[X] My Assistant

[dburt]

Okay, here's my alternative hypothesis for berry formation: [EDIT: several hours pass as I stare at my screen...] Okay. There are two types of blueberries. Type I berries are hematite concretions with distinctive, odd surface textures formed by repeated H2O saturation as evidenced by the extensive sedimentary deposits in Meridiani. Type II berries are artifacts of many, many meteoritic impacts in the region during wet periods characterized by smooth surfaces due to their relatively rapid formation and cooling. Both types are chemically similar due to the fact that they both precipitated out of the same matrix and very similar aqueous solutions; the significant variable that produces morphological differences is duration of favorable conditions for formation.

Send me my Nobel Prize or a dunce cap now, whichever is most appropriate... Also, just for fun, here's a pic of the biggest Type I berry-analog in the whole Solar System...

nprev - Umm, so you'll allow the Late Heavy Bombardment to temporarily warm up the climate (as independently suggested by the presence of clays in the most heavily cratered terranes), but not to grow spherules, even though spherical accretionary lapilli are typical of terrestrial impacts, and smaller glassy spherules are typical of lunar impacts - both, BTW, result from vapor condensation (so do rain and hailstones). Instead you'd prefer there to be two types of concretions, neither of which look like terrestrial examples? The ONLY thing that's unusual about the Meridiani spherules is their hematite-rich composition - otherwise they'd fit everyone's preconceived notions of what an impact should produce. And sorry, there's no Nobel Prize in geology.

Also, also just for fun, here's what soaking in a warm brine (such as the MER team proposes for Meridiani) might be expected to do to all those sulfates (keeping in mind that gypsum is the least soluble - the others should recrystallize even larger or faster):
http://www.crystalinks.com/mexicocrystals.html

Keep in mind that what that website says about "hydrothermal fluids" is wrong - the crystals just grew from warm groundwater at about 58 C (only somewhat warmer than the outdoor temperature in Phoenix today - see "In the News" below the main article). Any hotter and the gypsum (variety selenite, named for the Moon) would have dehydrated. Enjoy.

That's an extreme example, but if they were ever soaked in liquid water, as claimed, those allegedly windblown salts really should have recrystallized!

--HDP Don

[stevesliva]

Also, also just for fun, here's what soaking in a warm brine (such as the MER team proposes for Meridiani) might be expected to do to all those sulfates (keeping in mind that gypsum is the least soluble - the others should recrystallize even larger or faster):
http://www.crystalinks.com/mexicocrystals.html

Don, you missed this thread... pretty amazing...
http://www.unmannedspaceflight.com/index.php?showtopic=4383

[dburt]

Dburt,
You make the case that Mars basalt is Fe rich, the planet is exceptionally salty and salty, steamy vapours produce blue-grey hematite flakes as a very common insoluble mineral in terrestrial fumaroles. So when an impact occurs steamy salty surge clouds on Mars should be analogous, and should produce blue-grey hematite nano-scale hematite flakes that would condense and accrete into the spherules. But this scenario requires almost instantaneous oxidisation of the basalt Fe content. Michelle Minitti et al found that it took 3 days at 700 C to oxidise a 0.1 to 0.6 um hematite coating on a mars meteor composition in a CO2 environment. http://minitti.asu.edu/publications/abstracts/hem_ab.pdf
I appreciate that you have argued that the surge cloud will create its own atmosphere, and vapourisation as well as melt is involved, but I still have reservations over the speed at which this process must occur. I find the scenario hard to accept in the absence of any rigorous modelling or terrestrial analogue, and in the light of Minitti’s results. Not impossible, but the sequence of events necessary to form hematite spherules seems far more complex and problematic than the formation of terrestrial impact microkristites.

Also, if this combination of impact energy and martian basalt can produce the spherules, why has this process not occurred in a number of impacts rather than being isolated to a few comparatively small regions? And the regions where grey hematite has been identified (Aram Chaos, and Ophir and Candor Chasma in Valles Marineris ) all have indicators for aqueous activity in the distant past. This seems to point to an aqueous rather than impact cause.

