Mike, you may be right, but it might just be due to the different viewing angles.

On a different topic, all this talk of bedrock in the dark streaks reminded me of this cluster of exposed rock a few bays east of us:
Click to view attachment
It stands out because it's about the palest ("whitest" in this false colour image) outcrop around Victoria. It's also near a dark streak. Unfortunately we won't get that far according to the current plan.

I'm gonna have to agree with mike. There seems to be a slight amount of movement all around the base of the rock. My first impression was that the IDD must have disturbed the soil in the lee of the stone. But it now appears there is real soil movement going on. It's really most obvious just to the right of the circle. Quite a few berries have been covered.

Nice catch mike...

Sand grain movement, hopefully not requiring an airspeed of > 70 m/sec 250kmh, but in more of a 'tumbling-along' sort of way, since there must be some easier mechanism to explain the grain movement we've seen at Alicante. its certainly not undermining as in the rover track berryfalls.

i'd suspect that bare bedrock such as the exposure shown here tends to stay clear since there are no other grains holding on to the ones on top, so its easier for the grains too tumble and berries to roll away.

This type of net deposition (sweeping is certainly going on as well) would also be explaining most of whats going on the bottom of, for instance, this HiRise image grains blowing uphill, no?

It may be impossible because of different viewing angles, but could someone warp the berry part of the images to superimpose and then do a flicker image? It would really help with seeing the differences.

Floyd

Horton did this a little while back.

Are fines coming out of the crater responsible for the apparent layering (dark and light layers) in the dunes we saw on the way to Victoria?

dune layering on the plains consisting of fines blowing in from the whole planet in general to mix unevenly with the larger local grains i think...

..which brings me back to: did anyone ever hear of any research trying to link the dune layering with any sort of seasonal/epochal timeline? if we could count tree-rings, then we'd know what were looking at. i dont know if anyone has even submitted a theory arguing whether the sand dunes are fossils or not.

I used to think that as well, but I went back over the dune pictures, and it looked like the layering became more distinctive as Oppy approached the crater annulus. I starting thinking about what fines could come out of the crater and what that additional deposition might look like. I'm having second thoughts about how the dark layers in the area around the annulus were formed. I'll still lean toward "global dark fines floating down" but how much dust did come out of that crater? Any? I mean, if that much wind erosion went on, it couldn't all stay in the crater. Did many of the blueberries knock together enough to grind them into "blueberry dust" and then got blown off the annulus? I don't know. There's more to the wind profile than meets the eye.

From this thread, there was recently a podcast featuring an interview with the Rover mission manager Byron Jones. He made some comments about the dark streaks. Remember that, as I understand it, Jones is not a member of the science team, so we should be careful about interpreting this, and his comments do contradict what we've apparently heard from Jim Bell. Nevertheless, his statement was quite unambiguous. Here's my transcript:

Well now...that's interesting, isn't it? I thought this was mostly settled with Jim Bell's comment, and now I'm not quite sure how to interpret Byron's statements. They were just ambiguous enough to start me wondering again.

Cosmic,

How do you get "we do know that it's material that was carried out of the crater" to be ambiguous?!?!

The ambiguity is in the fact that a scientist is saying one thing and an engineer the other

PERHAPS...the answer is that we're ALL right. It's fast winds all right, clearing the lighter dust, and depositing heavier dark sand as well. Consider El-Dorado....where was the dust there....none to be found...just dark sand. You need stronger winds to carry that stuff. But stronger winds will get rid of dust as well.

Just a thought.

Doug

That's not ambiguity, that's Normal Working Practice, surely?

I really don't think we're going to crack this until either Oppy heads into the crater and examines some of the dark material, or she catches sight of a haze of dark dust approaching from out of the crater after a strong wind gust. There just doesn't seem to be enough evidence in the surface pictures taken recently to wrap up this argument one way or t'other. It's going to take a guy or gal walking around Victoria, taking samples and working it out the good old fashioned way.

