This is the way I see it at the moment.

1. Corner crater is too small to throw this amount of ejecta this far - this amount of ejecta would only be found within a couple of crater diameters of it. So this is from a more distant source. Corner is indeed very young.

2. Endurance had no blocky ejecta... the evaporite, I think, does disintegrate fairly quickly, and a lot of Endurance ejecta was poorly cemented dune sands which would disintegrate immediately. A lot of Victoria ejecta would be like that too.

3. This stuff is either a more consolidated layer, so it hangs together better, or it's shock-lithified or glass-welded much more than Endurance ejecta was - after all this is a bigger impact. It would be useful to get a look at it. But I suspect much of the outer rim of Victoria will be covered with this.

4. Victoria isn't really very old. It looks a lot fresher than other craters MOC sees throughout Meridiani. I'm not saying it's just 20 years old, it might be 10 million, but it's not a billion years old either. I think the larger ripples are inactive and only the smaller transverse ripples we see occasionally are active.

Phil

Shaka:

Yup. Victoria is old and worn down by time; it's secondaries must have vanished ages ago.

Bob Shaw

We are beyond the coherent ejecta blanket of Victoria, but I'll still suppose that these rock piles we are and will be seeing are clumps of boulders, etc, thrown out by the Victoria impact. Much like the Copernicus rays.

We'll be seeing more of this "dark basal unit" (my own holy grail that I harp about) which seems to be basaltic and more weather-resistant than the evaporite sand-silt-stone. I say "basal" because underlies the evaporitic sequences.

--Bill

Sol 831 was supposed to be a moving day IIRC. I haven't seen anything about Sol 832 (currently in progress). Do we have any information on where Opportunity got to yesterday? Is this a stay put day (most weekends seem to be)?

Victoria is certainly younger than some of the other craters in the MOC imagery but it's still got to be much more than 10My old. Victoria's ejecta was somewhere in the region of 10-100million tons, even if that was well shattered and fairly uniformly distributed it needs an awful lot of time to reduce that sort of ejecta to the fairly uniform sand\dust that appears to be in the surrounding area. I'm definitely no expert in these things but the theories seem to be mostly in agreement that the current erosion rates are extremely slow (3nm-30nm per year for Meridiani over the past 400My ) To virtually completely eradicate the debris field of something as messy as Victoria requires a couple of hundred million years at least.

That said your point about this rock pile possibly being a fairly resilient shock lithified or glass welded chunk makes sense - I hadn't considered that. It seems to be well worth some examination even if it is out of context, it is an interesting chunk of geology in itself.

According to the tracking web, sols 831 and 832 are dedicated to "other business" and no IDD work. The next driving sol is 833, meaning that the rover drivers will get fresh images from a new site on Monday morning.

Mmm, still on "restricted sols"?

Although the scaling rules of impact cratering are designed around craters bigger than Victoria, the maximum excavation depth should be less than half of the transient crater diameter, the latter being smaller than the current collapsed/eroded diameter. That means a depth of less than 400 meters in an accumulation of sediment 800 meters thick.

Yep only one person minds the store on weekends....see here:
http://www.unmannedspaceflight.com/index.p...indpost&p=55502

Bill:

Hopefully, we'll see Burns Cliff II at Victoria, and will be able to get a good look down through the strata. I see no discontinuity within Victoria, however, in any of the orbital images, which suggests that there has *not* been a 'punch' into a basaltic layer. It's all very smooth! If the bedding isn't perfectly flat (and why should it be - we've assumed a gradual dip across the region previously) then I'd have hoped to see some sort of arcuate features within the crater bowl, defining the radical change of composition even if shrouded in surface debris. I certainly can't see such a feature, which suggests to me that the lower basaltic units are still beneath the lowest part of the crater. That would mean no remnants of the Victoria ejecta blanket (though there might be ejecta from other, larger and more distant impacts).

