It looks like the edge of the VC ejecta blanket to me. The large dark patch at about the same range and slightly offset to the right of feature 'D' also lines up neatly with a small 'island' just beyond the main boundary of the ejecta blanket.

Is it an optical illusion/my overactive imagination, or is it a low 'cliff' or ledge at some points around the boundary?

Back on June 20, I suggested this might be the case;
the 'scoured' evaporite just beyond the edge suggest to my untrained eye that a
bluff at the edge of the apron was channeling the wind and increasing its velocity. Also,
the lobate and often sharply defined edge made me think of a 'splash' of muddy
material which flowed a short distance like lava before coming to a halt. Perhaps
VC was formed at a time when there was still a fair amount of permafrost in
the soil and rock.

Fortunately, the edge NE of Beagle seems much less defined, suggesting that
Oppy can get up onto the apron.

CE

This is my personal attempt to manually stitch the four L257 color images from sol869, giving also more "realistic" hue:
Click to view attachment
We can see a lot of new details (already highlighted by Theseiner and others) and also first detail of Victoria crater internal (far) rim on the extreme left, in my opinion; see this 5x vertical stretch:
Click to view attachment

Thats an interesting thought, almost counterintuitive. The difficulty i see is that the streaks being blown out of Victoria (as you can see in the overhead view) have a 'point-source'. so the model presumably goes that you have wind scooped up and pouring out of a small keyhole of the crater rim (the 'point source') then it spreads out as if it were a thin blanket creeping over ground, losing its effectiveness at dust removal in exactly the same pattern as would be evident if it were instead actually depositing material. in this case, however, i wouldnt expect the patterns to be the same, a removal pattern should be much more abrupt, imho, i wouldnt expect a wind-tail so nicely blurred as if it were due to dust settling out gradually as the air travels over and loses its agitation, id expect the removal process to stop when a windspeed threashold is reached, looking much more defined like the ElDorado edges. However, im no aeolian expert and i digress...


stunning stitch, Dilo. i almost feel like im there at sunset, er sunrise?!

woaw dilo, yes, the detail is there! I'm very pleased to see these first colorshots

Nico

One thing that I would say that the black streaks coming out from Victoria Crater are the ones with lowest height of around the north rim. The streaks has the formation toward the North West. I coincides it with the CosmickRocker's comment: "currently predominant wind direction on Meridiani is SE to NW." Other point that I am doubt that on the Meridiani Planum has Dust Devil. I think that the streaks of VC are not caused by DD but by a constant direction gussing wind that has removed the light color sand.

Rodolfo

>Thats an interesting thought, almost counterintuitive. The difficulty i see...

Good points, atomoid. We pride (or fool) ourselves into thinking that we understand what is happening here, but these wind streaks show otherwise. North of Victoria, they could either be light dust removed or dark dust deposited. You can see the a similar dark tail north of Endurance, but as wide as the crater. Think that over...

We'll have ground-truth in a few weeks.

--Bill

They definitely could be either. I only based my hypothesis on the fact that such elongated and dark things have been observed all over the planet, and appear to be created by the removal of the ubiquitous light dust. But it is a valid observation that darker material deposition is also commonly observed in crater depressions and places in the lee of other obstructions to the wind, like El Dorado and its nearby relatives.

As Bill says, we really will not know until we have ground truth. Hopefully it will be obvious once we get there.

I'd bet on the dark streaks being areas where the global dust isn't being laid down, rather than the streaks being, er, dark dust.

You see dust 'shadows' of that nature all over Mars - sort of 'anti-Ultreya' features...

Bob Shaw

These dust tails are ubiquitous, and also anomalous. In some cases, they should be named "Eschers": are they stair-steps going up or stair-steps going down? Depositional or erosional? We'll know more, soon.

The two dark cobble areas west of Beagle are showing wonderful detail in the color stretch, as well as positive relief. One wonders if they are small crater rims disturbing the dark ejecta, or lumps in the "ejecta batter"? We are going to get some good science from this ejecta blanket: some mixed-up lithology, but a better understanding of the erosional-depositional processes on Mars, which is the key to understanding the geomorph. IMO.

From what I'm starting to see on the ground, I'll guess that the evaporite will begin to take on this "jumbled" or disrupted character, as opposed to the neatly-fitted paving stone appearance we usually see. The may be due to the disturbance at Beagle, but I'll figure that Victoria plays a major role here. Now the geologists can get to work: we have multiple strata spanning multiple timeslots in a relatively small area. And roadcuts all around so we won't have to pull out the trenching tool.

--Bill

Yeah, all this dark/light deposition/removal stuff...
...maybe we need a 'pool for arrival at determination of dark/light origins' thread now.

...but i digress again, who knows if the MER team is considering investigating this issue, it may be some time before they look up close to get ground truth of these patches. we might stay west and not venture near the dark streaks before entering VC.

From orbit, Occam's Razor might suggest that it just 'looks like' the dark stuff was eroded inside Victoria, presumably from the crumbling walls, since winds will increase turbulence and speed over varied terrain and pick up dust, even though we expect those layers to be light evaporite, but maybe there are dark interlayers too...
...or the dust is created and transformed by frosting/exposure/UV/oxidation processes on certain mineral layers (did we get spectra on Eldorado dust?? if so is it oxidzed iron making it dark or is it simply basalt dust?), and was transported out the keyhole and deposited on the blanket as the wind spread out and slowed. ...but then again Mars surprises us and neither interpretation may be entirely or even at all correct, and the different dark areas may share different origins...

