So you're saying that when a crater is buried and subsequently revealed, ejecta and possibly detached pieces of the impactor would be covered and revealed just as the crater is, thus recreating the scene at the time of impact. Sounds good to me, but the process would also reveal all chunks of iron that had fallen to the surface after the crater was formed. The final result would be a removal of all soft material deposited since the crater's formation with a concentration of all resistant material -- berries and iron meteorites. There would be no way of telling if a chunk of iron on the surface fell at the time of the crater's formation or millions of years afterward.

Perhaps the distribution of fragments around it can tell the story of what happened to the crater, if there was one.

If there was a solid ground that got eroded, maybe they would have piled up due to cracks or slopes.

Ah yes, of course, even sand grain sizes impact at hypervelocities. Any remains would be mostly minute. I suppose the old studies (1970's) of bulk lunar regolith found a proportion of nickel-iron particles representing such residue. There's no apples vs oranges comparison, just an apples vs. "apple pollen grains".

The surface of BI seems to show some signs of atmospheric friction melting (among the pits/vesicles), which puts some constraints on its trajectory. The fact that it survived impact means that it was most like a grazing trajectory (or low-angle secondary). Or so it seems. When we get some composition hints, we will know a bit about how strong this rock is.

Some musings on martian meteorites here if anyone wants a look...

http://cumbriansky.wordpress.com/2009/07/3...tian-meteorites

Does this look like a meteorite to anyone else? My second thought is weathered basaltic rock to give it that texture.

http://marsrovers.jpl.nasa.gov/gallery/all...RP0713R0M1.HTML

Latest pancam of Block Island (top), and a reminder of Heat Shield (bottom).
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They look suspiciously similar.

Two chips off the old block!
Guess we should get back to the westward trail.

Good point, Dan. I can't help but wonder if any parts of the moon escaped melting and homogenization in the event.


Oh, yeah. That changes everything. There are not going to be many macroscopic samples of early earth on the moon. That's a good argument for a sample-return mission to Mars.

http://qt.exploratorium.edu/mars/opportuni...B8P2390L5M1.JPG

Wow, the pits are full of blueberries!

That means that Block Island must have been buried and then exhumed by erosion- just like terrestrial desert meteorites found on deflation surfaces!

Maybe - or it might have had showers of ejecta from the small local craters scattered over it from time to time, with the fines blown away and the coarser stuff left behind.

Phil

Good point. Do you think there is there any kind of test that could be done to distinguish between these two possbilities?

Definite metallic glints apparent as well in this shot; Pasadena, we have an iron-nickel meteorite!

Phil, I can buy the ejecta covering/exhumation idea for transporting the blueberries up there. The average thickness of the dust layer (dunes excluded) doesn't seem to be more than 50 cm or so (if that) and am beginning to suspect that this thickness has been steady-state over the past billion years or so. The rate of deposition from normal atmospheric fallout is at equilibrium with the rate of erosion...until something big goes splat & buries an area for awhile.

The spheres on BI seem to be more uniformly small in size than the populations on the adjacent plain. It would be nice to have MI's of both to see if they have undergone similar degrees of weathering.

Yeah, I noticed the apparent blueberry size constraints on BI too, Shaka. My best guess is that IF they were put there by ejecta then the big 'uns tend to get blown off more easily since they present more surface area to the wind. The little ones are concentrated in the hollows.

Easy way to check that idea, maybe: Is there an enrichment of larger blueberries immediately surrounding BI?

And here is the color views


The anaglyph (dedicated to Stu )


And a closer view with the mosaic :


For sure, a very beautiful rock! Very close to HSR.

Ant, what can I say but WOW!!!! Fantastic, absolutely gorgeous!

I'm especially intrigued by that sort of crystalline-looking structure just above & to the slight right of the big hole...a sharp metal shard?

EDIT: Ant, I defaced your beautiful work in MS Paint to add a circle around the feature I was referring to.

Click to view attachment

Awesome imagery, Ant103. Thanks.


The first thing that comes to my mind would be a survey of the meteorite's surfaces, studying the three dimensional distribution of blueberries and other sediments in its hollows.

Looking at the distribution of berries apparent in the latest imagery, it seems that the largest berries have collected in the lowest hollow, with smaller concretions at slightly higher elevations. There are very few, if any, visible in the highest hollows. We can't yet see into the hollows around the sides of the meteorite. I can think of several ways to interpret the available observations.

Beautiful! I'm struck by the contrast between the smoothly rounded left (leeward?) side of the rock and the rougher, pitted, right (windward?) side, indicating that even metal can be eroded by wind-driven grains on Mars. The raised rims around a couple of the "vesicles" inside the big pit are also interesting- do they indicate that the "vesicles" are intrinsic structures and not just erosional features?

