Dynamical constraints to the masses of large planetesimals

The formation of the planets is a two-step process in which an aggregational phase is followed by an accretionary stage. The transition between both stages of pre-planetary growth is characterized by the occurrence of kilometer-sized objects: the planetesimals. The most recent model of the formation of planetesimals from early solar nebula dust has been published by Weidenschilling (Weidenschilling, 1988, Weidenschilling, 1997). In the accretionary stage, the gravity of the planetary embryos plays the dominant role in their mutual interactions and dominate electromagnetic forces, gas drag and collective gravitational effects. The planetesimals continue to agglomerate via pairwise mergers. esimals and comets play a key role in discussions of the origin of the solar systems. The formation of the planets is apparently accompanied by the production of smaller bodies (e.g., asteroids and satellites), which would be like ice in the outer solar system and some of which would necessarily be perturbed by planetary encounters into orbits that would place them into the Oort Cloud. Thus, comets are a plausible by-product of planetary formation and are suspected to be a population of unaltered primordial objects that make up the outer planets. Therefore, the size distribution of observed comets and the Oort Cloud are probably a measure of the primordial size distribution of planetesimals. The size distribution of observed comets are only indirectly obtained and the actual discrete distribution approximates a continuous power-law distribution with exponent q < 2 (Fernandez, 1982), which is in agreement with Safronovs scenario.