The magnetosphere is the space around a heavenly body in which the movement of charged particles is determined mainly by the magnetic field of the body, rather than by its gravitational field.

The Earth possesses a magnetic field which surrounds it. It is produced by currents due to the convection of matter in our planet’s iron and nickel core. The activity of this magnetic field gives birth to a region in which the movement of particles obeys this field: the magnetosphere. This region extends up to 60,000km from the Earth in the direction of the Sun. In the opposite direction it forms a tail which stretches over several millions of kilometres.

When particles with origins in the Sun (solar wind) approach the earth they are, for a very great majority, deviated by the terrestrial magnetic field and they thus bypass the magnetosphere. It is in this way that the latter protects the Earth’s atmosphere. The particles which are not deviated penetrate the magnetosphere and circulate within it according to lines of the magnetic field, leading to the creation to two zones rich in particles, the Van Allen Belts.