This artist's impression shows the four ESA's Cluster satellites flying through the Earth's magnetosphere and observing the 'magnetic reconnection' process.

Magnetic reconnection is a process that can occur almost anywhere that a magnetic field is found. In a reconnection event, the magnetic field lines are squeezed together somehow and spontaneously reconfigure themselves, releasing energy.

When it occurs near the surface of the Sun, such an event powers giant solar flares that can release thousands of millions of tonnes of electrically charged particles into space.