Yes, *something* must have persuaded the dusty stuff to turn solid, whether or not the original deposition was into water or a smidgeon of water came later. In any case, nice tasty acidic water, loaded with salts would bind the essentially zero-strength debris into layered rock (and, once the water dries out the mineralised outer skin would be tough, until eroded away and the softer interiors revealed). Perhaps a test would be to look for a physically cracked-open rock which has been preserved from weathering by some chance and to examine the 'inside' vs the 'outside....

Bob Shaw

This panorama should be quite impressive at the end!
Currently almost all of sol 748's 6x3 frames have been downlinked -- L7R1 only, the "color" should be waiting on the priority queue -- and more shots are planned for tosol.



Doug, I guess "a little bird" told you about it.

Another "preview" (at half-size).

(447k)

What is that strange, two-toned box on the right side of the image?

Assuming Spirit retains its Energizer Bunny status, where are they planning on having it explore after Home Plate?

I guess if the prelimenary results dont show any evidence for water in the formation of these rocks they wont stop at HP long....

I think that is a great alternative explanation. My first thought on the lower interbedded unit was that it looked like rhythmic/episodic lake beds. With some of the recent ideas about low-latitude glaciation on Mars, it would not be hard to visualize the pre-Homeplate crater as containing ice and a subglacial lake.

The closest to an eolian "dropstone" I've ever seen was a large (5-6 cm diam), rounded, polished, quartzite pebble embedded in dune foresets the Jurassic Navajo/Page eolian sandstone in Utah on the Colorado Plateau. However, the likely interpretation of that clast was that it was a dinosaur "gizzard stone" and I'm not sure we want to go there for Gusev.....!

http://www.space.com/missionlaunches/06021...home_plate.html - Spirit Mars Rover Reaches 'Home Plate': Formation Has Researchers Puzzled

--- For his part, Crumpler said that he refuses to accept one spectacular interpretation: "Namely, that it is a volcanic vent structure." Crumpler said more detailed rover images are needed.

Currently these include such possibilities as playa, exhumed crater floor filled with typical Columbia Hills layered deposits, a tuff cone or maar, and a hydrothermal vent area, Crumpler noted. "In fact, it is a healthy debate within the team right now." ---

Just imagine if steam were seen coming out from under one of the rocks....

Hey...Is that a shiny perfect spherule right in front of Spirit?...

I'd imagine the mossbaur results will help reduce the number of theories, but it's nice to see that everyone's speculation is still in the realm of possibilities. Is the spectrometer requiring more than a 3-day soak time? Does such a long sample introduce noise that confuses the results?

I dont believe it adds noise - but depending on Iron content, a Mossbauer Spectrum could take 3 days - perhaps even longer.

The APXS is still fairly sharp - much longer half-life on its source.

Doug

I didn't think of the subglacial angle, but that is a very sensible idea. I've seen subglacial rhythmites in Norwegian caves which looked much like this.

I don't quite buy the indurated-sulphates idea. Morphologically this formation practically screams "harder than surrounding rocks", which does not fit with the softness of the Meridiani sulphates.

tty

How did this formation become so localised? We havent seen anything else even remotely similar in Gusev - we are seeing totally different rock types appearing at the end of a drive compared to the start - 20/30m. If it is some kind of volcanic related event, wouldn't that cover a huge area?

Probably has been said before, but what the hey: Could Home Plate be a large chunk of rock blown out by either a volcano or meteorite impact from far away?

Can we determine from orbital images and spectral data where it might have come from, going on this idea?

Oh Yeh...

Hematite at Gusev!