Origin of solar system

Abstract As the theory of the origin and evolution of the solar system should constitute the general background for the science of planetary interiors, I give a summary of some of the main problems in this field of research. Space research, especially in situ measurements in the magnetospheres (including helisophere) and ionospheres, has drastically changed our understanding of the properties of space plasmas in the density region 105–1020 particles/m3 and magnetization region 10−10–10−5wb/m2. This gives us a better understanding of the early processes leading to the formation of the solar system in the following respects. 1. Properties of interstellar clouds. Electromagnetic forces were of decisive importance. The clouds may have been formed out of diffuse interstellar matter by electromagnetic attraction (“pinch effect”). Their evolution is treated by the theory of highly inhomogeneous dusty plasmas, penetrated by a network of electric currents. Contrast-enhanced pictures of interstellar clouds support this scenario. 2. Chemical differentiation. From observations of particle ejection from the sun, we know that in plasmas of comparable densities a chemical differentiation takes place, resulting in regions with He or the CNO elements or the heavy elements dominating (or strongly enhanced). Similar processes should take place in interstellar clouds and give similar results. This is basic for our understanding of chemical differences between the celestial bodies in the solar system. 3. Band structure and the critical velocity. Next phase in the evolution is the falling in of chemically differentiated gas clouds and dust towards the primeval sun. (This process is later reproduced in a smaller scale around the giant planets). This leads to the accumulation of matter in certain bands, which explains the band structure of the solar system. Laboratory experiments and the theory of the critical velocity are now giving increased understanding of this process. 4. Discovery of the rings of Uranus and Jupiter. These fall within the bands where matter should be accumulated, thus confirming the importance of the band structure. The Uranus ring was explicitly predicted. 5. Transfer of angular momentum. In situ measurements of the auroral current system and the Io-Jupiter circuit makes it possible to base the theory of transfer of angular momentum on present-day phenomena, which can be extrapolated to cosmogonic conditions. The two-third fall down law at the condensation is supported. 6. The Io torus. The study of the Io torus provides information on the dynamics of particles, which is important for the understanding of the jet stream formation and evolution. Objections against the jet stream concept are partially correct, but can be removed if the early azimuth independent jet stream model is changed into an inhomogeneous model, similar to the observed Io torus. 7. Resulting differences in planetary structure and composition. The resulting differences in planetary structure and composition (which are the subject of this workshop) are discussed. The terrestrial planets should be formed largely from the dust content of the primeval cloud captured in the innermost cloud.