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First, equilibrium structure and maximum mass of a rotating isothermal cloud are described. Second, growth rate of fragmentation instability in an infinite disk and filament is presented. Finally, results of 2D and 3D simulations of collapse and fragmentation of rotating isothermal clouds are reviewed and comments are given.
Growth of perturbations and fragmentation of isothermal sheet-like clouds are computed three dimensionally. An initial cloud is a self-gravitating equilibrium gas layer with small fluctuations, which have the form ei(kxk+kyy). The simulations of models with various values of kx and ky are performed.
Of the formation processes of the solar system, the process of growth and sedimentation of dust particles in the primordial solar nebula is investigated for a region near the Earth's orbit. The growth equation for dust particles, which are sinking as well as in thermal motion, is solved numerically in the wide mass range between 10−12 g and 106 g.
A timetable for an evolutionary sequence of processes, which begins with the formation of the solar nebula being nearly in equilibrium and ends with the planetary formation, is presented. Basic features of the processes and grounds for the estimation of time-scales are explained for each of the processes.
When the Earth had grown to the present mass through accretion of the planetesimals in the solar nebula, the Earth was surrounded by a dense primordial atmosphere which was mainly composed of hydrogen and helium (Hayashi et al. 1979). Mass of the atmosphere was about 1×1026 g. We investigate the dissipation of this atmosphere due to the irradiation of solar EUV. The effect of solar wind is neglected. We assume that the flow of the escaping gas is spherically symmetric and steady. We impose the boundary condition that the flow velocity go through a sonic point. The results show that the primordial atmosphere is dissipated within a period of 5 × 108 yrs, which is the upper limit imposed from the theory of the origin of the present terrestrial atmosphere (Hamano and Ozima 1978), as far as the solar EUV flux is more than two hundred times as large as the present one. In this case, the rare gases contained in the promordial atmosphere are also dissipated owing to the drag effect (Sekiya et al. 1980).