Early Concepts of the Heliospheric Interface: Plasma

Abstract. The construction of the early hydrodynamic models of the solar wind interaction with the local interstellar medium (LISM) was stimulated by the poor knowledge of the physical properties of the LISM. In particular, the dynamics of the interstellar gas were unknown before 1971, when experiments on scattered solar radiation at Lyman-α wavelengths, obtained on board the OGO-5 spacecraft, proved that H- atoms originating from the LISM are moving relative the Sun with a bulk velocity of ∼20 km/s. This is the reason why different physical properties of the LISM were considered before the beginning of the 1970s. However, the early models are interesting, first from the historical point of view, secondly because they stimulated astronomers to undertake experimental investigations of the LISM’s parameters, and third because they predicted some physical phenomena discovered later on the basis of experimental data obtained by means of the spacecraft studying the outer regions of the Solar System (for example, the existence of the interface region or heliosheath). The early hydrodynamic models of the solar wind interaction