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I. Furuya, Y. Nakagawa (Graduate School of Science and Technology, Kobe University)
The solar nebula is considered to be turbulent more or less at early stages. After such turbulent motion has decayed, dust particles settle toward the central plane of the nebula to form a thin layer --- a dust layer. When the density in the dust layer exceeds the Roche density, the layer becomes gravitationally unstable to fragment into a number of planetesimals. The linear perturbation theory for axisymmetric mode shows only that the dust layer breaks into ring-shaped fragments whose width is the critical wavelength. Thus the mass of a planetesimal is usually estimated by assuming that these ring-shaped fragments break further in the azimuthal into sub-fragments with azimuthal sizes as large as the radial size, i.e., the critical radial wavelength. In the present study, we reproduce the gravitational fragmentation by 3D local N-body numerical simulations in order to see how the dust layer breaks and how much the initial masses of planetesimals are.
Our simulations show that any ring-shaped fragments are not formed; instead, we find that the process of planetesimal formation can be classified into three stages --- non-axisymmetric wake-like structure formation, initial clump formation, growth of initial clumps through mutual fast coalescence. The masses of initial clumps and finally formed clumps are about 0.1 and 2-5 times as large as the analytic estimate based on the axisymmetric linear perturbation theory mentioned above, respectively.
The author(s) of this abstract have provided an email address for comments about the abstract: furuya@jet.planet.sci.kobe-u.ac.jp