I understand that Geothite can transition to hematite in temperatures as low as 70 C in saturated water vapour given that in an aqueous system, crystal growth effects lower the transition temperature from that required in the dry state. (Catling and Moore Icarus 165 (2003) 277–300). So there is potential that low levels of hydrothermal energy could have created the appropriate conditions for hematite conversion from a goethite spherule precursor in Mars’ early life. A scenario possibly as tenable as impact accretion.

Aussie - Some of these questions have been addressed in previous posts, but bear repeating.

Regarding Michelle Minitti's results - what happens if you roast basalt in a dry CO2 atmosphere is irrelevant - water (or steam) is the great catalyst. Without it, very little happens in the mineral world. Look it up. Also, believe it or not, large impacts heat things to many thousands of degrees - they separate metals from oxygen, at least transiently, and vaporize everything, without exception. Plenty of kinetics, infinitely more interesting than, say, volcanic processes - and equilibrium is hardly expected, with the rapid decompression and cooling. Consider, as a simple example, what might happen to hydrated Mg-sulfate, inferred to be the most common salt at Meridiani. Mg would separate from S and O and H. Then rapidly recombine into MgO, SO2, H2O, and O2 - plenty of oxygen to oxidize iron, and plenty of steam to catalyze the reaction (not to mention salts - why you don't want to buy a used car from a seaside car dealer - too much rust). Iron-containing impact products on Earth, other than the tiny iron condensation spherules found right next to Meteor Crater AZ, are fully oxidized - and the oxygen in the air has little to do with it. It's the oxygen in the target minerals. Also, believe it or not, it's rather difficult to model (or even imagine, for most people) such extremely rapid, disequilibrium processes. So observation of the products may be your best guide.

Regarding "small regions" - that description hardly fits Meridiani. Also, believe it or not, orbital infrared spectroscopy is an extremely crude tool - at best it detects what's abundant at the surface, and at worst, only thin coatings on something else, or nothing. It utterly failed to detect the 30% sulfate in the Meridiani rocks (even though sulfate vibrational regions are easy for IR in the lab), and was lucky indeed to detect the specular hematite in the spherules. In any region where the hematitic spherules were all small, or less abundant than about 15% (or coated with dust or buried under/mixed with sand or layered rocks), the hematite would probably be invisible to spectrometers in orbit. Ditto if the spherules had a different composition. So far, rovers have landed at only two places on Mars. In both places they have detected spherules (much smaller, less abundant ones at Home Plate), and at both places they have detected what look like salty surge deposits (essentially identical bedding structures, although the MER team seems extremely reluctant to admit this, and papers on one site never mention the other site). Ferric acid sulfates occur at both sites (jarosite is reported from Meridiani, unspecified ones at Gusev). If our impact hypothesis is correct, I might predict that future rovers that land in similar well-bedded rocks should find similar features: surge-type cross-bedding, impact-related spherules, and salts, possibly including acid salts. So far, we're two for two - so feel free to complain about the statistics of small samples.

The "indications of aqueous activity" that you refer to for Aram Chaos, and Ophir and Candor Chasma in Valles Marineris are inferences generally based on the presence of bedding and sulfate salts - also obviously expected for impact deposition (although I'll be the first to admit that water deposition also produces bedding, but the rocks don't look anything like those at Meridiani or Home Plate). BTW, our impact model depends on "aqueous activity" too - but in the form of steam. And we never claimed that the neutral salts don't indicate liquid water - just that that the liquid water could be older than the deposits being observed (see earlier posts). The highly unlikely mixture of soluble and insoluble salts at Meridiani also converted the MER team to this explanation, but they blamed the wind blowing across a long-vanished playa, instead of an impact. Then they wanted to soak the soluble salts many times in brine without recrystallizing them, have water flow briskly across a flat surface, and similar implausibilities.

Regarding "hydrothermal activity" and goethite, that has not been suggested for Meridiani by the MER team recently, so why are you bringing it up? (When the blue-gray or specular hematite IR signature was first detected, a super-giant hot spring system was inferred, but this idea was later quietly laid aside in favor of a giant metamorphosed iron formation, which now has been laid aside in favor of a giant field of sedimentary concretions.) That Catling and Moore (2003) paper is dates from the iron formation hypothesis. Frankly, instead of dealing with the largest hot spring in the solar sytem, or the largest iron formation, or the largest sedimentary concretion field, I find it much easier to blame everything on an ordinary garden-variety impact or impacts, for which there are so many possibilities that it is hard to know where to begin. But that's just me.

