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."

Oops, sorry, the subheading was a bit long I guess and 'Meridiani' got cut off from the end of it, oh well.

The similarity to White Sands I find very interesting, and the evidence is right in front of us, I think...

Wow, I'm impressed. I thought only wind was ongoing now - and that not strong enough to shift the dunes.
We need to take some hazcam shots on the move to see if the wheels are sending up 'roostertails' of spray.

Do they explain why it should be "now" as opposed to 674,000 years ago?

There's nothing in the rest of the article that explains why now and now 3 billion years ago...

"Chavdarian and Sumner think that the fins are formed when water seeps into cracks in the sand, carrying minerals with it. The water evaporates away, leaving behind those minerals, which are exposed as the wind blows sand away."

All fits with the curreny accepted model of Meridiani..

"Windblown material sticks to the exposed fin, making it larger and stronger. If the cracks and fins seen by the Opportunity rover on Mars are formed in the same way as the features at White Sands, it would provide evidence for water at the surface of Mars away from the polar ice caps"


We already have that in the rocks of Meridiani, just not today, but many years ago. Nothing really new at all in what he says. It's a bit tenuous however - all he has is "they look like" - and that's not a great basis on which to make the judgement he has.

I'm guessing because of the seeming brittleness of the fins perhaps, that they feel they must be recent features, or else would have been eroded away a long time ago? I can understand that reasoning. Coupled with the observations that the similar fins in White Sands form at certain times and then get worn down, with sand filling the associated cracks, during other times.

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

Doug

I'll side with Doug on this one. This is a speculative article by an associate prof and an undergrad student. They don't know how the cracks form, and they've described how fracture fills form. Nothing here and now.
We'll look at that issue of _Geology_ and not a UC-Davis press release.

--Bill

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)...

So do our MIs tell us one way or the other? If a geologist looks at a "fin" like this one near Purgatory II
http://marsrovers.jpl.nasa.gov/gallery/all...LOP2956M2M1.JPG
Can he say, "Aha, that's growing! or "That's eroding, just a bit more slowly than the surrounding evaporite."?

I say it's a concreteish slab of foundation!

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

http://www.michaelalmond.com/cpg/displayim...tup&cat=0&pos=0

This a nice picture of Death Valley, or is it Meridiani with a few undiscovered thorn trees in the background?
Funny, that there is no layering visible in the mud slabs. Apparently you can have an evaporating lake leaving mud slabs without layering and/or cross bedding.

Cugel:

Point taken - but it'd surely all be down to the individual history of water-flow at the site!

Here's a 'Marsified' version of the same Michael Almond image:

Bob Shaw

It is images like the one below that make me think that these features are related to fracture-filling veinlets, some of them along micro-faults.

Stereo pair (parallel method)


Stereo pairs, cross-eyed method:
http://www.marsgeo.com/Opportunity/hedges_x.html