Remember they laughed at Galileo, they laughed at Albert Einstein and they laughed at Bob Hope.

Good questions. 1) Growth in a turbulent cloud does not mean they all have to be the same size - they just should not exceed a certain size (more mass than the cloud can support). If three spherules happen to stick together during growth, and are spinning about a common center of gravity, then they should tend to line up, and also be smaller than the largest spherules (so that their combined mass does not exceed what the cloud can support). That seems to be the case here. (BTW, can you imagine how tired I am of seeing that one triplet photo as "typical" of all the millions of spherules out there?) Actual concretions growing in rocks tend to merge together in nodular masses at random orientations, semi-random sizes, semi-random shapes, and random numbers of berries, up to dozens or many hundreds. I am still waiting to see such a feature (that is, wherever the spherules are densely packed together, they are still entirely separate entities). As you mention, another way to line berries up might be after deposition, if they land lined up along a pre-existing crack, and then develop salt encrustations that "glue" them together. No evidence of that here, though.

2) I have no idea at this point how many impact surges might be represented in rock exposures at Meridiani, or what the time interval was between impacts. If there were a Meridiani-like lag deposit on the ground when the second impact surge arrived, it would almost certainly be scoured away and incorporated into the new surge cloud. In that manner you could spread spherules across a much wider area that that originally covered, and that may have happened across parts of Meridiani (just look at all the spherules spread around by Victoria Crater).

Thanks for the great questions. Keep'm coming!

--HPD Don

MarsIsImportant - What can I say? I've never hammered on a Mars rock. The terrestrial surge deposits I've examined vary considerably in their hardness, but you generally need a rock hammer to break them. Nevertheless, they're softer than basalt (many are kind of like adobe). If the wind has only eroded 10 meters or so of Meridiani outcrops over 3.8 billion years, that probably has more to say about the ineffectiveness of wind erosion on near-vacuum Mars than it does about the intrinsic hardness of the rocks. Also, the impact surge hypothesis, unlike the vanished playa lake hypothesis, does not require Mars to be any different than it is today, so the topmost surge deposits could be considerably younger than 3.8 billion years, and still look the way they do. At Gusev, the various larger basalt pieces on top could well be impact ejecta of almost any age. Without any time calibration, further speculation trying to relate hardness to amount of erosion would be pointless, IMHO. Thanks for the discussion, though.

--HDP Don

I appreciate your honestly. You don't know how many impact surges were needed to create Meridiani.

If the new impact surge scoured the ground and incorporated the previous deposits, then many layers at Meridiani would be missing. Also, the layers themselves should be a lot thicker than appear.

Instead, Meridiani shows thousands upon thousands of very thin layers. In my mind that suggests more like seasonal dust deposits. Doesn't it make more sense that the dust storms that we see every two years on Mars deposits the thin layers? When water was available, then the dust was cemented. That process stopped a long time ago; but the seasonal dust storms continue. If this layering process occurred over a very long time, then it is possible that surge clouds of some sort might have created the berries--I don't know. But I still think that the groundwater significantly altered these rocks.

Regardless, your hypothesis does not account for the vugs found at Eagle crater. You asked where were the crystals. But they found the cavities where crystals once were. Then, the crystals later dissolved again in solution and the salts carried away by some presumed liquid. It's possible that all the evidence is really from groundwater or brine of some sort at various times in the distant past. Perhaps aeolian processes excavated large parts of Meridiani. But that would suggest Victoria would need to be more recent of an event (I doubt it).

When we have a known process for deposition--the dust storms--why would we need another one, especially when the known one would create the fine thin layers that we see? I don't understand why we need another process when lithification of these layers through groundwater is perfectly plausable.

You point out the concretions are not what they seem to be. Ok. They might have been formed by Volcanic surges tool Couldn't they have? You stated yourself that we have no good examples of impact surges. Even you are using Volcanic surges as a standard. If memory serves me well, even the MER team has been open to the possibility of some sort of volcanic activity nearby. Perhaps the berries are not concretions but a result of periodic volcanic activity. But I don't think the dust layers are a result of the surge mechanism you propose. A series of surges would simply not make such fine layers.

