...and finally we have also some pseudo-color (L257) of the rover tracks after unstuck:

I'm intrigued by darker material in the left border of the trench, it appear also different in color ("less brown"); could be simply more recently excavated/collapsed terrain?
The left track image quality si poor but it seems to not exhibit this anomaly...

Yeah...
Basaltic soil exposed!

I think you're right. Well, the drifts around Oppy's stuck position show layering, especially in places where older drifts appear to be in the process of deflation. Some of those layers are a lot darker than others, and in the color images I've seen, look grayer.

There are a few ways you could get layers of basaltic dust interleaved with layers of evaporite dust and blueberry paving/dust, including deposition during large dust storms and cyclic variations in prevailing wind directions.

If the layers in the drifts are from dust storm deposition, these drifts must be dynamic and young features, indeed, since we get major dust storms every few years...

-the other Doug

From Sol496 we finally have true color image also for the other track; if seems to me that we have same darker material also here...

Doug:

Or, we see layering because the dunes are v-e-r-y old, and we're seeing the depositional results of very long-term climate changes - the orbital eccentricityand polar wandering stuff!

Bob Shaw

Never mind the colours - look how astonishingly cohesive the whole trench wall is! It turns to a dust pile here and there, but elsewhere it's just so, well, firm...

...I hope they get a good look at the walls of the trench with the microscopic imager.

This is an interesting material. In Dilo's Sol 496 image, horizontal layering can be seen near the top of the trench. Vertical scuff marks can be seen on the left, and I'm wondering if those are blueberries I see in the wall. In other images light-colored (red/orange-ish?) material is being blown away by the wind. Earlier, we noted that the disturbed material darkens quickly when exposed to sunlight. Elsewhere (and take this with a grain of salt), blueberries are said to be emerging from the disturbed soil.

Needs more study...

--Bill

Bill, I agree on the BB origin of these features... In the left track (first image I posted), there are four similar vertical features indicated by the lower arrow and, maybe, two exposed BB immediately above.

Wath do you think about deep, very dark features highlighted by upper arrow? Could be a layer of different (older/basaltic?) material which eventually originated the color differences in both tracks? And why shows a so small horizontal extention? I think they should try to study it with miniTES...

A note of caution here, the wall in the trench that you are looking at may just be a whole mess of churned up material made by the wheels when they were going in. If you look at Dilo's whole image then you can see that the track is a lot wider than the trench wall that now remains and the blueberries that can now been seen in the wall may all have been close to the surface of the undisturbed soil, (they may not have been as well of course, but we can't tell from this).

I think my single biggest frustration on things the rovers really should have had but had no room or mass allocation for is a simple backhoe trenching tool. We're seeing spectacular soil salt enrichments at the Gusev site and interesting signs of layering and sorting at Meridiani, and all the rovers can do is scuff messy holes in the ground. Oh, well...

That and the lack of color imaging on the microscopic camera, when Beagle's Paw-cam had it... I've heard <second hand> allegations that was nixed by NASA HQ but never any real info on that.

I'll agree, Ed, there should be more, but Oppy and Spirit are the first of their kind and they couldn't include the kitchen sink. A trenching tool could have been easily added to the instrument arm, but who knew what we'd encounter. I'm sure that the next generation of Rover will be able to leap tall dunes in a single bound...

The track excavations are churned up, but here are a few areas where you can (apparently) see a sharp roadcut. The area in sol 496 and Dilo's followup image are good sections. What I think is happening here is that the "Meridiani plains formation" is pinching out at the etched terrain and we are seeing changes in the stratigraphy/soil profile as the blueberry desert pavement is absent or changing. This point in the column is the contact at a major unconformity/disconformity between the Eagle evaporites and the unconsolidated Plains sands. We may be seeing very old and dynamic features and I look forward to getting at the contact.

--Bill

Re Bob Shaw's observation about how firm the dune seems based on the sharpness of the trench wall, this would seem to revive the idea that Oppy got stuck, not because Purgatory is exceptionally soft or steep, but because its leading wheels locked up for some reaon -- and indeed I am among who those who originally raised this possibility. HOWEVER, it may also be that the Rovers, though exceptionally well designed, do have certain areas of vulnerability or discontinuities -- ie, an Achilles tendon -- in their terrain handling capabilities. We recall, for example, how Oppy got stuck trying to climb out of the shallow Eagle crater. Thus Purgatory, though not unusually soft or steep, might have had just the perfect geometry as encountered by Oppy to cause it to plow in.

Glenn

They started to use microcam (after 2.5 month of standby!) to examine recent tracks:

Very small blueberries, with some clustering where moved from wheels...

doubt very much that those are blueberries. looks more like that small pebbles that we have been seeing from the start. blueberries are hemitite concretions.



With regard to the quote above... With out a doubt, we are seeing changes in composition. But we know from orbit that the hemitite extends far more than the distance travelled, so far. We are not even close to reaching the edge of this formation. The edge is many tens of time farther than the most optimistic longevity of the vehicle. The etched terrain is a local phenomena in the much larger formation that is meridiani plenum.

Those microscopic pictures are interesting - is it a vertical panorama of three images? If so, the lowest image is made entirely of similarly-sized particles, with nowt else inbetween. How odd! Even if it isn't a mosaic, it's still a strange population of bits compared to those above - so regular...