Okay, now I feel like the kid that's being laughed at by everyone after they drop their tray in the school canteen...

Still learning this, will get better.

The blue dye used on the sundial is very very vivid in the near IR (i.e. L2 ) - I imagine it's the same dye used on that nasa logo. If you look at the L257 empty-nest pans, you can see it a lot there as well, on 'pink' foam that wraps around some wires and other logo's etc - all of which are actually blue.

http://marsrovers.jpl.nasa.gov/gallery/pre...-B009R1_br2.jpg

Doug

3D of cobble with links to MI pan, 3D MI and context hazcam and pancam images:



No blueberries. Not from around here.

Flickr really does have some great tools - nice work HHW.

No berries suggests either higher in the stratigraphy, or from somewhere more distant.

Doug

Oh you liddle bewdy, Hort! This just gets better and better. C'mon JPL, get that brush a spinning!

je suis "liddle bewdy"?

Qu'est-ce que tu veux dire?

He loves you for your mind.

That rock kind of jumps out at one, doesn't it? Some of my first thoughts upon seeing the images come down in my MMB update today were crystalline or recrystallized, angular fragments, unlaminated, and more resistant to erosion than the typical Meridiani rock. Upon closer inspection this rock is even more curious to me. There are a number of very well rounded structures within it. I hesitate to call them clasts, but that's what they look like. They are ovoid in shape. They all may not be visible in the reduced detail MI mosaic I am posting here, but if you inspect the individual raw images, they seem quite apparent. I was not able to eliminate the stitching error on the far left side of that mosaic.
Click to view attachment

If I can get them to upload on this lousy connection tonight, we also had some overlapping MI views that afford us a 3D view of some of the rock. OMG, I could almost count the individual bits as the anaglyph uploaded. If anyone wants the individual images, let me know, but you should be able to extract them from the channels in this anaglyph. I can't wait any longer...
Click to view attachment

Sure looks igneous or metamorphic, doesn't it? My first impression was that of a piece of flint or other SiO2-rich rock. There even seems to be some evidence of conchoidal fracturing.

Agree with HHW: not from around here...unless it's from someplace very deep indeed within Victoria.

On first glimpse the rock reminded me of suevite. But that's just a wild association.

Ooooohh! You said the S-word!

Do you get suevites in craters this small?

Jon

Who said it's from Victoria? It shouldn't be, since it is sitting as a piece of float on top of what most people think is a planed-down ejecta layer, topped by lag deposits of sand and concretions.. (I didn't say I believe that, yet.) It's true that Victoria falls off the bottom of the size/energy models used to assess terrestrial and planetary impacts, yet to some extent those models grow out of laboratory impact and nuclear explosion studies. Melts and breccias can result from those "popguns". I don't really know if the possibly unique characteristics of small, secondary impacts on Mars would exclude suevite production. I don't know of a model that covers such impacts.
The only way this rock could be suevite from Vikky would be if it were excavated and tossed here by some later impact like Beagle. But if if Vikky produced melt breccia, shouldn't we see it in the surface layer we are driving across. I've been straining my eyes to see some, but so far we haven't had a clear view. I wish Marvin the Martian would put his helmet to work brushing away all this damn dust and blueberries? Maybe the dark streaks up ahead will help. (I am leaning toward the "Clean Streakers" School of thought.)

Good point, even if a suevite, it need not be from here. If so, could be tell it apart from an orbinary igneous rocks from the instruments on Opprtunity? If it is melted sedimentary rocks it might be unusually siliceous compared to the basaltic igenous rocks seen to date.

My own take is that we have been driving across impact breccia from Victoria. The wall exposures of breccia are very clear and appear to show a disconformable relationship with more coherent though fractured units deeper down. The breccia is clearly trunctated at the surface though, with clasts planed off by erosion.

So if there was surface melt (which on Earth we get in craters as small as Henbury and Wabar) it may have been removed by now. Has any glass be found surrounding the similarly sized Meteor Ctrate? I know that there is a lot at Darwin crater (1 km) but none at Wolfe Creek (800 m). What about Monturaqui and Tswaing?

Jon

Jon:

There's lots of 'iron rain' in the desert around Meteor Crater - but I've never heard of any glasses. The small Empty Quarter crater (I forget the name of the thing, it's pretty famous) was only a couple of hundred feet across, but glass-lined, by all accounts.

