Launched in 2013, the three 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.

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.