dust was deposited in strata in low energy periods, and excavated by aeolian processes during high solar energy time periods. Throw localized water into the mix, and I wonder if a little water created some inverted channels that were more resistant to the wind erosion that removed the surrounding dust.

It would be interesting with a thicker, dustier atmosphere perhaps also including volcanic ash, whether you could come up with a plausible model for craters being filled with thick dry strata of dust in a period of relatively calm winds, followed by a clearer, windier epoch in which convection and winds undo what was done.
ngunn
An internal heat source beneath Gale can do more than locally hardening the sediments once formed. It could be the reason they formed in the first place. Imagine a largely frozen Mars with plenty of water in the form of ice or ice-capped seas. Now in Gale Crater picture a geothermally heated lake that is at least sometimes ice-free. The liquid surface acts as an effective dust trap 'quickly' filling the whole thing with horizontal sediments. This avoids the need to bury and exhume a similar pile of sediments on a planet-wide scale.
schaffman
QUOTE (dvandorn @ Dec 1 2012, 08:49 PM) *
Maybe it was such a dust devil breakout phase that deflated a lot of crater fill on Mars?

-the other Doug


When I think of geomorphic processes on Mars, I think of ice as well as wind. Aeolian deflation as the mechanism for removing large volumes of sediment from the floor of Gale is probably only part of the story. Ask yourself what type of material disappears at the edges first, leaving a behind a central core with little hint of where the missing material went. To me, that would be a big block of melting or sublimating ice. Perhaps a modern analog for the Gale crater mound are the central ice mounds present in polar craters such as Korolev.

So, at one time, the bulk of the interior deposits of Gale was probably ice with some admixture of dust. With a shift in climate, the ice sublimated leaving a residuum of dust at the periphery that was deflated. The central core, being more cemented (perhaps by precipitants from mineralized liquid water deep within the core of the mound) was more resistant to erosion and persisted until the present.

One problem with this scenario is that the crater mounds like those in Gale cover a largely equatorial swath from Meridiani across Arabia Terra to Gale. It seems unlikely that obliquity-driven climate change alone could account for such large amounts of equatorial ice, and some other mechanism, such as true polar wander, is needed.
fredk
QUOTE (dvandorn @ Dec 2 2012, 01:49 AM) *
Would this not... mean that the coriolis force would be noticeably stronger on Mars?
Actually, the Coriolis acceleration depends only on the velocity of the object in question and the angular velocity of the planet. Since the angular velocity of Mars is about the same as that of Earth (360 degrees per day), the Coriolis accelerations (or Coriolis forces for bodies of the same mass) would be about the same on Mars as on Earth.
QUOTE (dvandorn @ Dec 2 2012, 01:49 AM) *
on Mars the difference in rotational speed between me and the spot 10 meters to the north or south is greater than at the same distance on Earth.
No, it's less, since the rotational speed gets larger the larger the planet, for fixed angular speed. But the curvature of Mars's surface is greater, and the two effects cancel, leaving essentially identical Coriolis forces.
QUOTE (dvandorn @ Dec 2 2012, 01:49 AM) *
it is this difference in rotational speed that drives everything from typhoons to dust devils to the swirl of water running down the drain.
Typhoons, yes, but that's where it stops. For typical wind speeds, the magnitude of the Coriolis acceleration is so small that it only has a noticable effect for coherent air flows over very large distances. The Coriolis force is completely negligible on the scale of dust devils or sink drains. It's actually very easy to see this without doing any math: if Coriolis forces could consistently drive dust devils or drains one way instead of the other, then the same force should be noticable when driving at similar speeds in a car! But we all know that we don't have to steer to compensate for Coriolis forces when we're driving.

Anyway, pardon the myth-busting excursion into physics - we now return you to the regularly scheduled geomorphology...
djellison
Fred - thank you.

And Other Doug.....I've never had a visit to the dry deserts of California when I didn't see dust devils. They're very very common here on Earth. Far more common than you think.
Don1
I still like the spring mound idea.

The rover is currently seeing a lot of rocks which look spongy and porous. What if there is a thick layer of such rock underlying Gale Crater? In wet, high atmospheric pressure climates these rocks would fill up with water, creating a large aquifer.

Then the atmospheric pressure drops quickly, due to carbon dioxide freezing out at the poles.

The drop in pressure reduces the boiling point of water, and the water in the aquifer starts to boil. The porous beds slope upwards towards the center of the crater, so the warmer less dense fluids migrate in that direction. They erupt from Mt Sharp, leaving behind an evaporite deposit.

