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

[MarsIsImportant]

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.

That's good work Rocker. Thank you very much.

But my interpretation of those same images is very different. What you show is that the light colored areas are dusty with light colored dust; and the dark colored areas appear to have dark colored dust mixed in with the blueberries. IMO, this suggests the depositional theory is more correct--the one that takes into account the possibility of slightly different composition of the soil layer underneath different parts of Victoria.

I don't see the darker areas any cleaner at all; they are simply darker because of the dark dust. The fact that they are darker can create an illusion that they are somehow cleaner, but they are not. So, there appears to be deposition across the entire annulus of Victoria. Some streaks are light colored, while others are dark or darker still.

[atomoid]

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:
[attachment=9965:attachment]
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.

...and gosh i hate it how quoting removes the image attachments, so here is the link to the above quote

yeah, wow, is that a 'contrast enhanced' image? regardless, i'm stumped again, confusing the issue could also be the possibility that the dark streaks are laid down in episodic periods and are now dormant... the light streaks go against the current wind direction, whatever that is im no longer sure, did we rush to judgement and infer that by looking at the dark streaks? who knows what the wind direction is lately?

[fredk]

That image I posted was straight from this MOC image; I did no processing of my own.

My guess is that there may be seasonal wind direction changes, or temporary changes associated with major dust storms.

[CosmicRocker]

That's interesting, fredk. If I had looked at your image a bit more carefully I might have realized it was from the MOC. I had been playing with some contrast enhancements of HiRise imagery and that MOC resembled one of those.

You encouraged me to look again at some of the other orbital imagery available. I'm not certain I appreciate all of the differences that are taking place over time and between the various cameras. I think I'll stick with the close-up views from the rover's eyes that I am more familiar with.

I think the wind direction has been said to reverse every year, with the seasons.

[fredk]

To add one more layer of complexity, here's an animated gif with two MOC frames: The first was taken Febuary 1st, 2004, and the second October 11th, 2004:

In the second frame the dark streaks in the NNE of Victoria appear much darker. The images may differ in their calibration, but clearly there's a real change since the darkest streaks darken substantially relative to the fainter dark streaks. Eg, look at the east-most of the 3 darkest streaks, which comes out of Bay D5. There's a much fainter and shorter dark streak coming out of the same bay towards the ENE. The main, NNW directed streak gets much darker relative to the shorter streak between the two frames.

The illumination and imaging angles are different, but why would that cause a difference between the two streaks emerging from D5?

I don't think this is surprizing, since I could certainly imagine seasonal wind differences, and while the wind is blowing towards the SE, the main dark streaks should get covered in the ubiquitous light dust. It does mean though that the darkness of the streaks may have changed even since the hirise images.

[fredk]

Welcome to the Darkness!
Compare tosol's hazcam with the previous location.

This navcam is downright spooky looking:
http://qt.exploratorium.edu/mars/opportuni...IBP0642R0M1.JPG

[MarsIsImportant]

Welcome to the Darkness!
Compare tosol's hazcam with the previous location.

This navcam is downright spooky looking:
http://qt.exploratorium.edu/mars/opportuni...IBP0642R0M1.JPG

...clearly depositional. You can barely see the evidence of blueberries underneath the dark dust.

[Juramike]

Thank you very much Cosmic Rocker! That montage was excellent!

IMHO it appears that the WHITE streaks or rays around Victoria are depositional.

The apron around Victoria is composed of blueberries and dark dust. The dark dust is mostly in the NE quadrant, and blueberries seem to be of the same concentration everywhere.

After the initial apron formation - which would have been darker in the NE, the winds have blown lighter toned material on top of the darker area. Except in a few places where the winds were stronger due to local topography (deep crater bays). There you see that the light stuff was not deposited, so we see the underlying blueberries and dark (presumably heavier) dust.

Look closely at the attached image. How come there are no dark streaks in the middle two shallower bays? If dark dust is being deposited, there should be some dark dust lifted out of the crater and deposited beyond these two bays.

