The field of solar-terrestrial physics has evolved to a point where quantitative theoretical modeling and cause-effect predictive techniques can be foreseen. Instrumentation now exists to quantitatively test these theories and lead to a significant improvement in our understanding of the solar-terrestrial environment. The proposed Origins of Plasma in the Earth's Neighborhood (OPEN) program will be used to trace this theoretical and experimental evolution and describe a solar-terrestrial research scenario for the 1980's which includes specific problems related to solar and interplanetary dynamics.

Recent, fundamental discoveries of the phenomena of the Sun and of interplanetary space have led to a far broader definition of the term “solar physics” than was generally perceived a decade ago. The implications of this broadened definition of solar and heliospheric physics will be studied by essentially every solar space mission either now approved, or in the planning stage, for the period of 1980 to 1995. These missions include traditional Earth-orbiting satellites; Shuttle/Spacelab sortie missions, free flyers that transit the solar polar caps and probe the innermost corona (both frontier regions of the heliosphere), and finally possible semi-permanent orbiting platforms for advanced solar/heliosphere observations.

The mission of HELIOS had been started in order to investigate in situ the innermost regions of the interplanetary space. The two spacecraft achieved a perihelion of about 0.3 AU solar distance. Fig. 1 is a sketch of the two orbits. The orbital periods are 190 resp. 186 d.

Solar and interplanetary dynamics comprises dynamic and plasma-physical phenomena in the solar atmosphere, the corona and the interplanetary medium in the broadest sense. In this symposium, however, one has essentially tried to restrict the subject matter to the study of the propagation of a disturbance, produced in the solar atmosphere, through the corona and the interplanetary medium. In studying solar and interplanetary dynamical phenomena we find ourselves in the unique position, with respect to other astrophysical disciplines, to be able to relate solar observations obtained with the highest possible spectral, spatial and time resolution with in situ measurements made in the interplanetary medium. It has now turned out that the two fundamental questions to be answered are:

a) How does the medium in between the sun and the earth and beyond the earth's orbit, the socalled heliosphere, look like? Does a basic undisturbed heliosphere actually exist, and is one able to model its observed magnetic structures and plasma motions with their spatial and temporal variations?

b) How and where in the solar atmosphere are the disturbances generated and what are the characteristic time scales, geometries and energies involved?