Now scientists studying satellite data of Earth have identified something inside Earth we’ve never seen before: a new type of magnetic wave that sweeps around the surface of our planet’s core, every seven years.

This discovery could offer insight into how Earth’s magnetic field is generated, and provide clues of our planet’s thermal history and evolution – that is, the gradual cooling of the planetary interior.

“Geophysicists have long theorized over the existence of such waves, but they were thought to take place over much longer time scales than our research has shown,” says geophysicist Nicolas Gillet of the Université Grenoble Alpes in France.

“Measurements of the magnetic field from instruments based on the surface of Earth suggested that there was some kind of wave action, but we needed the global coverage offered by measurements from space to reveal what is actually going on.

“We combined satellite measurements from Swarm, and also from the earlier German Champ mission and Danish Ørsted mission, with a computer model of the geodynamo to explain what the ground-based data had thrown up – and this led to our discovery.”

Earth’s magnetic field is the subject of much fascination for scientists. Research to date suggests that the invisible structure forms a protective ‘bubble’ around our planet, keeping harmful radiation out and the atmosphere in, thus allowing life to thrive.

But the magnetic field isn’t static. It fluctuates in strength, size, and shape, has features we don’t understand, and is gradually weakening over time.

The reason that activity inside our planet is important is because that’s where the magnetic field comes from. It’s generated by a dynamo – a rotating, convecting, and electrically conducting fluid that converts kinetic energy into magnetic energy, spinning a magnetic field out into space around the planet.

That fluid is (mostly) the molten iron inside Earth’s outer core.

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