You haven't hammered on the rocks at Meridiani; but NASA has. You are forgetting that parts of the space craft slammed into the Meridiani surface and the heat shield was examine by opportunity. The impact barely made a dent into the surface. We can easily calculate all the forces involved. In does not take much to realize that the surface rock layers are very hard. They must have been cemented together by water over a long period of time.

Other Don - That's all well and good, but many things are theoretically possible (including little green men, perhaps). Just show me the evidence, please. More to the point, are there any features at Meridiani (or Gusev, or any of those many other salty layered deposits all around the Mars highlands) that CAN'T be accounted for by the impact surge hypothesis?

Thanks,

--HDP Don

Forgive me if this has been asked & answered earlier, DB, but how fast would blueberries be expected to form in your scenario? I have a hard time imagining that the 'splat' conditions would persist long enough to let them form via accretional processes, and frankly they just don't look like tektites or another form of melt product to me because of their symmetry and those weird little bumps some of them have (which seem to be more common on berries in protected locations; maybe they get weathered off of the surface berries due to rolling around by the wind?) The spectrum of sizes at different locations is odd as well, and seems to argue for a more gradual formation process. Has there been any sort of detailed morphological analysis of them?



Yeah, but for truly enduring comedy you just can't beat Hoaxland... ...how the hell does he get out of those straightjackets so fast?

Sorry, I have trouble quantifying "very hard" and rocks generally don't "dent" unless they're squishy mud or hit at hypervelocity, forming an impact crater. Also, if the grains were cemented together by water over a very long time, were there any cements available other than the abundant sulfate salts that we see? If not, how would that salt cement make the rocks harder than the surge hypothesis would account for? In fact, why weren't the basaltic sand grains simply altered to "soft gunk" (crystalline clays) if they were soaked for so long in liquid water? None of these problems seem to occur with "Boom!" (at least as I see it in in my admittedly biased way). Thanks for the good discussion.

--HDP Don

MarsIsImportant - I'd really prefer it if you could give me one question per post, rather than this stream of consciousness type of questioning. Much easier for me to try to answer, and much easier for people to read. Thanks.

Regarding missing and thin layers - the exposures in Endeavor are very limited, and haven't been matched yet with exposures in Victoria. Besides, the scouring in a given area would probably be fairly uniform. Each cross-bed represents a scouring episode, but probably just owing to turbulence in a single surge cloud. Surges have no problem building up numerous fine layers in a single episode, as covered in previous posts. Also, the Meridiani material seems to be mainly sand, not dust.

Regarding the crystal-shaped vugs - the impact surge hypothesis accounts for them just fine, if they represent a former chloride mineral. Chlorides are much more soluble and also subject to frost leaching (owing to much greater freezing point depression) than the surrounding sulfates. Minor post-depositional drainage or frost leaching also accounts for why the chloride content seems to increase with depth. This was covered in our original Nature paper from 2005 (attached to a previous post).

Regarding possible volcanism - as covered in a recent post, the MER team early on dismissed volcanism as a causative agent for the cross-bedding and berries, and we have never disputed that finding (although others have).

Remember, not so many different questions per post, please. Thanks for them though.

--HDP Don

Ok. Hardness doesn't matter. I only keyed on that issue because you stated that the layered rocks at Meridiani were soft. So it is Not a problem for either theory or hypothesis (whatever you want to call them).

I still have a big problem with the thickness of the layers. The thin layers observed, support the MER team's hypothesis.

Nprev - Good question, but I can't answer it. I would expect a time of something from minutes to hours, depending on the size of the impactor and where in the cloud they condensed. If they grew in a mushroom-shaped cloud directly over the impact site, that might give them longer and allow them to grow larger, but then a second nearby impact might be needed to distribute them over wide areas in a surge cloud. On the other hand, the mushroom cloud itself might eventually gravitationally collapse as it condensed and cooled in the very thin atmosphere (like a downburst in a thunderhead cloud), and form a surge deposit on top of an earlier blast surge. Pure speculation at this point, I'm afraid.

