Please forgive the generalism, but this may be a useful context question: How unique is Meridiani in terms of its geology?

I have been visualizing the area as a sort of Yellowstone Park of Mars in terms of its distinction from most of the surrounding terrain (only an analogy, of course, not trying to imply hydrothermal influences here!) IIRC, MGS data revealed very few hematite-rich areas, and none as extensive as those in Meridiani.

What I'm getting at here is that the berries may indeed be a product of unique, site-specific processes. The Gusev lapilli observed do not seem to be comparable in origin or morphology (except in the most gross perspective) to Meridian's berries. Therefore, it may not be useful to consider similar formation mechanisms, save in the most coarse particulars (i.e., presence of water).

This viewpoint weakly supports HDP Don's hypothesis, but any confirmation would, IMHO, require discovery of very similar geology elsewhere on the planet...a real dice-throw when we're talking current UMSF capabilities. We only get precious peeks of ground truth, demonstrably not yet enough to tell a coherent story.

There is a recent paper describing Meridiani as the area of convergence, and emergence, for groundwaters flowing laterally out of raised water tables under the higher ground to the south and west. It's been linked here somewhere - I even printed it out. Unfortunately my filing system is almost as unfathomable as the geological history of Mars.

It had it's own thread, though not many posts surprisingly:

Under Opportunity, 'Meridiani Planum . . .' started by Alex Blackwell.
http://www.unmannedspaceflight.com/index.php?showtopic=3999
http://www.space.com/scienceastronomy/0703..._evaporite.html

I notice the free access to the full paper is no longer available. Pity, it had nice diagrams.

Dburt

From day one the principal shortcoming of the impact surge model IMO was the look of the sediments examined, they just never really looked like impact debris as described for terrestrial impacts. They look just a little too neat and orderly. Granted paper after paper describes a spherule layer associated with Chicxulub impact debris the likeness stops there. It’s difficult to imagine melt globules or tektites going through deceleration and atmospheric compression to have the pristine look of the meridiani spheres. The presence of the spheres within cross bedded units imply formation within an energetic cloud not a gentle distal depositional rain as has been suggested for the surge model.

I guess we were extremely lucky to find distal ejecta layered on top of distal ejecta at meridiani. Odds are we would find proximal ejecta also spread across the plains of meridiani if we are talking about multiple impacts, so where is the diamictite, the coarse ejecta, target rock clasts? Chicxulub impact debris (I’ll ignore Gerta Keller for now) has been well documented and it doesn’t look anything like meridiani sediments. The likelihood of the demolition derby model of impact after impact eventually grinding down any ejecta on mars to a fine-coarse sand is dubious at best.

A comment in a July 15 Space.com article - It's fairly dark rock,'' Jirsa said. "They look like concrete, but in this concrete you would throw pieces of rock of all sizes and shapes and in all possible orientations.'' This was said of a possible discovery of Sudbury meteor impact debris in Minnesota. Now that’s impact debris !!

"the other don"

Shaka - Umm, well, golly, just what did you expect all those HDPs to say? The same question has also been raised with regard to the same abstract 3292, in a general way, in Post 184 from July 10, and answered, likewise in a general way, in my post 194 on the same date (and also in many other posts). As you correctly noted, most of the objections raised by the HDPs in question were already shot down more than a year earlier in our point-by-point rebuttals to their unpublished Nature criticism. Nature declined to publish it after their editor and two external reviewers had evaluated both their claims and our rebuttals. See the attachment to my post 170 of July 9. So if you would like me to evaluate a specific claim, please specify which one, or else I'll just be repeating myself more and more and more...

BTW, I suggest you look closely at Figure 3 of that extended meeting abstract 3292 and compare it with, say, Figure 5 of the following field trip guide:
http://www.gps.caltech.edu/~carltape/perso...136/NavajoB.pdf

You will see that, rather than being an original interpretion based on exposed Burns Cliff geology, it is basically a repeat of what has been the standard story for the Navajo Sandstone for many, many years, applied almost without change to Mars (ignoring the distinctly non-dune aspect of virtually all of the bedding, the 30% sulfate salt content, and most other features, including the unexplained huge gouge taken out of the left side of the single large cross-bed that was alleged to be an old water table). The Navajo and Page Sandstones, type examples for so-called "Stokes surfaces" or old water tables, consist almost entirely of equigranular pure quartz sand (insoluble) and are essentially salt-free. The interdune playas in them were true desert oases with shales containing muddy dinosaur footprints and somewhat palm-like trees called cycadoids growing there too (flowering plants like true palms hadn't evolved yet). I.e., distinctly not salty, with clear geologic indications of standing water. Read the above on-line guidebook for more details. There are no associated signs of flowing water (e.g., no alleged "festoons") at all in the Navajo, as far as I am aware and, as mentioned in several previous posts, the clumped-together to massive-nodular hematitic concretions in it and the overlying Page Sandstone are commonly concentrated at or just below the old water tables - not uniformly in the rock.

