All astrophysical plasmas are, as far as we know, magnetized and turbulent. They range in size, density, and temperature from relatively small, dense stellar plasmas to enormous, diffuse plasmas in clusters of galaxies. The magnetic fields and the turbulence play important roles in issues as diverse as cosmological structures formation and the origin of cosmic rays.

Closer to home, Earth also has a magnetic field, as do most but not all of the other planets. The geomagnetic field makes our planet more hospitable by shielding us from the Sun’s charged-particle wind. We have only a partial understanding of how the turbulent flow of liquid iron in Earth’s outer core generates the geomagnetic field. (Despite being hotter, the inner iron core is solid because it’s under greater pressure.)

That level of understanding does not yet make predictive forecasting possible, which is mildly alarming because the geomagnetic field has fallen monotonically throughout...

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