"Could the Meridiani Spherules be Surficial?" Options

[djellison]

This page - http://marsrovers.jpl.nasa.gov/gallery/pre.../20040818a.html - highlights many of the problems with a surface genesis for Spherules and active surface creation. It's a different composition at the top than the bottom - as well as berries being different ( and indeed absent ). Why is there material forming on rocks hiding berries, but not on the soil. Why is there a composition change in the surface that ties in to the morphological evidence as seen at Endurance if the surface is modern?

All credit for thinking outside the box - and without serious challenges, no scientific hypothesis can be said to be a robust or reliable one!

Doug

[helvick]

Kye,

I'm all for thinking outside of the box too but the idea must be able to explain all of the observations. One nit pick - I think the word you should be using is "surficial" rather than "superficial".

In any case.

1. To focus in on one area where I think HDP Burt has fewer dead grandmas than the MER team. What process are you going to use to create "high temperature shiny blue hematite" ? As far as I can tell the MER team's explanation relies on a very specifically balanced saturated brine as a plausible explanation but the high temperature surge "hailstone" idea seems (on balance) less dependant on a carefully balanced system. Both hypotheses are hampered by a complete failure to indicate an equivalent earth analog but then that would be asking for quite a lot.
2. Pavels comments on the mechanics of the formation process are very compelling and really problematic for your surficial formation hypothesis. Do you have any example(s) of a (non biological) process anywhere that produces fairly uniform spheres of any predominantly solid material?
3. At the most basic level we see lots of berries free on the surface, they are certainly embedded to a depth of a couple of mm in most of the RAT'ed rocks and they are present at the surface of all exposed rock formations. The simplest explanation is that they are present throughout the rock and those that we see on the surface have eroded out of the rocks. Your explanation may be possible but it seems overly complicated to me.
4. I don't see how your hypothesis resolves any of the difficulties with the two other hypotheses? Maybe I haven't read it all carefully enough though.

Actually to be honest I'd love to see one of the proper geologist types who are reading here lay down some basic pros and cons for the various ideas. Most of this stuff is way outside any area that I have any expertise in - for example I have no idea whether the claim that "shiny blue hematite" requires high temperatures to form is true or not, or how true it is as I suspect that the issue isn't totally clear cut.

All that said I've found all of these discussions extremely worth while and I hope they can continue.

[Kye Goodwin]

helvick re your post 17, Thanks. On superficial vs surficial, yes my language tends to be a mish-mash of English and technical terms when I think I understand them. I can go with surficial if you like, but its too late to change the title of the thread.

1. Here is a Tim Glotch paper that concludes on the basis of crystal structure that the spherules have probably formed under low-temperature conditions:

http://www.gps.caltech.edu/~tglotch/glotch_fresnel.pdf

2. Pavel's mention of surface tension as a possible cause of sphericity might somehow relate to surface spherule formation. Thin films of moisture are often invoked to explain how water could act under Mars surface conditions. I have to admit that I haven't been able to come up with a compelling reason why my surface nodules should be round and it bothers me that they do not usually show top to bottom asymmetry. One GUESS is that the sphericity and the size limit are related to the microclimate that the berry creates during a daily period of fleeting moisture.

3. and 4. Yes, at a glance, the simplest explanation is that the spherules occur throughout the rock, but on closer inspection problems remain. The surface nodule theory solves two of the thorniest problems faced by both the impact spherule idea and the sub-surface concretion idea. It explains why the spherules do not disturb the bedding layers, and it explains why the spherules show no clustering, not along bedding planes or apparent contacts in the rock, or in any way that would suggest that they were controlled by groundwater movement.

[MarsIsImportant]

1. Here is a Tim Glotch paper that concludes on the basis of crystal structure that the spherules have probably formed under low-temperature conditions:

http://www.gps.caltech.edu/~tglotch/glotch_fresnel.pdf

Kye, that is an excellent paper!

It pretty much rules out high temperature formation of the Martian hematite spherules. That means no volcanic lapilli, and impact surge is also ruled out. These berries were created at low temperatures. That also means that the MER team is 'in the ball park' so to speak. This is strong evidence to support the MER team's hypothesis.

