We would normally associate jet streams with the weather but, thanks to ESA’s magnetic field mission, scientists have discovered a jet stream deep below Earth’s surface – and it’s speeding up.

Launched in 2013, the trio of Swarm satellites are measuring and untangling the different magnetic fields that stem from Earth’s core, mantle, crust, oceans, ionosphere and magnetosphere.

Together, these signals form the magnetic field that protects us from cosmic radiation and charged particles that stream towards Earth in solar winds.

Measuring the magnetic field is one of the few ways we can look deep inside our planet. As Chris Finlay from the Technical University of Denmark noted, “We know more about the Sun than Earth’s core because the Sun is not hidden from us by 3000 km of rock.”

The field exists because of an ocean of superheated, swirling liquid iron that makes up the outer core. Like a spinning conductor in a bicycle dynamo, this moving iron creates electrical currents, which in turn generate our continuously changing magnetic field.

Tracking changes in the magnetic field can, therefore, tell researchers how the iron in the core moves.

The accurate measurements by the unique constellation of Swarm satellites allow the different sources of magnetism to be separated, making the contribution from the core much clearer.