Magnetosphere-ionosphere interactions as a key to the plasma Universe

Almost all known matter in the Universe is in a state, the plasma state, that is rare on Earth, and whose physical properties are still incompletely understood. Its complexity is such that a reliable understanding must build on empirical knowledge. While laboratory experiments are still an important source of such knowledge, the Earth's magnetosphere-ionosphere system, made accessible by space technology, vastly widens the parameter ranges in which plasma phenomena can be studied. This system contains all three main categories of plasma present in the Universe. Furthermore, the interaction between the magnetosphere and the ionosphere excites a wealth of plasma physical phenomena of fundamental importance. These include, among others, formation of magnetic-field aligned electric fields, acceleration of charged particles, release of magnetically stored energy, formation of filamentary and cellular structures, as well as unexpected chemical separation processes. What has been learned, and what still remains to be learned, from study of the magnetosphere-ionosphere system should therefore provide a much improved basis for understanding of our Universe.<>