Every time a see a yet closer image of the outcrop at Meridiani Planum, I hear this Krusty the Clown voice in my head saying: "What the hell was that?!?!?"

I've just about given up speculation on the origin of this stuff. But not quite...

Close-ups like this:

http://www.lyle.org/mars/imagery/1M1295157...33M2M1.JPG.html

continue remind me of textures and fabrics I've seen in travertine and sinter deposits, except for those spheres imbedded in it. In the first Navigation Camera images, while still on the lander, the outcrop looked like bedded clastic rocks (e.g. sandstone). As the rover got closer, both the PanCam and NavCam images looked more like ratty welded tuff (volcanic ash). Now, when the rover is right up against the rock, it looks like a chemical precipitate! And the roundy things are definitely a lag weathered out from whatever this stuff is.

It will be nice to get some close-up spectrometry for some idea of composition. No one has said carbonate or silica out loud yet, but I wonder...

If the spheres are the source of the hematite, what could the host rock possibly be?
---
Tim Demko
http://www.d.umn.edu/~tdemko

Are the spheres eminating from the outcrop as the outcrop erodes over time? I'm not so sure. They do appear to be embedded in the outcrop a little, but not in the volume I'd expect if you look at the quantity on the soil.

Also - comparing the odd blueish colour one can get in pancam imagery of these spheres to the colour of the distant plain (the same odd blue) I'm not so sure they're coming 'from' the outcrop as much as dribbling over it into the crater from the plain beyond.

Who knows They're going to be the story to follow with Meridiani for sure.

Doug

Doug:

I would suspect that if we see at least some of these things imbedded in the outcrop, then it would be the source of all of them. I think that the lighter layer has been significantly (wind) eroded and the spheres have collected as a lag on the surface in a residual soil. You can also see empty holes in the outcrop which seem to be about the same size as the spheres.

By the way, Joe Knapp has posted these links to pictures of volcanic accretionary lapilli on usenet:

http://volcanoes.usgs.gov/Products/Pglossary/AccretLap.html

http://www.kiseki-jp.com/english/stone-inf...canic-bean.html

http://volcano.und.nodak.edu/vwdocs/EOSsli...xt/slide35.html

Evocative, but the host rock seems to be different here.
---
Tim Demko
htttp://www.d.umn.edu/~tdemko

According to Steve Squyres at this morning's press conference, it definitely appears that the spherules are contained within the layered rock beds. Whether or not the rock beds originally were the host rocks for *all* of the spherules and spherule fragments within the crater and outside on the plains is another matter, but there is one good pancam shot showing a piece of Stone Mountain (formerly Snout) with four different spherules in varying stages of exposure from the host rock. Makes it pretty clear that they're embedded throughout the layered host rock.

Remember, the orbital imagery shows that the whitish rock unit, which is likely the same unit as we're seeing in the outcrop, is extensive in the Meridiani area and that it appears to have been re-exposed as a darker overlying plains unit has been weathered off of it. Perhaps the darker unit is not an overlying unit, but it what remains after the whitish unit weathers and leaves only the much more resistant spherules, which break down much more slowly and generate the darker soils that *seem* to overly the white unit?

One thing seems certain -- the spherules are much darker than, and weather much differently from, the underlying white unit. Which, as Squyres said, hints at a rather different composition. The best theories seem to be that the spherules are either blobs of magma that were ejected by colcanic or impact activity, or accretions of dissolved minerals from water than seeped into the whitish unit. Clues to look for will be whether or not the layering in the whitish unit seems to fold over the spherules (which will indicate that the whitish unit had spherules dumped onto it as he layers formed), or whether the spherules have remnants of the layering within themselves (which will indicate that the spherules formed within the whitish unit from precipitation out of water that has seeped into the bedrock).

- The Other Doug

Still no info on composition of the bedrock or spherules, although Squyres did let out the tidbit about the anomalous abundance of sulfur. Parsing his words, it seems as though he's leaning towards an interpretation of the spherules as concretions.

I've seen similar looking things in sandstones on the Colorado Plateau where they are called 'Moki' or 'Moqui' marbles (pardon some of the New Age BS):

http://www.utahphotowild.com/small/pages/small4.htm

http://www.crystalsandjewelry.com/crystals...quimarbles.html

http://www.earth-energy.com/21npages/4ac5.html

Margie Chan has a great (non New Age) explanation of them on pages 11 and 12 of:

http://www.ugs.state.ut.us/online/pdf/pi-77.pdf

One interesting parallel is that these types of concretions are dominantly hematite

Great links Tim. Sure is an interesting planet--so many ways to make spherules.

Seems like they need to RAT one ASAP!

I'm not at all familiar with martian geography; if those round grains are accretionary lapilli, how far away is the nearest volcano?