The interior of the Earth is a place far from quiet. Far below our surface activities, the planet vibrates with activity, from plate tectonics to convection currents flowing through hot magmatic fluids well below the crust.
Now, scientists studying satellite data from Earth have identified something inside the Earth that we had never seen before: a new type of magnetic wave sweeping the surface of our planet’s core, every seven years.
This discovery could provide insight into how the Earth’s magnetic field is generated and provide clues about the history and thermal evolution of our planet, that is, the gradual cooling of the planet’s interior.
Visualization of the waves at the core-mantle boundary. (University of Grenoble Alpes)
“Geophysicists have long theorized about the existence of these waves, but they were thought to take place on much longer time scales than our research has shown,” says geophysicist Nicolas Gillet of the Université Grenoble Alpes. in France.
“Magnetic field measurements of instruments based on the Earth’s surface suggested that there was some kind of wave action, but we needed the global coverage that measurements offer from space to reveal what’s really going on. .
“We combined satellite measurements from Swarm, and also from the previous German Champ mission and the Danish Ørsted mission, with a geodynamic computer model to explain what the terrestrial data had generated, and this led to our discovery “.
The Earth’s magnetic field is very fascinating to scientists. Research so far suggests that the invisible structure forms a protective “bubble” around our planet, keeping harmful radiation out and the atmosphere inside, thus allowing life to thrive.
But the magnetic field is not static. It varies in strength, size, and shape, has features we don’t understand, and is gradually weakening over time.
The reason why activity within our planet is important is because this is where the magnetic field comes from. It is generated by a dynamo: a rotating, convective, and electrically conductive fluid that converts kinetic energy into magnetic energy, spinning a magnetic field in space around the planet.
This fluid is (mostly) molten iron inside the Earth’s outer core.
The European Space Agency’s Swarm satellites are a trio of identical probes, launched in 2013 and in orbit around Earth to study activity inside the Earth, with a specific eye on the Earth. ‘magnetic and dynamic activity coming out of the core. It was in these data that Gillet and his team discovered the fascinating new waves.
They then studied data from other terrestrial and space observatories, collected between 1999 and 2021, and found a pattern.
These waves, known as magneto-Coriolis waves, are huge magnetic columns aligned along the Earth’s axis of rotation, stronger at the equator.
They sweep around the boundary between the core and mantle at a width of about 3 kilometers (1.86 miles) per year and move west at a speed of up to 1,500 kilometers (932 miles) per year.
Its existence suggests that other magneto-Coriolis waves could exist with different periods of oscillation, which so far we cannot detect, due to the lack of data.
“Magnetic waves are likely to be triggered by deep perturbations within the Earth’s fluid core, possibly related to buoyancy plumes,” says Gillet.
“Our research suggests that other such waves are likely to exist, probably with longer periods, but their discovery is based on further research.”
For now, as the waves carry information about the environment through which they travel, a new discovery could be used to investigate the interior of our planet in new ways, including the nucleus, which is difficult to study, as well as the core-mantle boundary.
The team’s research has been published in PNAS.