BTW, as mentioned in Post 194, I consider it a major advance that HDP Grotzinger has finally admitted that his 2005 "Navajo Sandstone on Mars" hypothesis is actually just a model rather than a discovery, and that he has given our impact ideas some exposure by explicitly attacking them. In science as in life you have to take what little you can get.

--HDP Don

Centsworth - I'm not asking you to imagine anything you don't want to, and you're not missing anything. As mentioned in previous posts, several different surge types conceivably might result from the same large impact - 1) an initial blast surge along the ground, like those imaged related to atom bomb testing in the Nevada desert, 2) a column-collapse type surge cloud containing the berries, analogous to a pyroclastic flow in volcanology (or an Arizona dust storm resulting from thunderhead collapse), 3) local phreatomagmatic type surges resulting from impact melt in the crater reacting explosively with melted ice or other groundwater (analogous to what the MER team has suggested for Home Plate in terms of a vanished volcano). This latter type mechanism is what Wohletz and Sheridan (1983) suggested for the formation of classic "rampart craters" on Mars. By whatever mechanism, the fact is that very similar (except for composition), considerably larger accretionary lapilli have formed in terrestrial impacts, and were more widely distributed in South Africa and Australia than the ones at Meridiani. Also, as mentioned in previous posts, even if you were to dump the hematitic spherules all in the same place next to a crater, it probably wouldn't matter, because later impact surges could scour and scatter them across the entirety of Meridiani Planum, and they would be embedded in the resulting cross-bedded sandy rock. Good question.

--HDP Don

Helvick - So what is the terminal velocity of a golfball- or tennisball-sized hailstone on Earth? They're not very common, but when they do occur, they can be an absolute nightmare for insurance companies, because they can take out the windshields of every ungaraged automobile in a town. And those form in normal thunderstorms, with no dense material (such as hematite nano-flakes of specific gravity of 5.26) contained in the upwelling clouds, and with energies many orders of magnitude less than those implicit in a decent-sized impact.

BTW, I like the way you are taking our argument - that the 5 mm size maximum for the berries might indicate the maximum size that can be supported in an upwelling impact cloud on Mars - and trying to turn it around to bite us. Good debating technique (verbal ju-jitsu). However, keep in mind that the specific gravity of the berries might be considerably less than that of pure hematite (5.26) if they contain other constitutents or were originally accreted loosely, with original porosity. Finally, you might want to share the equations, or at least assumptions and constants, that you are using in your calculations.

--HDP Don

Umm - Goethite as a precursor for hematite was studied by Glotch when Meridiani hematite was thought to result from 300 C metamorphism of a sedimentary iron formation. He was merely trying to find evidence in favor of a now-discarded hypothesis. However laudable that goal, I'd hardly call it "thinking outside the box." Of course, I may be fussy that way.

--HDP Don

ngunn - Good questions. I myself have trouble imagining how golfball-sized hailstones form on Earth, but they do, and for a Mars impact we have many, many orders of magnitude more energy available, with much less gravitational force. For Meridiani spherules, the environment(s) of formation is/are probably not the same as the environment(s) of distribution, and there can be as many periods of surge distribution as there are impacts, if the spherules initially were concentrated on the surface or in easily eroded rocks (mentioned in previous posts). Or several surges are possible per impact, as also mentioned. As to where other types of spherules related to vapor condensation might be, in previous posts I have hypothesized that either 1) they were soluble in late-condensing steam and therefore ephemeral, as most fumarolic condensates related to volcanism are or 2) if insoluble, they are too small to be distinguished from far more abundant sand grains (typical impact spherules, such as the iron condensation spherules that surround Meteor Crater, AZ, are very tiny). Keep in mind that the observational tools of Oppy are incredibly primitive by any terrestrial laboratory standard, however revolutionary they may be in terms of prior Mars exploration.

