The Swarm mission will study the complexities of Earth’s protective magnetic field. The magnetic field acts as a shield, protecting the planet from charged particles that stream towards Earth in solar winds. Without this shield, life on Earth would be impossible. The field is mainly generated deep inside Earth by an ocean of swirling iron that makes up the liquid outer core. How the magnetic field is generated and how it changes over time is complex and not fully understood. But with a new generation of magnetometers, Swarm will provide greater insight into these natural processes and the 'weather' in space.