Why can it not be that the inner slopes of Victoria are composed, all around, of
exactly the same material and the evidence shows that most of this material has
a coating of light-colored dust while at some spots the dust has been blown away?

While I might not be so brave as to propose as detailed a model as Shaka described, I agree with his assessment, that it is "both." I can't provide current references, but this kind of picture is so in line with basic geological concepts that the most casually observing geo-type would almost assume these processes were taking place. We clearly have evidence that the El Dorado drifts are dark through and through, but they do have a light coating of dust that we have somewhat recently seen partially and repeatedly removed by some kind of wind turbulence. I see it as a bunch of dark, very well rounded and sorted larger grains that were deposited in an earlier wind regime that are being covered by light dust, and then uncovered when the winds become more vigorous.

Might some of us be surprised by a particularly Martian process? You bet. But I am still thinking that some variation of the "light colored dust settles when the winds die down, but is selectively removed when they are more vigorous" theory holds at Meridiani, as it apparently does in Gusev.

centsworth II: That's exactly how I am interpreting the dark areas inside the crater. There are even some smaller, dark areas inside the southwest side of the crater that I assume were cleaned by winds curling over the edge as they entered the crater. I can picture winds setting up a general, crater-bound, counter-clockwise circulation that pulled air into the SW side of the depression and encouraged it to exit on the NNE side.

I'm sure there are lots of less obvious explanations for the streaks, involving multiple processes. Some have been discussed already. One that interpolates between the extreme depositionist view (darkness is currently, or seasonally, being deposited in streaks due to localized sources inside NE rim) and the extreme sweep view (darkness underlies all of the apron, and is swept clean only at the streaks due to localized winds) is the following:

At some time in the past, an event, such as a collapse of a section of cliff, or even just gradual erosion, exposes a dark source which erodes quickly and spreads dark sand around the NE of Victoria. The source is now depleted, but there are still today more/darker/closer-to-surface dark deposits in the NE. Then we don't need to postulate strong wind variations from E to W to explain the darker streaks in the NE, and we also explain the dark patches inside the NE rim. This might also explain the apparent lack of small berry pieces we see on-streak in the MIs - they were covered by dark deposits, but some time ago. To sum up, localized deposition in the past, and sweeping today.

Does this scenario sit any better with the devout sweepers? It does remove the need for an extra process (deposition of darkness) occuring today, but instead pushes it somewhere into the (relatively recent?) past.

A variant of this would be that the variations from E to W across the crater are due to pre-Victoria-impact variations, but I have no clue how likely it would be that such variations could survive impact so close to the crater. Also this would have trouble explaining the apparent difference in MIs on- and off-streak.

Well that's the thing about evidence. It points toward an answer. In this case, there is dark dust/sand moving in this area.

If there were no dark matterial moving here, I don't know what effect the winds moving through the bays would be. Maybe a light coating is being removed at the same time the heavier dark matterial is being deposited. But I agree with FredkHere's my best argument for deposition of dark grained matterial. Barring further evidence, Iwill leave it at this...

- the MI's show buried large grains. See Cosmic Rocker's post
- the color of the dunes in the crater matches the color of the streaks. See HiRise Image
- there are dark deposits on the crater walls. My previous post
- the proximity of the dunes to the streaks is beyond coincidence.

I have a particularly strong belief in the desposition theory. But it's all good. I hope y'all are enjoying this mystery as much as I am...

I'm not sure what to believe, but I do notice that on the original MRO strip, the blackness extends far to the north, and apparently well into the lighter dunefields beyond the apron.

If the wind is/was from the south, and encounters a higher crater wall to the NW than to the NE, an eddy would form. This subtle change in topography might be enough to cause a local wind speed increase sufficient to lift dust over the NE crater rim, for deposit downwind (where "downwind" very quickly reverts to "toward the north"), but I have a harder time believing that it can cause velocities far enough northward to sustain sweeping at ground level.

On the other hand, the ground appears darker south of the crater, and after the lighter dune fields north of the crater's dark streaks comes more of the darker ground further north.

I decimated the original 132 MB strip into the attached 91K version for those with lower bandwidth. The only other small version I can find on the forum cut off the area to the south.