Rolling along on the ground owing to the force of the surge cloud certainly seems possible, as mentioned in a previous post. Rolling owing to the wind, not observed. For me the only key observation about the spectrum of sizes is the strict size limitation at about 5 mm. Condensation-related impact spherules are entirely different from the shaped splash droplets called tektites, as covered in a previous post. I don't offhand know of a detailed morphological analysis, but would be surprised if one had not been done, perhaps by someone in another forum.

Keep'm coming, but I may not get to them for awhile.

--Don

Howso?

--HDP Don

P.S.: Sorry, I'll take pity on you - I think the thinness of the layers has already been discussed in numerous previous posts, as not being particularly diagnostic of either of the suggested processes. I just wanted to see if I could actually make a one-word reply, for once I dood it! HDP Don

The MER team ruled out Volcanism as a causative agent for the cross-bedding and the berries. The wording is important. This does not rule out the possibility of volcanism providing the heat necessary to have the liquid water given their hyposthesis.

One of the problems you seem to have with the MER team hyposthesis is that Mars has been a cold dry place for billions of years. Well, we now know that there was plenty of H2O around. But was it in the correct state? The current atmosphere suggests "No". But now we know that the atmosphere must have changed drastically over the billions of years, because the massive amounts of clays found by Mars Express cannot be formed with CO2 predominant in the atmosphere. The ancient atmosphere of Mars was not of CO2. As far as we know, the atmosphere could have been a lot thicker and supported liquid water on the surface at one time. We cannot be sure one way or another yet. But if we believe the MER team, the answer is highly suggested to be "Yes". Liquid water on or near the surface is the basis for their hypothesis.

From the beginning, I have not ruled out the possibility of impact surge contributing to the geology of Mars. I just don't believe it was predominant like you suggest at Meridiani. I don't know how you could convince me otherwise.

Your best argument seems to deal with the berries themselves. But their differing shapes over most of the terrain observed by Opportunity seems to be a problem (frankly, for both hypotheis). They have been completely round until we approached Victoria...yet not exactly round near Victoria. Why? How does the shape or change in shape fit with your impact surge hypothesis?

...because of the seasonal dust storms creating the mechnism for such layers. I already explained that.

Just one last comment on the relative softness of the rocks on Mars:

There is one other measure of the hardness of the rocks that hasn't yet been mentioned. The RAT on Spirit wore out considerably faster than has the RAT on Opportunity. The RAT cutting edges were identical on MER-A and MER-B, so there is a quantifiable and measurable amount by which the rocks at Gusev are harder than the rocks at Meridiani. (I believe some estimate of Mohs scale was made for the various rocks that have been RATted, based on the amount of electrical power required to make the observed cuts. I don't know where I read that, though, and so I can only offer it as a piece of potential apocrypha.)

My own take on it is that the Meridiani rocks are probably pretty friable when you apply pressure cross-layer. But the way those layers have cemented give the rocks a fairly decent load-bearing strength when you apply pressure along a layer's plane. In other words, it's like plywood -- you can easily crumble off the edges, but sit on a slab of it and it won't tend so much to crack and crumble. Or, to sound like I know more than I do, the material's axis of greatest strength is planar and alined with the layers...

The very few surviving blocks of ejecta made of this material show preferential erosion cross-layer, as well. An ejecta block with a flat, contiguous layer for much of an exposed face appears to erode selectively along its non-planar faces. This would tend to support that the material is stronger (i.e., more erosion-resistant) when force is applied perpendicular to the plane. However, the rather noticeable lack of extant ejecta blocks from this material, as well as the "ground-down" condition of what now look like flat pavement slabs at various places in this unit, also speaks to material that is soft and relatively easily eroded.

-the other Doug