Regarding the olivine suggestion, I am not convinced at all.

I really don't see how a soil layer a few cm thick, which neighbours with water ice below, and spends six months per year covered with water ice, could contain olivine. Since it reacts so easily with water, only olivine hydrolysis products should be there.

Olivine may point to dryness, but this cannot be logically reversed (and olivine was not detected)
All other instruments show that the Phoenix site is not dry.
The puzzle is how can the soil be consistently dry with so much water around ?
How can the soil be dry when we see water condense on the legs of Phoenix ?

I really enjoy the Scherlock Holmes elements this place offers us
MECA sees perchlorates, but TEGA does not (so far).
The TC probe points that the soil is dry, while we see the ice even with our own eyes !

I just love a good old mystery

Thank you. I love the clouds / haze movement just above the rolling sun!

A question for all: has anyone caught any mention of any glimpses of refractive phenomena (from ices) in any of the sky obs? I've not, but then I have not been able to follow the Phoenix as closely as I would prefer either .

-- Pertinax

sol 100 clouds at sunset movie:

Green Beach in Hawaii demonstrates that Olivine can co-exist with a lot of water for a long time (by our Mayfly yardstick). However, if any of the greenish particles we have seen from OM images are Olivine then given their size and the Martian timescales, it would seem proof positive that the probe is right and the regolith is totally dry. I don't know what the temperature of the permafrost is but I feel that it is cold enough for H2O to be just another rock. While they are not releasing even basic information all we can do is conjecture, but that couple of cm of soil seems to have some pretty impressive properties.

Speaking from ignorance here (my preferred position! ), could this observation be explained by a combination of the facts that 1) water never occurs in the liquid phase here, 2) ice does not chemically interact effectively with soil compounds due to the low temp, and 3) water vapor is in the same boat due to low ambient pressure and temp?

To explain 3) a bit more, even an RH of 100% at an ambient total pressure of 7 mb or so would still seem to be very little water vapor in terms of total mass, and the mean free paths of individual H2O molecules are doubtless much longer than they are at Earth's surface. Frost happens, of course, but that's about the water molecules binding to each other and to the rocks & soil, not electron exchange, so no chemical reactions take place, just phase changes.

That's all probably totally wonky, and in any case my thinking is not well-explained. However, since our direct experience with olivene decomposition is limited to its behavior on our comparatively sopping wet, humid, hot planet with a dense atmosphere, then it makes sense to consider physical factors that might greatly reduce the rate of (or even completely inhibit) chemical activity for such reactions.

My ignorance is at least equal to yours here nprev, but I am under the impression that forming frost requires a mobile, or 'liquid' monolayer at the forming surface of the crystals, kept liquid by the pressure of the van der waals forces between the atoms. I think SickNick or Dburt would have some knowledge on whether this is always true. I don't know if any studies have been done to see if frost forms without the monolayer under mars-like conditions?

If it is always true this implies some difference between the surface and near surface material.

Surfaces without thin films of (usually but not always) water experience much higher friction coefficients, as high relief areas, known as asperities, on the two surfaces bond together. This might explain some of the clumping, but not why the clumping seems to lessen over time.

EDIT: Actually it might. If the regolith beneath the surface is ultra dry, and the atmosphere in the soil pores to, then soil freshly removed from the subsurface will have no water monolayers and particles will be held together by cold welds between asperities. After some days exposed to the atmosphere above the surface, which does have some water content, monolayers will start to form, lubricate the particles and hey presto the stickiness goes away.
If there's enough H2O in the Martian air to make that a possibility (no idea myself) then this could be tested by scooping up some subsurface, testing it for monolayers, leaving it in a heap on the deck for a few days then testing it again. If the soil becomes 'damp' after a few days on the deck then we have an explanation in the making and I shall buy myself a new bottle of absinthe! END EDIT.

It's been pointed out to me on the the yellow and black rover forum that relative humidity is temperature dependent and would be expected to vary significantly as the temperature changes, as relative humidity is the partial pressure of the water vapour divided by the saturation vapour pressure of water at a given temperature. Is it possible there has been a misinterpretation somewhere, and the change in relative humidity is entirely due to temperature, and little or no vapour is coming off the ice? Again my ignorance of humidity and atmospheric physics s pretty profound

Sorry if this has been discussed (I'm back from a break), but these sol96 images show the solar panels flapping (presumably due to wind):

http://www.met.tamu.edu/mars/i/SS096EFF904...4_1B300R6M1.jpg
http://www.met.tamu.edu/mars/i/SS096EFF904...5_1B360R6M1.jpg

This is clearly panel movement, since the foreground and background surface are sharp, but the panels are blurred vertically. Have we seen this before?

Could it just be out of focus, since the panels are further away? R6 is one of the diopter filters. which the SSI vital statistics page lists as having best focus at 1.2 m, in focus from 1 to 1.4 m.

Can't remember that this was mentioned anywhere. There was already a strong wind at sol94 - see Emily's animation http://planetary.org/blog/article/00001628/ and lots of clouds around in those sols.

There's such comparable R6 images where it is sharper http://www.met.tamu.edu/mars/i/SS099EFF904...2_1B7C0R6M1.jpg

Fair enough! I'm convinced

Wow. I didn't expect that kind of power with Mars' air density...

It clearly is flapping and not blur as the blur is directed up-down, a regular motion blur pattern with the two amplitude peaks best exposed. One could probably be able to calculate the amplitude fairly straightforwardly from vertical extent of the blur.

Thanks for the links.

To add to ugordan's comment about motion blur, this can't be a focus issue because both the foreground (MECA etc) and the background (surface of Mars) are in good focus, but not the panels in between. No optical system can do that.

The images I linked to have exposures of 714 and 510 milliseconds (I believe those are the units - correct me if I'm wrong). So this is not a gentle flexing of the arrays as the wind varies - they had to flap at least once in a half second.

With this kind of movement in the arrays and wind I wonder if dust is being cleared off. But I suppose the reduction in sunlight will be more important than dust losses for Phoenix.

Makes the whole situation up there at the Martian Pole so much more vivid and "real", to see the panels flapping. A bit like the litle tell-tale, but more impressive...