The amount of ice in the soil can be higher than 20 microns if it is replenished daily subsurface and it is protected from evaporation by remaining covered.
I am saying this ice exists planet-wide and moreover this melting occurs over a large portion of the planet, mostly in the temperate zones. My key over-arching point is that this melting has been confirmed by the current orbiters observations of seasonal varyings in the bound water content of hydrated minerals (reported in the articles I cited in my sci.astro post.)
I'm arguing that these hydrated minerals form by liquid water on Mars as they do on Earth.
Whether or not the wheel dragging itself causes further melting of subsurface water is not a big deal.
Solar illumination itself I argue is enough to melt surface frosts with the addition of the known presence of salts.



- Bob Clark

We know the ice exists all over the planet - GRS telles us that, in quantites from not a lot - to huge ammounts.

What you are saying is that this regularly becomes liquid.

Where are the lakes, rivers, ponds, bogs, mud slides, streams?

If sub-surface water were becoming liquid regularly, then where is it? Where did it come from? What's pushing it to the surface?

You're trying to impose vast quantites of 'if' 'might' and 'may' onto some dragged tracks that look, at first glance with earth-bound eyes, a bit like mud.



Exactly.

Doug

This is incorrect and old tale often repeated, but unfortunately, wrong.

The slipperiness of ice and snow is not the result of pressure melting. Pressure melting does not occur to a useful extent even with ice skating (where the pressure/area is much greater than a ski or snowboard) once the temperature falls below -8C. Please read the Physics Today article: http://www.geo.hunter.cuny.edu/~hsalmun/ice_phy2day.pdf

Melting has not been confirmed in the wheel trenches, which is what we are discussing.



Ok, we can drop the wheel dragging friction or compression causing melting from discussion.



OK let's discuss solar warming of putative surface or subsurface frosts exposed in wheel-opened trenches as a mechanism for mud formation.

Assuming thin subsurface frosts exists, perhaps sublimation is more likely than melting once such frosts are exposed to sunlight. Unfortunately, we lack data, since most (all?) of the brine evaporation/sublimation experiments did not use a suphurous brine, rather they used alkali metal-halide brines. There will be differences in the evaporative properties when anions with -2 charge are present (probably helpful to your hypothesis).

Assuming melting (not sublimation occurs) from the putative surface and subsurface frosts, whether it can form a mud before the liquid water evaporates becomes a chemistry kinetics issue. Here are some questions (data) needed before making a claim of mud:
-1. How fast will briney water(l) be formed by solar warming compared to how fast it evaporates?
-2. Assuming the amount of frost is x% of the soil, what is the maximum amount of water formed in #1?
-3. How long would it take (seconds) for #2 (maximum amount of water)?
-4. Is there sufficient quantity of water (#2) to wet y grams of dehydrated soil dusts within z seconds (#3) before the putative water evaporates?
-5. Is there enough time within the brief period of time that the wheel opens and spreads the soils to actually make a mud (time required as defined in #4)?

Very interesting - Thanks for pointing this out.

To be more precise Pressure melting is not the whole story - as with most things "it's not as simple as you think"

To quote from Physics Today "Each mechanism [Pressure Melting, Frictional Melting and Liquid-like films] plays a role that depends on temperature."

I shall endeavour to be more rigorous in the future.

Nick

Well, we have seen examples of recent "streams", ephemeral they may have been. It's the Malin-Edgett gullies I mean. And the latest announcement is that such gullies are currently forming. I argue these currently forming gullies are also from liquid water.
As for ponds, I'm going to make a prediction that MRO will find small ponds located on Mars, oases if you will. These will be analogous to Don Juan pond in Antarctica.
My guess for where they will be found is at near equatorial areas that are known to have low lying fogs or clouds:

Clouds in Noctis Labyrinthis on Mars.
http://www.photovault.com/Link/Universe/Pl...octisLabyr.html

As for lakes, I believe they do exist currently on Mars though subice, like the subice lakes in Antarctica. However, I don't know if MRO will have sufficient sensitivity to detect them.



Bob Clark

Struggling a bit...

http://qt.exploratorium.edu/mars/spirit/fo...E2P1211R0M1.JPG
http://qt.exploratorium.edu/mars/spirit/re...BMP1301R0M1.JPG

Oh Dear. Things are not looking good for Spirit at all. I didn't expect this wheel problem to be quite so crippling after the progress they previously made on 5 wheels.

Of course, the genius of that argument is that you can always say "well - it's not found them YET...but it will" for about 10 years They'd have to be very very very small ponds to be visible with HiRISE but not with MOC, and MOC's been looking at Mars for nearly a decade.

Someone elsehwere has branded me as being 'anti' water. ( and I know they're reading - why not join in and make your case? ) and that's simply untrue. Think of the astonishing implications w.r.t astrobiology if we were to find liquid water on the surfafe of Mars. The impact would be huge, and it would be brilliant for exploration. Why would anyone so enthusiastic about space exploration as I be opposed to such a thing?

However - I'm pro-evidence - and I'm yet to see any evidence of water here.

Doug

Dealing with full time work and nearly full time elder-care, I have not been able to go down to the Univ. Texas. libraries, borrow the technical literature published by the Odyssey Gamma and Neutron instrument teams, xerox (lower case ;-> ) them and READ them. So I'm working from background knowledge here.

