On the Road Again - volume 5 - Page 8

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Author Message
LWS


Posts: 3062

Reply: 141



PostPosted: February 15, 2010 11:12 PM 

Serpens; Re. your 139, I remember those berries from the early trenching exercises. They were very few of them and they did indeed look fresh and blue in my composites. At that time I had concluded that they might have rolled down into the trench from the surface, especially since we all thought that there was a uni-layer of berries on the surface as was implicit from the disappearance of berries under the bounce marks at Eagle crater; the often quoted desert pavement effect that led to this uni-layer and, also, the early trenching operations that showed very few berries below the surface. Now, I'm not so sure, after Purgatory which inadvertently showed several layers of berries below the surface layer.

But I think the possibility still exists that they were indeed strays from the surface somehow wiped clean by the trenching action.

Pristine / polished / from the sub surface / together sounds like it was impossible for them to be coated with Martian desert varnish and these berries should not have retained a sheen after having been eroded from rock unknown ages ago. However, I thought that a possible rationale for this might have been that there was a water economy which cycled miniscule amounts of water just below the surface and could have been involved in keeping berries which would have been polished while on the surface still polished while they were under the surface.

Re. eroded berries which still retain their spherical shape. I've often wondered about the dynamics of the winds that erode small spherical objects on the surface of Mars and leave them still with a spherical shape. I am more in tune with berries being broken in two or four along clearly defined split planes and showing their innards; with berries eroded in some manner that leaves only the berry shell that one can look through and see nothing inside; with berries almost totally encased in evaporite "glue" and just peeping through, with the presumption being that they were being eroded out of their popcorn casing rather than that were trapped for Oppy to image them in the process of being encased at this time; etc.

But I think you are on the right track. If it were deemed important someone should check back through the images of berries and correlate where they came from as against the degree of "putative varnish" to get better data. Indeed it may be of some importance in aiding us to determine what the berries really are.

Winston

hortonheardawho


Posts: 3465

Reply: 142



PostPosted: February 15, 2010 11:21 PM 

sol 2140-2153 super 3D of Barsoomer's rock of reply 140:


Not a clue.

LWS


Posts: 3062

Reply: 143



PostPosted: February 15, 2010 11:33 PM 

Hi Barsoomer; Re your 140. The rock looks much less forbidding in colour. Here's my colour composite of the image

Original Size here

There seems to be a lot of the fracture fill or impact meld on these rocks. Some of it contributing to the somewhat gruesome appearance in Black and white.

Winston

LWS


Posts: 3062

Reply: 144



PostPosted: February 15, 2010 11:46 PM 

Hi Hort; Didn't see your 142 before I posted my #143. Great 3D as usual. Many of the nearby rocks seem to have that "impact meld" surface layer. There is also one rock which has 2 or 3 distinct fracture fills which must have predated the impact. That would be a good one to get a close-up of.

Winston

Ben


Posts: 2270

Reply: 145



PostPosted: February 16, 2010 12:25 AM 

IMO THe age of any berry that is not firmly attached to the host rock is highly questionable.

It could have fallen out yesterday or a million years ago.

Wouldn't any coated berries, on stems, attached to the host rock be those that have been exposed the shortest time?

Have we seen any that were coated?

Ben


Posts: 2270

Reply: 146



PostPosted: February 16, 2010 12:32 AM 

Hort; Your #142; IMO it looks like the remains of conduits that carried the subsurface fluid which deposited the fracture fill.

Serpens


Posts: 169

Reply: 147



PostPosted: February 16, 2010 2:15 AM 

Ben, Yep. I have been looking for rocks with domonstatable fracture fill. Most seem tp have parted along pre existing fractures on impact - as would be expected, leaving the fill exposed. But there are some with fracture fill within the rock and 143 seems a perfect example of a filled vein leading to a fracture fill.

I don't see any avenue for there to be both impact melt and fracture fill, looking identical, at this site.