You can have as many spherule depositional episodes as you want, but one would suffice for Meridiani, I think.

If you want a separate Ni discussion from me - ask for one (although much of it would be a summary of material already posted). My impression is that you'd like one from someone else?

Keep in mind that no matter how defensive or ineffectual I've been in explaining it here, the "impact surge" hypothesis is just one of three out there for Meridiani alone (let alone for Gusev or the rest of Mars). I'm just trying to make this group well-informed consumers of science. You all get to decide whom to believe for yourselves.

And hey, if I could do all the choreography, I wouldn't be sitting here typing this - I'd be a God.

--HDP Don

In early March 2004, about a month after Oppy landed, ASU experienced a severe hail storm around dusk like none it has experienced before or since. I managed to snap these photos before all the ice melted (bricks give scale):





You might call this a "Eureka moment" regarding the blueberries. Enjoy, and that's all for today.

--HDP Don

P.S. As I write this I'm getting a nice view out of my south-facing 6th floor window of a distant ground-hugging dust storm advancing across the plains south of Phoenix It presumably resulted from column collapse in a thunderstorm in the hills to the east. Such dense, cold air currents commonly knock over construction fences or trailer homes, but are real wimps compared to a volcanic surge, let alone an impact surge.

O'don: That's one of the things that bothers me most about multiple impact scenarios. As for the observed size distributions of various berry populations, all kinds of hypotheses can be erected to match those. I'm not certain any of them lead us to a confident conclusion. It seems that Fe diffusion below a slowly changing water table matches the data as well as other models.

Really, Don, that is the bottom line for me. Ever since Eagle crater I've been looking at this 'rock', and I just cannot believe that it is the result of the incomprehensible violence of impacts.
I stand in awe of impacts. I am convinced that they are the ultimate drivers of the macroevolution of earth's biology, and that all global mass extinctions, as well as many regional catastrophes, are their outcomes.

Where is that violence in the Meridiani evaporites? Where is the chaos? Where is the crushed matter?
You ask what at Meridiani cannot be explained by impact surge. I say "its totality".
Cheers,
Shaka

That's the point, isn't it? A volcanic surge or impact surge is Not the same thing as a hail storm--even though they might have a few similarities.

By the way, I've been through a lot bigger hail storms. Some of them covered the ground completely with 4 to 5 inches of hail. In a couple of instances, it was quite an experience--possibly life threatening if I had not found adequate cover for safety. And I do understand golf ball sized hail. It's the grapefruit sized and larger that are difficult to understand, although somewhat easy to explain.

Thanks again for your reply. I do appreciate that nobody has explanations yet for all the details, but whereas the 'official' model has billions of years to work its tricks your scenario has to do it in, say, half an hour. I think that makes having a convincing model for the choreography vital to the credibility of the case you're making. At the moment you leave a lot of important parameters in soft focus, so it's not surprising that some people express a 'vague sense of unease' in response.

For a while I thought the nickel clue might be a piece of hard evidence one way or another, but I'm beginning to doubt that now. I did read what you said about it in your paper, but it doesn't seem like very strong evidence there. Likewise the rebuttal by Squyers et al., saying that the nickel isn't enriched enough for the iron to be meteoritic simply begs the question of what mix of meteorite and target rock would have gone to form the spherules - another enormous free parameter in your scenario. Yes I was hoping others would chime in but perhaps nobody sees much mileage in it.

CosmicRocker

Fe diffusion in some form makes sense. Why would Grotzinger lead us astray? As I’ve stated before, the proposed surge deposits don’t resemble anything we have here on good ol’ earth. The hallmark or fingerprint of a large impact on earth is chaotic rubble - diamictite beds on a grand scale and shock metamorphism on a micro scale. Obviously the micro-scale isn’t available to us with MER but the large scale evidence should be. Burt and Knauth try to keep the debate to the small scale where Grotzinger et al are vulnerable; raising a red flag is relatively easy at that scale. Look at Chicxulub ejects beds and then meridiani sediments, you won’t see many similarities, yet we should if multiple ejecta beds are ubiquitous at meridiani.

Don’t get me wrong Burt et al have been the greatest thing to happen to the MER team in terms of keeping people on their toes and looking over their shoulder for the latest volley from ASU. The surge model did get some unconstructive recognition at the recent Seventh Int Conf on Mars but I’m sure even that was encouraging for its supporters.