I am curious as to how you could form an alternative low temperature hypothesis that creates these spherules on the surface. Since you have some good sources, I am willing to have an opened mind. But on the surface (a pun), this looks like a crazy idea for an alternative. I'm listening.

[djellison]

or in any way that would suggest that they were controlled by groundwater movement.

The varying morphology and density as seen at Endurance, Eagle and Erebus would be indicative of such movement would it not?

Also - invoking any water at the surface to create the spherules would preclude the existance of Olivine
http://marsrovers.jpl.nasa.gov/gallery/pre...y_bw-B011R1.jpg

i.e. http://www.astrobio.net/news/article653.html
"Olivine is significant because it decomposes rapidly in the presence of water. Finding olivine on the surface is therefore a good indicator of a dry Martian surface."

Now - it does say one of the things it can be decomposed into is hematite - but - how does the decomposition of soil turn into a hematite rich ball and/or how can there still be olivine when it's widely assumed Mars has been just about the same for a billion years or more.

Doug

[dvandorn]

OK -- here are two points that might possibly lead to further discussion. Here's hoping.

First point: If this hematite didn't form within the rocks, but is low-temperature hematite, then how did it form? Perhaps it formed some distance away from where it is now and was transported to its present location. And since 1) hematite can be produced from olivine-rich lavas and 2) there is a lot of olivine in unaltered Martian lavas, it's conceivable that low-temperature water processes could have formed this hematite -- just not in situ.

Second point: I know I've read that hematite, once formed, does not melt. If a hematitic bed of rock (formed in whatever climate and under whatever conditions were conducive to such formation) was struck by an energetic meteor (or even a basin-forming event), that hematitic rock bed wouldn't melt, it would be pulverized. Broken into pieces, smallest (dust-sized grains) nearest the impact point and larger away from the impact. Thus, it would be possible for an impact to distribute hematitic fragments within its ejecta blanket. (However, since the hematite would not melt, it would likely not accrete into spherules out of dust-sized granules within the ejecta cloud/surge. I can't imagine anything other than melting that would form the hard, solid berries we see out of hematitic particles and dust, and as has been said, hematite won't melt and therefore can't be annealed into a single solid mass from pulverized particles. And these berries are strong and erosion-resistant, they don't appear to be hematitic dust bound in some other kind of matrix.)

I am not siding with an impact origin for the spherules at this point. I need a lot more convincing before I will go that far. However, I believe there *is* a not-altogether-impossible sequence of events which which would allow for it. For the distribution to be so widespread in this area, multiple large impacts would have had to occurred into hematitic rock beds nearby the area. If the layered sulphates actually were laid down on top of berries as they sat on the surface (a process I just don't see evidence of in the MIs of embedded berries), then it is just possible that repeated impacts over time have excavated hematite, spherized the ejected granules either due to impact stresses or due to extreme erosive conditions within the impact cloud/surge, and covered the surface evenly enough and regularly enough for it to *appear* that they are uniformly distributed throughout the rock.

However, it just doesn't look like there are berry "deposition planes" within the rocks that would define the surfaces upon which they were deposited. Unless the putative impacts which distributed the berries (all at different distances and releasing different amounts of energy, thus excavating different amounts of rock and ejecting it different distances) somehow produce unformly-sized spherized pebbles each and every time, which I consider highly improbable, then I'm afraid our friend Occam won't approve.

The only thing that would make any sense whatsoever, if the berries are ejecta, is that they were ejected from a basin-forming impact partway across the planet. A single large impact event could create zones of ejecta of similar content and character that are hundreds to thousands of miles in extent, in one dimension or another. But again -- if the berries all came from a single huge impact, how did they get so uniformly distributed through the Meridiani sulphate-rich rock beds?

-the other Doug

[MarsIsImportant]

Well, the distribution of the spherules was a problem that the MER team used to criticize Dr. Burt's conclusions. Yet, Dr. Burt doesn't accept that argument in opposition to impact or the others. In fact, he turns the argument right around stating that the distribution is a bigger problem for the MER team's model, because there are no major clusters observed to support the idea of spherules as concretions. Again, instead of addressing the problem with respect to impact surge--which he should--he simply says that the distrubution is an even bigger problem for the MER team's model.