Bob Shaw

It looks to me as if Victoria is surrounded by a very smooth layer of dust, perhaps dust that filled in around the biggest chunks of ejecta material. Even worse, Oppy's approach appears to be from the down-wind side where the dust blanket would be expected to be thickest. There may be a significant amount of time spent traveling around the rim looking for a way in before we ever will get to see the basin of the crater.

Perhaps the blanket we see around it is a big pile of hematite blueberries, and the sulfate surrounding them was pulverized and blown away in the wind.

That's probably as good a guess as any I might offer. I am hopeful that it will be sufficiently firm for Oppy to cross. It is not pushed into ripples as far as we can tell, and a number of small craters retain fairly crisp outlines. With any luck we may be able to push straight from Corner up to the rim near Boat Ramp (Of course after a brief pause to pay our respects to the Beacon. )

Shaka:

Endurance is the model, not the baby craterettes! If so, the remnants of the ejecta blanket will be... ...dull.

Bob Shaw

Victoria is deep enough, or so I hope, to get well down into the section. I'm thinking that it does because the dark ejecta blanket is likely basaltic and we aren't seeing that discontinuity because of weathering and dustiness. In Victoria, once you get past the scallops and bluffs around the rim it turns depositional and dusty.

As the phrase goes, we'll see what we see when we see it...

--Bill

Bill:

Absolutely! I can hardly wait!

Ground truth looms...

Bob Shaw

That zone, around 300-400 meters around VC's rim seems to be flat and absence of ripples. I don't think that their sand would be fluffy but sufficiently compact to permit Oppy to transverse. Since it is flat, no slopes, so the rover traction on that land won't be a problem. I am assuming, not 100% sure but according to the MOC interpretation is that zone will have a very soft negative slope toward the rim.

Rodolfo

Hesperian! I can't imagine our sweet Victoria is _that_ old!

Sorry, Tom, I know it's a shock, but underneath all that sulfate-and-hematite paint and rouge...
It's the way she sags. Find a fresh crater with a sinusoidal, depressed rim! Impossible.
She's still capable of love, but it's strictly platonic.

Some questions to determine the origin of the rubble piles:

- If the rubble fell like a lava bomb, er, ejecta cobble-bomb, then the spread pattern on the ground should give away the direction and inclination from which it fell, revealing the direction of... Victoria?

- if it fell onto a existing dune field, then over time, wouldnt any large pieces tend to not saltate to the top like smaller pieces, but instead settle their way down to the bedrock as the sand waves pass over? so, are all the 'larger' (whatever the threshold might be) rubble fragments resting on bedrock?

- is this 'rubble' really just larger peices of the same "cobbles" material we've been seeing all along?

- since the small cobbles weve seen before tend to group up inside the trough of the dunes, it suggests they are migrated by sand action, carried along inside dune troughs as they propogate downwind? seems far-fetched, is this a known phenomena? if so, these recent bomb-cobble fields might suffer a resultant lack of small cobbles as they are swept away. maybe the main source of all the previous cobbles weve seen in this very process, inferring how 'long' the dunes might have been active for, at least since the cobble-bombs fell, in how many wavelengths have been propogated ?

Atomoid:

Interesting suggestions - there must be some sorting mechanism at work, though which (or which combination) is up for debate. Here's another thought - some analogue of terrestrial 'frost heave' may force rocks *out* of the soil. We could have several mechanisms warring among themselves!

I wonder if a rock going down might leave a mini-crater above it?

Oh, for a shovel!

Bob Shaw

O for a Muse of dirt, that would descend
The saltiest heaven of discovery...

or, we could just shake a spear...



--B

Shaka: I don't know what you mean. What "sinusoidal, depressed rim?" The Hesperian era was from ~3.5 to 1.8 billion years ago, and I can't imagine a such small crater in such easily eroded rock appearing so fresh after all that time. I can imagine that Erebus _might_ be that old.

atomoid: That is an interesting idea. The recent rubble pile does appear to be elongated more or less in line with a radius from Victoria. I don't think this rubble is the same as the small cobbles we so often see. This feature looks like a small impact crater to me in the anaglyphs. It appears that it is mostly obscured by the nearby drifts and the surrounding rubble itself.

