Perspectives in space plasma theory

The past half century has been characterized by the birth of space plasma physics and its rise to maturity which has led into a certain mood of satisfaction and partial saturation with its achievements. Indeed, on the global scale our knowledge about the magnetosphere, the solar wind from the Sun out to its boundaries, even of the conditions on the surface and in the atmosphere of the Sun and the Sun's interior has to a high degree become complete. The degree of completion is indeed such that it allows predicting up to a certain precision their behavior. New names like solar seismology, solar meteorology, and space weather have been coined indicating the transition of some of the sub-field of Space Plasma Physics into the domain of an industry of monitoring and predicting in the interest of the needs of a general society. This is an entirely healthy evolution of a scientific field that is on the path of completion. Still there is a large number of questions which should and can hopefully be answered by space plasma theory. Some of them will be listed here in view of what has been achieved and in which direction future theory could proceed in order to contribute to their resolution when addressing the already operating and the new and upcoming space missions like Cluster, the planned Magnetospheric Multi-Scale mission MMS and others, respectively, most of which are designed to become multi-spacecraft enterprizes and also in view of the new theoretical and computational techniques and methods that have been developed during the past decades. These directions reach from the detailed understanding of the processes in the solar atmosphere and solar wind through the detailed physics of the formation of collisionless shocks, magnetosheaths and turbulence, the microphysics of reconnection and particle acceleration, and the substorm mechanism to the detailed understanding of planetary magnetospheres, the outer heliosphere with its heliospheric termination shock, heliosheath and boundary layer. All this research though already in flow has by far not been completed yet. It requires new efforts as it implies resolution of the smallest though still non-atomic scales, but it has high implications for the understanding of the processes in space plasma and, in extension, of processes in the remote astrophysical systems which can be understood only by observation of their radiation in all wavebands.