We have all gone through this over and over again. I cannot arrange the arguments against impact surge better than what the MER team already has done. Dr. Burt rejects them. Yet, I think the MER team has come up with valid objections to the impact theory. That's my opinion.

I'm ready to vote in a poll.

[Bill Harris]

Agreed, Mars. His argue-ments remind me of http://www.mwscomp.com/movies/grail/grail-04.htm .

---Bill

[Kye Goodwin]

MarsIsImportant, re your reply 22, I agree, both the impact-surge hypothesis and the MER team hypothesis have a big problem explaining the distribution of the spherules, and both groups have been effective in pointing out the problem for their opponents while glossing over a similar problem for their own scenario. I think that the answer lies in realizing that the spherules are not an integral part of the deposit but occur only at it's surface, not the plain's surface but the entire present surface, which includes the crater interiors.

I just thought of another puzzling observation that can be simply explained by the surficial spherule idea. Both the MER team and impact surge authors believe that the spherules have eroded out of layered rock and accumulated on the surface of the soil on the plains, but the one place that we would most expect to hold accumulations of released spherules, Endurance Crater, shows no extra spherules at all. I have always had difficulty with this. The crater walls are studded with spherules and many are standing well above the rock suggesting that they are near to breaking loose. Many spherules must have already rolled from the crater walls if sufficient rock has been eroded to fully expose the spherules still in place. But where are those accumulations of loose spherules? They are nowhere we can see them, not in depressions on the slopes or at the base of slopes. The surficial spherule idea has a very simple answer: the spherules are not eroding out of the rock, so there is no need to explain why they have not accumulated downslope in Endurance Crater.

[Gray]

... but the one place that we would most expect to hold accumulations of released spherules, Endurance Crater, shows no extra spherules at all. ...

I have two responses to this objection. First, the large drifts as the bottom of Endurance indicate that sediment is being deposited there. That sediment could easily cover many of the spherules that have eroded from the cliffs. Second, even with the deposition that is occurring, I believe there is an accumulation of spherules at the base of the cliffs.

This image: http://marsrovers.jpl.nasa.gov/gallery/all...0P2415L2M1.HTML was taken on sol 195 when Opportunity was near the large rock Wopmay and near the base of the Endurance Crater cliff. I could be mistaken, but those look like spherules.

[denis]

Kye,

When what looks closely at the spatial distribution of the spherules, one concludes that the plains spherules are randomly distributed at small scale, and that the crater (I mean Endurance) ones are more clustered than random. That means that the plains spherules have probably not moved from their original location, while the clustering of the crater ones is a result of their (limited ) accumulation following their release from the host rock. An other consequence is that in the frame of a surface growth hypothesis, there is no short distance interaction (soil nutriment depletion for instance) between spherules. This is contrasting with the MER team claim that the berries embedded in the rocks are more uniformly distributed than random as is expected in a concretion process (McLennan).

denis

[Kye Goodwin]

Gray, Thanks for considering this. What I wrote is that Endurance shows no apparent extra spherules. The image you posted does very likely show spherules, and these are distributed thinly over the surface much as they are on the soil of the plains. What I think is missing at Endurance is any sign of spherules as scree deposits. We have not seen deposits of spherules anywhere that appear to have accumulated to a depth of more than one. On deeper soil, where trenching has been done the spherules are revealed to form a thin layer on the surface, though a few were seen at shallow depth in trench walls. In your image from Wop May's vicinity, we can be fairly sure that only a thin and partial layer of spherules is present because the bedrock is visible through the berries and soil. Here is another image from that same station that shows that bedrock is very near the surface.

http://marsrovers.jpl.nasa.gov/gallery/all...00P2415L5M1.JPG

The spherules that have rolled from the crater walls could be hidden in some way but it would be reassuring to see them somewhere as a colluvial fan if they are descending the slopes.

