Gravitational Instability in Two-Phase Disks and the Origin of the Moon
Abstract
Two-phase disks may be gravitationally unstable at temperatures or surface densities at which a disk composed of either single phase would be highly stable. It is argued that two-phase disks can achieve a marginally unstable state (in addition to a highly unstable state that leads to fragmentation), limited by the ability of the photosphere to radiate the energy dissipated in the disk. A self-consistent prescription for the viscosity induced by the slow instabilities is provided. Two-phase disks are more centrally condensed than single-phase disks, and their secular cooling time may be comparable to their spreading time. A circumterrestrial disk of sufficient mass to form the moon provides a detailed example of all the preceding points. Its stability, structure, and dynamical evolution are investigated, and it is concluded that its spreading time is short (about 100 yr); the moon is formed molten, or partially molten; the moon's initial orbit lies in the earth's equatorial plane; and only a small fraction of the disk mass is lost in a wind, although this may represent a substantial fraction of volatiles. Most of these conclusions are independent of how the disk was formed, e.g., from a giant impact.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 1988
- DOI:
- 10.1086/166760
- Bibcode:
- 1988ApJ...333..452T
- Keywords:
-
- Lunar Gravitation;
- Planetary Evolution;
- Planetary Gravitation;
- Planetary Systems;
- Earth Gravitation;
- Extraterrestrial Environments;
- Liquid-Vapor Interfaces;
- Natural Satellites;
- Photosphere;
- Astrophysics;
- MOON;
- PLANETS: FORMATION