Click to view attachment

--tc

As a Depositionist, and to build on Ed's petition above, i also have to reconcile my creed with the observation that "light colored dust blows away first, leaving the dark", so it should follow that there is light dust blowing away from inside the crater, so i'd guess it should leave dark areas inside the crater. however, the dark areas inside the crater look clearly depositional and dont appear to be evident of any sort of wind dynamic when viewed at this range. (well unless of course the streak and crater dark deposits are formed by different processes).

It also follows that the dark streaks emanate from what seems to be the area of most ongoing debris removal, given by the number of boulders and the offset (closer to north) placement of the inner dune field. Whether the boulders are merely evidence of deflation in the north side or are just recent rockfall debris, both processes would suggest that there is more debris transport from the north side where the dark streaks emanate from. Since the debris has to be deposited somewhere, i expect it to be pinned up against the highest areas of the cliff, especially if that is their source, as well as the dark streaks themselves.

If the dark streaks are to be interpreted as the prevailing wind direction, i can imagine the prevailing wind setting up a Clockwise rotation tendency inside the crater due to the preferential exits of Duck bay and bottomless bay. This should tend to nudge the dark deposits to drift to the NNE, right where we see them. While much of it should remain stuck beneath the steep parts the upper cliffs right where we see it, some of this should eventually spill over the top, which is in itself a strong sorting mechanism, and deposit the highly regular grains seen in teh dark streak MIs.

I have an easier time thinking of talc-size dust blowing around and burying the blueberies like this rather than the larger sand grains as appear to be in the excellent MI images studies that have been assembled here, but even if thats also going on, perhaps there wouldn't be much of a streak to look at, since it would have blown away. the larger gains can stay around, whereas the light dust may be too ephemeral.

Something I notice too in the "excellent MI images studies" picture: the berries in the streaks are shinier. Dust carried by wind could easily provide this polishing service.

Thanks folks, for your "excellent" comments on the picture, if not on my interpretation of it. Does anyone think that a few berries in the recent MIs appear to have been pushed into the soil by an instrument on the IDD, or perhaps a rover wheel. The missing images will hopefully clarify that.

Without a doubt, fredk. To clarify, when I made my "most casual observer" comment I was referring to the processes taking place at El Dorado. It is not nearly as obvious to me here at Victoria as it is on the other side of the planet. The darker stuff inside the crater, in the vicinity of the dark streaks outside the crater, really does open the door to other and multiple interpretations.

We kid around with terms like "believer," "devout," "depositionist," and other words that remind us of certain religion versus science debates, but there is no room for beliefs in planetary exploration. I'm having fun, and I feel as if I am exploring another planet in a way I have never previously experienced. It seems that most of us have a similar mindset, and that enhances the experience for me. Thanks to everyone for that.

Until new imagery or other blessed information is delivered unto us, we can only continue to speculate, pray, or go back and dig through available information for scraps we might have missed on the first go-around.

Amen! (You asked for it, Rocker! )

More seriously, the latest status update tells us what Oppy's been up to in characterizing off/on-streak soils. Sounds pretty extensive:

I think the point is, they are shiny because they are
clean of dust, which has been blown away. The matte
appearence of berries in the bright areas between dark
streaks is possibly due to a coating of dust.

Well, the JPL people are clearly devout Depositionists. In the status update they speak of "dark wind streak material which emanates from Victoria Crater". Of course, they prematurely put the beacon on the far side, too.

Brian

I interpret the shiny as being a result of polishing action, not so much the removal of dust. They are also spherical, so dust would be more prone to fall off, especially with gentle wind flowing over.

Hopefully we'll have an official explanation soon.

A drive today roughly southwards towards the next (unnamed) bay. We still seem to be "in the dark". This may be the closest view we get of the fresh looking rockpile crater we've seen from a long way off:
http://qt.exploratorium.edu/mars/opportuni...NEP1977R0M1.JPG

I had always interpreted the 'pushed-in' blueberries and being pushed in by the MI (perhaps as some sort of setup for getting a focus distance measurement). I can't see those spaces as preexisting since they would long be eroded away or filled in. ive always assumed they were made in the process of taking the MI.


Regarding the "polished" look of those dark-streak blueberries, if its a dust coating, then it has been somewhat modified (by humidity?) mainly since its shiny and not diffuse, you can see the bottom area where its not polished and this is supposed due to slower grain motion at ground level at this scale. I can see some sort of polishing going on, but i dont think thats just due oto the polishing ffc removal of blueberry material, i think it has added something, i might be reading too much into it, but it looks as if the dark material has imparted some of itself, in a sort of lacquer coating to each blueberry.

