Correct; was making a bad UMSF-related joke, sorry!

What I meant was that perhaps the additional weathering on the left side of BI (from this perspective) was caused by the meteorite's passage through the atmosphere during impact rather then long-term exposure to Martian surface winds.

It's difficult to be completely sure, though surface wind erosion over a long period of time does seem more plausible. A look at the underside of the rock would be revealing, but of course it's far too massive for Oppy to move by any means. Just a minor mystery that might not be decisively solved for a few hundred years...

The rover might possibly be able to rotate it in place (a yawing movement) by pushing on one side. Not sure if that would reveal anything additional.

Not a chance.

Agreed - this thing is several hundred KG, more than half a ton, possibly more like 3/4s of a ton or more - there is nothing the rover could do to it.

Could Heat Shield and Block Island have been part of the same rock?
Will the instrument integration on the other side of BI require the same amount of time?

Eoin

They're not rocks. They're metallic meteorites, that show all the evidence of being 'complete' - with entry heating features on all sides.

Is there any hope of inferring anything about the age of Block Island from the isotopic ratios as measured by the APXS?

Well... they are rocks.
http://www.astronomynotes.com/glossary/glossm.htm

"It's a rock!"
"It's not a rock!"

Usually this discussion involves reference to fossilized skulls or other bones.

More progress around Block Island...

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... and in colour....

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Nice view of the drift.

...and in pancam 3D. We can now see most of the "backside" of BI. Clearly the smooth side.
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Simulated view of Opportunity at Block Island, for a sense of scale. This is an MMB screenshot, slightly touched up using Pixelmator.

Darn. No bolts.

mhoward: Simulated view of Opportunity at Block Island, for a sense of scale.

So my guess for scale might not have been too far off. Cool
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EDIT: With Stu's latest images of BI, I've updated the animation in a later post.

Latest postcards from Oppy's "Tour of Block Island"...

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Fascinating difference between one side and t'other... looks like something blasted the poor thing with a shotgun...

Hi

My owns versions of BI views from different sols.

Sol 1996 :

Color anaglyph


Sol 2000 :

Sol 2001 :



I think it's possible to make a 3D model of BI. I will try that.

Beautiful views, thanks Stu! The last view clearly shows a colour difference between the "farside" (smoother and dustier) and the "nearside" (the side we met first, rougher and more metallic). That seems to contradict the idea that windblown sand has shaped the surface - less dust on the nearside presumably means that's the windward side. But the windward side is not the smooth side.

Perhaps I'm wrong about expecting the windward side to be smoothed by the sand. Or perhaps the wind directions have changed (actually we know they do because the windstreaks out of Victoria change with the seasons). Or perhaps the rough/smooth areas were set at entry.

I'm surprized at the quick move around the farside. I'd guess a decision will be made soon about whether to study the farside in more detail or to continue driving...

And more beautiful views, Ant! Just one little thing - I have to hold my red/green glasses backwards to get the 3D effect correctly...

As far as the shape and surface textures of Block Island goes, it is quite possible that the meteorite has tumbled one or more times over the aeons in erosion/burial cycles (remember the pedestal discussion). There is no particular reason (besides trusting in a couple billion years of inertia) that the orientation of BI has been unchanged.

Thanks

Okay, I've made the correction for the anaglyph (mistake between left/right).

This my take for a "Sol 2000 celebration", based on the Sol 2000 panorama :


Just a simple "Sol 2000" 3D incrustation in the direction of the future drives .

What's the theory behind the cavity? Could the entry forces have separated that piece to oblivion, or is it sitting in fragments on Meridiani ?

Here are two MI images of Vail Beach, the gravelly area in front of Block Island, taken way back on Sol 1974:
http://marsrover.nasa.gov/gallery/all/1/m/...XP2956M2M1.HTML
http://marsrover.nasa.gov/gallery/all/1/m/...XP2956M2M1.HTML

Some heavily pitted materials can be seen in the second image (Block Island fragments?)

All this begs the question: Why is Vail Beach here? Are these the result of a small long gone crater that sat well above this layer and ablated away?