It might be time to move on, move in, raise your eyes to the sky again and start looking up at some of those outcrops Oppy instead of staring down at the ground beneath your tired wheels...

Stu, I haven't been as pessimistic as that. JPL has access to a lot more data that we, and (perhaps) better arguments. Still, the apparent disagreement between the two is disheartening.

Doug, I (for one) have been pointing out again and again that things may be more complicated that pure Sweep or Deposition. The real question is do we have a dominant mechanism.

Still, I expect we will find out what the Bigwigs are thinking very, very soon.

Not really being pessimistic Fred, just think it's time to stop flogging a dead berry and go see some more of the sights. I'm sure the explanation will emerge eventually, but Oppy is a Mars Exploration Rover, not a Mars Stare At The Ground For Days On End Rover Time to get rollin'; again...

Unless there are some of those endlessly fascinating festoons just lying on the ground...

-the other Doug

Stu: It is ambiguous because he made no specific comments about the timing of events. The dark material could have come out of the crater rather recently, or it may have come out quite some time ago. The former scenario would correspond to the depositional idea as I understand it. The latter scenario would be consistent with the removal idea if the dark material was later covered with light dust that was selectively removed recently.

Ah, I see what you meant now CR, thanks. I thought his statement was pretty unambiguous in that he was saying the dark stuff came from inside the crater, but you're right, the lack of a timeline still leaves the waters muddy.

About time this was sorted once and for all now... Oi! All you MER people reading: will someone PLEASE tell us what's going on?!?! You know, don't you, you're just enjoying watching us tie ourselves up in knots here!

Here's what I meant:
From the latest planetary society update.

Depositionists rejoice!

To quote an Olde English folk song from days of yore...

"Oh it's all gone quiet over there... yes it's all gone quiet over there..."

So if future HiRise passes see the streaks fade, will that make everyone satisfied?

"...even the fruits of victory would be ashes in our mouths."
-John F. Kennedy

"..everything is dust in the wind"
-rock 'supergoup' Kansas

Not so fast.

I don't think it would take too much prodding to get Squyres to say further
that keeping the streaks dust free is essential to keeping them dark.

"The dark material appears to be just sand blown out of the crater," informed Squyres.
It could just as well be sand NOT blown out of the crater, but blown in from somewhere else.
The ESSENTIAL is that, wherever the sand came from, it has been blown free of dust.

"It's dark because the sand on Mars is dark." He says. The dark sand blown
out of Victoria was probably blown into the crater at some previous time. And is
probably not significantly different from sand being blown all about Meridiani all
the time. It is not the fact that much of the sand in the streaks came from the crater
that makes them dark, it's the fact that the streaks are dust free that makes them dark.

Poor Stu, you don't see that Steve Squyres has burst the bubble of all
who imagined some unique dark substance unearthed in Victoria:

"[it's] just sand.... It's dark because the sand on Mars is dark."

The deposition theory always said there was a cycle. Dust blows out forming a dark streak. Seasons change, wind patterns change. Streak fade due to dust deposition. Cycle starts over.

There is no cleaning going on. There is dark sand deposition and light dust deposition. That's it.

I'm satisfied to see the cause of the streaks as two sides of the same coin.
The same wind blowing dust clear of the streaks is also depsiting sand from
the crater. However, the streaks would be dark if no additional sand were
blown onto them from the crater, if only the ubiquitous sands of Merridiani
were present and blown free of dust. Yes, sand from Victoria is deposited
on the streaks. But I still give the bottom line to the sweepers: the
streaks are dark because they are dust free.

Steve has spoken. Let no mere mortal question...

-the other Doug

I don't see any way to prove that by what we see.
The dust that is present below the surface could be from a windless period
when no clearing of dust or deposition of sand was taking place, only deposition
of dust. When the seasonal wind is present there could easily be deposition
of sand from the crater and removal of dust by wind too weak to hold onto
the sand but still strong enough to carry dust away.

edit: When the winds start up again, some of the dust buildup is removed
but some is covered by deposited sand and preserved as a layer beneath,
waiting to be exposed by some roving rover.