--HDP Don

[dburt]

Don, you missed this thread... pretty amazing...
http://www.unmannedspaceflight.com/index.php?showtopic=4383

You're right - thanks for the link.

--HDP Don

[dburt]

In connection with this question, my impression is that the hematite signature of the Meridiani region forms a confined shape with a fairly defined edge. I would expect that if the hematite was formed by large impacts that it's signature would be more widespread, with less shape and definition. Each large, hematite producing impact would shoot a surge out radially. In my mind, I have to imagine the hematite from a series of impacts being shot toward what would become the Meridiani region and not shot outward in other directions. From space, it looks like the hematite of Meridiani collected there rather than shot there by impact. Why was hematite not shot in directions away from Meridiani as well?

Elk Grove Dan - You're right - I made up an answer Centsworth II - From what I've learned about regional geology, the edge of the Meridiani hematite deposits is, in part provided by the sharp topographic edge of the plateau - wind erosion has preferentially removed the finer-grained material next to the heavily cratered hills. Having finer-grained material next to the hills is, incidentally, the opposite to the pattern you would expect had any of the Meridiani bedding been caused by water runoff (you'd expect coarse alluvial fans next to the hills instead). It is typical of surge deposits, though, as mentioned in previous posts. The rest of the "edge" may be merely a detection limit of about 15-20% spherules. In other words, a diffuse edge would probably be indetectable from orbit. (Anyone is welcome to correct this supposition, if they can do so authoritatively.). Finally, remember that Meridiani is not where the spherules are, it's where the wind blowing across a plain has left a lag deposit of spherules by eroding friable (poorly cemented) rock. Any spherules still in rocks, or buried beneath sand or dust, are indetectable from orbit.

Enough possibile answers?

--HDP Don

[dburt]

About as likely as frogs spontaneously generating from mud. Interesting belief, but where is your proof?

From the many MOC and MRO images taken of the Meridiani Plains where is the indication of the brine splat/base surge?

--Bill

Bill - Umm, as a scientist I don't believe, I hypothesize, and absolute proof is impossible, by definition. All that a scientist can do is test various hypotheses for the same observations against each other, and try to decide which one best fits the data. Even for the best, there will always be holes and imperfections. In the Meridiani case, there are two other hypotheses. The first is volcanic surge, which is quite similar to ours, but hasn't gotten much traction, inasmuch as it has to call upon a vanished volcano. That little difficulty hasn't stopped the MER team from hypothesizing a vanished volcano for Home Plate, however. The second is the vanished playa hypothesis of the MER team, with which you may be familiar. That has obviously gotten a great deal of traction, even though there is no direct evidence for any of its complex individual parts, and considerable evidence against some of them, plus it contains many internal contradictions, and doesn't explain all of the observations (see my earlier posts). If you wish to "believe" in it, you are welcome, but that makes you a true believer, which is a religion.

If you wish to treat the impact surge hypothesis as science and not religion, I suggest you find some observations that it does not explain, or some internal contradictions within it, or some data that directly opposes it. So far no one on this forum has had much success, although it does have minor warts, as people delight in pointing out repeatedly (and believe it or not, I am extremely grateful - that's why I signed on). Mostly people seem to object because it runs counter to their beliefs and assumptions, or they have difficulty imagining parts of it. I continue to be amazed at how many people object to our proposing impact as an important process for a planet covered with craters and coarse impact debris.

Regarding the hematitic hailstones part, BTW, are you willing to grant me the very carbonate-rich accretionary lapilli of the Chicxulub impact that probably killed the dinosaurs, owing to the carbonate-rich target rocks (limestones), but unwilling to grant me very iron-rich accretionary lapilli for a probably iron-rich target rock on Mars? Wouldn't that make you somewhat miserly?