Here’s a possible scenario:

Block Island meteorite smacks into sediments and forms a crater on a plain well above the current level. As the surrounding deposits and the crater ablates away, more resistant rock and pebbles and blueberries roll and concentrate into the crater bottom. Eventually the Aeolian erosion level reaches the crater bottom and the loose friable deposits ablate away, slowly lowering the concentrated pebble fragments onto the current level we observe today. The pebbles form a nice armor, and prevent dune formation directly in front of Block Island. Behind Block Island, the lower windspeed causes sand deposition. (Just Immediately behind Block Island, there is a small patch of brighter dust visible in Stu’s images.)

This would make Vail Beach the remnants of a fossil “internal mold” of a long gone crater formed when Block Island smacked into Meridiani...


(This is following a train of thought that Fran Ontanaya started here.)

Updated animation of the circumnavigation of Block Island.
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EDIT: Removed between-frames. Continuous loop.

Since the erosional force would have been horizontal rather than primarily vertical as in Earthly pedestal rocks I would think that BI is in the same orientation as immediately after the impact. As the pedestal(s) eroded BI would probably have lowered with a rocking motion once erosion exposed it and created the pedestal effect.

Mike, you're describing a lag deposit, of which we've seen quite a few examples on Mars (most significantly in the blueberry paving in the flatlands of Meridiani). When you have such a friable surface, these sulfate-rich rocks being very soft and crumbly, the stuff deflates pretty quickly over geologic time, and the surfaces achieve a dynamic stability when lag deposits become thick enough to armor the underlying surface.

And serpens, I'll note that BI seems to be sitting on one side of a ripple-like rise, tilted up and lifted off the ground on the far side of the ripple crest. Looks exactly as you describe -- a rock in the process of doing a gentle, eons-long rocking descent as the surface erodes out from under it.

In terms of Vail Beach itself, I can well imagine that the impact event could have crumbled off "flakes" (small pebbles) of a superheated meteor, which would end up embedded close to the main embedded meteor. Also, the thing would have been quite stressed and shatter-damaged (as much as a piece of nickel-iron can be shatter-damaged) from the time it created its crater through to the present day. I can well imagine subsequent weathering causing pebbles to break off.

Finally (here's the real wildcard), it *is* possible that Meridiani was at one time a polar environment, and BI impacted not into a rocky surface but into layers of water and dry ice. It was then subsequently dropped onto the surface after the polar ices had all sublimated away. That's one excellent way of explaining how a meteor can be deposited, as if by a gentle hand, onto the Martian surface (as we've seen in several places).

-the other Doug

From the latest update:

Sounds like we may be hitting the road soon...

Today's plan (sol 2002) is move to the sixth (and last?) position in the circumnavigation and take some "drive-direction" pancams. The latter is an indication that we will be leaving the area quite soon. Tomorrow or Sunday, maybe?

Now that's poetry... absolutely beautiful, thank you.

I see one major problem with this line of thought. Let's take a look at the bigger picture. Why are all the iron meteorites exactly on the surface, not just this one?

If there was surface excavation along with ablation through wind erosion, then the chances that these would all be on the surface would be next to zero. At least some of these big meteorites should be at least partially embedded into the ground.

But if the former surface that is now gone used to be ice, then everything makes sense. The meteorites would eventually all sink down to the same level were there was no more sublimating ice. Everything would appear to be gently laid down on top of the surface - because basically it was.

Do we have any examples of iron meteorites at Meridiani embedded into the ground where only part of it can be seen?

Every crater has a probable buried meteorite - or the fragments thereof.

If the pale colored bedrock is salts deposited by a drying salt lake/sea, I wonder how long a time there might have been when the conditions were right for BI (and the others) to land, but not get covered in salt themselves.

This is probably giving us an idea of rate of "resistant" impacts vs. ablation erosion rate.

Imagine a surface dotted with craters of varying depth. Some containing resistant meteorites.