Layers.

A mosaic of bedrock taken on Sol 819 with the L7 pancam.

jvandriel

Thanks for the mosaic jvandriel. I've been "ooh"ing and "aah"ing at the various parts of that this afternoon, they look great put together like that.

Yes lovely mosaic jvandriel so much detail, texture and tones, but even when the pictures are this clear I still want to look at every inch of the scene in MI images.

Roy F

Tom, I have probably succumbed to hyperbole invoking the Hesperian, but, dammit, what can you do with a time scale that has only 3 subdivisions since the formation of the solar system? If I say it's Amazonian, which it probably is, that can mean the impact happened 1.8 billion years ago or last year! Victoria looks old to me, not fresh, because the sinuous (aka "sinusoidal") rimline in the overhead view is not characteristic of fresh craters. It can only have gotten that way through a lot of erosion. The rim is not raised above the surroundings as in a fresh crater, and our lingering difficulty in resolving an edge, near or far, as we approached over the past weeks suggests that the near edge was depressed from undermining. We can't be sure of this until we get there, and I confess to being premature in this characterization. But it all points to a lot of erosion. What this equals in years is where Mars flummoxes me; the best I can do is pick relative ages of adjacent structures. A sharply angular, 3-centimeter shard of erodeable (?) evaporite sitting up high on a sand ripple can't be anywhere near as old as a half-mile crater that to my eye has the marks of great age. The former can't have been produced by the latter. I should not have ventured beyond this to absolute ages.

Oppy should be on the move again about now...

I don't know about that. Monday is a holiday here in the US. I neglected to ask Dr. Adler if the weekends off include major holidays as well.

Well according to the tracking data for tosol it is.

I still see a gently raised rim. Victoria still seems to me to be reminiscent of Barringer Crater in Arizona -- about the same amount of erosion. Of course the erosion rate on Mars is...umm...significantly less than on Earth.

I don't understand why some folks are saying that we will be driving down to the rim, as if Victoria were the drain hole of a sink -- and we are already in the sink.

That whole smooth area around Victoria is gently sloping upwards toward the rim. The orbital elevation data is invalid at this level of detail.

This is a very classic crater.

Scott

And confirmed, data is on the ground.



About 24m

Yeah, over the last year or so, there seem to have been be a lot of the smaller order of "up-chucked" pieces of the bedrock evaporate puched up either a few centimeters with others tilted at crazy angles or even pushed up entirely out of their sockets, implying a sort of frost-heave has been hard at work.

I've been hoping we would see something more large-scale features caused by this but... until now maybe this.

Seeing these rubble piles made me remember the theory about explosive CO2 releases (Hoffman?) that was sort of disproven (at least to me) by all the MER discoveries, but anyway, to reconsider, in this case a small CO2 pocket would be breached and sputter blocks of evaporite out of the ground as the gas forcefully decompresses. I'd thought that some of this might be what is keeping the cracks between many of the plates clean, in stead of being filled up with sand, they are being blown out periodically by CO2 escape events, but most arent strong enough to do more than blow sand out, these stronger ones signal the existance of larger CO2 reserves or just larger fault lines that lead to them, and due to the force they would blow out a few rocks, creating a crater-like gap that partly fills in with sand and rubble. That would help explain why the rubble appears to lie on top of the sand, rather than buried under it, so in this scenario it would allow a different explanation for a potential sand dune vs crater ejecta timeline discontinuity. However, i still cant buy it since since id have to ask where all the CO2 comes from and what would set it off to escape in these events.