We’ve not seen Oppy taking pictures of whirlwinds (‘dust devils’,) as conditions in Meridiani don’t seem as favorable for formation and sustenance of them as they are in Gusev.

But, what we see at the North edge of VC looks much like the tracks of atmospheric vortexes that rise out of craters at Gusev as whirlwinds, picking up dust and leaving behind a darker trail.

(Photos below at Gusev (and a snip of VC) show crater-created whirlwind tracks lasting varying amounts of time, dependent on crater size, depth and prevailing wind speed.)

Ahh. Thanks for that convenient set of comparison images, and you make a good point that we haven't seen dust devils around here. That set of images nicely displays the similarities and differences between the dark streaks.

The main difference that I notice is that on VC they do not end in fingers and don't show the long, high contrast trails formed by dust devils removing the global dust. I was looking at the model as vortices either removing or depositing dust from/onto selected areas. It may be that Bob's more subtle suggestion that they are "areas where the global dust isn't being laid down" is the answer! ...fascinating...

I don't think these are DD related to be honest - just the wind whipping in and then out of VC.

Doug

The dark streaks at Victoria are different than we've seen anywhere before. Whereas the downwind streaks at Gusev are sharply-defined and convergent, the streaks at Victoria are soft-edged and divergent. Clearly aeolian, but not DD-features.

--Bill

Here is the view in the drive direction.

Taken with the L2 pancam on Sol 869.

jvandriel

They could turn out to be similar to El Dorado. Just a place in the "shadow" of the wind, where dark dirt happens to to fall out quickest.

or they could be little abysses...perhaps chasms? The children of Ultreya!

[relocated post to Moving south to Victoria thread]

Has anyone noticed the "layered effect" of the south faces of the dunes (towards Beagle Crater)? They appear to have light and dark layers laid down at different times.

David

If I'm reading this paper by Ken Edgett correctly, there's a good chance that we won't be getting much of a glimpse at the original Victoria crater and its surrounding ejecta blanket. I'm specifically referring to the following passage (p. 19):



I put together the following diagram which, I think, illustrates the steps involved. The actual size, depth and shape of the crater and layers are obviously just guesses.

Click to view attachment

This also better explains the lack of a more defined rim, ejecta and other impact features around the crater. If correct, we will be able to get a good view of the top resistant layers, the less resistant crater-filling material (hopefully) and a lot of rubble.

I've read that paper, but I'm not so sure that Victoria is buried/exhumed. Eroding, yes.

Good drawings, BTW.

--Bill

How does this relate to Endurance crater where we saw layers at Burns Cliff of the before impact geology (if my understanding is correct)? I'm expecting to see the same types of layers at Victoria. Is Victoria's history so much different from Endurance's that this may not happen? Victoria's rim sure seems to have the same sharp outcrops as Endurance in the orbital images.

Figure 21 of the same paper has a side-by-side comparison which clearly contrasts the two craters' rims. The sentence following the one quoted above says:



[EDIT]I cut-n-pasted parts b & c from Figure 21 of the pdf. I don't know how to cite correctly, so set me straight if I need to write something and/or delete it.[/EDIT]
Click to view attachment

Here's another possibility. Think of this model as equivalent to throwing a rock into a pond covered by a thin layer of ice (fun). Replace the water with sand (or mud), replace the ice with evaporite. Assume that the rigid evaporite shell constrains much of the impact energy by ballooning up, with radial fractures, then collapsing again to nearly the same level. The result is a shallow crater bounded by a rim of evaporite (I'd expect a scalloped form), overlain by ejecta.

Click to view attachment

Just to play devil's advocate

At these energy levels, the evaporite would not have necessarily acted like a rigid shell, if such behavior was possible. The cratering process tends to overturn beds, so the surface evaporite end up on the bottom and the underlying "dark basal unit" will end up on the top.

I think that the differences in morphology of Endurance _vs_ Victoria craters is simply one of size and thereby the energy input by the impacting body. Grapefruits and watermelons are both delectable but different.

--Bill

I'm inclined to believe that you're right. Above a certain impact energy a rigid shell would cease to have any noticeable effect on the resulting crater. Intuitively I know that such a threshhold must exist, but I don't know where it is. My intuition suggests that an impact just large enough to break through the shell, yet not much greater than that, might have this sort of behavior.

Just wanted to stir the pot

It's good to ask questions "outside the box", that fosters creative discussion. I think that the "rigid shell" idea may be applicable on smaller craters like Fram and those craters between Erdurance and Erebus where the top couple of meters of evaporite is broken and tossed about. No doubt we'll be seeing some of these little bumps on the way across the ejecta apron.

--Bill

I notice that as we get closer to Victoria, the evaporate layer that we see in this pancam image is starting to take a ripple shape which is similar in size, shape and direction as the dunes. What do you think we are looking at here? Is this the edge of the ejecta blanket from Victoria that has been eroded by the wind or are the ripples formed from the impact itself and coincidently line up with the dune ripples.

1N205688004EFF735TP1902R0M1.JPG