Turbulence in a Molten Core May Cause Earth's Magnetic Field

It turns out that turbulence may be responsible for strengthening our planet's magnetic field. Scientists have modeled Earth's outer core using liquid sodium and have found that random motion that takes place in the molten metal of our planet's core could be making a contribution to Earth's field.

Like many other planets and most stars, Earth produces its own magnetic field by dynamo action, which is the motion of an electrically conducting fluid. This ocean of liquid metal, the outer core, surrounds the inner core, which is made of solid metal. It's set in motion by the convection caused by the cooling on the core.

In order to better understand the interactions between turbulence and the magnetic field, the researchers used the Derviche Tourneur Sodium experiment, which was begun in 2005. This miniature model of the Earth's core was created from 40 liters of liquid sodium enclosed in a space between two concentric spheres. What makes this model unique is that a magnet at the center of the inner sphere provides a strong magnetic field. Under these conditions, the liquid sodium undergoes both large scale motions and random fluctuations.

The scientists placed sensors around the outer sphere and inside the sodium in order to map the magnetic field. In the meantime, ultrasound beams measured the rate of flow of the fluid using the Doppler effect.

In the end, the researchers found that turbulent motion increased the fluid's ability to conduct electricity and amplified the magnetic field. This phenomenon was then confirmed by numerical simulations.

The findings don't just apply to Earth. They also apply to planets with a magnetic field and to stars. This discovery of a new component of the magnetic field may explain why in the case of Venus, the liquid metal core does not produce a magnetic field.

The findings are published in the journal Physical Review Letters.