Formation of the terrestrial planets
Abstract
Two growth mechanisms are identified for the development of the terrestrial planets: (1) gravitational instability leading to a collapse, and (2) gravitational accumulation caused by two-body collisions and coherence. The presence of a dynamically-significant gas phase would not affect either mechanism. Theoretical expressions are presented for the production of giant gaseous protoplanets by gravitational instability within a central dust layer. Gravitational accumulation is discussed with reference to the accumulation of planetesimals from a gas-free circumsolar swarm of bodies. Numerical simulations are given for the early stages of accumulation. The Safronov steady-state velocity is considered, noting that the competition between mutual collisional damping and gravitational acceleration by the members of a solar swarm yields a steady-state velocity distribution where the mean velocity is comparable to the escape velocity of the largest body. A time scale for accumulation is postulated on the basis of the radial distribution of a swarm of non-accreting bodies of equal size. The simultaneous gas-free accumulation of several terrestrial planets is noted. Attention is also given to growth mechanisms in gas-rich interplanetary media.
- Publication:
-
Annual Review of Astronomy and Astrophysics
- Pub Date:
- 1980
- DOI:
- 10.1146/annurev.aa.18.090180.000453
- Bibcode:
- 1980ARA&A..18...77W
- Keywords:
-
- Gravitational Effects;
- Planetary Evolution;
- Solar System;
- Terrestrial Planets;
- Astronomical Models;
- Gravitational Collapse;
- Planetary Nebulae;
- Protoplanets;
- Astronomy