Any speculation as to what the line of white pebbles are in the foreground? Look just left of the antenna mast, and you'll see a segment of "vertebra" that seems to be embedded in the evaporite.

http://qt.exploratorium.edu/mars/opportuni...00P0605R0M1.JPG

Has this kind of feature been seen before?

Probably scuff marks from the wheels.

Indeed, these marks are of rover's wheel. An attention has brought me up is that inside of the outcrop is even whiter than on the surface. That outcrop surface Looks like a chalk.

Rodolfo

Or an artefact of the image manipulation process? There might be similar textures within the fuzzier peripheral areas, too...

Bob Shaw

Here is the navcam frame for your consideration.

Another view.

Yup, it *does* look like something has given the pavement layer an almighty whack - but there's very little debris. Is this a fossil crater root, perhaps? Or are we looking at a relatively slow impact speed (which brings me back to the 'burps')?

Anyone out there been doing any crater-counting in terms of area vs numbers? Obviously, craters - if impacts - shouldn't form only in dunes, although the morphology might be quite different on the hard(ish) evaporite layer...

Bob Shaw

Thanks for the insight. The rover did drive very close to this area, and the "scuff marks" do seem to be on the surface rather than associated with a layer/strata in the rock...

but how come we don't see these kind of tread-marks more often on the highways - including this very outcrop? Is it a sign of slippage, or dragging from the one wheel that is having trouble? Is this particular rock softer than usual, or is there a soft rind covering the rocks?

Bob is probably correct, this radial pattern has to be the root of a fossil crater. A paleo-thwack, so to speak.

Remember that Oppy is a gimpy rover, the right front wheel doesn't steer and when she turns, that right front wheel is dragged sideways and the metal treads scrape across the rock surface. This can be seen easily on sand turns.

--Bill

If paleo-thwack is not a word, it darn well ought to be.

Phil

Gentlemen, I hate to bring this up, but there are geologically-challenged people in the forum
Would you care to elaborate on what the root of a fossil crater exactly is ?

I think the definition is based on the the particle size and the flow velocity that created them. I saw a graph showing where the dividing lines are not long ago, but now I look for it I can't find it (or anything like it) typical!

They were created by paleo-thwacks.

Mars has received impact upon impact over time, and the resulting craters are eroded completely away. For example, Victoria is a young crater and has a deep bowl with steep sides. In millions of years the rocks will weather and erode and Victoria will be be left as a low-relief ring, much like Erebus. Millions of years later, the Erebus ring will erode down to no relief and the crater will be no longer. But the impact that formed the crater shocked, fractured and disrupted the rocks of the plain, and this disturbed area was concentrated in the center of the crater. What we are seeing here is this disrupted area of a crater that has eroded away.

That is the short answer; let me see if I can find a website on crater formation or make a diagram to illustrate this.

We are hypothesizing; we don't know this for certain, but it surely looks possible.

--Bill

Paleo-thwacks? Are that the forbears to the guys with big sledgehamers that go-bump-in-the-night?

Here is an image of fossil crater formation with a core or root.

Adapted from:

http://homepage.smc.edu/balm_simon/images/...r_formation.gif

--Bill

It's not just that the evaporite is more extensively cracked around the periphery of (and, presumably, underneath) the "campfire" than it is elsewhere. For one thing, the "campfire" area seems to be a low spot, a small depression in the evaporite. That would tend to indicate it might be the root of an ancient, eroded crater.

However, the tops of the evaporite pebbles in the more shattered area look "rinded" exactly the same as adjacent non-shattered evaporite. It looks like the whole thing eroded down to the cracked evaporite paving and *then* was shattered further, into the spiderweb cracks and pebbling that we now see.

Speaking of the pebbling, the fragments of evaporite in the highly shattered regions are more rounded and broken up, with pieces lying together in place, than you would expect to see if the evaporite was shattered as part of an underlying layer that has since been exposed, with the crater above it having been totally eroded away.

The dark cobbly material in the middle of the "campfire" depression looks for all the world like dried mud that was left after a rainstorm washed surrounding dark dust into all the depressions. The evaporite pebbles also look as if they could have been rounded by standing water. I'm sure that's not what happened, but it really reminds you of a dried-out mudhole in the middle of a cracked desert floor.

One thought just occurred to me in re the campfire, and in specific in re the spiderweb cracks around Phil's "bullet hole." We're on the rim of Erebus, here -- the remnants of the rim of a large impact crater (nearly as big around as Victoria). Could these small circular features possibly be remnants of shatter cones that were formed in the rim structure as it was heaved out of the ground during impact? If you had shatter cones developing near the lower boundary of the evaporite layer, could that form instrusions of a darker underlying layer into the evaporite through the centers of the shatter cones? That would explain the bullet-hole appearance of the one feature, as well as some of the "ponding" of dark, cobbly material...

