On the Road Again - volume 4 - Page 13

Sol 2140 false color detail + saturated color of very, very interesting area in the crater on the south rim:

Er, the "bluish" stuff seems to be associated with a particular level.

A water level of some sort?

OK, IF the cratering event cracks the bedrock deep enough to reach the subsurface water-ice ( don't tell me ther isn't any! ) THEN for how long over a thousand years could water escape to the surface and alter the surrounding rock? Just sayin'.

Hort;

From Eagle Crater until now that blue discoloration around fractured rocks at the edges of craters in Oppy's false colour images has been evident and standard. I've pointed them out several times without being able to get anyone to discuss what could actually be causing them. Your linking them to cracks in the bedrock and putative escaping moisture from subsurface ice and thereby chemically altering the fractured rock edges extends the dimensions of this observation as I only suggested that water was somehow involved in the phenomenon.

I think that the phenomenon is a current ongoing one. That water, perhaps in miniscule amounts but sufficient to catalyse certain chemical reactions, has continuously been involved in the development of berries in those bluish areas that are also present in the microchannels and on the cracked surfaces of the pavement rocks seen between craters as well.

I think that the evidence of fracture fill around many of the craters that Oppy have visited relates not to a process that was completed eons ago but one that is ongoing.

That current water has not been discovered by Oppy's instuments in the areas of high berry prevalence at the rock edges and on the surfaces of pavement rocks would then be merely due to Oppy's instruments not having the capability to identify water, not that water isn't there at certain times.

The huge number of berries seen in layers in the broken ejecta rocks are merely records of the surface from millions of years ago that has become covered by alternating layers of dust.

I don't think the berry making process stopped billions of years ago.

Winston

Here is an earth- biased view.

The fracture fill and the dark MN ? rich dust are closely related.

The fracture fill occurred billions of years ago below an active water table,probably several meters below the ground surface. At that pre-erosional time, the ground level was an unknown distance above the current surface.

Exposure of the filled fractures by eons of erosion has resulted in the disintegration
of the dark fill material and its resultant dispersal by the relentless winds.

Where the fracture fill has been exposed by recent impact (as in this case) it has suffered very little erosion and much can still be seen attached to the host rock.

The limited period of erosion has allowed the resulting dust to accumulate around the source fractures and only after a long period of time will most of it have been worn off during which time the winds will have dispersed the dust so it will look like older impacts.

The blue stuff with a life of it's own? I think it's hematite dust. Very fine, derived from the blueberries, specific gravity double of other minerals present and shows up BLUE in the pancams. It's pervasive, looks like it "flows" around rocks (see Endurance and Victoria, or any other crater for that matter). Since it is so dense, wind tends to concentrate it in "still" areas.

At Erebus-Olympia, the Overgaard site, the hematite dust was observed to slump and flow:

1P186861178EFF64KCP2585L7M1 Sol 652

1P186064185EFF64KCP2422L7M1 Sol 661

Ther emay be some deeper story behind this stuff, but I think "it's just a rock"...

I had couple of animations of that, let me dig them up or recreate them.

--Bill

I think you are spot on Bill in identifying the 'blue' material as hematite. Not sure about berry erosion as the provenance though. McLennan identified that only around half the hematite in the outcrops was in berries, with the rest being dispersed throughout the outcrop material. It would seem more likely that the hematite dust eroded from the fragile and impact fractured bedrock material, and as you say the higher SG hematite remained while the rest of the dust blew and settled elsewhere.
There does seem to be fracture fill on some surfaces of the ejecta and it does make sense that during the impact event the bedrock would tend to separate along pre existing fractures. IMHO these deposits are the result of a long ago aqueous event, not an ongoing happening.

But if the erosion rates for Meridiani are correct (

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less than 1 nm per year then I don’t see that this amount of hematite dust could accumulate in the (JPL declared) 1,000 years since the impact. That particular time line pronouncement seems to me to reflect the same level of scientific rigor as Levin’s puddles at Endurance.

Serpens said:
"I think you are spot on Bill in identifying the 'blue' material as hematite. Not sure about berry erosion as the provenance though."

Good observation, I agree. I just done the "new batch" of L2-5-7 Pancams and note that around the actively weathering/eroding boulders we see hematite dust, sometimes enough to drift, and it seems more than could be accounted for by fresh erosion of b'berries. Clearly, this much dust has to be a component of the rock.

More later...

--Bill

Here are sol 2141 ( Jan 31, 2010 ) L257 x2 posted so far to Exploratorium. I will assemble into panoramas when the rest are down.

The most puzzling to me is this one:

When did the weathering of this block occur? Before or after it was blasted into this position?

There does not seem enough time ( a thousand years? ) to produce this weathering after it was uncovered.

The pattern looks very much like Wapmay in Endurance crater, which was atributed to water alternation.

Was the pattern created billions of years ago and this rock just happened to be on the present surface when it was disturbed?

Sure. Why not? You rock guys see million to one events every day. BUT, if there is a second - and a third - and a fourth occurence of this pattern nearby... Well,maybe it's not just chance.

Hort;
If you saw those cracks on earth you would say dessication cracks which formed on originally horizontal strata.

Why then would you start imagining some bizarre process, even if there were several similar chunks all standing on edge.

As they say thats just the way the cookie crumbles.

The latest Planetary Society report on the Rovers is out.

