I've been watching this with interest but in silence (almost) so far. Doug, I understand why you are concerned - the discourse is rather one way. I would like to ask dburt (no fancy handles here) if anything at all has been gained by taking your ideas out for a spin on this forum? Have you heard it all before? If so, I think you should do us the kindness of withdrawing. We are not just here as hired devil's advocates.

BUT (and I hope this is the case) if in your view the discussion has been productive, i.e. has thrown up some new ideas, then I'd like to hear that. We are here I believe an open-minded and at the same time sceptical community, and I'd like to think we don't exclude ideas that challenge the consensus of the day unless we ourselves have the refutation to hand (as in the case of the water puddles). We don't just accept 'authority' - this is a separate court to the court of peer review, but I think it deserves respect in its own right.

Hope I'm not speaking out of turn . . .

I'd agree with everything you've said there Nigel.

Doug

Doug - I much regret if I have been giving the wrong impression. I have nothing but the highest respect for this forum, its outspoken members, and you as an exceptionally gifted and successful moderator. I've been reading this forum for years and I have always admired its free-wheeling debate on the merits and significance of various observations and ideas, including my own. I also have nothing but the highest respect for the MER team and all of its individual members, as highly trained, professionally distinguished scientists (else they never would have been chosen by NASA to be members of the team). If the MER team developed an unforseen problem, it was only that some of its members were perhaps TOO distinguished in their chosen fields (i.e., they may have been real HDPs, not total phonies like me). Nevertheless, they more than compensated, in my eyes, by placing all of the MER images and preliminary data interepretations on the web, thereby allowing all of us to see what we see and do what we do in close to real time. "Letting it all hang out" as they have been willing to do is perhaps the greatest breakthrough in planetary science ever, and I cannot praise it highly enough. I just cannot.

That's all besides the point though. My main point, as made in previous posts, and as some of you have politely made to me, is that when it comes to Mars, we all arrive wearing huge blinders. That is, we all have our biases and blind spots, derived from our professional and personal experiences, all of them so far on this planet, not Mars. My co-author Paul Knauth likes to say that Mars is nothing but a giant Rorschach ink blot, and that we all reveal ourselves when describing it. My biases are obviously drastically different from those of anyone on the MER team, owing to my background with volcanic surge deposits, and a long period of hopeless contamination with the ideas of ASU's late Robert F. Dietz, an iconoclast who spent the latter part of his life (once his ideas on plate tectonics had become scientifically acceptable) trying to convince other geologists of the importance of occasional large meteorite impacts in Earth history. My research specialties, other than the scientific study of mineral deposits, relate to the joys of exceedingly complex phase equilibria and crystal chemical interactions among minerals, so when it comes to Mars, many "pros" choose to dismiss me as an amateur, comparable to most of you. (And yes, I do have a mineral named after me.)

One other apology - science making, like sausage making, law making, and family feuding, is an extremely rough and tumble business, very different from its depiction in press releases, news stories, and freshman textbooks. It's also incredible fun, if you let it be. The way I have been speaking to you is no different (actually, far nicer - no use of "idiot" or "moron" for example) than the way we all speak to and of each other in the hallways of scientific meetings. I am deeply sorry if I have offended anyone with my unedited remarks or ironic sense of humor, or sounded patronizing, because that was not my intent. In compensation, I hope you have enjoyed this unique opportunity to witness and perhaps participate in a little of the real rough and tumble (and humor) of science. If you never think about a scientific press release or news headline in the same way again (e.g., "Scientists find cure for cancer"), then this little experiment in scientific communication will have succeeded. (Now in unison, class, all shout, "Show me the evidence!")

If I am allowed to continue on this forum, perhaps through mutual blinder removal we can arrive at original insights about what once happened on that utterly alien little planet, and have some fun doing it. Amateurs have always had an essential role to play in scientific discovery, and the modern science of geology itself is usually said to have been started by an amateur (Hutton, a Scottish physician). If not, it's been a real pleasure, and you all have inspired me to tremendous insights already. Thanks to you all, and thanks especially Doug for the chance (I was going to say opportunity, but ... ).

--HDP Don

Centsworth - Vague and wishful it is, you got me. I wasn't there. We're just observing the possible results, and trying to explain them (we don't get to do this experiment in the lab). My candidate for "other sticky condensate" would probably be some sort of early-condensing salt or concentrated brine, but I'm open to suggestion. A large variety of spherically-shaped condensates and accretionary lapilli characterize both impact events and volcanic surge deposits, and they all are believed to form in a manner similar to hailstones in a thunderstorm - that is, by condensation. They aren't necessarily the same composition as the rock around them. Tiny native iron spheroids (condensates) surround Meteor Crater, AZ, for example, and that wasn't even close to the size or potential chemical variety of a good-sized Mars impact. What may or may not have happened at Meridiani is still open to debate, as you know. My "innocent" starting point was that those suckers sure don't look anything like real concretions, but they do look an awful lot like tiny hailstones (i.e., condensates).