Barsoomer


Posts: 344

Reply: 148



PostPosted: February 16, 2010 11:44 AM 

Looks they have given the rock of reply 122 the full treatment in today's pancams. L4-L6 and R4-R7.

The rock looks like it may have something like bedding fibers in a roughly two-dimensional array instead of bedding planes.

Thanks to Winston and Horton for their enhancements of the other weird rock, and Ben and Serpens for their explanatory comments.

Bill Harris


Posts: 72

Reply: 149



PostPosted: February 16, 2010 11:46 AM 

Many, many interesting rocks in these views. And this is just the first stop here! It'll be great to get to the SE of the crater where most of the ejecta was cast.

--Bill

LWS


Posts: 3062

Reply: 150



PostPosted: February 16, 2010 12:07 PM 

Some more pancams came down today on Exploratorium. We are now seeing more rocks with some very interesting features. Some surfaces on some images seem to suggest a process that does not look like fracture fill. Why not impact melt?


Original Size here



Original Size here



Original Size here



Original Size here


Look at the original sizes

Winston

Bill Harris


Posts: 72

Reply: 151



PostPosted: February 16, 2010 4:05 PM 

We're seeing more examples of this "fracture fill" as we Pancam around. It makes sense that we usually see one side of the fill, that is where a soft rock, already "weathered" along a fracture, would part. We've seen examples elsewhere of what it looks like in a fracture (making rock hedges), now we see it in another aspect. I think we'll get a view across a fracture. I don't know what to expect of the fill material mineralogy. The usual fracture fill forms deep with hydrothermal fluids moving through the fracture. I look at this as a low-temperature, shallow groundwater deposition in the fractures. Depths on the order of meters and not kilometers. And what could crystallize out of groundwater passing through a rock composed of magnesium sulfate, etc, which has to be way up there on a solubility scale.

I don't see an impact melt. Not enough energy in a 2-3 foot rock making a 30 foot crater to melt anything. The constituents of the evaporite-- silica and kieserite respectively melt at 2800*F or decompose below that temperature, the minor constituent, hematite, also melts at 2800*F. If there was enough energy to melt the rock, I have no idea what would result from the melt of silica, hematite, magnesium vapor and whatever the SO4 would disassociate into. And then, since it would be draped over the falling ejecta, quenched.

Mars is an odd place.

Speaking of odd, we've taken berry-stems to a new level. This rock shows berry-umbrellas:

Imagine that.

Digging around on fracture fills, I can across this reference to (apparently) a low-temperature fill connected with methanogenic bacteria. We may have to dig around for the full paper, but this ref is a beginning. Just a thought.

http://www3.interscience.wiley.com/journal/118928784/abstract?CRETRY=1&SRETRY=0

--Bill

Barsoomer


Posts: 344

Reply: 152



PostPosted: February 16, 2010 4:35 PM 

The rock in reply 151, seen in color in Winston's reply 150, looks like it has a chunk torn out of the top part. If we could identify that chunk in the other ejecta, it might be illuminating. The shape of the cutaway is somewhat reminiscent of the Canuba Beach rock.

MPJ


Posts: 250

Reply: 153



PostPosted: February 16, 2010 4:57 PM 

Bill, I think impact melt as of molten ice (ground ice) is what they refer to - at least it would be more likely. Larger rampart type craters nearby Opportunitys roving grounds as well...

Bill Harris


Posts: 72

Reply: 154



PostPosted: February 16, 2010 5:07 PM 

"looks like it has a chunk torn out of the top part. If..."

Actually, it looks like a solution cavity. As does the fractures to the left and below it.

--Bill

Barsoomer


Posts: 344

Reply: 155



PostPosted: February 16, 2010 5:19 PM 

Wouldn't a solution cavity appear smooth? The one I am referring to has ragged edges.

LWS


Posts: 3062

Reply: 156



PostPosted: February 16, 2010 6:55 PM 

Ben, Bill, Serpens, MPJ;

I think it is reasonably well established that there is a possibility of significant ice just below the surface at meridiani. In addition the top surface has been estimated to contain up to 5% water mostly held as water of crystallization bound to salts. The ejecta stones surrounding Concepcion could not have come from deep underground layers representing conditions of billions of years ago but only from relatively shallow subsurface areas since the crater is a relatively shallow one.

