There must have been ejecta flying around back when the Meridiani sedimentaries were being layed down, so there should be, theoretically, cobbles embedded in the rock, to be exhumed recently. However, I am underwhelmed by the abundance of partly exhumed cobbles I have seen, while admiring a hell of a lot of the bedrock. Ergo, I must question the numerical significance of these "fossils". YMMV

Very good point.

There doesn't seem to be a large number of cobbles on the surface. If they are indeed fossil relics, the inference would be that they are very thinly distributed in the strata.

Hmmm. Thinking on this, then anywhere larger amounts of Meridiani material were eroded, there should be more cobbles. So if this were true, there should be a statistically larger number on the Victoria annulus (since more of the rock column was ablated there).

OK. I think I just destroyed my own hypothesis.....

Greater love hath no hypothesiser...

It's possible, I suppose, that the erosive/acidic milieu of the nascent bedrock was not 'fossil-friendly'.

You've got to wonder about the mechanism by which meteor fragments are emplaced on the Martian surface. At Meridiani, several of the meteor fragments (most specifically Bounce Rock, plus the couple of others I seem to recall) seem to just be lying free and open on the surface, with no apparent relationship to impact features (or any other features). They're not buried, and they seem not to have left indentations on the ground, so they seem not to have hit the ground very hard. They certainly look like they landed a lot more gently than, for example, the heat shield.

This would make a lot of sense if the meteor fragments we've seen have eroded out of local rockbeds, and were emplaced in more traditionally violent manners onto the surfaces that existed when they fell out of the sky. The rockbeds that built up around them have now eroded off, leaving the more erosion-resistant meteor sitting on the surface as if a god's hand had gently laid it there.

Swarms of small meteor fragments, and meteor frags which were badly shocked and thence broken up during the build-up and subsequent deflation of their entombing rockbeds, could account for some of the groups of cobbles that we see scattered around.

That doesn't mean that all meteor fragments are cobbles, or that all cobbles are meteor fragments. I'd bet more on the possibility that a majority of the cobbles may be examples of the otherwise-seemingly-absent impact melt from local impacts. You'd expect some impact melt to be tossed out along with the more intact local bedrock, and the melt might well be more erosion-resistant than the sulfur-rich bedrock (especially if it was glass-enriched). This mix of friable sulfur-rich bedrock and harder, fused impact melt would erode over time, the softer bedrock leaving behind little piles of impact melt.

That may not turn out to be true (though I am peplexed as to why we can't find much impact melt anywhere near Victoria), but it makes a certain amount of sense to me...

-the other Doug

It is called falsification and is an essential part of the scientific method, so well done!

Although we have yet to make an intensive study of a cobble patch, we have seen enough cobbles up close in passing that I think we would have noticed if the majority of them were meteorite fragments or glassy ejecta. I still expect the great majority to be Mars surface rocks, slightly to moderately shocked and dispersed by impacts, occurring during the late Amazonian. If large numbers were ancient and had been exhumed, we should see some of them sticking out of the bedrock and distorting its beautiful laminations.
Signs of the impact of small meteorites and secondary ejecta would not survive long in the turbulent activity of the Meridiani sand sea. That activity may occur on the temporal scale of tens or hundreds of thousands of years (linked to obliquity cycles), but that is still short versus the potential lifetime of the cobbles.

Given that the ratio of ejecta mass to meteorite mass is always going to overwhelmingly in favour of the former it seems very likely to me that the vast majority of artifacts on any Martian surface like Meridiani that are significantly out of place will turn out to be Martian in origin albeit from some very different part of Mars. As Shaka points out almost all debris from localized small impacts will have eroded away at the same rate as the local surface material but harder ejecta from (say) distant impacts into basalt or otherwise hard bedrock should be relatively common. Whatever their ultimate origin I think that any analysis that shows that cobbles are significantly different to the surrounding area will be both interesting and scientifically worthwhile, although for me any discovery that ties a cobble to a major Martian impact event in the past would be more interesting than establishing that it was the remnants of a meteorite. What would be truly stunning would be finding that a cobble was possibly originally a piece of Earth but the chance of that happening seems vanishingly remote to me.