The chemistry of the evaporite depends on the chemistry of Martian water and the atmosphere at the time. When the atmosphere was rich in sulfur dioxide, sulphates were formed. More recently, another mineral, maybe carbonates was deposited. Martian winds have eroded Mt Sharp over time, giving the deposits an aeolian appearance.

The lowest clay bearing layers might be old lakebed deposits which were covered and protected from erosion by later materials.

Mt Sharp could be the result of a long history of oscillations in atmospheric pressure which alternately filled an aquifer and then dropped the pressure enough to boil it.
nprev
I dunno; sounds like a bit of a reach to me.

Meh; we'll know a LOT more about Gale in a couple of years, certainly enough to constrain these hypotheses based on actual data. wink.gif
serpens
Maybe. But despite Curiosioty's impressive capability compared to the MER she is still pretty much constrained to analysing the immediate surface. Translating findings to the macro environment of the far past may be a bit of an ask.
nprev
Didn't say 'solve'; just constrain. wink.gif
serpens
Oh yeah. Gotcha. Duuh - put it down to a senior moment.
JRehling
As currently conceived, scientific value vis-a-vis the structure of Mt. Sharp is that the most interesting stuff is the oldest materials which are at the bottom. First Curiosity has to get there. Then, as Curiosity ventures higher, it will basically be visiting more recent areas in martian history and perhaps arrive at the same location/era that typified Meridiani - wet but acidic. This is a bit less interesting for several reasons, not least of which that Opportunity already spent years exploring it (with a poorer set of instruments), and that acidic water is in various ways less earthlike and perhaps depleted in other interesting dynamics. Additionally, the structure of Mt. Sharp appears to have much, much thicker layers representing more recent layers, so even given a constant speed of march in terms of terrain, the rate of march into more recent martian history will slow dramatically; in essence, the upper layers appear to be less diverse than the lowest layers.

All of that, is of course based on the best speculation. There's no guarantee that the most interesting single rock on Mars isn't perched high on Mt. Sharp. But rational planning will be based on weighing the expectations with the effort and the risk.

This is all simply to say that when (if we are fortunate enough for all to proceed with success for decades) Curiosity reaches a certain high location on Mt. Sharp, there will probably be a desire to bring it back down, and that will probably be slowed by terrain.

So if I had to place my bets, it'll be that we'll have a wait for the most interesting stuff, then we'll have a long bonanza of peak interest followed by diminishing returns before Curiosity reaches a peak altitude and the decision is made to bring it down to explore the lower altitudes laterally. While layers are emplaced according to chronology, this arrangement is "patchy"; whichever route it takes up, there'll be other units on other paths. Anderson and Bell describe two ascent routes with similar but non-identical attractions. I think we'll have to wait through a relatively boring descent, before a "second coming" when Curiosity gets back down to the layers of primary interest and finds some of the things it missed on the way up.

And of course, this is only an educated guess. The most interesting thing(s) Curiosity finds may come at any time and in any place. That's why it's exploration.
Explorer1
'Relatively boring descent' is relative, of course. The roads to Victoria and Endeavor certainly weren't!
Gerald
QUOTE (Don1 @ Dec 2 2012, 10:15 PM) *
The rover is currently seeing a lot of rocks which look spongy and porous. What if there is a thick layer of such rock underlying Gale Crater?

I think, the spongy-looking surface of those rocks may be explained by conglomerates similar to those at Bradbury Landing. Easily weatherable rounded stones might be embedded in a more resistant material. As soon as the conglomerate is exposed to the acidic and oxidizing environment, embedded stones fall out of their holes or weather rapidely.
To an explanation of the embedded stones being more weatherable might contribute acidity: Embedded stones are older than embedding rock. So they probably will be more basic (alkaline) due to increasing acidity of the Marsian surface over time; they might be more basic, if they are of magmatic or plutonic origin (basalt), as well. Alkaline rocks will tend to weather more easily today than acidic ones.

QUOTE (Don1 @ Dec 2 2012, 10:15 PM) *
Then the atmospheric pressure drops quickly, due to carbon dioxide freezing out at the poles.

Water will freeze out first, before carbon dioxide. Freezing produces warmth. So a runaway freezing at the poles looks to me rather unlikely.

QUOTE (Don1 @ Dec 2 2012, 10:15 PM) *
The drop in pressure reduces the boiling point of water, and the water in the aquifer starts to boil. The porous beds slope upwards towards the center of the crater, so the warmer less dense fluids migrate in that direction. They erupt from Mt Sharp, leaving behind an evaporite deposit.

