Planetesimal Formation through Gravitational Instability

Introduction. Two prevailing processes of planetesimal formation are proposed. The first is the gravitational instability of a dust layer (e.g., Safronov 1969, Hayashi 1972, Goldreich and Ward 1973). The second is the growth through the mutual sticking of dust particles in a turbulent nebula (Weidenschilling and Cuzzi 1993, Stepinski and Valageas 1997). We consider the first one in this study. 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 (Weidenschilling 1980, Nakagawa et al. 1981, 1986). The linear stability analysis gives the condition for gravitational instability of a self-gravitating disk in terms of Toomre’s Qvalue as