I'm not convinced we're seeing impact structures in Victoria at all!

Bob Shaw

Long time to reply - just catching up after Christmas / new year.



Fair enough - I guess it is in a way. I was just under the impression that we were talking about individual features (up to whole capes and bays) in individual threads and that this thread was for pulling those ideas together for Victoria and Meridiani as a whole. Parts of this thread have been fascinating and taught me a lot and I didn't want to see it descend into a 'ooh look at this odd rock' thread and away from the big issue. But that's just me, if people want a geology hold all so be it - back to Santa Catarina...

James

I'm not sure, Jon, whether Oppy's tools can detect the elemental, isotopic or mineralogical indicators of impact, but I was hoping the RAT could give us a clear enough view to reveal shock metamorphosis in some of the clasts I can see. I'm not sure that there is any volcanic activity close enough in location and time to be responsible for this rock, however. Impact, on the other hand is ongoing throughout the solar system.
Impact melt breccias tend to fully line the crater, so some should appear near the rim in spite of erosion, if there is any crater left at all. Melt under the crater is often buried, of course.
Google Scholar turned up a number of references for melts at Monturaqui, and, since it is half the size of Victoria, may be a useful indicator. I couldn't find anything on Tswaing, though that is substantially larger.

Bob Shaw's skepticism about an impact origin for Victoria is understandable given it's unusual morphology, but I do think that the hole in the ground we call Vikky does lie over the site of an impact. I have been waiting to get a decent close-up look at the in situ rocks forming the 'capes', but I continue to be frustrated.

Hot off the press this a.m....

Click to view attachment

zzzzzzzzzzzzz...... off to work now... stupid time of day to be going out into the wind and rain...

Lovely, but I hope we're not just going to take lovely color portraits of this ejecta from 2 meters away. Let's get RATing!



Then again, Stuey,(he said, glancing out at the swaying coconut trees), if you wait for it to stop, you might be there till July!
Affectionately,

Shaka:

I'm not saying at all that Victoria wasn't formed out of an impact crater, just that by now the visible effects of the impact have all gone, leaving us with an eroded hole in the ground. Drill in the centre of the crater, and there's an impact structure buried underneath, but all the usual overturned strata, debris fields, even shocked minerals are gone, gone, gone from the surface. This is no bad thing, as the capes and bays provide us with access to a really excellent cross-section.

The evolution, and indeed early structures, of Martian impact craters are *not* simply the same as Lunar (etc) impacts. The Rampart Craters, with their distinct lobate aprons are Martian - as are the class of holes-in-the-ground-previously-called-impact-craters!

Obviously, there are variations on a theme (exhumed, infilled fossil rampart craters, anyone?) but the key point is that while geological processes on Mars are Earth-like, geology on Mars isn't quite like on Earth!


Bob Shaw

Yes, Bob. I think our views are rather similar. Before we reached Vikky I hypothesized that all we would see there was collapsing roofing layers of evaporite, concealing a cavity that was once an ice-filled Victoria Crater. Now I'm not sure whether that is defensible - it is certainly a minority view.
You may not yet have seen the recent issue of Meteoritics & Planetary Science (vol. 41, issue 10, 2006). It is a collection of papers dealing with impact cratering on Mars. No authors specifically address the unique characteristics of Victoria, but the consistent focus is the effect of frozen volatiles in Martian target crust on crater morphology. Very enlightening!
Relevant to a question JonClarke raised about the MER ability to identify impact breccia, I managed to unearth a possible answer this morning. Barbara Cohen of the Univ. of New Mexico presented a paper at the recent IAU meeting in Prague titled: Identifying in situ Martian impact products with the Mars Exploration Rovers .
(How's that for service, Jon? ) This ADSABS link may not work, but I'm sure you can track down the abstract.LINK
It suggests the problem may be manageable.

Kowabunga! This has been a productive morning at ADSABS. I swear I haven't seen this before, but with respect to minority views on Meridiani Planum, and the departure of a Meridiani Sea, we should take a look at the recent writings of T.J. Parker, of JPL and a member of Steverino's own authorship team!
Follow this link if possible: LINK
The paper glories in the title, Testing the Marine Hypothesis for the Opportunity landing site at Victoria Crater, and I can't resist quoting from the Abstract:
Hee Hee! .