Some water might evaporate or sublimate; boiling might have occurred in the context of vulcanism. Capillar forces are too weak to drive water upward more than a few hundred meters, I think. Pressure from shrinking rocks will erupt surface water at most once, thereafter the pores will allow less water contents. Repeated formation of new pores by solvents probably leads to a net shrinkage of the mountain. The only way, I can imagine, able to change this may be periodic hot vulcanism. The other question is: Why doesn't the water flow sideward as ground water on a layer of clay and form springs at the laterals of Mt. Sharp?

QUOTE (Don1 @ Dec 2 2012, 10:15 PM) *
When the atmosphere was rich in sulfur dioxide, sulphates were formed. More recently, another mineral, maybe carbonates was deposited.

Normally carbonates will tend to be more alkaline than sulfates. So I guess, that carbonates might have formed in the Noachian, i.e. early in Marsian history, together with clay minerals. Later, in the Hesperian, sulfur oxides might have transformed some of the carbonates and clay minerals to sulfates or sulfites.
Many sulfates are more water-solvable than the corresponding carbonates or clay minerals. So acidic weathering sounds rather plausible to me.

Acidic weathering, together with acidic deposites in riverbeds, might also contribute to the inverted river and pool beds, because acidic beds within more alkaline surrounding rock will tend to be more resistant under the present acidic conditions. Same with reduced stuff under oxidizing conditions.

I could imagine an ice cap or permafrost helping prevent Mt. Sharp from fast erosion, much the same as mountains on Earth.
Don1
I like the idea of acidic weathering being responsible for some of the spongy rocks, but I don't know if the present environment is acidic. The soil at the Phoenix landing site was alkaline, so recent Martian conditions might be more suitable for forming carbonates. I think Glenelg makes most sense if viewed as a big stack of magnesium/iron carbonates with a variety of concretions. For earth examples of a carbonate terrain, see 'Concretions and nodules of North Dakota' .

A result from the Grail mission caught my eye, which was that the crust of the moon is about 12% void to a depth of several km below the surface due to it being fractured by impact. If the ancient Martian crust is similar, then at one time there should have been a huge amount of water in subsurface aquifers. At past Martian surface pressures, hydrothermal is going to mean something different from what is found on earth. At 60mb pressure, water will boil at 36C, so you don't need a lot of volcanic heat to drive a hydrothermal system.

Drop the pressure to 10mb, and water boils at 7C. Previously stable aquifers will boil until they cool below 7C. For a mixture of 90% rock and 10% water, 14% of the water will turn to vapor, if the system starts out at 36C.

An interesting question is what happens if the pressure falls below the triple point pressure of 6mb. If a cup of water starts out at a little above 0C, I think 12% of the water will end up as vapor and the rest will turn to ice.

How much vapor do you get if you start with 1 cubic km of aquifer with a 10% void fraction and turn 10% of the water in the voids to steam over 100 years? That works out to 3kg/s of steam, which should give you a small geyser.

QUOTE (Gerald @ Dec 18 2012, 06:10 AM) *
Water will freeze out first, before carbon dioxide. Freezing produces warmth. So a runaway freezing at the poles looks to me rather unlikely.



True, water will freeze first, and water is a greenhouse gas. The result is a dryer and cooler planet, so I think that runaway freezing at the poles is quite possible. The present Martian atmosphere varies by about 25% in mass over the course of a year, so significant changes may be possible over a 100 year period.
Gerald
Thanks for sharing the idea of acidic weathering of some of the spongy rocks!
I like the paper 'Concretions and nodules of North Dakota', you pointed to. Several features look rather similar to features near Yellowknife Bay. I had been looking for some paper of that kind, because it may explain the "bubbles" and more.
I can duplicate your calculations, under the given assumptions.

Nevertheless, several things are not quite conclusive to me. Still open is especially: How is the water forced to the mountain top, although there will be needed a hydrostatic pressure of more than 100 bar at the foot of the mountain in porous material? I'd expected a fountaine there, at the foot.
Don1
QUOTE (Gerald @ Dec 19 2012, 10:03 AM) *
Nevertheless, several things are not quite conclusive to me. Still open is especially: How is the water forced to the mountain top, although there will be needed a hydrostatic pressure of more than 100 bar at the foot of the mountain in porous material? I'd expected a fountaine there, at the foot.


