Origin of the Solar System
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概要
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By the contraction of an interstellar cloud with finite angular momentum the sun and the disk-shaped nebula around it are formed. The nebula is initially in a turbulent state. It is shown qualitatively that, as the turbulence dissipates, the nebula is gradually divided into rings and that the orbital radii of the rings satisfy Bode's law. The mineral grains are included in the rings of the inner planets and ice grains in the others due to the different temperatures. The rings, except at Jovian and Saturnian orbits, are in mechanical equilibrium. In these rings the grains sink to the central parts of the rings and the central density increases. But the pressure does not increase much because the mean molecular weight increases. Therefore, these parts which are mainly composed of grains become unstable and begin to collapse at some stage. In this catastrophic phase the central part of the ring breaks into many fragments and the protoplanets, with little hydrogen and helium, are formed. The time required for the formation of the protoplanets is 3×10^4 to 1×16^6 years since the disk-shaped nebula is formed. The mean mass of the protoplanets is 10^<20> to 10^<25> g. There are some fluctuations in the orbits of the protoplanets belonging to the same ring and they have chances to collide with each other. The masses of the protoplanets increase by the gravitational accumulation as they collide, and finally the planet is formed in each ring. The masses of the rings at Jovian and Saturnian orbits are large and their gravities are strong. As the solar luminosity decreases with time, their temperatures and pressures decrease. At a certain stage their pressures become too low to maintain mechanical equilibrium and they begin to collapse. At this state the grains have sunk only little to their central parts. Therefore, the photoplanets, and then the planets.formed in these rings contain much hydrogen and helium in contrast with the other rings. The sun has a deep convective envelope and is magnetically active for about 10^7 years since it was formed. The matter ejected from the sun and dragged by the solar magnetic field carries away much angular momentum and the solar rotation is decelerated. Since the matter is ejected mainly in the ecliptic plane, much angular momentum is given to the gas in the planetary space. In time the gas is swept away from the solar system.
- 1970-07-25
著者
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Nakano Takenori
National Radio Astronomy Observatory : The Research Institute For Fundamental Physics Kyoto Universi
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Nakano Takenori
National Radio Astronomy Observatory : The Research Institute For Fundamental Physics Kyoto Universi
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NAKANO Takenori
National Radio Astronomy Observatory : the Research Institute for Fundamental Physics, Kyoto University : Associated Universityersities, Inc., under contract with the National Science Foundation