Is there gravity under the earth

Understand the core of the earth in weightlessness

The American space shuttle Atlantis took off successfully on February 7, 2008 for the International Space Station ISS. On board was the European Columbus space laboratory, in which researchers will be carrying out numerous experiments under weightlessness or, more precisely, under microgravity over the next few years. A total of ten standardized, cabinet-shaped components can be found on the outer walls of the module. For weight reasons, Atlantis first brought the first four experimental cabinets into space. Further test facilities will follow for future shuttle missions to the ISS.

The Columbus module

The Fluid Science Laboratory plays a central role in physical research. And the flow physicists and geophysicists of the Brandenburg Technical University Cottbus (BTU) were able to secure one of the extremely sought-after experimental sites. Geoflow is the name of the experiment, which from January will almost automatically provide new knowledge about the flows of hot, liquid materials in the earth's interior. “The model experiment simulates convective currents in the liquid core of the earth,” says Christoph Egbers, Professor of Aerodynamics and Fluid Mechanics at the BTU. Together with French and British colleagues, Egber's group has been developing the Geoflow experiment since 2001, which was built at Astrium Space Transportation in Friedrichshafen and tested for flight into space.

Simulation of the earth's core in weightlessness

Laboratory model of the GEOFLOW experiment

The step into space is of central importance for the success of this experiment. Because only without significant gravitation can the forces acting in the liquid core of the earth be simulated satisfactorily. In a laboratory on the surface of the earth, the force of attraction disturbs the test process too much. In order to get as close as possible to the conditions in the Earth's core, a central force field acts in the Geoflow experiment, which is comparable to the radial, all-round gravity of planets.

These conditions are realized with two nested, rotating spherical shells. Between these there is a gap about 15 millimeters wide, in which a transformer oil with low viscosity can circulate. The inner spherical shell is heated, while the outer one is cooled. This creates a temperature gradient of a maximum of ten degrees, which is comparable to the heat distribution in the earth's interior. Of course, the several thousand degrees as in the Earth's core are not reached. But even at significantly lower temperatures, the transformer oil behaves somewhat like the liquid iron currents that move around the solid core of the earth.

10,000 volts replace gravity

In order to generate a radial force field, a high voltage of around 10,000 volts is applied between the two spherical shells. Just like the gravitational field in our planet, it works centrally symmetrically towards the center of the spheres. Temperature gradient, rotation and the electrohydrodynamic force field now act on the transformer oil and set it in motion. Currents arise that can be analyzed with a so-called laser interferometer. The laser beam detects changes in the refraction of light that are characteristic of the movements of the transformer oil. "All parameters are set in such a way that the physics of the flow can be transferred to the conditions in the Earth's core as a model," says Egbers.

Predictive model of the GEOFLOW experiment

If the Geoflow experiment starts at the beginning of January 2007, the researchers expect a large amount of data. During the experiment, these are initially stored on board the ISS. If there is a connection with the space station via a so-called downlink, these measurement results are first sent to the control center in Oberpfaffenhofen and then via a dedicated line directly to the Cottbus University. Here they are gradually evaluated by Egber's team.

Customizable test software

Each series of measurements is planned down to the smallest detail so that the test can be successful. If the first evaluations of the data show a geophysically exciting development, the parameters can even be adjusted afterwards. For this purpose, Egbers and colleagues have the option of changing the test software via a data channel to the space station.

If Geoflow delivers the expected data on the behavior of liquids in the Earth's core, Egbers is already thinking of further experiments. With more viscous oils, the dynamics could then be simulated and understood more precisely not only in the liquid core of the earth but also in the earth's mantle.