Where the solar wind blows

What exactly happens when the solar wind meets the magnetized plasma around the Earth? This question has been puzzling physicists for decades. Besides the inherent difficulty of analysing the interaction between the charged particles in the solar wind, the interplanetary magnetic field and the three-dimensional time-dependent magnetic field at the Earth, most of our data has to be gleaned from expensive, and therefore infrequent, satellite missions to remote space – and not from the relative comfort of well-controlled laboratory experiments. Given this background it is not surprising that space physicists are eagerly awaiting data from the Cluster mission, due to be launched by the European Space Agency in November.