[X] My Assistant

[tdemko]

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

[dvandorn]

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