Soil Experiments
Attempts To Duplicate The
Properties Of Martian Soil
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When viewing the MER
microscopic images, it is very clear that the Martian soil has some properties
that do not coincide with those of dry soils. All samples that are on the
ground seem to be moist or damp, showing excellent cohesion and taking a print
clearly. Samples that are on ledges of rock are almost always dry and
granular, and show very poor imprinting ability.
Experiments with
various soils reveal that even very powdery soils will not easily reproduce
these properties without some moisture content. Consider that even talcum
powder, thought to be bone-dry, is not. It contains water of hydration,
bound directly to the molecules of magnesium silicate that talc is made of.
The chemical formula
for talc is Mg3Si4O10(OH)2,
and it is technically known as magnesium
silicate hydroxide. A very fine powder of talc will take an imprint well,
but most fine powders can do this to some degree. However, most fine
powdered minerals contain some moisture, whether as adsorbed onto the surface of
the granules or as a chemical constituent of that powder.
Even Plaster of
Paris powder will take a print, but once again, it has water in its
makeup. Plaster is calcium sulfate hemihydrate- CaSO4
+ 1/2 (H2O).
It is hygroscopic, drawing moisture from the air to recombine and make the
hardened plaster that we are familiar with. Lime powder, however, is good
at taking a print even though it has no water in it. It is a desiccated
powder made of calcium oxide. But many desiccated powdered minerals will
take in moisture from their surroundings and solidify, rendering them into a
solid.
| A look at the
Martian soil reveals that the granules are clearly shown- they appear very
much like sand. But in many of the images, the sand seems to cling
or take a print easily.
Here is a cropped view from
Sol 012, Opportunity. Notice the rough granular structure of the
soil, and how it shows its granules on surfaces.
It seems pretty clear that
there are few, if any, small, silt-like particles in this mixture.
It appears of the same general texture as builders' sand.
But also pay attention to
the imprint at the top of the image- the grains clearly cling together and
form a perfect impression, which indicates that the soil might be moist. |
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| Even under
magnification, there is no evidence of finer grains. Each individual
sand grain stands out pretty clearly, without the appearance of a silt or
finer clay-like material coating the objects or showing up between the
grains.
This would seem to support
the idea that the sand is not really that fine, although there is arguably
fine dust in the environment. It seems that something has segregated
out the finer particles and left the granular materials behind.
If that is true, then some
other agent must be responsible for the stickiness of the grains, and
water seems to be a very logical candidate. Water can wash fine silt
out and leave the larger granules behind.
First, let's look at sand
properties- with and without salt. |
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