...And, luckily, the chances of it containing a trilobite even more vanishing!
That would really put the cat among the pigeons!
Such confusion we don't need.

Kryptonite. (Sorry, couldn't resist.)

While Opportunity hangs around 'Conjunction Road' (do we have a name for this area yet?), she has been taking some wonderful images for the panorama (how's that one going James?).
A quick stitch of some shots from Sols 1720&1721 of this excellent 'pavement' on my webpage.

Astro0

Apropos to the discussion of fossil meteorites - such finds are known from earth but they are rare. One quarry in an Ordovician limestone in Sweden has yielded 12 meteorites.

Here's a ref:
Schmitz, B., Lindström, M., Asaro, F., and Tassinari, M.,
1996, Geochemistry of meteorite-rich marine limestone
strata and fossil meteorites from the Lower
Ordovician at Kinnekulle, Sweden: Earth and Planetary
Science Letters, v. 145, p. 31-48.

Gray: Thanks. That was fascinating, and nicely quantified.

That sounds like an excellent name to me.

Err, I've been busy (and unwell - can't cope with these northern hemisphere winters! I'd be on the beach if I was back in Oz.) Will get going again with this soon.



That is great. I love these 'low-sun' images of the pavement at Meridiani, it brings out so much detail

BTW, these aren't shots for the big panorama; they were specifically taken late in the day (1700 LST) for another sequence. No colour with these - but there are some anaglyphs to be made.

James

Copy.
Click to view attachment

Or perhaps an old railroad name, "Conjunction Junction"?

Conjunction Junction - What's your function?: http://www.youtube.com/watch?v=mkO87mkgcNo

(for those of you not exposed to Schoolhouse Rock TV ads back in the '70's)

So many fascinating / bizarre rocks in this pic I could happily spend an hour just standing right here at this spot...

Today the Society staff went out for our annual holiday lunch and who should we run in to at the same restaurant but a pile of MER people, including Squyres and Callas. Steve said that (as we knew already) both rovers rode through conjunction OK; Spirit's at 192 Wh. He said Opportunity has a bit of a "conjunction hangover" (his words!) because they went on a data-taking binge during conjunction and now her flash is packed right up near the limit with files.

OK, what's the best hangover remedy for a Mars rover?

--Emily

Mine is an apple Trinaranjus...but I doubt Oppy will find one of those at Meridiani...

A Sprit(e).. Oppyfully.

...wouldn't it be called... a marsover?
:groan:

Since its on Santorini, it probably needs a Greek hangover cure, a soup called Patsas . Or maybe thats a load of tripe..

I'd say Opportunity needs to download all the excess data into a porcelain bowl.

Would that be done in a purge-atory?

Doing some healthy exercise and get those rusty legs moving again

How about publishing new mosaics in honor of her 5th birthday in Spaceflight magazine

The Road to Endeavour: Coming very soon to a thread near you collaboration courtesy of several UMSF members

ken

PS : snowstorm cancelled my Phoenix/Rover talk tonight

Never tire of looking at beautiful layering like this...

http://roadtoendeavour.wordpress.com/2008/...up-on-meridiani

I never tire of seeing the view change as we continue driving toward Endeavour.

That was an excellent question to stimulate discussion in these quiet times. I had a good response, but Google Chrome ate it.

When are we going to get moving again?

Let me check the DBs...

Opportunity: Mossbauer integration seems to have finished and the focus now is on MIs of Santorini. No driving plan, yet.
(OT) Spirit: Did the first bump after conjunction three sols ago (1763).

Well I still haven't found a satisfactory way of removing the lens dust effect, so here is Santorini without any correction.



Polar projection (links to same blog entry)



Enjoy,

James

Awesome. Full res is the only way to view these. The only improvement I could suggest is the addition of NSEW marks.

Isn't there some not-too-difficult way to allow these to be viewed with MMB?

(edited for spelling)

Yes - in 6 months time when Dan's Calibrated pancam frames are in MMB

Doug

That's about it, I'm afraid. I won't be putting any more work into MMB anytime soon... although I might be working on some related projects.