In the light of the above could you explain why it is unlikely that at the time of the impact water could have been flowing through the "solution cavities" and other crevices unearthed by the impact situated not too far from the surface? In other words is it totally impossible that berries could have been actually forming in some of these crevices as lately as the period of the impact?

Also, I take it that the consensus on this board is that classical impact melt cannot explain the surface features we have been seeing through Oppy's images at concepcion while NASA seems to be sticking to their guns that it is indeed impact melt. Could there be some differences in the interpretation of impact melt? Why would some somewhat irregular surfaces that do not appear to have been joined to other rocks and are now coated in the peeling, mysterious texture be considered as fracture fill? Could impact melt include a relatively low temperature effect on the exposed surfaces of rocks which do not go to the full extent of melting those surfaces but merely modifies them in some way rendering them more susceptible to swift erosion on exposure? Could the "impact melt" here be actually impact modified rock surfaces rather than melting of the surfaces?

Winston

Barsoomer


Posts: 344

Reply: 157



PostPosted: February 16, 2010 7:14 PM 

[link]

Quote:

This rock has a thick, dark-colored coating that is interesting to scientists because many of the rocks in the surrounding area have the same mysterious dark stuff. The coating could be remnants of a layer that was changed by the action of water and weather or, it could be a layer of rock that melted when a meteor (less than a foot across) impacted Mars, ejecting this rock and others and creating the crater "Concepcion". Knowing its origins will help them understand the history of Mars. Opportunity's mission is to figure out the "ingredients" of this morsel by studying the chemicals in it.

Ben


Posts: 2270

Reply: 158



PostPosted: February 16, 2010 8:39 PM 

I have never examined impact melt up close so I am no expert; but
As Bill says, the size of the impactor would not be expected to melt rock,
Subject material here seems to be exclusively on VERTICAL rock faces (fractures).
Melt would be more randomly distributed on different surfaces including planar.
Apparently melt is very often associated with impact breccia ,of which, I haven't see any.

serpens


Posts: 169

Reply: 159



PostPosted: February 16, 2010 10:07 PM 

LWS, Impact melt is the result of an instantaneous increase in pressure above say 70 GPa. (Some 10 million pounds per square inch). I cannot see this forming a nice laminated melt and leaving the fragile underlying rock pristine. Pressure sufficient to cause melt would have destroyed the underlying rock. I haven't seen the term used by the science team and I take the PR updates on the MER site with a pinch of salt. If Squires etc state 'impact melt' then I think we may start questioning our assumptions.

Most of the fracture fills seem reasonably thin which would seem to imply a short term event (or possibly minimal water wicking up from a lower groundwater table over a long period). The fill at post 142 seems much thicker. Could this imply that it came from a deeper layer? The concept that these fracture fills are caused by atmospheric vapor exchange just doesn't fit the image at the tip of Cape Verde that showed that the fill went very deep.

Bill, In a wicking scenario wouldn't this be a saturated solution with a neutral ph? So we would have ions of magnesium, sulfate, with some iron and who knows what else all wanting a home. Outside my comfort zone. I haven't been able to find any data on the composition of previous fills although they seem to have a false color signature similar to the berries which could imply hematite content.

Mars is indeed a strange place, but I believe in Ben's assessment. The processes on Mars and Earth are the same. One is just much slower.

LWS


Posts: 3062

Reply: 160



PostPosted: February 16, 2010 10:49 PM 

Hi Barsoomer, Ben, Serpens; Thanks for the comments. It would therefore appear almost certain that;

Impact Melt is highly unlikely to have produced the flaky "skins" on the concepcion rocks.

Moisture exchange through the wicking of miniscule amounts of water through crevices and cracks in the rocks is also unlikely to be the cause but is not ruled out

Winston


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