The interior of the Earth is a place far from calm. Deep beneath our surface activities, the planet rumbles with activity, from plate tectonics to convection currents circulating through hot magmatic fluids far beneath the crust.
Now scientists studying Earth’s satellite data have identified something inside the Earth that we’ve never seen before: a new kind of magnetic wave sweeping across the surface of our planet’s core, all the seven years.
This discovery could give insight into how the Earth’s magnetic field is generated and provide clues to our planet’s thermal history and evolution, that is, the gradual cooling of the planetary interior.
“Geophysicists have long theorized the existence of such waves, but they were thought to occur on much longer time scales than what our research has shown,” says geophysicist Nicolas Gillet from Grenoble Alpes University in France.
“Magnetic field measurements from instruments based on the Earth’s surface suggested that there was some sort of wave action, but we needed the global coverage offered by measurements from space to reveal what is really going on.
“We combined satellite measurements from Swarm, as well as the previous German Champ mission and the Danish Ørsted mission, with a computer model of the geodynamo to explain what the ground data had produced – and this led to our discovery. .”
The Earth’s magnetic field fascinates scientists a lot. Research to date suggests that the invisible structure forms a protective “bubble” around our planet, keeping harmful radiation out and the atmosphere, allowing life to thrive.
But the magnetic field is not static. It fluctuates in strength, size, and shape, has characteristics we don’t understand, and gradually weakens over time.
The reason the activity inside our planet matters is because that’s where the magnetic field comes from. It is generated by a dynamo – a rotating, convective, electrically conductive fluid that converts kinetic energy into magnetic energy, spinning a magnetic field in space around the planet.
This fluid is (mostly) the 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 suspended in Earth orbit to study activity inside the Earth – with a particular eye on the magnetic and dynamic activity emerging from the Earth. core. It was in this data that Gillet and his team discovered the fascinating new waves.
They then studied data from other ground 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, strongest at the equator.
They sweep the boundary between the core and the mantle with an amplitude of about 3 kilometers (1.86 miles) per year and move westward at a rate of up to 1,500 kilometers (932 miles) per year.
Their existence suggests that other magneto-Coriolis waves could exist with different periods of oscillation, which we are unable to detect to date, due to lack of data.
“Magnetic waves are likely to be triggered by disturbances deep in the Earth’s fluid core, possibly related to buoyancy plumes,” says Gillet.
“Our research suggests that other waves of this type are likely to exist, probably with longer periods – but their discovery relies on further research.”
For now, because waves carry information about the medium through which they travel, a new discovery could be used to probe our planet’s interior in new ways – including the core, which is difficult to study, as well than the core-mantle boundary.
The team’s research has been published in PNAS.