Global structure of the heliosphere and interaction with the local interstellar medium: three decades of growing knowledge

According to the wish of the organizers of this session this article should broadly have the character of a review of work in heliospheric research which was done in the last three decades. The readers of this article should thus not expect to find too many brand-new results from this research field, rather than finding a historical illumination of the way heliospheric research went to bring us to the present understanding of heliospheric structures. We start from facing the reader with the fact that fruitful concepts of heliospheric research only developed after it had been realized that the solar system is in motion relative to the ambient interstellar medium. With this conception it became clear that neutral interstellar gases should have the chance to enter deeply into the inner heliosphere and become resonantly excited there by the resonant solar emissions. With the observation of the interplanetary resonance glows of hydrogen and helium it could be derived in a straightforward manner that the local interstellar gas is partially ionized and advances towards the solar system with a speed of 25 km/s. The full context of this complicated plasma-gas interaction scenario has only been comprehensively understood in the more recent years after realisation of the fact that multifluid concepts are needed to satisfactorily describe the complicated network of interwoven physical processes. In the following we shall analyse the dynamic and thermodynamic roles of these different interacting fluids like H-atoms, pick-up ions, anomalous cosmic rays and galactic cosmic rays, besides the background solar wind protons. Comparing the heliospheric views which one had three decades ago with those of nowadays, one can frankly state what an enormous scientific progress has been made in this research field. (C) 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.