[link]

Strange comment by Squires on concepcion - "This is by far freshest crater on Mars and probably freshest either rover will ever see...,” Squyres explained'. Que? We have seen a number of impact craters appearing between orbits of the current satellites. Perhaps he means the freshest seen by Opportunity? (Provided we don't classify the heatshield impact dent as a crater). Yes I know I am being picky but I don't believe that the 1000 year pronouncement is based on particularly firm reasoning. Yes the ejecta overlays the ripples, but how long ago the ripples froze in place would seem to be very debatable.

Many of those rocks, especially the ones that have lots of blueberries, look like they are decaying by some active chemical process rather than simply being eroded by the wind.

Hort spake:

"When did the weathering of this block occur? Before or after it was blasted into this position?"

Likely, they were, pre-impact, paving stones on our yellow-brick road. The bedrock at Meridiani consists of siliceous clastics with minor clays (a dirty, fine sand) cemented

with kieserite (magnesium sulfate) which is quite soft, somewhat the hardness of chalk or plaster of paris.

Lets look at the impact process: a large rock, a meter or two in size, coming in at orbital velocity strikes the Meridiani plain. This not a large, hypervelocity impact, so no

major vaporization, melting or shock cones were involved. Here is introductory material on "Understanding the Impact Cratering Process:"

[link]

On impact, the shock wave fractures the rock to varying degrees and displaces the rock mass upwards and sidewards. Rock nearest the impact is finely fractured into rock

flour and farther from the impact, rock fragments and finally, larger cobbles and boulders, especially those unconstrained and at the surface. So I would expect the distinctive

dessication crack rocks to be least fractured and dropped off on the surface.

I'll note, at least for these first images, that the freshly-fractured rock appears to be a bit bluer on color than the weathered material.

Serpens, I don't buy some of the age estimates, either. I think they're off by an order of magnitude.

--Bill

serpens re your 251, Here is another abstract, maybe pertinent, from LPSC 2010 titled: Constraints on Ripple Migration at Meridiani Planum from Observations of Fresh Craters by Opportunity and HiRISE.

http://www.lpi.usra.edu/meetings/lpsc2010/pdf/2373.pdf

These authors conclude that the last episode of ripple migration (the big north-south oriented ripples) took place between 100,000 and 300,000 years ago. Their evidence comes from several lines of evidence some that I can't yet follow. Their model for the ripples is basically terrestrial granule ripples that have not moved for a very long time. I wonder what sort of aeolian processes have repaired all the damage- ejected rock bounce and roll marks - that must have happened during the Conception impact event. If the ripples are stable only because they are lagged on the surface with granules then why don't we ever see blow-outs where impact damage has cut through the stable layer of large particles? There seems to be a confidence that sand-sized particles are mobile even in the present wind regime, but apparently all this process can accomplish is repair not erosion. Hmm?

Nice image here:

This eroded piece of breccia with multiple spherules and spherule-tails might tell us something about erosion at Meridiani:

I hope that we get more and better images of this block but I'll stick my neck out already. It seems to me that the spherule-tails on the steep faces of the block extend downward from their point of attachment at a large angle from the horizontal. Also it seems that tails extend from steep faces oriented at right angles to each other. A few tails visible in outline along the lower right edge of the rock seem to illustrate both these observations. Neither fits well with a saltating sand scour hypothesis for the erosion of the tails. Saltating grains should be striking a vertical face almost horizontally. Prevailing winds must be hypothesized to create tails "behind" resistant obstacles to erosion. Changes to prevailing winds can be used to explain multiple sets of tails pointing in different directions, but what was protecting the tails pointing right (and downward) while the ones pointing toward the viewer (and downward) were being created? I think that these are serious problems for the saltating sand scour erosion theory.

Then there's the new wrinkle that whatever has happened to erode the block it has to have happened fairly quickly and relatively recently. I'm thinking about it.

The latest Exploratorium pancams are fascinating. Lots of layering, possible cross bedding and all those juicy berries. For example:

But the ejecta and surrounds just don't look very recent and some of the layering seems to be very well eroded. How long would it take for a fresh crater to fill with dust?

Kye Goodwin. Interesting observation. As I understand it when wind encounters an obstacle like this the pressure gradients created can cause a reverse flow at the base and an upward flow that then curves over the top, as well as local pressure gradients influenced by the topography. This would seem likely to produce what we see.

Here are the sol 2142 L257 images near Concepcion.

This is my favorite:

Lots and lots of blueberry stems.

How did all that wind erosion happen so "quickly"?

If Concepcion Crater is only 1000 years old then these pieces of impact breccia have eroded at a really surprisingly fast rate:

I'm looking particularly at the places where some layers in the blocks have eroded more quickly than others creating deep groves in the surface, a familiar sight at Meridiani. Fracturing in the impact could in theory have contributed some of the depth but the way the recessed layers wrap around the block corners is pretty compelling evidence that those grooves corresponding to "soft" layers have been eroded subsequent to the impact. That's on the order of ONE CENTIMETER in 1000 YEARS?

Serpens, agreed-- this close to the ground and with all the rubble around ther ei snot going to be a laminar airflow. It going to go every which'a way, what we observe here.

I don't know which of today's treasures I like best. I do favor Hort's choice, whih I informally call "The Leaning Tower of Jabba the Hut...

--Bill