The Copycat Core: Recreating Earth's Magnetic Field in the Lab

If you have ever used a compass, you have experienced the effects of Earth’s magnetic field—in fact, you experience the effects every day without even realizing it! The magnetic field shields us all from harmful solar radiation and allows for our electronics to function properly, but have you ever wondered why Earth has a magnetic field in the first place, or how we study it? Earth scientists explain its presence with something called the geodynamo, and build laboratory experiments to simulate it.

What is the geodynamo, anyway?

A depiction of Earth's magnetic field. Blue lines represent
magnetic field lines. Figure credit: Hyperphysics

The geodynamo is Earth’s magnetic field engine, similar to the engine in your car. Instead of using little explosions to convert gasoline into motion the way your car does, however, it uses swirling liquid metal to convert electricity into a magnetic field. The idea is that Earth has a solid core, with liquid metal material surrounding it. Since the Earth is spinning, the liquid metal sloshes around like a fish tank on a turntable, and that turbulent motion throws off electrons from the metal. Electrons in motion create an electric current which induces a magnetic field. Once the process gets started, it can keep going and make the magnetic field bigger by cloning itself into lots of tiny engines, increasing the overall field strength.

Sounds nice…but can you prove it?

Despite what Hollywood wants us to think, we cannot travel to the core to confirm if the magnetic field engine idea is correct. Instead, we build experiments that simulate the Earth to test and study the phenomena indirectly.

Meet the 3-meter Geodynamo Experiment

A 3d depiction of the Geodynamo experiment. 

Figure credit: Laurent Hindryckx. 

The largest experiment studying how the core makes a magnetic field is nearly 10 feet in diameter and lives in a hangar at the University of Maryland. It consists of an interior sphere, meant to represent the solid inner core, encased in a larger sphere, with 24,000 lbs of liquid sodium metal between the two, meant to represent the outer core (that's approximately the weight of 2 helicopters!). Motors on the spheres allow for each to rotate independently and copy the way the Earth spins.

So far, the experiment has been partially successful at making an Earth-like magnetic field, but only with extra equipment to start the process. In order to better match real-world conditions, the entire setup is being given a rough makeover. Right now, the inner sphere has a smooth surface, so even though the metal is flowing in a chaotic way, it is not quite enough for the magnetic engine to start on its own. It is like trying to strike a match against a smooth surface (or start a car without spark plugs)--we do not have the right surface to create a spark. Adding roughness to the inner sphere increases friction so the engine can turn over and start.

How rough is rough enough?

The final design for the inner sphere of the 3-meter
Geodynamo experiment. Each bend helps increase
turbulent flow when the experiment is running.
Photo and design credit: Ruben Rojas

Based on smaller experiments and simulations, the winning design for the inner sphere looks similar to the ridges of a basketball, with each bend helping to increase the friction (turbulence) for the liquid sodium.

It is a logistical and safety challenge coordinating the modifications, but they are currently on track to be complete by summer 2020. Stay tuned!

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