"Matthew Montchalin" skrev i en meddelelse
...

snip

|Can you predict a mechanism that can explain the creation of the
|balls, whether by a biological process, or any other?

Why can't
|a small grain roll around, perhaps buffeted around by the wind, and
|gather other particles, adding onto itself like a snowball does?

It would more likely produce an oval or cylindrical object.

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Is there ever enough loose sand to form a one foot high dune?

http://www.msss.com/mars_images/moc/themes/DUNES.html

Enough
for a windbreak, or a rise sufficient to keep the sunlight away from
places where brine could percolate up, and not sublimate away? Then
if the wind shifted, ball-like kernals could roll down the dunes and
closer to the cracks where moisture might be found. The rolling motion
might make them roundish, where previously they might have been nugget-
like. If wind makes things round on earth, could not wind make things
round on Mars?

It would still tend to make an oval or oval/flat object as ordinary
erosional processes does (see pebbles in seasurf, alternatively aeolean
artefacts). Further more, the spheres seem developed in-situ, not deposited
in the sediment.

|If high moisture levels can be detected in the vicinity of the
|cracks, as by upwelling from a briny solution deeper down, or
|by precipitating from above, as from some kind of damp fog, that
|should encourage 'berries' to rock back and forth in the area,
|increasing their mass just like 'snowballs' increase mass.

The meteorology shows a very low H2O% in the atmosphere, but the
dew-point-temperature is equally low so the extreme 'dryness' is somewhat
semantic - I do not have the picture where water or CO2 ice-crystals cover
the ground, but it happens and should fuel speculations as to what
implications it would have on the structuring of the surficial sediment. I'm
not about to calculate the meltingpoint of a brine in low temperatures, but
I think that it could be acceptable that small droplets of brine may
develop.
To extend this speculation to the actual circumstances will take a
consideration on the nature of the matrix-sediment. I have defended a wet
origin as far as observations has provided no other clues - in my opinion,
the outcrop consist of dust, probably sedimented out in subaerial
duststorms. The mineralogical contents points to evaporites - I'll take that
as a hint that wet degradation over a prolonged period of time has evolved a
large stock of salts/evaporites to be distributed by wind.
On the above link you will see the 'ordinary' or sand-grain
wind-distribution that equals processes and constituents known on Earth.
I would like to elaborate a bit on the 'dust' that apparently has different
structural properties than the normal dunes formed. Without additional
adhesion dust could settle in large incoherent 'puddles' with an extremely
high porosity and low density. If electrostatic attractions are added I
could expect some dynamic that resembles what fx happens around the
abrasion-tool on the rowers. I do not find it very speculative that the
dusty sediment can get some additional coherency to produce rigid
sedimentary bodies - as fx the outcrop. I'm trying to omit a later
diagenetic compression as the outcrop in itself is surficial and probably
never has been buried.
If frozen dew falls on such a surface and makes a droplet with a saltcrystal
under a warm daytime temperature, this droplet could be sucked into the
porous dust. Would it necessarily disperse evenly in the porous sediment?
Can a viscous (low temp) brine self-organize into a spherical shape in a
perhaps hydrophobic sediment? I don't know, but if it can, it may well
dissolve and reprecipitate minerals in a spherical aggregate. It's
speculative, but the presence of moisture/brine may well provide a spherical
crystallization-front from a central dissolvable grain.
IMO, I'm a Mars-amateur.

The following link shows (to me) a 'young' dust that has filled a vally. It
is surrounded by a 'dust' that has undergone some diagenetic process that
has consolidated the rock.

http://www.msss.com/mars_images/moc/2003/09/22/

The foot may be dissolution/reprecipitation mediated by frosty dew - in
particular if the initial minerals are a product of precipitation from
whatever 'moist' available. This also applies if the moist has an origin
from the soil.

http://marsrovers.jpl.nasa.gov/galle...EFF0544P2953M2
M1.HTML

Carsten