[Kye Goodwin]

denis, re your 26, Thanks. On your first point: I have noticed that spherules occur less frequently on rock than on soil. This is pretty well established for spherules attached to rock, but it also seems to be true for loose spherules. The densest coverings of spherules seem to always be on soil and I tend to think that the presence of soil is somehow causing the denser spherule populations. The causality can easily be turned around, however, and soil explained by the presence of spherules, which would reduce wind at the surface and allow soil or dust to accumulate between them. Still, I would GUESS that your clustering of loose spherules within Endurance could be caused by the generally shallow and patchy soil cover in Endurance compared with the plains, that is, a mixture of rock and soil substrates is available.
You mention limited accumulations of spherules in Endurance but I don't see any accumulations that appear to be connected to gravity movements, and I don't think that there are overall more spherules per area in Endurance than on the plains.
You write of "short distance interaction between spherules". The average distance between spherules attached to rock surfaces is much greater than the average distance between spherules loose on soil, so if the ancient subsurface concretion model is used, wouldn't a long (or at least longer) distance interaction be required to explain them? What is the approximate "short distance" you are referring to and how does it compare with the average separation of spherules attached to rock? Dr. Burt might laugh at the idea that spherules forming in a groundwater system could be controlled by nothing but the distance to nearby spherules, and I have to agree with the criticism. The MER team have been forced to propose that their spherule-building aquifer was uniformly permeated at all depths with water and solutes and that the water did not move, which is asking a lot. A surface nodule explanation isn't obviously any better at explaining the spaced-apart spherule distributions, but it does avoid (through vagueness) having to invoke groundwater and earth-like concretion formation. It may help to explain why the more-uniform-than-random distributions are clear at the surface - it is in the surface environment that spherule growth has taken place and been controlled.

[MarsIsImportant]

I think Mars is throwing us another 'monkey wrench'. It might be possible that longer range interaction between spherules was in effect in the recent past.

http://www.unmannedspaceflight.com/index.php?showtopic=4397

If the CO2 ice cap at the south pole only started forming within the last 1k years, then the Martian atmosphere must have been thicker in the recent past. This is a possibility that I never considered before. So the MER team might not be as far off the mark concidering distribution as they first might seem.

Back to your idea of a some sort of surface event creating the spherules. I don't see how; but let's assume that something did happen. That would mean a drastic change in the atmosphere of Mars in relatively recent times. The only thing plausible I can think of is some sort of volcanic event. But there are no known volcanoes anywhere near Meridiani. Is it possible that some massive hydrothermal event occurred? ...something so massive that the atmospheric temperature around Meridiani reached about 300 Celsius?

We now have good evidence of possible hydrothermal activity at Gusev. Why not a much larger network at Meridiani?
(I have my doubts like probably most others reading this. I'm just brainstorming).

Edit: One thing about the hydrothermal event idea is that it didn't have to happen recently to have created the temperatures necessary for the creation of the spherules.

[Kye Goodwin]

I just thought of another remarkable observation that the surficial spherule idea might help to explain. The MER team has estimated that about 2% of the total rock volume of the Eagle Crater outcrops is made up of spherules. Here is a pancam image from Endurance that shows large numbers of spherules clearly against a band of brighter rock:

http://marsrovers.jpl.nasa.gov/gallery/all...MIP2274L5M1.JPG

This high density of spherules is surprising somehow. It asks a lot of the proposed aquifer, which has to be at least as deep as Endurance Crater and without significant water movement in the MER team scenario. How has it supplied the concretion materials in sufficient quantity to the entire volume of rock? If the spherules are present only as a surface concentration then the large numbers we see are not so remarkable. It is a weak line of argument, but I thought it worth adding because I think it has struck many observers intuitivlely that the spherules are strangely numerous in this rock.

I think that there was a fork in the road very early in the interpretation of Eagle Crater that went by too fast and has never been revisited. At pancam scale, such as in the Endurance image above, one might imagine that the protruding spherules are stuck to the surface of the rock. When more closely examined with the MI it is clear that some spherules are embedded in the surface of the rock. From this observation the conclusion was reached that the spherules occur throughout the bedded sediments at densities similar to those we see at the surface. I think that this decision should be revisited. It is at this point that the paradoxes of the spherules distribution and relation to the bedding are created. If we remain skeptical that the spherules are present throughout the deposit, then the contradictions never appear. I think that for this reason alone the surficial spherule idea is worth investigating.