Space Environment and Scientific Missions: Magnetic Fields in Space

Magnetic fields are ubiquitous. Magnetohydrodynamics (MHD) shows that they control both the structure and dynamics of space plasmas, in particular through the j times B force. This then leads us to consider the role of currents in space plasmas, be they transitory and carried by Alfven waves, or quasi-static. The currents flowing the magnetosphere are coupled to the planetary ionosphere by field-aligned currents. These currents can in turn require particle acceleration, resulting in the aurora. The magnetic fields associated with these currents can be small, of the order of only a few nT, while the ambient magnetic field can be tens of thousands of nT (for the Earth). This places stringent requirements on the instrumentation.