[X] My Assistant

[denis]

HDP Don,

One fact is missing from your class exam . As I mentioned earlier, we have shown on another forum that the size distribution of the berries is asymmetric, with a left-sided excess of particles. This has been consistently obtained for both MI and Pancam observations (*). I consider now this feature as correlated to the hard upper limit in size.
In your opinion, does the impact cloud condensation hypothesis, where the dropplet growth may be limited by gravity, fit with these observations ? I am anxious to get you comment on this particular point. Thanks.

denis

(*)
http://geocities.com/rlewis6/Spherule_Database.htm
http://www.geocities.com/jnelson351/statistics_paper.html
http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1001.pdf

[marsbug]

I was infamous for dozing off during lectures, but this one has kept my attention very well. To switch metaphors I think the brine splat hypothesis has gone the full 15 rounds and come out of its corner fighting every time. Certainly its true that it has been unfairly dismissed in some quarters. I would still say my gut reaction (and very possibly my earth bound predjudices) tell me that to account for several billion years of surface evolution with only one process is stretching even the best idea, but I can't find any specific objection. My gut, which is very talkative today because my brain knows little about either geology or chemistry, also finds the idea of a mars which is cold and slightly damp for a long time easier to digest than one which was recently warm and very wet. So congratulations Herr Professor, I'd say impact surge is a convincing alternative. I hope you can find time to post on some of the other discussions. I'd be very interested to hear your opinions on the features and processes of Titan for instance.

[djellison]

I hope you can find time to post on some of the other discussions.

Brine splat stuff stays in this thread however.

Doug

[centsworth_II]

I don't know if anyone has yet referenced the "Not a base surge" section at the end of
one of the MER papers presented at the Seventh International Conference on Mars.
I'm happy to see these issues formally addressed by the MER team. I see the arguments
as being in three categories:

1) "Regional geological context... no evidence for age-appropriate impacts of
sufficient size."

2) The berries: a) "Fe/Ni levels are inconsistent with such an impact origin."
b) "...spherules are dispersed across all strata, even at obvious erosional
surfaces..."

3) "Stratification styles" that "are most consistent with low velocity, subcritical
flows, characteristic of fluvial and eolian transport.

I have a hard time fitting the stratification models in my head, so I settle on
the berry distribution argument as the one I best understand.


HDP Burt, tell me where my reasoning is faulty here:

If there are layers, with erosional discontinuities in between, and the
distribution of berries across the layers and across the discontinuities
is even, what is the best explanation? That various base surge events
just happened to contain the same distribution of berries, or that the
berries formed after the layers were in place? I think the simplest
explanation is the second.

[MarsIsImportant]

I think the berries forming after the layers were laid down is the simplest explanation too.

The more I think about it, the possibility exists that the missing clumped berries that Professor Burt asks about might actually exist. Opportunity may simply not have found a good example yet. If Meridiani is primarily a current aeolian erosion area, then most clumps near the surface might have been dispersed already. So the only realistic way to find these clumps is to dig.

The other problem is the apparent limit in size of the berries. Some quick change must have stop the process that created them. Perhaps the condition that created them was marginal at best. So the quick change didn't need to be as drastic and quick as it sounds. Perhaps in other areas of Meridiani there are much larger berries. We won't know until we visit those areas.

Edit: I know that Spirit has found some clumped berry like feactures in certain rocks. It was long time ago and it would take some time to dig the images out. But they are there. Gusev is not Meridiani. But Like I said previously...we still might not have found good examples of them at Meridiani yet.

[MarsIsImportant]

I was looking thru Opportunities Micro-Imager files to find before and after images of the magnets on the rover. I found something very interesting that relates to the discussion of spherules.

They have been looking for the clumped masses of concretions that we have assumed were missing in this discussion. The MER team must have known that the spherules was their weakest point in the hypothesis. I now believe they have found good evidence of these missing clumped masses. I've found more than doublets and triplets in the files. I suddenly noticed that some of the larger spherules were actually composed of many many smaller spherules glued together!!! I was surprised to see that many clumped together. I have not gone through all the files yet. But I believe they have found plenty of evidence to provide the 'smoking gun' for their wet Meridiani theory. The MER team seems to be ready to provide the empirical evidence they needed.