In any event, the piles of dark, cobbly rocks and dust seem to be related to intersections of thick cracks in the evaporite, or are in the center of more-than-normally-cracked areas of the paving (which also tend to be depressions). All of that can't be a coincidence. Whether the dark cobbly material was eroded out of the layer that used to overly the evaporite paving, or whether it was dropped onto the paving after it reached its current state, or whether it's been extruded from below the paving through the cracks -- the highly cracked areas and the cobbly piles are obviously intimately related.

-the other Doug

Good analysis, Doug. Remember, too, that this is also on the rim of the older paleocrater Terra Nova. This is going to be a very interesting place!

Attached is a 3x exaggeration of a 10x1 panorama fromSol 632. Sorry for the 830K filesize, but I didn't like the "lite" version.

--Bill


edit: corrected filename to 1N184293573_pano_exagg3_sol_632.jpg
(was _631_)

Bill, thanks a lot for your elaboration on crater formation.
By looking at the latest Oppy route map, I realized that we are currently at a location where the rim of Terra Nova more or less coincides with that of Erebus.
Could it be that the "root" we see is a remnant of Terra Nova's formation then ?

You beat me to it, Bill

A 360 degree panoramic view around Erebus.

Taken on Sol 632 with the L0 navcam.

jvandriel

Jvandriel. I've polar panned it. Sorry if i'm treading on toes.
Click to view attachment

Here's my version of jvandriel's sol 632 polar pan.

Phil

Click to view attachment

This is interesting. If you look to the northeast (upper right) of Phil's polar projection, you can see the FourLane and those troublesome drifts Oppy just drove around.

BTW, that "interesting dark outcrop" that I mentioned a couple fo days ago is to the left of Oppy, it is actually a collection of the dark cobbles and not a solid outcrop. The low angle of view earlier gave that illusion.

--Bill

I've noticed that too, I was looking forward to getting close to some of the dark patches when Oppy first reached the Erebus highway hoping for a preview of the dark "outcrops" near Payson. So far the dark patches have all turned out clumps of dark cobbles.

Yup, I got bit a couple of times by the "dark outcrop" illusion. I hope that the dark tabular outcrop along Payson and the Mogollon Rim bluff aren't simply a windblown lag deposit that has collected in the wind shadow of the bluff. We'll know more soon.

--Bill

Folks, I keep looking at that dark tablular feature under the Payson/Mogollon Rim bluff. The more I look, the more I think it is shadow....not an outcrop, not a wind shadow collection of dark material...just a plain old shadow on the north side of a cliff-like evaporite outcrop.

Scott

This "dark basal unit" may be my windmill. My first impression was that it was a shadowed bluff. But many Pancam images show detail on the dark area and my feeling is that it may be a new unit. We'll see in a few sols; even though it will take time to get to Payson, there are dark outcrops along the way.

Signed with hope,

The Don...

That bullet hole is really fascinating, and I could imagine it to be the paleo-thwacked root of a small crater, but there are other heavily fractured areas around that are similar, though less symmetrical. The intensity of the fracturing sure does make me think about impact related shock waves, but another angle on that ocurred to me. When the major impacts to this area occurred, seismic shock waves would have radiated out from the center of the impact. As those shock waves travelled through the heterogenous rock, there must have been many waves reflecting and refracting off discontinuities, and creating constructive/destructive interference patterns.

Might we not expect to see areas where coinciding waves interferred to seriously disrupt the rock?

That's what I was talking about -- that's what shatter cones are, patterns of shocking in the rock caused by the seismic energy imparted into the rocks by an impact.

I think we're seeing shock patterns, some of which look like classic shatter cones in cross-section.

-the other Doug

Good to get around these.

dvandorn: Wouldn't it be nice to see Dilo's roadmap in high resolution? There are so many interesting geologic features that he has already mapped for us. I'd really like to see the wider view of the major fractures. I don't fully understand the processes involved in the formation of shatter cones, but I have only seen them in hard rocks on earth. It may very well be that the feature is a cross section of a shatter cone. Surely it is some kind of shock feature.

This is somewhat off-topic, but I was afraid I might forget to mention it elsewhere. It may have already been mentioned elsewhere. There is a very nice Power Point presentation available that contains an interesting overview of the Meridiani depositional environment, and other things. It has a stratigraphic section from Burns Cliff at Endurance, and also some interesting terrestrial analogue images. Look for the .ppt link on the upper left side of this page. It's about 10 MB, but worth it...

http://www.esi.utexas.edu/outreach/ols/lec...er.php?pid=none

Good thinking. That would be similar to the ANFO-thwack used in modern surface mines. Seems to me that a soft fissile shale ought to be similar to the Burns Formation. I'll keep an eye out for that and ask around.

