Formation of the planetary sequence in a highly flattened disk of frequently colliding planetesimals Academic Article uri icon


  • The kinetic theory is used to study the evolution of the self-gravitating disk of planetesimals. The effects of frequent collisions between planetesimals are taken into account by using a Krook integral in the Boltzmann kinetic equation. It is shown that as a result of an aperiodic collision-dissipative instability of small gravity disturbances the disk is subdivided into numerous dense fragments. These can eventually condense into the planetary sequence. Solar system formation is thought to start with dust particles set- tling to the central plane of a nebula to form a thin dust layer around the equatorial plane. During the early evolution of such a rapidly rotat- ing disk it is believed that the dust particles coagulate into numerous kilometer-sized rocky bodies (planetesimals). See Taylor (1992) as a review of the problem. In a swarm of planetesimals direct physical collisions inevitably be- come an important factor (Taylor 1992). One can suggest that planets (Mercury, Venus, . . ., Neptune) accreted subsequently from a hierarchy of colliding planetesimals. (The combination of low mass with a highly inclined and eccentric orbit is a major reason for not according Pluto planetary status: observations point to the orbit of Neptune as the true outer boundary of the planetary system.) Our principal idea is to regard the formation of the planetary system as a possible last stage in the formation of the self-gravitating, highly flattened solar nebula with frequent, almost elastic collisions between rocky planetesimals. We argue that a collision-dissipative collective in- stability of small-amplitude gravity perturbations developing in such a disk leads to the formation of an arrangement of dense aggregates. We speculate that subsequent substantial gravitational interaction between these dense aggregates circling the primordial sun would result in the formation of the planetary sequence. When cores of the giant planets reach a critical mass (∼ 10 masses of the Earth) they begin to accrete the interplanetary gas. The collision motion of an ensemble of identical planetesimals in the plane, in the frame of reference rotating with angular velocity , can

publication date

  • January 1, 2004