Edit: Look in the May 2007 files for the Micro-Imager to see what I'm talking about. There are a LOT of images.

[hendric]

Dr. Burt,
One big difference between Earth and Mars is the presence of life here. Maybe the Martian concretions are how they would grow on a lifeless world, but here the growth is more irregular due to bacterial contamination in the water or sand? Perhaps in a lifeless environment concretions do not form as readily as here on Earth, so the volumetric density is not as high preventing conglomerations, and the growth is more even allowing for spherules instead of flattened discs?

http://www.daviddarling.info/encyclopedia/E/endolith.html

I guess that option doesn't reduce the number of "dead grandmothers", but it does open up some possibilities.

Has anyone tried creating concretions? I found a semi-crankish site on the web that said nobody has, but the tinfoil-hattery was everywhere (concretions and blueberries are formed by electric discharge!). It would be interesting to try to create concretions with well water (with appropriate added salts) and dune sand vs distilled water and sterilized sand.

Do we know how long the it takes concretions to form?

[centsworth_II]

Doug Ellison, Thanks for asking. It will be a long haul ...

I hope you start you own thread as you mentioned.
This thread should just be for questions and comments
to Dr. Burt.

[dburt]

Well, I for one find all this very interesting, even though my lack of relevant knowledge means I'm a million miles away from actually holding an opinion.

Sadly, however, I note that we are now 'students' who have been given 'homework' and even for the brighter ones an occasional 'mark' !!! This is an excellent strategy for deterring rather than encouraging intelligent comment. Why oh why do you do it, dburt?

Only to provoke a response from you and Doug, and thanks to both of you for yours. Also, to misquote Arne in T2 again, "Of course. I'm a professorator." - I've been programmed, after 35 years. I can't help that. I just hope no extra grandmothers die during the quiz (if you followed the beginnings of this thread).

--HDP Don

[dburt]

As I mentioned earlier, we have shown on another forum that the size distribution of the berries is asymmetric, with a left-sided excess of particles. This has been consistently obtained for both MI and Pancam observations. I consider now this feature as correlated to the hard upper limit in size.
In your opinion, does the impact cloud condensation hypothesis, where the droplet growth may be limited by gravity, fit with these observations ? I am anxious to get you comment on this particular point. Thanks.

Denis - Great question, and of course I am utterly unqualified to answer it. Luckily, my co-author Ken Wohletz filled with the gap (what else are co-authors for?) with an e-mail containing the following quote:

I did a sequential fragmentation/transport analysis on the referenced
data. To my surprise, the distribution of berry sizes is almost perfectly
described by an SFT distribution with a mode at -2.22 phi and
dispersion value of 0.39. Dispersion values greater than zero generally
indicate aggregation (rather than fragmentation); thus my results suggest
that his observations perfectly support an accretionary hypothesis.

It's all pig-Latin to me, but that definitely sounds like a yes for accretion. Contact him for more details. In a later message he added the following general words of wisdom:

I seem to get that one of the problems readers have with the impact surge
hypothesis is that thousands of layers of similar thickness seen in
Meridiani suggest thousands of surges all depositing similar layers. It is
very important to get across the idea that a single surge may wax and wane
hundreds of times at any single location during its runout, resulting in
deposition of numerous layers. This phenomenon comes from the breakdown of a
shock wave into a train of hundreds of waves because of shock reflections
off of the substrate, off of internal density contrast surfaces, and off of
each other. Think of thunder and how the sounds rolls, cracks, and rumbles
all from one lightning stroke moving through air of different density,
temperature, and moisture content. The flow regime in a surge is a response
to a pressure gradient, and that pressure gradient is analogous to a sound
wave. So just like thunder, some surges can be loud and short lived, while
others can be prolonged starting with a crack but followed by numerous
booms.

So yup, that's why we all need co-authors.

--HDP Don

[dburt]

... So congratulations Herr Professor, I'd say impact surge is a convincing alternative. I hope you can find time to post on some of the other discussions. I'd be very interested to hear your opinions on the features and processes of Titan for instance.