If frost heave could instead explain the rubble piles, then these rubble piles might mark locations where there might be a sort of fault or spring where water is congragating or being allowed to percolate to the near surface and then progressively heaving the bedrock in such a small area to produce these features. Additionally, instead of CO2 blowing the inter-plate cracks clean, the frost would keep working the thin plates upward with sand settling down underneath them. they do seem to be displaced easily as the MER drives over them with its wheel, which might suggest they are long-since detached from their underlayer by frost action this way, even if its just small amounts of subsurface moisture working over millions of years. or maybe this particular thing merely due to temperature fluctuation breaking off the uppermost layer from the temperature stable layers beneath.

Amen...

http://qt.exploratorium.edu/mars/opportuni...GBP1211L0M1.JPG

http://qt.exploratorium.edu/mars/opportuni...GBP1311L0M1.JPG

Damn! Hope it's not due to a jammed wheel

NO!!!

Not again pls...

Not again, please!

Hopefully (almost sure), they are driving in what is called "visodom" mode i.e. slip checking every each, mmm, 5-10m.
Remember a similar situation at Erebus' northern rim; stuck one day, unstuck on the next one.

No!? It's not true? Say me that it's not serious?
An other Purgatory Dune - edited-

watch your language - doug

Now I really don't like this number.
Have a look to these pre-drive (sol 830) and post-drive panoramas; there is barely no change in the rover's position, meaning (my wild guess) that those 24m are almost all wheel turns at the same place.

Click to view attachment
(Sol 830)

Click to view attachment
(Sol 833)

It's not too bad - a sol or two and they can drag out of it. It's an NPE...Near Purgatory Event - like we had at the NE rim of Erebus - nothing to get too worried about.

(PS - we have no idea how much driving actually occured)

Doug

Dam! Your right.



Anyone remember what sol the NPE was?

It was on sol 603.
On sol 605 they drove again (backwards) leaving the sand trap.

Click to view attachment

BTW, I added a new thread for this Purgatory mk.3 topic. http://www.unmannedspaceflight.com/index.php?showtopic=2788

Here is the view in the drive direction on Sol 833.

Taken with the L2 pancam.

jvandriel

True, our knowledge of absolute ages for Martian rocks, other than from the few Martian meteorites that have been identified is very limited, and we can only guess from which rocks on Mars the meteorites came from. I agree that Victoria has undergone a fair amount of erosion, and for that reason I should have described it as "relatively fresh." We just have different perceptions of the erosion rates.

Regarding the angular shard, it might be difficult to know it was young. It could have been buried in the drifts and protected from erosion for a very long time, it may be a piece of rock that has been mineralized and is more resistant to erosion than most of those near it, or it may simply have been eroded to its angular shape by the wind. I can't rule out the possibility that the recently passed rubble pile is ejecta from Victoria or rubble from a secondary impact, yet.

I don't know, with all this rubble apparently sitting on top and embedded in the dunes at all heights (apparently at least, but i guess without "being there with a shovel!" we wouldnt know if the dunes are merely just sandy frosting on a larger rubble pile beneath and therefore would actually predate the dunes). i cant picture Victoria crater being younger than these dune formations.

so, taking that tact, it looks otherwise like what we have is a 'very fresh' (whatever that means) "rubble pile" (whatever that is). back to zero i guess.. ..Because it certainly doesnt have the hallmarks of an impact crater, not even much like the apparently young Fram, but instead looks more like somebody detonated some dynamite less than a meter below the surface here. -but then again im a self-proclaimed non-expert at these things, so i digress...

so, for now at least, the picture speaks for itself, however abiguous and muddled that speech may be... im just hoping the MER team will take a SOL or two to check one of these out.

Atomoid:

CC looks like a low-velocity secondary to me - if Opportunity looks at some of the individual rocks it'll quickly reveal whether they are local or from a more distant region. CC may be a goldmine!

Bob Shaw

Yeah, but there may be diamonds in the next one...

-the other Doug

It's worth a 'fram' look at. Quick scratch-n-sniff, pancam postcard...then onward.

If they're cunning (and they usually are) they'll 'mount' a small rock to get a nice solar tilt and do the flight software upload

Doug