Soil Experiments

Attempts To Duplicate The Properties Of Martian Soil, Part 5

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   Now we will look at some of the images from the microscopic imager.  You will see how the soil adheres to the fossils and other bits of material in the images.  First, let's look at the Martian sand on a dry ledge.

   This is a crop from an Opportunity image from Sol 039.  It shows that the sand on a rock ledge is dry and granular, with no apparent cohesion.

   This material looks windblown and is most likely deposited on this rock and within its crevices through that mechanism.  Windblown materials can in theory be larger than sand grains even though there is very little atmospheric pressure, due to the great wind speeds that are apparent during the dust storms.

   The rock itself is also quite clearly dry and shows no overt sign of water or any other potential solvent or liquid.

   The original image is at the NASA web site at this link.

  
   Here is a second image, also from Sol 039, that illustrates clearly that this is dry sand.  Notice how it is "space-filling" and packs loosely over the urchin fossil and the exposed rock surfaces.

   Once more, the individual granules are not clinging and they look dry to the eye.  Tests with beach sand and other types of dry sand show that there can be no significant moisture in a soil that shows this particular form.

   The original image is at the NASA web site at this link.

  
   A test done with a dry "Mars sand" simulant and some small plastic spheres and washers (meant to schematically represent the fossils found in some of the images) shows that the dry sand is virtually identical in properties to the sand in the two previous images.

   Note that the sand "drapes" and does not adhere at all- the picture shows that nothing is sticking to any of the structures, and that the look is a nearly perfect replica of the look of the two previous images.

   Notice how the spheres and rocks tend to either be immersed or set entirely on top of the sand.  This is completely uncharacteristic of the fossils in the next few images.

(NOTE: this image is a simulation, not MER data.)
   Now compare this to the actual image data in this picture.  This is from Opportunity Sol 063.  Look at how the soil sticks to the fossils and also has a "patterned" look to it.  This is identical to the pattern produced by tiny droplets of water that strike the soil at high speed.

   This soil is in fact wet and it shows all the cohesion of damp or wet soil to the objects imbedded in it.

   An attempt to duplicate this look with dry soil failed completely.  Only when a spray of fine droplets at high speed was applied did the surface texturing shown here emerge in test soils.

   This image was contrast and difference enhanced to show the finer texture of the soil surface.

   The original image is at the NASA web site at this link.
   After several experiments with dry and damp soils, some observations of natural raindrop patterns in exposed sand showed the proper method of duplication.  A spray nozzle under pressure with a moderately fine mist emerging produced this very good replication of the soil look and texture as it appears in the Sol 063 image above.

   The only real problem with this replication was that the droplet size was still a bit too large, and the soil too wet at the end of the experiment.  This was solved by using a finer and faster mist and applying it for a short period of time.

   What is implied is that small droplets of water at high speed are required to be present to produce this look.  No other methods tried produced even a similar look.
   With the smaller droplets and higher spray velocity, a near perfect scene is created.  Now you can see how the sand sticks to the spheres and rocks in this setting.

   Because of this success, I have very compelling evidence that Mars is not only wet below the soil, but also must experience periodic rainfall.  But there is always the question of whether it really rains on Mars.

   Without actually witnessing it, there is little way to be certain.  This simple experiment does lead to the solution that if it did rain, the rain droplets would have to be small and very fast to produce the soil texture that we observe.

   So the next question is, if it were to rain on Mars, what would it be like?

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