Instead, we see lighter colored material.

-Mike

Attached thumbnail(s)

 

[Stu]

(a hand goes up hesitatantly at the back of the class)

Seems to me that there might be a mass of darker material just beneath the apron to the upper right here... maybe as bays erode they eventually eat into this subsurface layer and the dark streaks are blown out...? Thought about this after noting how, if you look at the bays which are the sources of the dark streaks, they all go back to a line I've marked in blue on the pic... the two streak-free bays haven't reached that far back yet... maybe when they do, through more erosion, they'll produce their own streaks, too...?

[Juramike]

[Lecturer's eyes glaze over, turns and stares at the blackboard, realizes alternate hypothesis fits observations. Shrugs resigningly as wave of desperation washes over him.]

Yup. That seems also to be a possibility.

I'm thinkin' a couple of wheel scuffs by Opportunity with an MI inspection would be nail it.

-Mike

[Juramike]

Here is what might be a sequence of events leading to what we observe (need to click to enlarge, sorry!):

-Mike

Attached thumbnail(s)

 

[Guest_Edward Schmitz_*]

Look closely at the attached image. How come there are no dark streaks in the middle two shallower bays? If dark dust is being deposited, there should be some dark dust lifted out of the crater and deposited beyond these two bays.

Why wouldn't I say the same thing about the "clean sweep" theory? If there are winds sweeping out of the bays and cleaning the ground, why not in those two bays?

The answer is the same in both cases. The walls of those bays are much steeper than the ones with streaks.

Those in the clean sweep camp... Can someone explain to me how these tiny little bays are creating these powerful dust-cleaning jets?

If the bay was acting as a nozzle, it should (at least initially) shoot straight out along the center line of the bay. It doesn't. As soon as it enters the wind stream, it is swept down wind. There is very little difference in the vector of the wind leaving the bay and the wind stream itself.

If we suppose that the bay is instead causing turbulance, there should be some kind of swirling pattern. That clearly doesn't exist. As further evidence that this is not formed by turbulence, the streaks form at the tips of the bays. Turbulance would form at the tips of the capes and flow down wind. The capes that would form the most turbulance are the ones that extend perpendicular to the wind flow. The darkest streaks form off capes that are almost parallel to the wind flow.

I look forward to more lively debate on this subject. For those who think this will resolve with MI images, I am skeptical...

[Juramike]

For those who think this will resolve with MI images, I am skeptical...

What type of experiment/observation do you think would be required to provide evidence?

What would the result be for "clean sweep" theory support?
Then what would be the result expected for the "dust deposition" theory?

-Mike

[atomoid]

What would the result be for "clean sweep" theory support?
Then what would be the result expected for the "dust deposition" theory?

Deposition should be easily apparent, shoudnt it? we should see less blooberries and darker dust burying many of them, we should be able to scruff a wheel and get an MI to determine a depth of the depositional layer.

As for clean sweep, we should see more blueberries (even though bloobs are darker!) since they should be forming more of a desert pavement, if indeed there is soil removal going on and everywhere else we see blueberries at the top. there's no reason to assume differing blueberry concentrations in the initial apron deposits before these dark streak patterns emerged. Again a wheel scruff and MI will presumably be done and we'd be able to tell whats going on under the surface, if anything.

[fredk]

While we wait for MIs, here are two hazcam views, from sol 1134 (between streaks) and 1137 (on the darkest streak). The local times of the images differed by only 5 minutes, so the lighting is identical, and the rover was pointing in almost the same direction in both. The exposures appear to be quite similar, based on the sky and rover parts, but of course they're not calibrated.
Off streak:

On streak:

On streak is of course darker, but to my eye the berries look less distinct on streak as well. It's possible this is due to a coating of dust, but I could easily be wrong. I think the difference in coatings (extra light dust off streak or dark dust on streak) would be very thin, so I think we really need the MIs.