A European mission to study the Earth’s magnetic field with unprecedented accuracy is being launched later this month [November 2013]. The three Swarm satellites will measure the magnetic field from the centre of the Earth to the outermost reaches of the magnetosphere – the protective bubble that shields us from dangerous solar particles and radiation. Swarm is the fourth of ESA’s Earth Explorer missions and results from the mission will be used to predict the effects of solar activity and investigate why the Earth’s magnetic field is weakening.