John

Block Island Ramblings...
Well, Block Island seems to be significantly metallic, with possible stony inclusions (I'm basing this on appearance). The many vesicles seem to be gas bubbles from the ancient solidification, although some of them could be from inclusions that have since evaporated/dissolved/eroded away. The raised rims around some of the vesicles indicates something inside the vesicles reacted with the structure of the meteorite and made that surface slightly more resistant to erosion.
The vesicles could have been refilled for a time after the meteorite fell, with ice, Meridiani sulfur-salt goo, dust, or whatever.
The elaborate filigree structure around the big pit indicates a hard material with tensile strength (metallic), and it looks like it is being slowly eaten away chemically. The filigree structure could also represent a fine-grained soft component in the metallic matrix that is being preferentially eroded.
Looking forward to microscopic images.
The presence of 'blueberries' in the hollows could be remnants of previous burial, and/or wind-driven deposits from an episode where Mars had more atmosphere.
There we go, enough opinionated ramblings to power Oppy for a day, at least!

-- MarkG

Block Island seems to be sitting on the flat, rocky layer of Meridiani like it was just placed there. If BI at some point had been buried in layers since eroded away, I would expect to see it either sitting in a depression or up on a pedestal. On the other hand, I don't see how it could drop on the surface as it is with no sign of an impact mark.

No depression or pedestal to indicate layers being eroded from around BI, no sign of an impact on the current surface....
I'm confused.

Couldn't they be regmaglypts that have been subsequently enhanced by eolian erosion?

If BI has been eroded by chemical means, is that not something of a confirmation of a highly acidic water table in the area (admittedly, long ago)?

-the other Doug

Would a big dune be enough to damp the impact before it touched the bedrock? I imagine that, even if the bedrock was damaged, as long as the meteorite was embedded above it, a seasonal water table could have erased the crater before Meridiani dried, the dune was blown away and the meteorite was left on top.

Stu, thanks for the great review of Rover meteorite finds. And no wonder you're the poet laureate -- from the Lake Country!

SFJCody, in line with your thought on regmaglypts enhanced by aeolian erosion, and extending the same idea to John_S's windward and leeward sides, I am imaging that I can see remnants of an orientation -- bleeding edge on the right -- as Block Island roared through the Martian atmosphere.

Another truly remarkable find by Opportunity! Who would have predicted that it would find, not one, but two picture-perfect iron-nickle meteorites (if that proves to be the case) on the surface of Meridiani?

BI is very cool...but now we're here I'm waiting for "the other reason"

What about the meteorites that they find in the Antarctic? Don't they frequently find ones just sitting on the surface, with no impact crater? Are there similar aeolian erosion and ice sublimation processes at work over a prolonged period?

You might be. I'm not. You're miss-interpreting Tim, as I explained earlier.

Ilbasso,
Antarctic meteorites mostly represent lag deposits left behind by melting and evaporation of the ice cap they were previously embedded in. They got into the ice after entering the atmosphere, which slowed them to terminal velocity - from maybe 12 kilometers per second down to only 0.1 km/s, more or less. They hit the ice cap or snow without enough energy to make a proper crater or significantly damage themselves. Subsequent snows buried them in the cap and they rode it as far as the dry valleys or other erosion zones where they were lag deposited centuries/millenia later.

It would be premature to postulate a similar ice cap deposition and concentration mechanism for Meridiani, but Block Island need not be sitting on the same surface it originally hit. Erosion could have removed that ages ago. Still, if Oppy had the ability, it would be fascinating to turn BI over and closely examine the bottom and the underlying bedrock for scars of impact.

Thanks Ant, great work! I missed the new BI pics coming in "live" 'cos we were away camping, again, but back now and having fun with them. This is my fave rock for yonks, and not just 'cos I was getting stir crazy looking at mile after mile of undulating dust ripples... :-)

Click to view attachment

And amazing structure in the "hollow"...

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... oh, and if you thought the "Yeti" got the tin foil hat wearers excited, wait til they see this HR Giger beauty...

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IMHO, this is one of the most important finds for opportunity so far. Why?

...Not because of the iron nickle meteorite. It's because the blueberries in the hollows appear to have been formed basically in place! That is an important clue as to the origin of the blueberries.

Like Antarctica, I'm willing to bet that this meteorite originally landed when a substantial layer of ice was near the surface. The now gone crater was in the ice. Aeolian forces spread dust from the atmosphere into the hollows. Interaction between the dust and the ice created the blueberries over a very long time. Wind eventually blew out the blueberries in the upper hollows. The blueberries in the lower hollows remained somewhat shielded and stayed basically in place. The ice sublimated and left the meteorite on the present surface.

This meteorite almost confirms the newest theory of the icy formation of the blueberries!...In My Humble Opinion. Of course we need a few tests before we accept this explanation, but I think it is a sound one.

Imaginative, to be sure, though I can't say I'm convinced.
What, pray tell, is the "newest theory of the icy formation of the blueberries"?
What "few tests" did you have in mind?

I don't suppose wind could have blown blueberries into the shallow depressions in the rock?

There is a part of pedestal visible on the lower left, the rest may be hidden under the ripple. Easier to see in this R721 image
Click to view attachment

It's interesting to see how differently people are interpreting this fascinating rock.