The MI has a probe on a spring as a contact sensor - if it touched, you'd just get a little hole where the end of the probe hit the soil.

http://marswatch.astro.cornell.edu/jpeg/as..._Inst_Set_1.jpg

un-needed quote removed. - doug

so thats the little pin with mid-spring at the lower right of the assembly? im not sure how this could be pushing in the blueberries like we see, so something else must be going on, i thought they might be first pressing down with the other tool (at upper right in the image) as we've seen in many other MIs before (the circular ring imprint in the dust), but now im newly mystified whats causing the pushed in berries without compressed dust ring, i wonder what theyre doing to cause this...

According to the latest update they've also been doing apxs measurements - could that result in pushed-in berries? Does the apxs give the circular outline? A circular outline might be hard to make out if it only contacted the berries and not the surface between them.

The Mössbauer and APXS both have circular contact plates. I suppose if pushing the berries into the soil encountered enough resistance, the IDD could stop before making a circular impression in the soil.
APXSMössbauer

I noticed for a long time that the apxs will make a deep impression to a bearly visible impression and everything in between. I think it's safe to assume any pushing of berrys is due to one of the instruments. If its just one berry, it could be a direct hit with the MI probe on a previous frame.

Oppy has made a slight shift to study a rock nearby. This was followed by a humourous shadow puppet performance which was well received by all present:
http://qt.exploratorium.edu/mars/opportuni...O7F0006L0M1.JPG

Big Bird and Gonzo?

Soup Dragon and a Clanger!

Curiously, I see a leprechaun on the rock, being attacked by a dodo bird.



Brian

Tennessee Tuxedo and Chumly

I was thinking more of "Mystery Science Theater".

Something like this? That was great. I saw that image come down today, but I totally missed the shadow puppet show. I've got to stop looking at rocks.

This became a topic on irc today, and a guy from Argentina noted that it reminded him of Mystery Science Theater 3000. There was something familiar in those shadows, but I couldn't pin it down without his clue. This is my small attempt at humor, but there might be other potential captions.
Click to view attachment

Someone playing golf with their friend the T-Rex.
Roy F

Sorry, all I could think of was this when I saw that image.
The flamingo strikes!!!!
Enjoy
Astro0
Click to view attachment

Florida Stowaway Finally Emerges from Hiding

Could there be a causal relationship between this and your avatar, Brian?
Obviously there is a connection with our generational cartoon Weltanshauung.


P.S. Lots of new images of surfaces in and out of streaks. More to come. Our statisticians can get to work counting and measuring blueberries.

Thanks for the show, Oppy!

Getting back to business, one consistent difference between the new pancams off- and on-streak is in the wheel tracks. Compare off-streak, sol 1136:
http://marsrovers.jpl.nasa.gov/gallery/all...D2P2401L2M1.JPG
http://marsrovers.jpl.nasa.gov/gallery/all...D2P2401L7M1.JPG
with on-streak, sol 1139:
http://marsrovers.jpl.nasa.gov/gallery/all...IBP2403L2M1.JPG
http://marsrovers.jpl.nasa.gov/gallery/all...IBP2403L7M1.JPG
The local times are over an hour apart for these images, but it's pretty clear there is a difference in the tracks. Off-streak, the tracks are dark and smooth, with no berries showing through. On-streak, the tracks are much lighter in L2, and many berries show through. As I said, this is consistent across all the new pancam imagery.

I can think of two interpretations at the moment: one is that the fine soil on-streak is shallower than off-streak before a harder layer is reached, so the berries can't be pushed in as far. The other is that the soil off-streak is "softer" than on-streak, so berries are more easily pushed in.

Regardless, the off-streak behaviour has been the norm at meridiani, I believe, so something new is clearly going on on-streak.

Going off what fredk points out, here is a little photo essay, off-streak vs. on-streak. I have no idea what any of it means, I'm just in it for the pretty pictures.





I will say it doesn't seem like the first time we've seen tracks like these. I bet there are comparisons around Endurance. Just speculating, though.

Fred, I think I see what you are talking about. What chemical action would cause the soil to be relatively stiff on streak? Moisture of some sort in the recent or distant past? Is this observation real?