Most people, including me for years, have real problems with surge deposition doing so much work in such a short time. Our geological training biases us in exactly the opposite direction (processes that take place slowly over millions of years). Nevertheless, high temperature gas-phase processes can occur extremely rapidly, and condensation is one of those processes. Volcanic fumaroles can develop and change extremely rapidly too (they are basically roaring steam jets). To separate the tiny hematite flakes from the rest of the solids, an earlier post hypothesized that hematite condensation occurred in the hotter, gas-rich upper part of the cloud, and that the "hematite hailstones" worked their way down to join the rest of the solids once they had reached a large enough size. Also, condensation really only had to happen in one narrow zone of the expanding, cooling cloud, and after that hurricane-force movement could scatter spherules over the whole of Meridiani. But again, I wasn't there, and am open to suggestion.

Great questions, as usual.

--HDP Don

Kye - I appreciate your doing your own investigation of surges. Also I'm always glad to meet another fan of Occam. Regarding single particle layers, still not my field, sorry. Perhaps Prof. Demko can enlighten us? If not, I doubt if such claims for Meridiani are important to the big picture. (When all is said and done, those wonderful MER machines are still somewhat limited investigative tools. For example, their Pancams can't bend down to look at things sideways...)

--HDP Don

MarsisImportant - That's a quite long quote, and perhaps it should get edited out, but I wasn't sure where to begin - you have a lot of interesting comments to make. Regarding the apparent hardness of the Meridiani rocks, remember that Mars gravity is weak, the Meridani cliffs are visibly crumbling, and the wind appears to have carved them like a knife. So they can't be all that hard. The RAT isn't necessarily a good indicator, because it's going to be stopped by the hard sand, not the soft cement (would you want to rub your face with butter-cemented sand, as opposed to butter?) Also, I've walked across plenty of volcanic surge deposits that formed in the proposed manner (steam condensation), and they were all about as hard. For strength, the rock cement, in addition to the salt mixture, probably contains much of the dust in the cloud. That makes it relatively strong, so long as you don't add much liquid water. Remember that - almost no liquid water since it formed. (Magnesium sulfate, apparently the dominant salt at Meridiani, is the most water soluble of all the common sulfates.) By our surge hypothesis, everything was once moist (or "wet" if you will), but never more than that - it never saw large quantities of liquid water, or it would have fallen apart. The MER team gets around this objection by special assuming that all of their hypothesized brines fortuitously were saturated in all of the salts present, but they apparently forget that even then, all of the soluble salts should recrystallize into large crystals (put some fine table salt in jars, add various amounts of water, and come back in a month - let me know what you see). I may have mentioned this in a previous post - I'm losing track now...

Regarding self-contradiction, in terms of the possiblity of torrential rains or blizzards, I was talking about the height of the great bombardment, that could be sampled very deep in the section, not the very tail end, that has perhaps been sampled at Meridiani at the top. (Because layered rocks are always deposited from the bottom up.) By then I think Mars had largely reached its present cold, dry state, as mentioned previously.

On Earth, low areas can easily gain great elevation, owing to plate tectonic processes, but on Mars, I doubt it, unless you intruded a huge body of molten rock underneath, and rafted things up. There is little evidence of such a process. You can erode off the top, to a certain extent, and fill in low spots, and build extremely tall basaltic volcanoes, which need to be gravitationally compensated via extemely broad and gentle warping elsewhere, and accumulate polar ice caps, but that's about it offhand (I'm probably leaving something important out, although I'm including glaciers and outflow channels in the above).

Capillary action of migrating salts combined with dune accretion on sticky surfaces might indeed eventually form and preserve sandstones - a thoughtful suggestion - but they would not contain spherules. It was the spherules that first made us think of impact. Also, in terms of "incomplete water record" I would instead argue at this point that we have "no water record" at all in terms of liquid water - and I have spent much of my professional life looking for indications of the passage of liquid water in mineral deposits. I agree that exposures deep in Victoria may change that, but I'm not optimistic.