Nprev,

Remember the chonchoidlally fractured pebble that we saw several months ago on the cleared area surounding Vicky?

Glenn

I'm delighted to hear this at last. I'm still betting that, though a significant volume sublimed away after the impact, there is still plenty of the volatile stuff buried deep under the visible rim strata and Victoria's aeolian fill. The stuff is obviously very good at just vanishing - they should call it Macavitite.

Stu, I like the picture and the rock. The rock is nearly white at 535 and below and black at 601 and above. How does the absorption of these "black" rocks (by Navcam) compare to blueberries? Is this a new type rock for MER, or has something similar been seen elsewhere (by Spirit)?

Mmm...barely. Do you have an approximate sol? I'll try to find it tonight.

(quote from Parker, T.J., quoted by Shaka above -- I seem to have broken the 'quote' function somehow)




Well, I'll be a Dutchman's aunt. I swear - I swear!, at some point between Erebus and VC, when the pronounced cape/bay rim was being first discussed here, in a feverish moment of extreme sleep-deprivation and over-caffeination, I found myself imagining -- well, exactly as the Abstract says, 'water pouring over crater rim...' being responsible. Looking at the morphology of the rim, and wondering why on earth one portion of the rim would appear to have collapsed down into a flat shelf, whilst the adjoining section formed a steeply cliffed cape, brought to mind the image of water draining off the surrounding plain into VC. Somehow the image seemed terribly life-like in my mind's eye. Eventually the illusion was shattered by the obvious objection: for water to flow down the slopes (as opposed to lingering in a fast-evaporating puddle as the bottom) surely it would have to have been draining away at the bottom of VC? I mean... tidal or storm surges just doesn't do it for me. There are capes and bays all around the circumference, but a tidal or storm surge would be much more asymmetrical. (No?)

OTOH Parker, T.J. wouldn't have published a paper on the idea if it were as easily knocked down as that. What did I miss? Or did I misunderstand the scenario the paper describes? (I haven't got access to the full article.)

Water draining away? Well, why not?

We could be looking at an analogue of a limestone karst landscape. Water flows along, then just vanishes. And as well as the familiar dry karst you can also get 'blue holes', drowned caverns beneath the ocean as in, I think Bermuda. We've seen queer features such as the Anatolia feature out on the plain, and funny little holes.

All in all, it's not quite crazy!


Bob Shaw

Surely karst landscapes have very characteristic surface features - and apart from VC, there's no significant relief anywhere else on the landscape. For flowing water to erode gullies like the bays, it'd have to be moving pretty fast, which would imply substantial sink holes and cave systems - wouldn't there be some sign of these on the surface?

Wow. Have you seen the pancam subframes of that outcrop behind cape B3? I hope they will take a closer look at that.

When I first read that abstract I almost fell out of my seat as I imagined the glorious sight, then I began to think about it's implications, as you did, and I began to think "what if." It would be difficult to imagine storm surges creating so many points of entry for elevated seas. In these soft and soluble rocks, I'd imagine one or a few initial channels would cut their paths and essentially pirate future flows away from other areas.

It appears that this paper was written for the Fall 2006 AGU meeting, so all of the observations we currently have of the crater from the rover's POV were not available at the time. We didn't have a good view of the crater's interior until October of '06. I can't help but wonder if the Mars Ocean Hypothesis was on his mind at the time. Damn, that would have been a glorious sight.
I know what you are saying, but if this karst terrain had already dissolved subsurface channels, wouldn't the water from the ocean have already found a shorter route into the crater and filled it before the storm surge arrived?

Lots of little rocks round these parts... and what's with the dark edge to that feature over there..?

Click to view attachment

Oh, I dunno. Limestone pavement, anyone? Try Googling 'Malham Cove'!

I confess that I'm not exactly, er, 'committed' to the soluble landscape solution - it's just an interesting idea!


Bob Shaw

Tom:

A suddenly extant large volume of water might not be able to find it's way through small holes, but would catastrophically erode a pre-existing big one, perhaps? Maybe not so much a storm surge as a one-off flow after an ice-dam broke, a la Bakker's Washington State Channeled Scablands as an analogue for Mars?


Bob Shaw

As it happens I did quickly skim the Wikipedia articles on Karst, and Malham Cove / Gordale Pike in particular (the limestone scenery I was taught about) to double-check that I hadn't hallucinated the whole "limestone pavement / collapsed tunnel ravine" scenery bit.