Howard, we need closer close-ups for a good comparison in those images.

The dark dust is on the down wind side of the rock. Case for deposition.

Click to view attachment

Not necessarily, though I've moved from smack in the middle of the clean-sweep camp to somewhere on the fence, at the moment.

On the side of clean-sweep, it seems to me that if dust was being removed from the streak in general, a well-sorted amount of that dust would tend to fall out behind uneven, jutting protrusions (like rocks). That sorting might well favor heavier, larger-grained (and darker) particles, while the lighter dust (both in mass and in hue) blows further away.

If the dark dust is blowing out of the crater and being deposited, I'd expect it to pile up on the upwind side of the rock, not the downwind side. If it takes a rock to make the dark dust pile up, I'd argue you're seeing the minor movement of dark soil components, not dust blowing out from the crater.

Of course, without a good model of the wind dynamics in and around this crater, it's hard to tell just what's happening, here...

-the other Doug

Any sign of djellison there?

fredk: That's very interesting. Really interesting, actually. Is this driving you mad, or what? It seems that so many raw observations can be interpreted favorably for either camp. What's with the uncommon L1 pan we saw today?

Floyd: That sol 1143 image was taken through an L2 filter, right on the edge of the near infrared band. The views through other filters appear quite differently. Take a look at the L7. http://qt.exploratorium.edu/mars/opportuni...NEP2599L7M1.JPG

More importantly though, that tiny patch of extra darkness would be very hard pressed to explain the overall darkness of the streak in the HiRise images. Just guessing, but it might be enough to influence a pixel, if that bright rock was not nearby.

Nice imagery has been coming out of the queue in the past two days. Can't wait to see some more.

dvandorn: I'm still leaning clean, but this isn't the slam-dunk I thought it would be.

No signs of that other Doug on this end, either, centsworth_II. We really could use a tie-breaker at this point.

They are a fairly regular event, an albedo observation of the surrounding terrain usually used to tie in with an observation by an orbiter.

Doug

You've missed the boat entirely. There is no dark streak, only a bluish area that appears darkish when viewed with a red filter. The source material is the blue-toned talus at the base of the cliff.

Nice colour sets down today...

Click to view attachment

Click to view attachment

I'm still firmly in the cleaned streak camp folks - we have a harder sorted crust layer with a higher visibility of (slightly cleaner) blueberries => stiffer surface as per mhowards demonstration and an effect that is only significanlty "visible" in a filter that highlights blueberries.

I love the first picture, Stu. And it made me wonder about the effort required to shove the blueberries into the soil. A few minutes with Excel later, and I see that it's straightforward. With minimal wheel sinkage the ground pressure on the rover can be quite high: about 40kPa (<6psi) for a tween-cleat's area-worth of support. This is about 2/3rds of the pressure of a human foot on the ground.

It's no surprise that when the aluminium wheel is initially contacting, say, the tops of 50 of these berries per tween-cleat-area, the pressure rises: the load is the same, but the surface area is reduced. Pressure on the berries as they're forced down is around ~320kPa (46psi). Say about a pound (Earth pound!) per 3mm berry. No wonder they disappear!

Thanks for the mathematical wandering!

Andy G

I'm late to this dust-up... mostly because I didn't think there was much doubt about what causes the dark wind tracks at Victoria. However, obviously there's a lot of people thinking 'deposition' versus 'swept.'

When you look at the same light-dark phenomenon at other craters, it is easy to see that it is wind-caused - almost always in the prevailing wind direction, and often extended by vortices ('dust-devils') ranging from small eddies to well-formed powerful whirlwinds that form in craters and travel some distance before collapse.

Whirlwind formation happens best at craters of the right size and depth for a given wind speed and time of year. Below are two pictures showing whirlwind tracks that begin at craters and travel various distances away - note that all of these craters are not known to have dark material inside them to provide 'deposition.'

Click to view attachment Click to view attachment

Vortices cause the 'deposition' folks a problem because they don't pick up dust in a column until they are well formed which occurs after exiting the lee side of a crater, then they carry it away dropping it across a large area down-wind after the column disintegrates.

At larger or smaller craters whirlwinds of any strength are rarely well formed and their 'tracks' are shorter - as at Victoria, and the famous 'double crater' below.

