How can we image the Earth's interior when the deepest drillhole is 12 thousand meters deep?
Right, we go into space on the ISS. Ok, honestly this is quite counterintuitive, which is why this experiment immediately caught my attention as well. Today I read the Geoflow 2 experiment that is supposed to shed light on the interior of the Earth. In a very simple form, they took two solid spheres and put a liquid in between and gave it a spin.
However, the sciencedaily article doesn't cover some important fact. They're writing “The liquid, of course, is the mantle“, since the Earth's mantle is anything but a liquid, how is this a valid experiment? Any computer simulated convection model of the Earth works with plastic flow. A scientific fact that is confirmed with every earthquake strong enough we measure, because there are certain seismic waves that do not propagate through liquids.
Let's first look at the setup of the experiment.
As before, they take two solid spheres and put them together. In between they put a liquid. Whereas, the solid spheres are the core and the crust. But now it gets tricky. How do you simulate gravity on a model, when “real” gravity of the Earth is influencing your model? Yes, this is where you go to your local space agency and better have some good arguments. And they did.
They can regulate the temperature of the model within an accuracy of a tenth of a degree. This is very important for applied different temperature gradients on the model. A high voltage electrical field between the two spheres to simulate gravity. (This only works without “real” gravity.) Now you can start to rotate the spheres and observe.
Now about this liquid that is supposed to resemble solid rock from the earth's mantle.
This is where it gets tricky. When you do experiments including fluid dynamics you usually have some large scale phenomenon and need to fit everything into a small-scale model. Now fluid dynamics has some nice tricks. They're called dimensionless quantities and resemble the combination of some important properties of the earth. I'll give you an example: The Rayleigh number is a number that describes the relationship of buoyancy and viscosity in a fluid. When this number gets below a threshold heat transfer only occurs in the form of conduction, when the value exceeds a threshold heat transfer occurs in the form of convection. Now we have some good estimates of the Rayleigh number of the mantle and some other dimensionless quantities, if we get the fluid to resemble the dimensionless quantities of the mantle a fluid is a valid substitute for solid rock in small scale.
The team has worked several years to get this tiny experiment into space. It's just as big as a shoe box but to work with all the data they get, they had to update their computer cluster quite a bit.
Let's see if this experiment will revolutionize our understanding of the Earth's interior.
Sciencedaily: http://bit.ly/Mm67K3
ESA: http://bit.ly/Mm65Sp
Or directly at the source: http://bit.ly/Mm6cgN
-JSD