If the cratering rate (of resistant impactors) was really high, and the erosion rate really high: then we should see exposed meteorites all over the place. There would be a few still partially buried, but those would get completely exposed in the blink of an eye. (Once exposed, they remain exposed. The time it would take to exhume would be the time it took for the surrounding sediments to be removed along the Z coordinate of the embedded meteorite.)

If the cratering rate (of resistant impactors) was really low, and the erosion rate really high: then we should see a few exposed meteorites lying around completely exhumed, only a few would be buried (but not for long).

If the cratering rate was high, and the erosion rate really low: then we would see only a few popping out of the surface. Most would still be buried (and they'd stay that way for a while)

If the cratering rate was low and the erosion rate low, then the few resistant impactors would be buried.

We've got an n=3 of exposed meteorites that we've seen in our journeys. Is this a "few" or "a lot" or "all over the place"?
The unknowns are still the resistant meteorite cratering rate and average emplacement depths (most of the meteorites are within a few orders of magnitude in size), the absolute time-averaged erosion rate, the absolute age of the current surface, and the absolute age of the highest layer in the historical stack.

At least we can safely say that the resistant-impactor cratering rate is significantly above "never".

What is interesting to me is that we have seen three relatively good-sized, exposed meteorites in a relatively small area. Combining the length of Spirit's and Opportunity's travels, if you walked for 20 miles on Earth, would you expect to encounter three meteorites of that size lying around on the surface? Or even would you expect that there were three meteorites of that size buried in the ground where you were walking? I don't have any answers, I just think that for our day-to-day travels on Earth, that would seem to me like "a lot" of meteorites to encounter.

As an amateur space enthusiast that sounds like a good starting point to me.

Can we go any further?

As long as there has not been net deposition since the meteors' appearance on the surface they would remain on the surface. It does not matter if they were originally buried in soil which was removed or in ice which melted.

Look at how many craters there are! I imagine a lot more meteors reach the surface of Mars than Earth due to the thin atmosphere. Also, we hear a lot about Near Earth Objects threatening Earth impact, but I wonder how the number of Near Mars Objects compares.

The biggest difference from Earth is just the surface age. The Meridiani plains may erode by a meter or less in hundreds of millions of years, so meteorites (especially erosion-resistant iron ones) have much more time to accumulate than on Earth, where it would be rare to find a meteorite that's been lying around for more than a few tens of thousands of years. So you might expect 10,000 times as many meteorites on Mars as on the Earth even if atmospheric entry survival and impact rates were identical.

If the rovers have surveyed about a square kilometer for meteorites (2 rovers x 10 km x a 50 meter wide strip along the track, say), then we have 4 meteorites per square kilometer on an average Martian surface. So on Earth you might then expect a meteorite every 2,500 square kilometers, an area 50 km or 30 miles on a side. That sounds about right...

John

Latest postcard home from Oppy as she continues her 2009 "Tour of Block Island"...

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And there are some new 3D views up on my Twitpic gallery...

http://twitpic.com/photos/mars_stu

Opportunity's 2009 Tour of Block Island...

http://twitpic.com/hhfdi

One good turn deserves another....animation that is!
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Here you go Alan. Two seconds per frame. Hope that helps.
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Could you slow the animation down? its difficult for my eyes to keep up with.

Edit: thanks astro0

http://twitter.com/MarsRovers/statuses/3943115122

"Both rovers are operating w/ 1 stuck wheel."

something i missed? I know oppy's rf has been touchy but stuck???

MI mosaic of Vail Beach assembled from 4 of the images taken on Sol 1974.
(Lotsa fun warping to match perspective and playing with masks.)

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The non-cropped full resolution version is available here: http://www.flickr.com/photos/31678681@N07/3913837681/

-Mike

Verrrry nice, thanks!

The RF steering actuator is stuck since a looong time ago.

Well the atacama is a comparatively prolific source of meteorites. Arid desert like meridiani with minimal erosion

Sol1974 Vail Beach MI Mosaic localized. It is just in front of Block Island.

Visible in Sol1973 Pancam image (numbered rocks correlate - in the MI mosaic down is towards Block Island):
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And another shot on Sol 2003, just before leaving:
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-Mike

No MI's of the blueberries on BI? .....hmm