I wonder what you think he has said.

Mere mortals parse the phrases of the
Bible all the time to support their views.

No need to "Poor Stu" me; my idea was a long shot and I put it forward as such. I'm happy to have my unconventional bubble burst when it has been shown that the basic idea it bubbled up from was basically right:

crater + wind + dark material = streak.

Click to view attachment

With the recent statement, I revived these quotes from the thread. It sorta all fits together:

When deposition>removal, you get a layer.
Dark sand out of crater blows out from crater/dark streak on annulus and goes all over plain = dark zone in sequence.
Light dust from all over Mars filters down from atmosphere = light dust buildup makes light zone in sequence.



There's probably a pretty tiger stripe sequence of altenating dark layers and light layers as you dig down in the streaks. I'd expect dark streaks when more wind is present, and light streaks all other times.
Just like tree rings. Everybody wins.

Any imagemeisters got any patterns from image analysis of dunes near the annulus? Might give a clue as to the seasonality....

-Mike

Stu: I think you've discovered a burst bubble... And it's not yours, either!

I take Steve Squyres' comments to mean that there is nothing special
about the sand being blown out of Victoria onto the streak. It is the
same as the sand laying all around on Meridiani. In fact, the same blowing
out of Victoria once was laying on Meridiani, before it was blown into
Victoria were it lay until being blown out back onto the plains.

The dark layers in the dunes did not come from Victoria, but are due to
some Meridiani wide process.

Hmmm. So how come the layering gets more distinct as you approach the annulus (as WindyT noticed)?



-Mike

I don't think the gusts that carry sand out of the crater drop so quickly in energy that
they dump their sand load and have no power to sweep away dust. I think the fanned
out, feather edged pattern of the streaks indicates a wind which loses strength over the
length of the streak. The wind could not have carried some sand all the way to the end
of the streak while not removing any dust along the way.

Steve is making fun of us!
It looks like Spirit is winning this round.

Ok, just to show I can have an open mind, I thought of a way this could happen.
Perhaps you all have thought of this before. The wind blows up over the rim and
does not stay on the surface and causes no turbulence on the surface, so no
dust is removed. As the wind loses energy, sand drops to the surface, more at the
beginning of the streak and less toward the end.
Click to view attachment
It doesn't necessarily happen this way though.

That's the only reason you're saying this? It doesn't have anything to do with figuring out what is really happening?



Actually, it is exactly what is happening...

And, I might add, it's been explained that way many times in this thread already.

And it's what S S has said (twice) already...

But thanks for coming up with that indendantly.

The same strong winds that carry the heavier sand out the crater will also be keeping it clean of the dust that falls everywhere surely?. If it was ALWAYS deposition and nothing else- then it would be a huge big pile would it not? A big pile built up at the lip of the crater.

The dust falls everywhere - it's why the sky is the colour it is.. In light winds it forms dunes of its own. In heavy winds, it is blown away totally. Only stronger winds carry the sand. So - for this to be a place of all sand and little dust - both deposition AND erosion have to be occuring. Not only because we see no dust that we know to be falling everywhere, but also because if there were no erosion at all - we would have a sand mountain to see.

Doug

Can you blame him, though? This has gotten quite silly...

I disagree. El Dorado is a trap. The grains are being blown up the hill and roll back down. They have nowhere to go.

The streaks are not a deadend. The grains are being lofted out of the crater by the wind funneling thru the bay. Once on the apron, the streak is subjected to the same (weaker) winds as the rest of the apron. If the streak was being swept of dust, the rest of the apron would be as well. The reason that the sand is being deposited is that the wind is weak in the streak zone.

The dark patches below the crater rim are in a topography similar to
El Dorado, but above the rim who knows how the wind behaves?

