From dust to terrestrial planets - Introduction - Timescales for the formation of terrestrial planets

摘要

Terrestrial planets are accreted in a disk orbiting a central star. The basic challenge of their formation consists of assembling micron-sized or smaller dust grains to bodies with over 10(4) km in diameter. This formation process, ultimately based on collisions, occurs in three very different physical regimes depending upon the size of the bodies present: 1) Early on, micron- to mm-sized dust grains, chondrules and chondrites are strongly coupled to the gas. 2) As they grow larger, gravity increases the collisional cross section allowing runaway growth to occur. 3) After this runaway phase stops from exhaustion of matter in the immediate surroundings of the protoplanets, further growth occurs on timescales typical of mutual gravitational perturbations. The emphasis of this book is on the timescales corresponding to these formation phases as well as the characteristic chemical and isotopic composition of the bodies involved. [References: 20]