The critical way that the MER team changed their story between 2004 and 2005, apparently in response to our impact hypothesis, was to admit that the highly improbable (in terms of evaporation) mixture of salts must have been transported from somewhere else. Why did one of them publicly deny that change in 2006? I don't know. Perhaps because the putative "playa" had by then logically lost its home at huge Meridiani, unless the depths of Victoria reveal some highly distinctive lake beds, not seen in any ejecta. In terms of what they originally considered, I have been led to believe, possibly erroneously, that they considered only volcanic surge, not impact surge, as a possibility for the cross-bedding and spherules (in part because a person they consulted was my co-author Ken Wohletz). I freely admit that I am trying to poke holes in (or "belittling") their arguments - that's the only way science can advance. Please feel free to belittle mine - that's what I'm here for. I won't take it personally. (And even if I did, what could I do about it except get banned from this forum?)

I fully agree with you that today's Mars is dynamic and geologically active. That's part of its excitement. My personal prejudice, which I have certainly made no secret of , is that most of the really "heavy lifting" got done billions of years ago by impacts. Most Mars scientists agree that impacts and wind are the dominant processes affecting the entire surface today, and seem to have been for a very long time. And impacts may provide the real "bursts" to which you refer in terms of active processes.

Thanks for helping me clarify some of my ideas. I much appreciate it.

--HDP Don

Dburt,
I've had a few nagging questions on the impact surge hypothesis:

1. How can an impact surge explain berry multiples where the berries are not the same size? See, eg

http://marsrovers.nasa.gov/gallery/press/o.../20040312a.html

My thoughts are that if the berries meld together on the ground, then they should have all fallen at about the same time, and therefore should be the same size.

If the berries melded together in the air, they should also be the same size, for the above reason, except moreso.

Also, the chance of them forming a straight line is very slim by impacting one another in a cloud or on the ground.

2. The ground is currently covered in blueberries, at least around Eagle and Endurance. If the berries were caused by multiple impact surges, where is the record of the previous lag deposits? IE, there should be occasional layers of berries in the outcrop, corresponding with time between impacts where erosion extracted them from the deposits, yet we don't see any.

Yes, but... the rocks at Gusev are all dense basalts (as can be observed empirically and also inferred from dozens of different sensor measurements), and *they* have also been carved by the wind, like a knife through butter.

Doesn't matter how hard the rocks are or how thin the air is -- if you blow on rocks with wind for long enough, you get aeolian erosion. Doesn't matter how dense or light the rocks are.

-the other Doug

Good point "the other Doug".

I'd also extend this idea to point out that the cliffs at Victoria are still there after billions of years. The mere fact that they are still there is a good indication that these layers are hard indeed.

The point that the Professor made about not being able to tell the hardness from the RAT tool is not accurate. Yes, you can determine the relative hardness from the rate of the RAT digging into the rock (at least to within a certain parameter, not exact but we don't need exact--just relative). And the MER team can determine a relative standard of comparison from Gusev. Spirit has found a variety of hard and soft rocks. The soft rocks at Gusev may correspond well with what the Professor has talked about; but the layered rocks at Meridiani are much harder than those soft rocks at Gusev.

As for the weight of the rover on Mars being a lot less because of less gravity, that point is well taken. But I had accounted for the less gravity already. The rover is still relatively heavy and should have made some kind of mark on the underlying layered deposits, if they are as soft as he suggests. Given the uncertainty factor, I pointed out the RAT tool evidence as confirmation. But if that was not enough, then the view of Victoria crater should be. Either the soft rocks are much younger and Victoria is NOT billions of years old; or the relatively HARD rocks are old and Victoria is billions of years old. You cannot have it both ways. If the layered rocks were soft, then billions of years should have eroded the crater to look more like Erebus. The possibility that the rocks are soft and Victoria is relatively young has drastic implications that destroy many of the assumptions that the Professor holds dearly. For that matter, it would also destroy many of the assumptions that the MER team has operated with too. My point is that I don't think any of us "want to go there".

dburt - A repentant Prof Burt !! A tear just rolled down my cheek. Where was this quality when you were grading Igneous Petrology papers back in our youth ?

I agree with your statement about personal bias, you’ll see what your comfort level allows you to see. For me the bias is groundwater/aquifer geochemistry. So from a 50,000 foot view the MER team account of a paleo-regional groundwater system at meridiani with an extended diagenetic history has some merit. Obviously the story gets complicated as the resolution increases but that may be a hindrance at this time - we see only the tree in the proverbial forest in terms of rock geochemsitry. Granted, the devil is in the detail, but given our inexperience with >3 byr old terrain, I suspect we have overlooked a detail or two.

If water was retained within the sediments for even a fraction of the rocks proposed age ( >3 byrs) the potential for diagentic alteration is endless - interaction or mixing of different aquifers, dewatering of the aquifer, aquifer recharge with different water type, volcanic gas flux, impact, surficial water infiltration, etc. In other words, throw out those mass balance models for now and you’ll sleep better at night. Finally, the geographic coverage of meridiani is great but certainly in line with the areal extent of the High Plains aquifer that underlies parts of eight western U.S. states. Size alone should not an obstacle for an exhumed aquifer at meridiani.