However... as CosmicRocker said, the more I think about it, the more intriguing an analogy it becomes. (You did say "analogous to limestone karst" - in other words, soluble bedrock, you're not suggesting it actually IS limestone, right?!)

Perhaps water ice (or ice-rich subsurface layers) behaves analogously to soluble rock in some circumstances. If the temperature or pressure was temporarily raised enough to thaw ices, how would it behave? I imagine it would tend to trickle down to the lowest local point (anticline..? I'm still very much a geological newbie) until it refroze. I imagine that would happen quite early in the history, the overlying surface wouldn't necessarily show much effect as any water or CO2 liquid would stay at the same location, but just migrate downwards.

Now, if the local surface has a large depression (like, say, an impact crater - exhumed or not) the fluid would tend to run into it. Then it disappears - today that's because it sublimes away into the atmosphere very quickly, but in a putative warm wet era it could be draining into subsurface voids left by ices that evaporated during a dry period. Consider a cross-section of VC. Now draw a line parallel with the surface line a few tens or hundreds of meters below the surface - the post VC surface, I mean. Between this line and the actual surface, there will be in-place ices which will evaporate / sublime after the excavation of the crater, because 30m of overlying rock have just been removed. This would presumably happen in a concentric bowl 30m larger than VC itself. Lo, voids are formed, into which later surface water could drain, after an ice-dam burst or other sudden influx of surface water.

That's approximately the theory behind the well-known gullies that Mallin and Edgett have described. Now, imagine that process occurring a long time ago - hundreds of millions if not billions of years ago - until the local ice reservoir runs dry. If there's an overlying layer of harder or stronger rock, then (with a spot of Handwavium) the alcove could become sufficiently deep that when the overlying layer finally cracks and collapses it forms a VC-type bay. The visible surface expression (the gullies) would be eroded or covered in aeolian material very quickly in geological terms. Running liquid might then continue draining into sub-surface cracks and voids below the crater floor. That would then be analogous to a "Gordale Scar"-type limestone ravine. There might be a small amount of settling of the surface at considerable distance from the crater as temporarily-liquid ice migrates, causing Anatolia features. So Anatolias would be not like a limestone pavement, but more like... er... permafrost melting in the Arctic, causing surface subsidence. Say. Perhaps. (All this arm waving is tiring me out!)

That scenario doesn't necessarily suggest water flowing down the surface of the bays, but it might do if the sub-surface melting coincided with an episode when there's a sea or lake (ice-damn breaking, Milankovic cycles, whatever.) Indeed, melting ice could even happen below the sea-surface, whereas you don't get limestone pavements underwater. Argh!! Bob, Shaka, stop making me think about things like this! I haven't the time!

Interestingly karst in very dry environments is almost completely underground with very slight surface manifestations except an occasional collapse doline or very shallow circular depressions. The classic example is the Nullarbor plains in Australia which actually has quite large cave systems and even small underground lakes.

Also note that old impact craters can noticeably influence karstification processes. The "Cenote ring" which is the only trace on the surface of the Chicxulub crater for example.

tty

I'd forgotten about that! And in those underground lakes are tiny shrimp and other beasties, isolated from the inhospitable environment above (hey, you're a shrimp, in Australia - you'd last until the next barbie!) and each with unique adaptations. The folk who study them drill boreholes, then cap them to stop other organisms getting in.

Sounds familar, doesn't it?


Bob Shaw

No, not limestone, that'd be silly! Let me rephrase that...

Have a look at this brief overview of thermokarst: http://ougseurope.org/rockon/surface/thermokarst.asp

I have yet to see a Martian pingo, though!


Bob Shaw

The topography of the crater rim is not level. There is no way that a uniform erosion of the bays by water draining in could have occured. If the rim difference were even a few feet, the flow volume would be enormous to reach all the way around the crater. In that case, it would not be eroding bays. It would have altered VC beyound recognition as an impact site.

Addtionally... If there were a flow of water that created the bays, it would mean that the terrain was similar to the way it looks today. It would have left tell-tail marks all over Meridiani. The source flow would have cut deep channels that stretch for miles and miles. If those channels had been eroded beyond recognition, the bays would have too.

ed

Geez, Imi, why should you be immune to cerebral meltdown? It's a standard symptom of advanced marsaholism, and we all suffer from it sooner or later! If you find a cure, save some for the rest of us.