And hey, here in Arizona frogs (or at least toads) do spring spontaneously from mud, according to direct observation. Of course, I may have failed to observe to the mother toad laying eggs in that puddle late some night before it dried up.

Finally, if you wish to see possible direct evidence of impact surge, I suggest you look at some of the nearly eroded flower petal-like ramparts around Victoria Crater, beginning about one crater diameter out (anything closer is concealed under berries). See the July 5 HiRISE browse image, for example. Oppy must have driven right across these possible eroded surge deposits, without imaging anything different from the rest. I may have more to say about Vicky's surge deposits later. For tonight, that's all, because I'm writing this from home, and so lack access to any photos to post. Thanks for your brief comments - they gave me a great excuse to lecture about science (not that I ever needed one...).

--HDP Don

[Aussie]

Dburt
I regret that I have grave reservations over your theory. I suspect that if I had presented your concepts and proofs for a PhD you would have torn me to shreds for lack of sustainable logic. Please do not take this comment as disrespectful but I suspect that your interest in the impact surge concept has become personal rather than scientific and your arguments seem centered on attacking the JPL theory without providing sustainable arguments for your alternative scenario. I do note that JPL considered the impact surge scenario as one of their favoured models and then rejected it based on tests and feedback from the rovers. Lets face it, Innocent Bystander raises significnt questions with respect to your theory.

[Bill Harris]

We'll wait to hear your suppositions on the aerial photos...

--Bill

[don]

dBurt

"Can you explain that scour in terms of their model? They appear to have hypothesized a "supersurface" ("Wellington contact") of regional extent on the basis of a single large cross-bed with a large channel-like scour taken out of the top of it - which scour, on the face of it, makes their hypothesis untenable. Do you disagree? If so, why?"


Why not a channel cut or similar for the “scour” in the Wellington contact? If there was surface water in the area as the MER model states all you need is a small gradient and you have flow, which in turn could cause down cutting (I hear the surface rocks are easily-scoured sand). If there was a fluctuating water table at ancestral meridiani perhaps there was also topographic relief (even minor) just enough to generate flow once groundwater breaks through the ground surface (aka springs). Here is perhaps evidence in the shape of “scours” for a local surface hydraulic gradient at meridiani. Seems more plausible IMO (small wart) than a surge generated vortex (big wart). I would hold back on speculating a regional extent for the Wellington contact however. I’m still hoping to see a similar feature in Victoria.

Question – the surge model seems to apply more directly to the layers examined in the Columbia Hills then meridiani, yet there seems a lack of enthusiasm from you to really hit that hard. Are you taking one landing site at a time, or is there a more fundamental reason for that, or am I just completely out-of-the-loop crazy ?

[djellison]

I am going to do the same thing to this thread now as I have planned to do in another, similar thread - close it.

It's going around in circles, it's getting nowhere, it should have been healthy discusion, but for whatever reason it's not happened that way - it's frankly damaging to the forum.

dburt's written more than 41,000 words. If that's not going to get a point across, nothing will.

If people wish to discuss his Meridiani theory further, then please do so elsewhere or via email.

Posts in other threads on this subject will be deleted - as a subject it's been exhausted with this thread.

Doug

[dburt]

I could go on and on about all of the erosion processes on Earth that are real and observable on a timescale of a few months, but you get the idea.

Absolutely right, EGD. Or even on a timescale of a few seconds, for a landslide or avalanche or flash flood. On Mars some of the most spectacular sudden erosion seems to occur in the vicinity of minor impacts, where shock waves toss dust and sand into the atmosphere, and then dust-storm-like super-fast density currents (a.k.a. impact surges) sweep radially across the ground surface and scour the subsurface (such scouring commonly reveals itself as cross-bedding in the sedimentary record). The aftermath of this scouring is clearly visible on orbital images, where all of the dust near very recent small impact craters has been cleaned out, leaving circular dark zones. Older, larger impact craters commonly display radial erosional grooves. (And apologies for pedagogical repetition; it's the professor in me .)

-- HDP Don

[dburt]

http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1171.pdf

This paper is of the opinion that "The sedimentary rocks examined by ... Opportunity ... are part of a statigraphic sequence greater than 1 km in thickness". It also states that "The amount of rock that once covered the MER-B site could have been as much as 200-300 m".

