Home Plate Is..., LPSC update - Science magazine Options

[Guest_paulanderson_*]

...a mini-volcano!

http://tinyurl.com/z4qx4

http://www.sciencemag.org/cgi/content/full/311/5769/1858b

"Mars rover scientists have concluded that the cryptic "Home Plate" that the Spirit rover spent 3 months reaching is the remains of a little ash-spewing volcano"

Magazine subscription or article purchase necessary to read full article, but there should be other updates soon?

[CosmicRocker]

I'm not sure this little blurb really tells us much that is new, but the way it was portrayed was a little misleading, I think. Titling a piece about Home Plate as the "Martian ring of fire" seems to imply that HP is the vent of the "little ash-spewing volcano." What we have observed is that the upper sediments of HP are rather spectacularly crossbedded (or cross-laminated, if you prefer) in a fashion known on earth to be formed by wind-blown ripples or dunes. We have also seen that the grains in the upper units are well rounded and well sorted, characteristics that are not typical of a primary ash. It seems as if this must be reworked ash, if it is ash. I don't have a problem with a model where the particles that comprise HP originated in a volcano. I'm not convinced HP is the volcano.

My notes about HP from Steve Squyres' presentation at LPSC are interesting (and in a few places, illegible, because I was writing so fast). I got the impression he was fascinated by HP, had some ideas about what it was, but didn't have the whole story sorted out yet. To put things into perspective, Spirit had just driven off of HP to head for the hills, and had looked back to take that detailed panorama of the newly visible edge.

He commented on the lovely cross-stratification visible in that panorama, and that the clasts seen in the MIs were "extremely well sorted and extremely well rounded." He then said that El Dorado was the closest thing they had seen up to this point, as a modern analog for HP. He went on to describe the minerological composition as 18% olivine, 23% pyroxene, 30% magnetite, and 28% something that is illegible in my notes. He said this was essentially an altered basalt. Steve described the APXS results as a "somewhat altered basalt" and mentined that they don't know how widespread the Home Plate formation is, and that there may be some on McCool Hill.

Then, he went on to speculate that the lower HP strata are volcaniclastic or impact related, and that the upper layers may be basal surge or aeolian in origin. (I'd love to see an example of a X-bedded basal surge deposit that displays such well-formed sets.) He mentioned the possibility that the upper strata might be the result of aeolian reworking of material from the lower units, since they have the same compositions.

Since we have left HP we haven't seen much other than somewhat variable dips and a bedrock that looks much like lower HP. Let's hope we soon see Spirit leave its salty quagmire.

[Guest_RGClark_*]

I'm not sure this little blurb really tells us much that is new, but the way it was portrayed was a little misleading, I think. Titling a piece about Home Plate as the "Martian ring of fire" seems to imply that HP is the vent of the "little ash-spewing volcano." What we have observed is that the upper sediments of HP are rather spectacularly crossbedded (or cross-laminated, if you prefer) in a fashion known on earth to be formed by wind-blown ripples or dunes.
...

I saw this on the MarkCarey.com/mars forum:

3D of brushed rock with yellow soil at base of homeplate, Gusev crater, Mars. Taken by Spirit February 14, 2006.
http://www.flickr.com/photos/hortonheardawho/105427976/

Click on the zoom button to see the most detailed view of the image.
The undulating quality of the lower layers, like a wave flowing, gives the impression of a material that flowed and then later solidified.



Bob Clark