I think you've found the flaw in my scheme. I don't have the pressure to get water to the top of the peak. I can get steam out of the top, which could condense to water or ice when it hits the cold air. This could provide enough moisture to cement the Martian dust into a layer that won't blow away. Or I can entrain some droplets of moisture and salt particles into the gas flow if the velocity is high enough. There should be quite a lot of nitrogen and CO2 in addition to steam because dissolved gases will come out of solution when the pressure drops.
stewjack
As a non-geologist I wonder if sedimentary rocks can tell MSL anything about their compression history?" Would they have a different signal depending on either a history of being overlain by a couple of kilometers of sediment for a billion years or so OR a more recent formation, and therefore a less deeply buried history. I understand that this entails the assumption of Gale crater being significantly buried.

Edit I did some research and discovered some better terminology, lithification & metamorphism, but can the extent of lithification or metamorphism, due to pressure, be indicated directly or indirectly by MSL. Some of these rocks look pretty weak!
Gerald
Metamorphim, of course, by CheMin, because metamorphism changes crystal structure. That is well detectable by X-ray diffraction, I'm almost shure.
I cannot give a unique answer to the determination of the degree of lithification, because weathering might make things ambiguous, imho, probably the reason, why some rocks look weak.
Gladstoner
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Gladstoner
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stewjack
QUOTE (Gerald @ Dec 20 2012, 04:02 PM) *
metamorphism changes crystal structure. That is well detectable by X-ray diffraction, I'm almost sure. ...weathering might make things ambiguous

Then I guess it isn't pure coincidence that we happen to have a x-ray diffracting, drilling into rocks, Science Laboratory Rover available. I love it when i can connect some activities to some questions.

Thanks Gerald
ngunn
Gladstoner: I'm not sure but I think it's a 'no'. There has to be a special way of accumulating mound sediments - dampness?
Gladstoner
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stewjack
QUOTE (Gladstoner @ Dec 20 2012, 06:35 PM) *
Question: Is the Mount Sharp material present anywhere else in Gale Crater or in the surrounding terrain,

Once again I will say I am not a geologist, but I may be able to get you on the right track. You don't explain why you are interested in this subject. If I asked you to explain New York City to me you would have a lot of different approaches. You might spend hours writing a reply and I might not even be interested in the subjects you chose to write about.

Are you talking about the bottom phyllosilicate material, the middle sulfate material, or the top "dust" material.

1. As far as the phyllosilicate material the answer is yes, but quite near the base of the mountain.

Phyllosilicate-bearing Trough p 105 Anderson and Bell III
Observations. The phyllosilicate-bearing trough (mapped in Figure 17) is a depression that parallels the south-east side of the light-toned ridge, and shows a clear nontronite signature in CRISM observations (Milliken et al. 2010). The same phyllosilicate signature is not clearly visible on the opposite (northwest) side of the light-toned ridge, but a thin bed with a similar signature has been detected in the large canyon in the western mound (Milliken et al.2010).

2. As far as the sulfates go I don't know.

3. The wind blown material is probably just common dust that is blown all over Mars in dust storms. It may not be very interesting. I doubt it would stand out in orbital observations.


You don't give us any background of your level of understanding. It would be a help if we knew if you are familiar with the consensus view of the history of Gale Crater. It has been explained on more than one NASA briefing. Someone could probably provide a link to an archived briefing.

I notice that you have some experience as an amateur astronomer. Are you familiar with the concept of a "central peak"crater? If you are familiar with the consensus view of the history of Gale Crater, you would probably not be surprised to learn that the official name is Aeolis Mons (Wind Mountain) It is not a central (?rebound?) peak, or at least, if it exists, it is hidden within the (wind blown) sediments.

Now watch me get cut to pieces for massive errors. I will ignore all criticism unless it is quite a massive error.

Gladstoner
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serpens
QUOTE (Gladstoner @ Dec 21 2012, 12:44 AM) *
I guess my preemptive apology in that post was warranted.


On the contrary - it was a most reasonable query. As far as crater mounds go (as opposed to central uplift) Mount Sharp is not an orphan but we need to keep the scale in mind. Mount Sharp is 5.5 kilometers high and so we are talking about massive volume of material with structural and geochemical clues that indicate deposition spanning a range of environmental conditions. We can see from the remnant fluvial channels that the material we are currently traversing came from the rim and surrounds (which covers a heck of a lot of square miles/kilometers).

There are a couple of things to think about. Central peaks (and inner rings for really complex craters) should rebound no more than the pre impact surface level. Potentially Mount sharp outer circumference could have been determined by the inner ring. The structure and geochemistry will become clearer as Curiosity climbs but I guess we can already surmise that the clays reflect an initial, neutral pH wet (possibly lake) environment. Then came the sulphate environment we have come to love in Meridiani (mainly aeolian with potential volcanic fall contributing) followed by aeolian diminishing as the atmosphere vanished and the current benign environment began ( a long time ago). Mount Sharp formative hypothesese based on current atmospheric pressures, temperatures,etc have little to recommend themselves as, when Mount Sharp (and surrounds) formed, Mars was it seems, a really dynamic, warmer and wetter place with a thick atmosphere. Personally I don't think that we have any real understanding of the young sun or even orbital parameters billions of years ago - but the evidence is that both Earth and Mars were a lot warmer and wetter (liquid water) than we expected.

