CAN GRAVITATIONAL-INSTABILITY FORM PLANETESIMALS

Gravitational instability of a particle layer in the solar nebula is inhibited by effects of the nebula gas. Particles must grow to at least meter size in order to decouple from shear-generated turbulence and allow the layer to reach critical density. The radial velocity dispersion induced by drag further delays onset of instability until the mean size is similar to 10-100 m. This velocity dispersion, with the lack of damping in a layer of bodies this size, prevents instabilities of scales that could collapse to solid planetesimals. Collisional coagulation is the dominant growth mechanism for bodies of all sizes. (C) 1995 Academic Press, Inc.