Click to view attachment Click to view attachment

At Victoria as at any crater, there are times of the year, and times of the day, that these tracks appear darker due primarily to dust removal, and the effects of lighting and reflection of light. Below is a picture of very dark wind-tracks at Victoria - and a picture of Oppy's tracks taken shortly after leaving ‘Jason' on Sol 382 that appear light.

Bottom line, when these wind tracks at Victoria are the darkest, they are more likely caused by dust removal than highly unlikely greater deposition of dark material from within the crater - and Oppy's tracks can appear light or dark depending on were the sun is more often than what the material under the wheels is.

Click to view attachment Click to view attachment

I don't believe the presence or absence of 'blue-berries' has any effect or plays any part in the appearance of the wind (most likely numerous small whirlwind) tracks at Victoria.

One last point - I don't know if there is likely to be wind at Victoria at this time of year, but if there is any likelihood of wind - Oppy should stand by where she is for a day or two in the hope of getting several nice cleanup jobs done on her solar panels.

It would have been most interesting had the operators taken photos of the panels before heading into this likely place to get a cleanup job done - and some after photos afterward, if there is any wind...

Regarding the L1 albedo pan, I don't recall one in the past which was 2 frames high. Am I wrong?

Bill: I'm sure you meant "bluer than the rest of the apron" - we haven't seen anything genuinely blue-hued yet. The streaks have been essentially invisible in L7. But since reddish hues dominate here, it makes sense to call the streak "dark". It's certainly worth pointing out, though, that this "darkness" is more than just albedo and presumably that tells us something about composition. Regardless, there's something to explain here!

dvandorn: why do you expect depositional dark dust to pile up on the upwind side, but dust swept off to pile up on the downwind side? By postulating that sweep picks up dark as well as light dust, but drops only the dark, you are adding epicycles!

Isn't it just a matter of wind speed, and I'd expect that to be slower in the lee. Therefore deposition of dark dust from inside Vicky would be more likely in the lee. If this was sweep, we should see less sweeping in the slower wind speed lee, and hence a lighter surface in the lee.

A reminder that we've seen these lee deposits on the rim at VwP:
http://marsrovers.jpl.nasa.gov/gallery/all...ARP2396L2M1.JPG
This means that there is dark dust originating upwind of the rim, which sounds like Deposition to me!

Rocker: it's the red bands where the streak is visible - it's invisible in L7. This "tiny patch" certainly doesn't cause the entire streak to be dark, but it does show that deposition of dark dust does occur as a process.

Yeah, this is driving me mad! But I think we're closing in on Depositionism here. The good news is the planners are clearly taking this very seriously, judging from all the pancam/MI observations.

Sattrackpro, I don't beleive we've seen any individual dd trails in meridiani, and certainly no active dd's. Also, the dark streaks from Vicky and Double don't look like dd trails. Why wouldn't we see individual dd tracks coming from smaller craters in Meridiani?

The Double crater image is interesting, but I can see dark deposits (not just shadows) inside the rim. Likely the same thing is going on here as in Vicky.

Here's another very interesting observation that I interpret as evidence for Deposition (heck, puts the final nail in the coffin of Sweep!), but no doubt Sweepers will claim it supports them.

These frames were taken from the sol 1137 location, looking WSW at the rover tracks:
http://marsrovers.jpl.nasa.gov/gallery/all...IBP2298L1M1.JPG
http://marsrovers.jpl.nasa.gov/gallery/all...IBP2298L1M1.JPG
http://marsrovers.jpl.nasa.gov/gallery/all...IBP2598L2M1.JPG
They clearly show that light coloured dust has blown towards the left out of the rover tracks since they were formed.

Sweepers: where does this light dust come from? Deposition predicts that there is light dust under the dark deposits, which could be exhumed by the wheels.

It's interesting to see that the wind direction is towards the rim. I speculated before that winds vary seasonally here, so it seems that deposition from the crater is not occuring now.

No need for photos, just keep your eye on that energy dial.
This is how previous "cleaning events" were documented.

Where is the dark dust that should be swept onto the tracks from the right
as the light dust is being swept off the tracks?

I get the impression that "all" dust on Mars is light and darker materials
come in larger, sand-sized grains. maybe this has to do with optics and
not composition, or is dark basalt harder and less likely to be ground
into smaller than sand size particles?

Are you saying that the dark deposits in Victoria can not possibly be explained
by the same process used to explain the dark deposit that is El Dorado?