[X] My Assistant

[Guest_paulanderson_*]

Interesting new article re the fins and cracks in Meridiani, from UC Davis:

Soggy Sands of Mars?
http://www.news.ucdavis.edu/search/news_detail.lasso?id=7698

"Cracks and fins in the sand in an American desert look very similar to features seen on Mars and may indicate the recent presence of water at the surface, according to a new study by researcher Greg Chavdarian and Dawn Sumner, associate professor of geology at UC Davis. "Recent, as in ongoing now," Sumner said."

[djellison]

But his description is that they are growing, not eroding...
Windblown material sticks to the exposed fin, making it larger and stronger

Doug

[Guest_paulanderson_*]

But his description is that they are growing, not eroding...
Windblown material sticks to the exposed fin, making it larger and stronger

Ok, right, it's the cracks that get eroded. But I still wonder, if little thin fins like these only formed such a long time ago, would they still be so well preserved up until now? Of course, they may have been larger initially, also, and what we see now is all that's left of them.

The MER team did also seem to agree on this type of water origin for these features, in one of their updates a while ago, although in their interpretation, they are probably ancient. So if we can agree that water was probably involved here (almost undeniable, imo), then the question is simply whether it was recent or ancient. Ancient might be more likely, but I wouldn't rule out recent activity, we simply don't know yet. I wonder if the frost seen previously by Opportunity could be involved if it was more recent? Is that plausible? (and, yes, as I noted in another thread, that was ordinary water frost, as stated by the MER team some time ago, not CO2 frost as someone had asserted). Would thin films be enough to produce features like this?

I would say too, that the alternative scenarios proposed for Meridiani's origins by the other two research teams are also only speculative, although some people have proclaimed them as fact now because they seemingly just don't like the "wetter Mars in the past" idea (I'm thinking of some postings / media from outside of this forum)...

[Bob Shaw]

The short answer to fins and water is *yes*. As to whether they are currently 'growing', well probably, but - and here's the BIG 'but' - you'd not be seeing them at the surface, but instead would be seeing them inside the the soil. Except you can't because they're, er, below the surface of the soil! So you see them when their less well cemented surroundings are eroded away.

They're just expressions of the well-known 'desert rose' formations, albeit reflecting the local mineralogy.

On Earth, desert rose is the common name given to rosette formations of the minerals Gypsum and Barite with sand inclusions. They occur in arid sandy conditions, such as where a shallow salt basin has evaporated. Gypsum roses usually have better defined, sharper edges than barite roses (see photo).

Gypsum is a very soft mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. Barite has the chemical formula BaSO4 and is often associated with Haematite on Earth. Any of these constituents seem... ...familiar?

I wonder what a dune looks like with a desert rose growing inside it? Perhaps a little scooped out area forms, but only where the dune is big (ie deep) enough to trap sufficient water molecules. Hmmm...

There's a good online article at:

http://www.earlham.edu/~greshjo/Rosette.htm

Bob Shaw

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