Nature of Victoria's dark streaks, swept clean, deposited, or other? Options

[MarsIsImportant]

Well, the color of the depositional dust would depend upon its source. Perhaps the compositional differences within Victoria create different sources of the dust deposited over the surrounding area. If the dust in the east is the same basic color as the blueberries, then it would be difficult to distinguish the two from a distance. So you have light colored dust deposits in the west covering the berries, and dark colored deposits covering the east. So the difference would only be the east to west difference in the composition of the underlying rock or soil, in which the impact that created Victoria occurred.

This all adds up to something...more things for Oppy to investigate. HURRY up Oppy! I'm getting impatient.

[MarsIsImportant]

Does anybody know what day this image was taken? It must be fairly recent because it was posted today. It's important because it shows split and mangled blueberries along with sand or dust particles. If this is from within that first dark streak, then it supports an impact deposit origin. If not, then I'd still like to know exactly where it was taken.

http://qt.exploratorium.edu/mars/opportuni...D2P2936M2M1.JPG

[fredk]

As I just posted, that's 1135, between streaks.

[atomoid]

Ever notice how the only area in Victoria with the dark streaks is also associated with what is pretty much a linear feature that is the cliff boundary layer.
again, here is Fredk's linked image

I'm not sure if anyone here has already pointed this out, but this might be a very important detail, as it could be that this is a fault boundary, meaning one (or perhaps both (or neither)) of two things:

1) being a fault, its is composed of compositionally different (that is, water-modified) materials.

2) it could have experienced more geologically recent rockfall so there is relatively new dark material to blow out of the cliff face. elsewhere in the crater these exposures have long depleted.

[MarsIsImportant]

Ever notice how the only area in Victoria with the dark streaks is also associated with what is pretty much a linear feature that is the cliff boundary layer.
again, here is Fredk's linked image

I'm not sure if anyone here has already pointed this out, but this might be a very important detail, as it could be that this is a fault boundary, meaning one (or perhaps both (or neither)) of two things:

1) being a fault, its is composed of compositionally different (that is, water-modified) materials.

2) it could have experienced more geologically recent rockfall so there is relatively new dark material to blow out of the cliff face. elsewhere in the crater these exposures have long depleted.

I've mentioned that...not nearly as well put as you though.

[MarsIsImportant]

As I just posted, that's 1135, between streaks.

Sorry, I guess I didn't click on all of your link in that post.

[SteveM]

I just wonder if a CRISM image wouldn't tell us a lot about the characteristics of the dark streaks. Given CRISM's 19m/pixel (38m resolution) they should be able to get a nice spectrum of the streaks.

On an off-topic tangent, it just seems unlikely that there are no CRISM images of Gusev or Meridiani in the system somewhere. (in mild conspiratorial mode)

Steve

[Jeff7]

Put me in the deposit camp. El Dorado was also a dark region, and it was clearly deposition. True, this could be an entirely different material, but it just seems to me like it'd be deposition. The wind could come in, hit the cliff faces, cleaning them off, and bringing dust along with. It loses energy as it climbs the crater wall, but maintains some speed because it's being constricted by the funnel-like shapes in the scalloped edge. When the wind finally makes it over the edge and into the open, its speed drops as it dissipates, and it's no longer able to keep the dust airborne. Plop, down it falls = dark streaks.

[fredk]

Just a reminder to people (like myself!) who thought they had the streaks all figured out, that things are perhaps more complicated than you thought:

It looks like there's a broad light coloured streak trailing to the SE of Victoria. That's consistent with light streaks from other craters in the area, such as Endurance. I'm guessing that's due to bright dust eroding off of the bright evaporite along the rim. We're obviously dealing with varying wind directions and distinct processes.

[CosmicRocker]

That's interesting, isn't it? I've played with various stretches of the HiRise imagery, too. I am not yet certain what to make of that. I have been concentrating on the ground with Opportunity's eyes.

There is a series of foreground pancams taken on many sols that gives a nice sampling of the near surface views. Setting MMB panoramas to a rover relative view and skimming through the sites, one can quickly notice the places where useful imagery exists. I really don't think complicated theories are needed.

Here is one of the quite early images from a relatively light area from sols 1016-1019. To me, it looks like berries buried in dust. You really need to look through the whole series of such images to notice the changes. If some of you don't look at all the images, you might not see the larger picture. I'm sticking with that razor guy.

[Guest_Edward Schmitz_*]

It doesn't strike me as possible to have such a long thin jet of air coming off of a feature that has virtually no relief above the plain.

On the other hand...

If a small "fountain" of dark dust were being thown into an otherwise laminar flow, this is the effect you would see. The "fountain" would be a jet of air coming up one of the bays carrying dust particals from those dunes at the base of the cliff.

Fred's enhansement seals it for me. There are streaks off of ever bay (some more than one). They're all about the same length. That indicates that the phenomenon is effecting the whole crater. There is simply more dust on that one side.

[CosmicRocker]

I should apologize up front for posting a montage that is kind of a mess, but I am tired of adjusting the layers to make it prettier. I've assembled a sampling of 10 false color pancam images from light and dark areas around the crater and then drew arrows to their approximate locations on Tesheiner's route map. It seems to me, at least qualitatively, that the surface appears generally dustier in the light areas, and generally cleaner in the dark areas.

[Shaka]

That's a nice start at organizing the data for systematic comparison, Tom. But with only one view from a truly dark streak, it's still a bit early to draw conclusions. The next few days of pans and MIs should tell the tale. I for one need the close-ups to be confident of what I'm seeing.

[fredk]

Thanks for the post, Rocker. I think it's very hard to judge dustiness based on uncalibrated colour images, though. Different channels may have been stretched differently at different times.

I am really looking forward to an MI from the dark streak to compare with the sol 1135 one. Without access to minites data that'll be about the best we can do ourselves. I'm afraid we may have to wait till after the long weekend, though.

[CosmicRocker]

That's right, guys. I wasn't trying to say anything too definitive; that's why I used words like qualitatively and generally, etc. Apparently I find the trend displayed by this set of images more convincing than you. We should get other imagery in the darkest streak eventually, but I'm not sure that uncalibrated imagery is a huge problem. The colors may be wrong, but dust can usually be identified by its texture. Anyway, I have some other stuff in the works, but I'm still waiting for a few images.