I just don't know if my cerebrum is ready for Victoria being the drain-hole of the Meridiani Sea, connecting with a subterranean storm-drain system. As you said, how could all this exist without it being revealed somewhere by the erosion of the fringes of Meridiani. Surely Edgett would have seen it by now.
Gotta cool the brain - time for a coffee.

Another abyss covered by dunes. Coincidence? I think not.

Brian

Ice (or at an least ice/soil mixture) is a soluble karst-forming rock even in some areas here on Earth.

As far as I know karst here on Earth occurs in the following materials:

limestone
dolomite
gypsum
anhydrite
rock salt
ice (particularly ice/loess mixtures)

Note that gypsum and anhydrite are sulfate rocks.

tty

What if there were a more uniform, fairly thin "ice cap" over deep, somewhat uneven permafrost? Could an impact create enough heat to create this feature in a single event of localized thawing and flooding, followed by longer term slow melting or sublimation of the remainder of the overlying ice?

--tc

Ed:

I'm not trying to be particularly contrarian by pursuing the karst topographic aspects of Meridiani, but instead I'm trying to extract some interesting ways of looking at and understanding what we see - it's a thought experiment for me as much as anything!

But, it's an attractive one!

As for the terrain, who's to say that - apart from regional tectonic changes - the landscape would have been quite the same shape when/if a water/ice substrate with/without a liquid water topping was extant? We might be seeing a tilted landscape, shrunken down over previously water-filled voids and ice lenses. There's good reason to think there may currently be ice lenses in Martian polar dunes - imagine if they sublimed...

As for the 'tell-tale marks' - well, we certainly see a strange pavement over/under the area we've traversed, including the slopes of Endurance and Victoria. There *are* troughs and holes, too. And there's the ripples, and a few indisputable impact craters. I think the jury could vote either way!

The notion of a karst landscape isn't at odds with any of the theories put about by the MER PIs - they've concentrated on the small-scale processes as evidenced by the cross-bedding etc, but I can't see any way that a karst interpretation precludes any of that (and, indeed, it fits well with the Anatolias out there).


Bob Shaw

Ted:

I think you're perhaps touching upon the circumstances around the formation of rampart craters - good HiRISE images of which may be very illuminating (once they've finished with Northern Plains sandpaper).

I'm also intrigued by the famous Mars Express image of the 35km-wide crater with an ice-cap inside it, and the way that would interact with the local geology (although in that case the ice vastly postdates the formation of the crater).


Bob Shaw

A very small rampart crater, perhaps. There would need to be water flowing back into the hole, and having it flow over a layer of ice might address the issues of irregular topology of the existing surface but fairly regular scalloping of the crater itself.

--tc

What we need are predictions from each theory than can be tested with observations. It seems to me that there's at least one problem with the standard theory, ie. that it doesn't account for the capes and bays...

Nprev,

The cochoidally fractured pebble was discussed on page 5 of the thread "Victoria Annulus; Discussions about Victoria's Apron", Sept. 3, 2006. Doing a search on keyword "chert" will help you zero in on this page.

Glenn

I still haven't seen any explanation for vertical cliffs that does not involve three things: undermining, collapse, AND removal of the detritus.

The "prow-like" form of the capes is interesting. The cliffs are vertical or near-vertical everywhere where they are deeper than... a small distance, 0.5m or so, at a guess. That would imply (if you are correct that there are no other explanations of vertical cliffs) that the undermining process occurred (or is occurring) all the way around the edge of each cape, but lower and lower, the further away from the rim the cape gets. Or, that the very tip has been exposed to the process for longer than anywhere else, and the further back from the tip you look, the shorter the exposure. (Just thinking out loud...

Earlier up the thread I had a wild idea about the bays being due to the surface sagging down as a distinct unit as material was removed below it. Now I come to look back (eg. Capo Verde ) it's interesting that the bedding plane of the surface of the bay appears to be parallel with the present-day surface, ie sloping inwards at 25-30 degrees. However the planes exposed in the sides of the capes are roughly parallel with the surface of the annulus.

Shaka, you're right... I've got a bad case of Marsaholism here. It's gone midnight, I have a big pile of real work half-completed on the dining table to be completed by tomorrow evening, and here I am, busy not doing it... :>