Marsbug - Thanks for waking up, and thanks even more for the compliment. As for being profound about Titan, I'm already partly faking it here (as you may have noticed), so consider it unlikely unless I stick strictly to P-chem aspects (and even then you'd have to provide me with the relevant phase diagrams).

--HDP Don

[MarsIsImportant]

Thank you Professor,

You finally addressed my biggest problem with the surge idea. You showed how it is not necessarily a problem at all.

If the surge made so many thin layers, then how would we distinguish between it and the wet Meridiani model?

[Kye Goodwin]

It seems that Dr. Burt and his co-author are having some success in changing minds. I wish that more Unmanned Spaceflight readers would tell us where they stand.

[dburt]

I don't know if anyone has yet referenced the "Not a base surge" section at the end of
one of the MER papers presented at the Seventh International Conference on Mars.
I'm happy to see these issues formally addressed by the MER team. I see the arguments
as being in three categories:

1) "Regional geological context... no evidence for age-appropriate impacts of
sufficient size."

2) The berries: a) "Fe/Ni levels are inconsistent with such an impact origin."
"...spherules are dispersed across all strata, even at obvious erosional
surfaces..."

3) "Stratification styles" that "are most consistent with low velocity, subcritical
flows, characteristic of fluvial and eolian transport.

I have a hard time fitting the stratification models in my head, so I settle on
the berry distribution argument as the one I best understand.
HDP Burt, tell me where my reasoning is faulty here:

If there are layers, with erosional discontinuities in between, and the
distribution of berries across the layers and across the discontinuities
is even, what is the best explanation? That various base surge events
just happened to contain the same distribution of berries, or that the
berries formed after the layers were in place? I think the simplest
explanation is the second.

Centsworth - Congratulations on doing independent research. I believe you're the first to mention that particular long meeting abstract (which appears to be the first ever to acknowledge the prevalent Meridiani interpretation as "a model"). Regarding your item 1) I seriously doubt this, inasmuch as relative age is assigned solely by superposition (what's on top of what) and the assumption of original horizontality. These assumptions work rather well for "wimpy" deposits deposited by wind and water (or for ballistic ejecta on the Moon). A large impact surge could completely cover low spots such as craters, giving them an apparently young crater count age, yet completely scour even slightly earlier deposits off the nearby heavily cratered highlands (as stated in a previous post to you), giving them an anomalously ancient apparent age relative to the nearby lowlands. Also, I imagine he is basing his size statement on 1) the wrong assumption that the Meridiani exposures had to result from a single large distant impact and 2) the conventional wrong assumption that impact deposits only reach about 2 crater diameters out. Models are only as powerful as the assumptions that feed them (classically known as "GIGO" - garbage in, garbage out). That's why I prefer stick with observations, where possible.

Regarding 2a), as stated in previous posts, even if the spherules are oxidized iron condensates (which we mentioned in 2005 as only one possibility among many), we regard their assumption that the Fe/Ni ratio in vapor-condensed accreted spherules has to match that in Fe-Ni meteorites as completely mistaken and misleading (see our unpublished Nature critique refutal attached to my post 170 above) - there is no conceivable reason why there should be a match. More to the point, despite special pleading to the contrary (see, e.g., abstract 3231 at the same meeting), they cannot explain why water-deposited hematite, containing only Fe3+, should be at all enriched in Ni2+, given that Ni2+ at Meridiani had so many other favorable crystalline sites to go to, such as the Mg2+ sites in Mg-sulfates or silicates. Look up, e.g., the terrestrial literature on the mineralogy of Ni-laterites (as I believe I mentioned in a previous post). This concept is called "partitioning" and in those terms, Ni2+ is "incompatible" in hematite (should never be enriched). Remember, you're talking about a couple of my supposed fields of expertise here (no co-author needed).