If these estimates are correct then Opportunity would need to find a crater of at least 700m in depth if it was to have a hope of finding the clay deposits beneath the sulphate rich sandstone. Victoria at only 70m in depth is clearly not deep enough to provide exposures of clay deposits...

Thanks for the reference, PaulM. FYI, later that year, Ken Edgett published that work as an extended article (with numerous photos) in the Mars journal, web accessible to anyone:
http://www.marsjournal.org/contents/2005/0002/
As I recall without looking them up, most other estimates of erosion off the top of Meridiani are lower, on the order of (at most) tens of meters, rather than hundreds. The dense hematitic spherules, once eroded out, seem to have formed a "pebble armour" or "desert pavement" that slowed further wind erosion.

The Edgett paper says, AFAIK, nothing about clay deposits at greater depth, although he does refer to buried erosional channels, apparently lacking near the surface. (Note: not only flowing water, but also vortices in radially flowing surge clouds, can erode channels.) Deep clay-rich layers buried beneath Meridiani, if any, would presumably be older than those layers exposed near the surface, and therefore not directly related to them genetically.

Two quotes I originally enjoyed reading from that 2005 abstract (given our 2004 hypothesis that impacts alone could have deposited the Meridiani sediments imaged by the rover) include "These rocks are not superimposed on heavily cratered terrain, but rather are an integral part of it" (Introduction) and "Impact craters of diameters from < 50 m to > 100 km have been filled and buried by and within the strata." (p. 2). In other words, Edgett and Malin concluded, from orbital evidence (MOC images) alone, that Meridiani sedimentation exactly coincided with or at least heavily overlapped with impact cratering (a.k.a. Late Heavy Bombardment, LHB), although, unlike us, they did not hypothesize a cause-and-effect relationship between the two processes of cratering and sedimentation.

Furthermore, they noted a near-zero regional dip "All of the rock units that extend across Sinus Meridiani are horizontally bedded at regional scale" and "the [regional] dip [today] is only about 0.02 degrees" (p. 1). This important observation casts doubt on any hypotheses involving flowing or standing water, because water puddles or ponds, rather than flows, on a horizontal surface. Clay layers are characteristically deposited in ponds, which also characteristically lack cross bedding. The exposed Meridiani layers are cross-bedded everywhere and lack bedded clays, as well as obvious flow channels. To us, by far the simplest hypothesis that satisfactorily explains all of these features (as well as the uniform tiny spherules consisting largely of the high-temperature blue-gray form of hematite) is impact-related sedimentation.

Sorry, more pedagogical repetition from the professor.

-- HDP Don

[Kye Goodwin]

Paul M, Regarding your post 406, Yes, that Edgett and Malin paper is an interesting read. I have been aware of their contention that Endurance and Victoria are exhumed craters for a couple of years and brought up their ideas on the other Mars blog. As I see it now the prediction that Victoria would be rimmed with layered material above the original rim has not been born out. The top layer around the present rim seems to be jumbled ejecta from the impact, not layered bedrock, suggesting that if Victoria has been overlaid with hundreds of meters of material this has now eroded down into the ejecta but not the pre-impact surface. The bright planar beds that surface most of Oppy's traverse seem to lie just under the ejecta and more layered bedrock just under that. Its looking like Victoria and Endurance have the simpler history, that is, they are eroded craters rather than filled, buried and exhumed craters. (I still wonder why some areas of the outer rim of Endurance look so much like bedrock but after seeing Victoria I am swayed to accept Endurance as having a similar history.)

In that paper Edgett and Malin never quite spell out what sort of sedimentation they are visualizing when synthesizing their stratigraphic sequences. In any case, their scenario failed to predict the strata around the rim of Victoria and cannot be taken to prove that Oppy's landscape has been exhumed from under 100s of meters of rock.

[ngunn]

Maybe, but we're talking about the possible short term erosion of Rover tyre tracks here. Are you attributing this to impacts?

[dburt]

That's obviously where this discussion started, but it had wandered far afield before I contributed. No, I don't believe impacts have eroded rover tracks (at least, not yet).

-- HDP Don