--Bill

Closest view yet of the rim (Sol 634 Pancams):

Great view, but difficult to get there, it seems. What would be the best route to approach Mogollon Rim (and Payson)?
Perhaps making a little detour would be better than taking the straight route?

Now that Opportunity is in the right "groove" between dunes, I doubt it would be wise to attempt any more east/west travel unless it comes across an impassable obstruction (like a shelf). Worst case, they can always backtrack to the current point and attempt a detour later.

Besides, the geologist are probably tired of dune travel by now!

I think after finishing with the immediate area, she should head south a bit and survey the situation - a better view of the rim from that perspective might be helpful. As you say, they can always backtrack if necessary, but it may not be necessary.

6x3 Panorama from 634 (one image missing)

Notice how the drifts to the left of the dark 'outcrop' have been stained.

Wonderful images today. Not only Pancams of the Mogollon area, but also Pancams of the rich Olympia area. I don't know where to begin.

Attached are two images that demonstrate why I think that the dark outcrop is a dark unit underlying the usual Burns Formation evaporite unit. The first is made from today's Sol 634 Pancam images and is vertically exaggerated 5x. The second, shows the same area under different lighting and from the FourLane outcrop a few Sols ago. Clearly, the dark unit is tabular unit persistent over a few hundred meters and has a different spectral signature. Both are L257 tricolor images.

--Bill

What a bonanza of imagery today from both rovers. I was getting worried about exploratorium. I'm a bit overwhelmed by it all, but Bill's dark layer is looking pretty real to me.

As to the path forward, I'd have to guess Oppy will follow the inside path on the rocks, as far as possible. At the end it looks like she might be able to cross a few drifts to drive right up to the base of that ledge, which would be an ideal investigation site. It's not that far, and there are interesting targets along the way. If it does not apppear possible on closer examination, it will be easy to backtrack and try an outside route.

Ah -I'm getting them in too now. No more worries CosmicRocker.

I just needed an Oppy-fix.

Nico

I'm still positively giddy. It's like getting home and finding an envelope in your mailbox containing a dozen pieces to that jigsaw puzzle you've been working on for a year...

There are so many "purty picturs" (pretty pictures) here at Kavalrita that it's going to be hard to decide where to start. The "almighty thwacks" are significant, as are the "purplish" areas noted. My own career work involves the Pottsville formation of Pennsylvanian age. This consists of boringly alternating beds of sandstone and shale with enough coal to make it economically interesting. The big unifying principle is the depositional environment of the paleo-deltaic setting of the coal swamp, and change is good since that implies a change in environment, and that is an indicator for the formation of iron sulfides, which nowadays makes acid drainage from mine sites. Oneof the little side-observations I've had going for the last 20-odd years is marine fossils in the deltaic sequence, which suggests very interesting change. One of these days I'm going to pull all those puzzle pieces together, present a paper, and have my own 15-minutes of fame...

Oppy is plinking around on a large outcrop. Spirit is coming down off the mountain. Dilo is back. Could life get much better?

--Bill

Just don't leave the location of where you're pointing your telescope (rock hammer?) accessible to all on Google... some Spaniard may come along and scoop you

Can't argue with that. Life is good. We've got to follow this road in, don't we?

The Pottsville formation...now you are testing my memory. I think I may vaguely recall something about it from an all-nighter while preparing for a stratigraphy test as a student. I hope I can at least get partial credit. Wasn't it one of the units of sediment shed from the growing Appalachians? ...(fingers crossed)...

Nico: No more worries for now. I needed that fix, too. It was too long to wait, wasn't it. I do feel better now, though.

Yep, that's it, 100%. Think of the Pottsville Fm as the Mississippi delta on steroids.

--Bill

http://www.unmannedspaceflight.com/doug_images/0634B_725.jpg 1MB

There's another two columns to the right to be had yet I think - but not fully down.

Doug

Just one column missing, Doug.
It was a set of two 4x3 shots.

Looks like Doug needed an Oppy-fix too. Nice work!

Nico

A panoramic view of bedrock around Erebus.

Taken on Sol 634 with the L7 pancam.

jvandriel

good color calibration work !
although it must be composed of the "stretched" JPL JPG frames, the color balance of this image does look like one of the true-color images from the calibrated PDS raw images ...
(also the slightly reduced contrast and illumination resembles the radiance calibrated images of the same area ...

... captures the dark & hazy mood of the typical martian landscape

Just the jpgs - I use a lot of photoshops ' match colour ' tool with a sample from the Naturaliste pan.

Doug