But regarding low latitude *HYDROGEN* on Mars. Note that we have no direct evidence for on-surface or subsurface water at low latitudes on Mars AT ALL. We did see water ice (presumably and most plausibly) on the top of Oppy's deck and or solar panels one near-dawn morning, deposited from the chilled atmospheric boundary layer pre-dawn. I do not know what current thermal modeling of the top surfaces of Oppy at that time of year with the Mini-TES measured atmosphere opacity and temperatures, or the modeled near-dawn boundary layer temperature of the atmosphere was. But that's it.

We DO see diurnal ice-hazes and fogs, some clearly trapped in topographic lows like craters and valleys, but there is little indications that this ice is deposited on the surface in anything more than trace and very transient amounts.

<to be continued next post>

What DO we see in the Odyssey orbital data? We see indications of a small but decidedly non-zero amount of hydrogen in the low latitude martian surface. We see it with horribly low resolution: We can map gross regional variations but not local correlations with discrete topographic features and color/albedo/thermal soil units. We reportedly see seasonal variations in hydrogen/water low latitude regions on the order of a few percent. How accurate either the absolute abundance and variability measurements are, I do NOT know. Outside of high latitudes where signal-to-noise in the data are high, I do not know whether the modelling based on the different energy neutron data plus the gamma data indicates any depth variation of water content in the surface materials.

In addition, there are both statistical and systematic errors in the measurement. One cause of systematic errors may be the the seasonal atmospheric pressure variation on Mars. I know atmospheric attenuation is a problem with the gamma data, I don't know how much it may complicate the different energy neutron bands. The published maps are so smoothed I get very little idea what's noise and what's feature. Lunar neutron data showed systematic effects due to surface composition and raw maps based on that data could mindlessly be interpreted as "water" at low latitudes where it's not plausibly present. For Odyssey, I have not seen seasonal maps, nor seen any comparison between Year 1 and 2 seasons in 2002, 2004 and now (presumably not processed) 2006 Mars Year 3 data.

So what is it we see? Hydrogen. It may be ice. Certainly a significant amount of it is water of hydration in sulfate minerals. That is likely to be the vast majority of hydrogen/water in non-ice-bearing soils planetwide. Additional amounts of hydrogen may be present in clay minerals or as yet poorly defined (some may not really be definable minerals of definite composition) weathering products, as well as bound hydrogen in water in igneous rocks and minerals. Some hydrogen will be present as adsorbed water, trapped on and in the surfaces of mineral and mineraloid grains.

<more next post>

While you guys are arguing over the "could be, shouldn't be" frost you have all taken your eyes off the ball. All I see is the wheel sinking deeper. Can it ever get out of here on five wheels?

Is the dream over?

Is this the final panorama?

Ultimately, we will need (among other things) an aerostationary orbiter instrumented for martian meteorology, and climatology. This is needed to complement time-zone limited data from sun synchronous polar orbiters.

Meteorology instruments can observe the full diurnal cycle of ice and dust hazes and clouds, as well as regular meteorological events like winter cold fronts and special events like regional and global dust storms.

We should also be able to directly observe full diurnal temperature curves for the surface and infer sub-surface thermal layering to a depth of a centimeter in low thermal inertia regions like Arabia to centimeters in high inertia regions like Meridiani Sinus. We should also be able to directly observe post sunrise and pre-sunset albedo changes of the surface in the visible and near infrared and and set solid limits on frost deposition and hydration changes in sunlit surface minerals.

Note that temperatures where it's easy to have ultra-saline brines stable at Martian surface pressures tend to be present in only the very very uppermost layers of the surface. The "thermal skin depth" of the martian surface is one or two centimeters in low inertia regions, maybe 5 or 8 centimeters (I'd have to dig into literature on Viking IRTM observation modeling to get the exact numbers) At a depth of 1 thermal skin depth, the diurnal temperature variation is sharply reduced, I think to 1/e the variation at the surface or something similar to that. A very few thermal skin depths below the surface, the temperature variation is only a few degrees or so. Because this is a diffusion process, mathematically, the seasonal skin depth is only a few times deeper than the diurnal depth. At maybe a meter depth, there's almost no temperature variation year-round.

Low inertia materials, like those in Arabia, seem to require surface material with physical properties like unconsolidated cement powder. High inertia materials seem to require sand. Some very high inertia regions imply somewhat cemented sand or coarse sand to granule dominated surface material. Rock abundances are generally low but can be estimated in the multi-spectral thermal data and are near-zero (few percent or less) in low inertia regions and many percent to some 15% in higher inertia regions. Rocks can be partially dusted bedrock, loose cobbles and rocks, or highly cemented materials.

Most materials the rovers excavate seem to behave as dry powders, some granules, some coarse to fine sand, some silt to clay sized particles, sorted or mixed in varying amounts. Some gives the appearance of "mud", but the proponents of these materials being mud have to provide evidence that clay-sized or clay and silt-sized powders can NOT explain the mechanical behaviour and appearance of the seemingly wet soils.

Enough ramblings for tonight. I'll sort some more of this out later.

Good grief, one high-slip drive, and people are calling it the end of Spirit - for all we know there may have been some cunning engineering exercise going on.

I'd have thought after nearly 800 sols, we'd have all learnt to be a bit more patient than that.

Doug

Engineering exercises aside, it looks Spirit is making a right turn probably (imho) looking for a less sandy path to the hills.