Details, details. A major reason why I have become convinced that the impact-surge hypothesis is realistic is that the rough fit with Mars is so excellent. Huge impact craters are the single most prominent feature of the Southern Highlands from space. They are clearly ancient and yet have been preserved, a fact that makes it very likely that the inter-crater plains are still covered by their ejecta. Land in the highlands and you are very likely to see ejecta. Outside the volcanic areas impact ejecta should be the commonest sort of material. Mars craters over a certain size (roughly 5 km diameter) often produce a continuous ejecta blanket that suggests fluidized emplacement, and the indications of fluidization generally increase with crater diameter as does the trend to produce double and multiple layers of ejecta.

The large-scale regularly-layered landscapes visible from orbit have been especially difficult to understand. Really there has never before been an explantion that seemed better than barely possible. The brine-splat authors have made this connection, but only in the most general way. I am glad to read that Doctor Burt is not shy about conjecturing and I am hoping that he will be willing to write something more for us about how impact-surge might explain the widespread large-scale layers.

Well, since conjecturing is in play. Another possibility is that the Late Heavy Bombardment is not the only evident heavy bombardment that occurred. Just conjecturing and brain storming but (and I have my doubts about this) maybe Mars records multiple and even later bombardments which we have not accounted for yet. Perhaps our solar system was relatively recently much more like Tau Ceti is now. Then the question becomes what event changed things here. It's a huge "can of worms" that crosses many disciplines.

Perhaps instead, many craters were secondary and tertiary products from a late planetary type impact. Or possibly the large Volcanoes on Mars created such large explosions that many projectiles created crater impacts all over the planet. If that is the case, then terrain that seems very old may not be nearly as old as it first appears. Again, 'a monkey wrench' is thrown into our original thought processes. And again, I have my doubts about these issues I'm bring up in this post.

The problem with positing a series of heavy bombardments, dating up until fairly recent times, is that we don't see a record for such a bombardment on Earth or Luna. While it is possible, I suppose, for bombardments to be set into motion that only affect a certain portion of the local neighborhood, I'd imagine that a heavy bombardment which would affect Mars would also affect Earth/Luna, and probably Venus and Mercury as well.

There have indeed been models put forth to explain the LHB in terms of migration of major outer planets -- the one I can remember best suggests that Jupiter originally formed farther from the Sun than Saturn did, and that as it migrated closer to our star it tossed Saturn further out and disrupted whatever rocky body (or bodies) occupied the orbital neighborhood that now lies between Mars and Jupiter. This disruption caused a great deal of the mass located in what is now the Asteroid Belt to fall towards the inner system... and smash into any inner rocky planet or moon that stood in its path.

Yes, there could have been other less major disruptions that could have caused a lot of the debris in the current Asteroid Belt to have meandered in towards Mars' orbit. But even without detailed mathematical calculations, my gut feeling is that anything that would have caused a major bombardment on Mars should also extend itself in towards the rest of the inner system. And the problem with that is that the most recent of Luna's large craters seems to be on the order of 100 million years, and those are very scarce. The shoulder-to-shoulder large crater structures on Luna are all of an age, and that age is somewhere around 3by ago.

Remember, the LHB resurfaced much of Luna, and from the looks of it, resurfaced much of Mars, as well. The same thing happened on Earth, of course, but Terra has effectively resurfaced itself many times since then and the crater remnants of the LHB are almost all gone by now.

I just don't see any way for a major disruption to pull enough mass in towards Mars to create a major bombardment and yet not toss enough of that mass in to the inner system to leave a record on Luna. I guess I'd say it's possible but extremely unlikely.

-the other Doug

That's why a more local event particular to Mars is more probable, such as one huge planetary impact. Debris could have been thrown into orbit and it fell to the surface much later. Perhaps the moons of Mars are remnants of such an impact.

One more big 'monkey wrench' that is not conjecture has been reported in the last couple of days. Mars Express has found a lot of clays on Mars that could Not form on the surface with much CO2 in the atmosphere. That highly suggests that the ancient Mars atmosphere was far different than anything we so far assumed.

http://space.newscientist.com/article/dn12...early-mars.html

The headline of the article makes an assumption. And that assumption is one of many possibilities. First of all, these clays were made. And they must have been made in the presence of water without CO2. So some major event or events changed things substancially on Mars.

Hey, along with a childlike curiosity about the wonders of the universe goes a childlike tendency to mock any authority that is perceived as foolish or pretentious. Call it a dangerous occupational hazard of scientists. In any case, feel free to mock my ideas all you want.

--HDP Don