I do not agree with stewjack that there is a consensus view of the history of Gale crater. I mentioned previously that despite the credentials and credibility of those proposing an area burial and then exhumation to form the mound, there is no compelling evidence for this. Anyhow keep an open mind and post your thoughts.
ngunn
QUOTE (Gladstoner @ Dec 20 2012, 11:58 PM) *
By dampness, do you mean a 'fly paper' effect on dust? smile.gif


Exactly - but note my question mark.
Zelenyikot
Interesting picture Nicholson Crater of Mars Express. Shows that Mount Sharp - not unique formation on Mars.
serpens

I linked this blog entry of Emily's previously but it is probably worth repeating to stress the fact that Mount Sharp, while enigmatic, is not an orphan.

http://www.planetary.org/blogs/emily-lakda.../2011/3144.html
atomoid
QUOTE (serpens @ Dec 20 2012, 07:42 PM) *
... Central peaks (and inner rings for really complex craters) should rebound no more than the pre impact surface level. Potentially Mount sharp outer circumference could have been determined by the inner ring. ...

I havent read enough of the right papers to know if the following is ruled-out, but i'd considered that such a rebound effect could be exaggerated somewhat by a the rebound areas serving as perhaps the only large scale 'relief-valve' areas for geothermal energy to expend itself (since the crust in general is thick and locked-up), so a shattered crust should perhaps help magma push up and expend to shove the central mound up higher than typical rebound effects would, building up something like Mt Sharp, which should probably deform the crust under its weight like Mauna Loa since some of that does appear to be going on at least locally around the base of mt Sharp. So even though Olympus Mons apparently doesnt exhibit such crustal deformation suggesting the crust is too thick, here it may perhaps be damaged enough by impact faults that such a thing may be possible at Gale or other impacts and epochs.

Of course, under-baked ideas remain compelling under dim illumination, so please do dispense with them as best to impart us armchair geologists with an improved perspective.
Zelenyikot
QUOTE (serpens @ Dec 21 2012, 10:51 PM) *
but it is probably worth repeating

Of course I read Emily's blog, but Nicholson crater more suitable example seems to me. More similarities in size and form of the mountain.
I just wanted to confirm your words "Mount Sharp is not an orphan"
Eyesonmars
Thanks for that post serpens. Somehow i had missed that entry in Emily's blog. That huge central dust covered mound in emily's blog brings to mind This paper i recently found.

Growth and form of the mound in Gale Crater, Mars: Slope-wind enhanced erosion and transport
Edwin S. Kite, Kevin W. Lewis, Michael P. Lamb. July 2012

The authors propose that slope winds alone might be capable of forming and maintaining these central mounds even under current martian conditions.

One appealing feature of this hypothesis is that it no longer requires the deposition and removal of thousands of cubic kilometers of material and all the related issues. Another thing of note is that it is consistent with the outward dipping mesas and buttes in the lower flanks of Mt. Sharp. ( the larger ones toward the base even look a bit concave to me)




Gerald
Line 47 of the paper estimates an erosion of 10 to 50 micrometers per year. That means 30 to 150 kilometers of erosion in 3 billion years. So, many things may be possible.
serpens
Thanks for the link - as a broad brush approach that katabatic driven deposition makes a lot of sense and this describes the vortexing effect that I previously admitted to not having the smarts to model. But I'ím not sure what effect the model start premise that the crater floor was non-erodible basalt has, since it was more likely erosion susceptible breccia/suevite. Given the clay beds at the lower level of the mound perhaps the start point should be a fluvio-deltaic period. I also wonder what would be the effect on the model if a warmer environment with reasonably high atmospheric pressure was used, which would increase wind energy.

Another possible consideration is whether adiabatic warming could cause temperature overshoot, where the katabatic wind on exit would end up warmer and less dense than the air at the crater floor, providing lift to aid central deposition. Throw into the mix effects like valley exit winds which would reduce erosion of the outer crater floor and the need for pretty extensive sensitivity analysis in the model becomes clear..

Overall this seems a a more satisfying concept than area infill and selective erosion.
Bill Harris
So once again we see aeolian processes at work as a major force on Mars. I see a pattern emerging...

--Bill
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