It clearly displays regmaglypts, but I doubt the deepest hollows can be explained as erosionally enhanced regmaglypts. I'm not sure it is appropriate to call them vesicles, either. I'm siding with a previous commenter who suggested that some hollows may be due to inclusions which subsequently corroded or eroded away. I think the deeper pits on the right side of the rock and the surrounding "filigree" features may be mostly primary structures.

It is interesting, however, that certain features seem to be aligned with the current wind regime in this region. I'm not sure how to interpret that. Has the morphology of this meteorite been shaped by recent winds on Mars, or is it due to the winds experienced by the intruder as it entered the atmosphere? If I had to interpret the morphology of this meteorite as being formed by its flight through the atmosphere, I'd suspect the leading edge was on the left.

Finally, regarding the pedestal, good catch, alan. A remnant like this is likely to protect a pedestal beneath it, but this most recently protected pedestal is not likely to have been the first pedestal this lagging boulder has perched upon.

I doubt that is possible given the atmosphere of Mars is too thin. Even if the atmosphere was tens times as thick when this meteorite landed, it would still be too thin to lift those berries vertically on top of the rock. The only plausible way I can think of is for the meteor having been buried and then excavated at a later date.

The simplest explanation is something similar to what I conjectured in my previous post. Certainly other things could have happened, but they would require a lot more complications. Perhaps other meteor strikes threw the berries onto this rock. But if that is the case, then explain why they are so uniform.

If you are unfamiliar with the icy formation theory, then I am surprised. It was all over the news. I don't have a link immediately handy; but I will look for one.

Here is one story that mentions it:

http://www.space.com/scienceastronomy/0902...m-mars-ice.html

Another more detailed story is in Nature but it is archived now and you have to have a subscription to view it.

There are others. I'll mention good links on the theory as I have an opportunity. (didn't mean to create a pun)

Here is a better one that explains more. I wish I could find the original paper on the topic.

http://www.universetoday.com/2009/02/16/ne...t-mars-equator/


(Three consecutive posts merged - ADMIN)

Fascinating...

Click to view attachment

Combine the fact that the axis of Mars has shifted many times in the past with this little tidbit...

http://www.universetoday.com/2007/12/20/ma...kept-mars-warm/

...and you have the makings of a possible viable alternative theory that incorporates water ice into the equation. It might also explain why the concretions don't grow beyond a certain size.

Sweet anaglyph, Stu!

BI is captivating, visually. That microcavern alone is crazy spectacular!

I literally wouldn't touch this side of it (if that was possible), though; all those shards look quite sharp & "snaggy".

(Me in spacesuit: "Ooo!!! Cool rock! <reaches out...> YEOW!"

Spacesuit: "Sssssssss.....")

Glad you liked the 3D view This really is a fascinating object. I think we may well be here for some time. I really am looking forward to seeing what the other side of BI looks like, and a peek underneath would be interesting too. In the meantime, here are the first MI images put together.

Click to view attachment

Very interesting object! And pretty too!
What cause the criss-cross linear features in the MI images? Some for of crystalization in the meteorite? Are these common?

Yeah, very good anaglyph Stu .

Here is an other view, a 4 frames mosaic showing the immediate surrounding of BI :


PS : happy to see that you appreciate my last pics .

Could Block Island be a mesosiderite (stony iron meteorite)? Yes they are rare, but that would explain much of what we see. Burial on impact, exposure to acidic groundwater, exhumation and eolian erosian producing yet another Mars mystery to ponder.

As the block island meteorite seems very similar to heat shield rock, the discussion regarding impact scenarios for HSR probably applies without much change. See this long Lunar and Planetary Science abstract for some detailed analysis, which comes to the conclusion that it must have come in at a pretty low angle to arrive in one piece, even in a range of martian atomospheres from today's thin version to a much thicker past version. So however recently it landed, it would have been expected to ricochet and not be near an impact feature from its initial hit.

Marsisimportant: "The simplest explanation is something similar to what I conjectured in my previous post."

Phil: "That's odd - I would have said exactly the same, but about MY previous post"

Yes, the simplest explanation is that they were thrown there as ejecta from the many small craters like Dolphin that occur all over the region. I agree that ice is possible, but it requires a change in the current environment. Ejecta doesn't. In fact, even if there were blueberries on the rock left from its icy past (if it had one), they should now be joined by ejecta-deposited blueberries.

Phil

Besides ejecta and ice, what about the possibility that BI was buried, through deposition, in the rock (not ice) layers in which the berries later formed and berries were left on it just as they were left on the rest of the Meridiani surface as the layers eroded away? And also, the possibility that BI impacted in and buried itself in berry-containing material which was later eroded away.

Yep, the simplest and most logical explanation.

Looks like a Widmanstätten pattern to me!

Fascinating...
John

tfisher, thanks for the link to the Lunar and Planetary Science article. It raises the possibility in my mind that Heat Shield and Block Island are part of one and the same fall . . .