On the road again...

http://nasa.exploratorium.edu/mars/opportu...WEP1211L0M1.JPG

I really hope so. Maybe we see Victoria before Christmas.

Goodbye Purgatory..we barely knew ye...

well, actually, we've gotten to know ye quite well

Doug

We got to know ye better than I ever wanted to!



-the other Doug

It's good to be moving again. As I'm mostly an onlooker I look forward to seeing who will be first to show the point on the route where Oppy will stop driving north and turn back toward the south. Will it be east or west first my guess north then west then south.
Thanks to all the forum contributions.
Reckless

I'll have to admit that I was skeptical that there was anything different about the makeup of Purgatory Dune when Oppy first got stuck there. In the image Tesheiner posted above, I'm amazed to see that Oppy dug in quite far into the dune surface even when it was positioning itself for its investigations over the past week. That is a MIGHTY soft dune!

I feel it is a sensate decision not to adventure going toward south unless its traction capability is improved as the required for that zone without any other help and also as remote robot. I know it is very brave to transverse thru chopped dunes. Hope that the team will get greater information about the land and trace the safest and easiet route toward to Erberus or Victoria????

Rodolfo

Panorame wheeltracks in front of Opportunity at Purgatory Dune.

jvandriel

Panorama wheeltracks at the rear of Opportunity at Purgatory Dune.
Taken with the L Navcam on Sol 510.

jvandriel

Glad to know we're back

And we're already starting to get downwind tails from the recent wheeltracks. These are potentially active dunes!

--Bill

Only if the "pavement" is broken I'd say. Then the fines underneath are exposed and free to go. My feeling says that the winds on Mars don't carry enough energy to break apart the upper layer. I wonder for how long this situation has been that way. And (even more intersting to know): What process is responsible for this tough upper layer ? Liberation of chemically bond water by intense and long UV-exposure, on it's turn cementing together the minerals ?

I put my comments, I have seen a fine sand cementing cap on the desert. This cementing strate is very fragil. Once it is pressed, it cracks very easy. This case was caused by evaporating wet sand. This is only valid for a short time that is not the case for Mars that the water might probably have gone completely after 1.2 Billones years since its conception.

Rodolfo

Actually, we've seen a surface crust on Mars' soil virtually everywhere we've landed -- the Vikings saw it clearly. It seems be a salt crust left behind by very small traces of surface liquid water left behind in the upper surface soil seasonally (along with some more dramatic moistening at intervals of a few tens of thousands of years as Mars' axial tilt changes and water ice thus migrates back and forth between the planet's polar and equatorial regions). It certainly doesn't ever require the existence of large amounts of liquid water on the surface at any time.

That is why I sail "potentially" active dunes. With the desert pavment/duricrust/"cementicrust" on the dunes it may take milennia for them to move. But we see here that the atmosphere can and does have the ability to move fine surface dust on a daily and routine basis. Oppy is not in the midst of a windstorm and the dust from the wheeltrack disturbance is rapidly moving in s short time.

In another thought, even though the density of the Martian atmosphere is very low and cannot move heavier particles like blueberries, it might happen that during dust storms and high wind velocity events, the wind can pick up sediment as a bedload and the density of the wind+bedload might be high enough to move heavier particles and thereby move dunes.

There is a lot to learn here.

--Bill

Marcel:

Got to agree. I reckon these are really *old* dunes!

Which doesn't deny the possibility of salty sludge moving about here and there - we've seen surface frosts, and micro-climates may allow water flow in locations with appropriate solar heating etc (like, perhaps, some crater sides).

Bob Shaw

During post-Viking geologic analysis, there was a fair bit of "arm-waving" discussion of salt transport by "monolayers" of water molecules on soil grains. Gas or liquid molecules can be adsorbed <not absorbed> on a solid surface, held there by relatively weak electrostatic bonds to the atoms and molecules in the surface.

One of the major objectives of Mars Polar Lander was to bake fine soils and measure the evolved gas composition with temperature to quantify gas and water adsorbtion on martian "fines" A significant fraction of the martian atmosphere could be adsorbed on soil grains, to be released at higher temperatures and humidities. Some suggested several times as much gas in the atmosphere could be globally adsorbed in the soil.

Water, with its polar charge distribution and hydrogen bonding between water molecules, likes to form adsorbed monolayers. As humidity goes up, they become multiple molecules thick, but are still not liquid layers in a conventional sense. Such monolayers, it was suggested could transport salts over long time intervals in apparently dry soils, and produce duricrusts like the Viking Landers orbserved.