Regarding 2b), as stated in multiple previous posts, I regard the observed pattern of distribution of spherules at Meridiani as a far stonger argument AGAINST the concretion hypothesis than it is for it. Perhaps the author in question should do some more field work in the Page and Navajo sandstones (as I have been doing for the past 3 years), inasmuch as he has made these his favorite Meridiani analogs (apparently based largely on published articles). Actual hematitic concretions there, other than being round, little resemble his model - e.g., they're commonly concentrated and clumped at erosional surfaces. Let me know if you'd like photographic documentation.

Regarding 3) the "stratification styles" such as so-called "festoons" that are allegedly unique to wind and water - haven't we already beaten that one near to death in previous posts? (I'd be happy to try to put it out of its misery, but only if specifically requested).

Regarding the allegedly even distribution of berries - certainly not true at the large scale, and at the small scale I remain satisfied by my prior analogy of injecting them with sand into a turbulent jet exhaust (little reason to separate, and every reason to mix). Keep in mind that once berries are formed, later impacts could further distribute and mix them across an even wider area and thicker stratigraphic interval (as must have occurred at Victoria Crater, prior to wind erosion). If wind ever concentrated them as a lag at the surface, as today seen at Victoria, later surges could scour and mix them in with the rest of the particles. Of course, at the extreme far end of the surge run out, as things calmed down, they might well be concentrated as a lag along bedding planes, but even that seems not strictly to be required (as in a perfect condensation dump-out, for example). One shouldn't confuse what is sometimes seen in wimpy little volcanic surges with what might be expected big he-manly impact surges (with apologies to Arne and SNL). All you Ph.D. clastic sedimentologists, please feel free to contradict me - like any professor, I sometimes make this stuff up as I go along...

Regarding their hematitic composition (thanks for not bringing that up again too ), my co-author Ken Wohletz today shared these general words of wisdom:

It is not uncommon that volcanic accretionary lapilli vary in composition
with the matrix in which they finally reside; the reason being that they
have sampled a different portion of the ejecta plume than what is mainly
represented in the surge. Lapilli can form high in the atmosphere, fall out
into a moving surge, and experience horizontal transport before being
deposited. The "sampling" process involved with accretionary lapilli is
complex and depends a lot on electrostatic potentials that are in turn
compositionally dependent. Thus it is entirely possible that accretionary
lapilli can grow by preferentially accreting particles of a specific
composition. These results are covered by an experimental study done by
Schumacher a number of years ago.

More or less equal to what I randomly made up in response to previous posts, but in much fancier words. Ain't co-authors wonderful?

BTW, the morning session of this upcoming Friday the 13th in Pasadena seems to have some the most relevant MER presentations - sorry I won't be there. Perhaps some of you who will be can comment afterwards, or I can comment on some more of the abstracts. Apologies to the rest, this is all I have time for now.

--HDP Don

[dburt]

Here's a final one before I go home (before the subject gets completely lost in the crowd).

As regards Ken's pig-Latin in my post 198 about berry size distributions, here's some more pig-Latin from him in a subsequent e-mail:

I stand by my analysis but cannot vouch for the
quality of the data used. In fact in all my years of applying SFT to natural
samples, I have not seen one so perfectly explained by SFT than these
blueberry sizes.

The fact that the distribution is perfectly unimodal is eye-catching; most
natural samples demonstrate some degree of polymodality caused by mixing of
fragmentation and/or transport processes. The fact that the distribution
dispersion value (gamma includes sorting, skewness, and kurtosis) is
positive strongly supports an aggregation process (smaller particles
sticking together to form larger ones tends to make a distribution more
peaked with a decreased fine tail).

An aggregation origin predicts a rather limited size range, with a mode
giving a hydrodynamic equivalent for turbulent suspension in a multiphase
fluid. If one observes average blueberry size of 4 to 5 mm over a wide
range, then one might suggest that the bulk Reynolds number in surges was
fairly constant, a situation possibly coming from runout over a surface of
fairly constant surface roughness and elevation. Other hypotheses from surge
theory can also be tested. One I like is the self-limiting process of
deposition, which tends to keep Re steady in some surge runouts.

Hey, I didn't even make that one up out of whole cloth first (I couldn't even if I tried). All I can say is it sounds like the original poster should contact him ASAP about possibly writing a paper together...

Whatever happens, remember, you read it here first!

--HDP Don