Plasma Science: From Fundamental Research to Technological Applications (1995)
Chapter: Background
6
Space Plasmas
INTRODUCTION
Background
Space plasma physics is the study of natural plasmas in the solar system and associated technological applications. It is concerned with the ionospheric and magnetospheric plasmas of Earth and the other planets; the physics of the solar plasma internal to the Sun, the solar corona, and the solar wind; the interaction of the solar wind with planets, asteroids, dust, comets, and eventually the interstellar medium; and technology applications ranging from electric propulsion to space "weather" predictions. This is a vast, multiscale, physical domain wherein there are large variations in plasma sources, average thermal energy, flow velocities, magnetic field strength, and other physical parameters. The results are a rich collection of plasma physical behaviors that provide important intellectual challenges to fully understand the underlying processes. It is important to consider the wide variations in physical conditions in terms of spatial dimensions. The largest is that of magnetohydrodynamic flow phenomena. These include the massive outflow of solar plasma as the solar wind, which, entwined with the solar magnetic field, sweeps outward past the planets to its mixing with the interstellar medium. On a smaller scale, within planetary atmospheres, more complicated plasma flows are driven by electromagnetic fields associated with the interaction of the solar wind with the planetary body and atmospheric heating caused by solar radiation. On an even smaller scale, microscopic physical processes are occurring within plasmas in space. For example, the selective accel-