Interesting interview with Squyres on SPACE.com.
http://space.com/missionlaunches/050705_rovers_update.html
In particular, this statement: “We also have a hunch that the dunes that run from northwest to southeast, like Purgatory does, may be a little younger and a little softer than the ones that run north-south”

And clays are "polarized" by the nature of their crystal structure. I'm not sure what the mineralogy of the very fine, pervasive dust is, but I wouoldn't be surprised if it were a clay. Given the small size of these clay particles and the resultant surface:volume ratio I'd suspect that a large amount of water could be involved.

--Bill

Hi Bill,
There's a huge difference between fine dust of mineral origin and clay. There's no evidence that there's clays at Mars at all. Maybe there actually is clay, but we simply did not have the instrument capabilities up there to proove it microscope needed). Clay is clay if it consists of a claymineral (with cation exchange capacity: C.E.C.) AND if it is built up in the form of micron/nano scale, uniformly oriented plates. Only then the material has the chemical and physical properties of a clay; the possibility of long term bonding of water and elements via chemically induced adsorption of positive ions on a TREAMENDOUS surface (Na, Ca, K, Mg, Li, etc.).

Besides clay, I cannot think of another soil that actually can hold water in the Martian environment for long periods. If it is just grains (round, angular, blocky, whatever), eventually everything will dry. Except for chemically bond water like in Gypsum, when the watermolecules are built in nanoscale crystals and can't get out.

However: your theory is interesting. I might be wrong. Maybe the extremely fine grains do (on a modest scale) hold water in their matrix. But i don't think the fines can hold "large amounts" of water.....

Would this mechanism account for the flows around the exposed platy surfaces in endurance, or on the steeply inclined surfaces at Methusalh? Or is it just a 'baking out' and mineralising effect in general?

Good discussion, Marcel.

I was actually thinking of clay as _one_ component of the mars dust. We don't know if clays exist on Mars, but we haven't been able to look at the minerology closely enough to say yes or no. I recall that clays are alteration or weathering byproducts of silicates but I'm not sure if the conditions on Mars were ever conducive to clay formation.

But clays are found, that could be another data point for a wet Mars.

--Bill

Bill:

Clays are also prime suspects in pre-biotic chemistry, possibly providing a matrix allowing not-quite-alive 'cells' to form.

Bob Shaw

It appears to me that Purgatory, and the tops of most dunes in general, have a pavement of somewhat smaller grains, spaced further apart, than the pavement between the dunes.

I *THINK* the TES team on Global Surveyor or some group working in the middle infrared (1 to 5 micromters) has reported seeing minor <few percent> clay mineral spectral signatures in global dust spectra. And not terrestrially familiar clay minerals like montmorillonite and others, but uncommon ones on Earth. I have not read the actual published papers on these results, so I'm mentioning things I've watched float by on the info-tide.

I've wondered about that, too. I suppose that, logically, smaller lumps of material should get the chance to float higher than bigger, heavier ones...

Have a look at: http://www.spacedaily.com/news/mars-future-05p.html

And what does granite weather to?

Granite? Weather?

*Everything* weathers!

On a galactic timescale, I suppose so.

The plagioclase feldspar component of granite weathers into a clay mineral; saprolite and/or smectite seems to ring a bell. Plagioclase is also a component of basalt, which is a common rock type on Mars; I'm not sure about the occurrence of granites on Mars. The alkali feldspar in granite and the olivine/pyroxene on basalt also likely weather into a clay.

It's been a long time since school and I've been stuck in a sedimentary world, so I'll let a ig-met type pick this up...

--Bill

It looks like Oppy now has driven back to the left side of Purgatory Dune.... seen off on the upper right of the photo. ...at least I think that's the PD stuck ruts.

http://marsrovers.jpl.nasa.gov/gallery/all...0P1916R0M1.HTML


It also looks like we're being very brave and "testing the waters" with our big toe:

http://marsrovers.jpl.nasa.gov/gallery/all...0P1214L0M1.HTML

According the above picture, I see the best way is to run as long as possible on the same Blueberries valley.

I realice that the importance to have a taller mast to hold the Pancam up to between two and three meters or even higher better like a submarine's telescope so that the driver can map better the best route. Maybe, with the help of powerful camera from MRO might help to surface map with good resolution. If this is true, the submarine telescope would not be necessary, and otherwise, this suggestion would be valid for MSL.

Rodolfo

It seems that in this direction ( East ) the dunes are lower.
Panoramic view taken on Sol 516 with the L2 Pancam.

jvandriel