Earth’s magnetic field—useful not just for navigation but for shielding the planet’s surface from the charged particles of the solar wind—owes its existence to the convective flow of the outer core. Heated from below and cooled from above, the churning liquid iron–nickel alloy hosts a self-sustaining dynamo in which electric currents and magnetic fields continually induce one another.

But the full picture is not so simple. The flow in Earth’s core is almost certainly turbulent—and therefore chaotic, nonlinear, and hard to model. Observing the flow directly is impossible. And modelers get their simulations to output an Earth-like field only when they input material parameters, such as viscosity, that they know are wrong. (See the article by Daniel Lathrop and Cary Forest, Physics Today, July 2011, page 40.) Clearly, something is missing from researchers’ understanding of liquid-metal turbulence.

Now Tobias Vogt, of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in Germany, and...

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