Me playing devil's advocate :
Do you think the case I diagram above (and below) -- where the winds leaving
the crater are shot above the surface and so do not remove dust
from the surface outside the rim -- can not occur?
Click to view attachment

We know there to be stronger winds at the streaks - that is the mechanism by which sand is being put here. Those stronger winds will also clear more dust off the surface than anywhere else. Why would the berries be polished if the winds here were the same as everywhere else? They're polished because stronger winds are blowing surface material along and bouncing it past all the berries surely?

That diagram is interesting - but it dictates that sand is gettting thrown onto a several hundred metre parabolic arc out of the rim surely? This isn't about one steady state of one speed of wind in one direction..it's about prevailing, statistics, distribtuions.

This is not a black and white issue guys - stop pinning your pet theory on one side of a fence that just does not exist. It is indeed very silly - as I told you all it would be some days ago. Superlatives, hand waving, football chants. It's childish.

Doug

(PS - I've edited my previous post to remove the El Dorado reference, that was not what I was trying to say)

Ahhhhhh... the polished berries.

Good point!

I don't pretend to have all the answers, others should stop pretending that they do I see a range of symptoms that no one simple theory here has covered unambiguously.

Maybe the simple fact that more sand ends up here dictates that more polishing of berries goes on. BUT - is the streak the same direction as the prevailing winds? If winds are picking stuff up from inside and dropping it out on this side of the rim - what is going on on the far side from here?

If the sand was being dropped just outside the rim then would there not be a large pile, maybe a mini dune field - from which it is then redistributed with the 'nominal' apron winds. For there to be no pile then that dictates it is being thrown out at a rate slower than it is being then moved on by normal winds - BUT - that then means the normal winds are more powerfull, more dominant that the ejecting stream and would that not mean that everything around here should be polished?

If it were whipping over a lip, perhaps you would have a stall on the rim edge, but we don't get that here it's whipping up a slope which aerodynamically blends reasonably well into the apron. How has the wind here altered the profile from ramp to apron compared to other ramps?

Notice all the question marks?

Doug

How much stuff do you think it takes to change the surface brightness or color?

Besides, no one is saying that no material is being moved on the apron. It's just not any more than the rest of the apron.

Take a look at the topo map. There is some hint that there is topology associated with the streaks.

Don't know. How much do you think it takes?



So if stuff is being moved within this streak no more than anywhere else - but sand is being thrown out of the crater preferentially at this point - where's the net balance of sand producing dunes or similar?



Nothing conclusive, nothing that isn't ambiguous, nothing more than lots of other places around the crater that don't have streaks

I thought we were all just having a good natured knockabout laugh with this debate, just a bit of fun, kind of a "Beacon Round 2", hence the football chant reference. My apologies.

People seem to want there to be some reason that the streaks act differently than the rest of the apron. They don't. The wind sweeps out of the crater through all of the down wind bays and carries material with it. It is simply that there is dark sand under the streak-bays that makes the streaks visible.

As for cleaning on the streaks - Why do we need to envoke it. The streaks appear rather suddenly and fade over time. It's a simple case of sand being deposited and then dust being deposited.

What happened to S S having spoken. He didn't say sweeping and deposition. He said deposition. Period.

How do you know this?

If sand is deposited then dust depoisted then repeat...where is the big pile of material?

Steve didn't say 'Deposition, Period'. He said 'Deposition'. You're infering more than he said. He said that deposition is occuring. If deposition is the only thing that occurs at these places - then over the past several billion years they would be huge piles of sand. These do not exist - thus an element of erosion must also be occuring. I'm not saying you're wrong. I'm not attempting to pose a theory of my own. But can you see that you are over-simplifying the processes here? If only one thing were happening all the time in these places, they would be very very different to the surrounding terrain. They're not. They're different in a subtle way. This isn't a trombone solo going on - there's a full orchestra at work. We can hear the trombone...but there's other instruments playing as well.

I've said it again, but it bares repeating. This isn't a black or white issue. It's a blend of processes.

Doug