Just found a bit with discussion (pdf) about...dirt.
The following PDF goes in to detail about the subject of SOIL CEMENTING,
and does discuss the cementing process when considered with ;
low pressure atmosphere, salt content binding of particles, and soil moisture content
all helping to CEMENT the soil in a fashion that would give it unusual cohesive properties,
and seemingly help to violate STOKES LAW, as described below.
ESTIMATION OF SOIL THERMAL CONDUCTIVITY FROM A MARS MICROPROBETYPE
Additional information on soil properties as shown below.
Soil Physical Properties
Soil mineralogical composition:
· Primary minerals: present in original rock from which soil is formed. These occur
predominantly in sand and silt fractions, and are weathering resistant (quartz,
· Secondary minerals: formed by decomposition of primary minerals, and their
subsequent weathering and recomposition into new ones (clay minerals).
· Humus or organic matter (decomposed organic materials)
Mineral type has large influence on soil behavior:
· Ion exchange, related to cation exchange capacity
· Hydration and swelling; dehydration and shrinking
· Flocculation and dispersion
· Preferential flow, as through soil cracks
· Barrier to flow, as by swelling clays
· Chemical adsorption of contaminants and nutrients, both in liquid and gas phase
Some information suggesting what was implied above,
in reference to the scatterred rocks
that seem to perpetuate on the surface.
This has to do with the appearance on the new mars images of
many rocks that seme to 'float' on the surface undisturbed.
Soil Texture Classification:
Soil separate equivalent diameter size (mm)
gravel > 2 mm
Sand 0.05 - 2 mm
very coarse 1 - 2 mm
coarse 0.5 - 1 mm
medium 0.25 - 0.5 mm
fine 0.1 - 0.25 mm
very fine 0.05 - 0.1 mm
Silt 0.002 - 0.05 mm
Clay < 0.002 mm (< 2 micrometer)
How to measure soil particle size ???
1. Mechanical sieving, if size > 0.05 mm
2. Sedimentation - Stokes law, if size < 0.05 mm
Soil is dispersed, and mixed with water (soil suspension);
Settling velocity of individual particles depends on particle diameter;
Forces acting on soil particle are gravitation, buoyancy and drag forces,
and all depend on particle size;
The larger particles settle first à Stokes law
Since soils are a mixture of different size particles, soils are classified using the so-called
soil textural triangle.(see PDF link page 4)
I also wonder if the rover is using this method of
testing any soil properties and possible moisture content?
TIME DOMAIN REFLECTOMETRY (TDR)
The speed (v) at which the EM wave moves along the conductors and through the soil
is reduced as the dielectric constant of the soil is higher. Hence, an increase in water
content increases the soils dielectric, and subsequently increases the travel time of
the EM wave. The TDR method measures the travel time through the soil.
Surface area of soil affects its physical and chemical properties and is largely
determined by amount of clay present in soil
If the soil on mars is experiencing a 'Cementing' effect
that might be caused by a high salt content from
'brine' left after any water on mars was blown
off the planet by solar winds, due to a low gravatational
field around the planet, then the soil would in fact be
cohesive until broken up and made loose. again.