Confirmation of the flow of pressurized steam in Gusev Crater
Now on Sol 480, a new moat rock has appeared, and this one is located right in a sand drift. The most interesting thing about the location is that the hardpan under the rock provides a flat reference surface and the sand is blown away all around it in a very clear and indisputable pattern.
| If we look at this image, we see a rock in a
sand drift. The outstanding feature is how the drift is
removed from the rock in an oval. The harder ground
beneath is not disturbed and can be seen outside of the sand
drift as well.
Whatever removed the sand from around this stone has done so and left radial lines in the sand drift. The original image is here at the NASA/JPL website. |
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| I have highlighted the radial line pattern and
the crater edge around the rock. Some fluid has emerged
at high speed and blown the sand away from the base of the
rock, clearing the oval we see.
A pressurized fluid, such as steam, would be the perfect solution to this mystery. This was my conclusion when observing the previous moat rocks that Spirit imaged in December of 2004. The placement of the sand in this case is perfect as it provides a record of the movement and how is was produced. Wind cannot come from many directions at once, and it certainly would not single out this rock from all the other rocks in the area. |
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| This is how the moat rocks are formed.
Water underground boils into steam through geothermal heat and
the lower outer atmospheric pressure. The temperature
for this boiling can actually be very low- perhaps only 30 to
40 degrees C.
When the steam emerges from the fumarole, it blows the sand away from the rock and creates the oval shaped clean hardpan zone that we see in the images. Liquid water is present underground on Mars and can emerge under the soil, wetting it, or it can spray from a geyser (as seen in Meridiani Planum) or it can emerge as steam from a fumarole, as in the case of these moat rocks. The capstone increases the steam pressure and allows it to blow the sand away, creating the characteristic ring that we see. |
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The conclusion is that some fluid material is venting from under the rock, and the rock is apparently serving as a capstone for the vent. Whatever the fluid is, it emerges as a gas and not a liquid. Water is the obvious candidate and steam pressure from water that is vaporizing would produce the precise effects that we are observing.
Here is a cross-eyed stereo view of the moat rock shown above. The true geometry of the sand crater around the rock is clearly revealed here.
