Growth of Orbital Eccentricity and Migration of Giant Planets
Abstract
A giant planet that is still embedded in a circumstellar disk exchanges energy and angular momentum with the disk material. Both the orbital properties of the planet and the dynamical state of the disk may be affected as a result of this interaction process. Two well-known consequences are radial migration of the planet and gap formation in the disk's mass density. The orbital properties of extra-solar planets discovered to date suggest that a substantial amount of radial migration has occurred in most cases. Observations also indicate that the average orbital eccentricity is between 0.2 and 0.3. However, it is not yet clear whether gravitational interactions between a giant planet and a circumstellar disk is a viable mechanism to excite orbital eccentricity.
We have investigated the possibility that tidal interactions can sustain orbital eccentricity growth by performing hydrodynamical calculations in which the disk is modeled as a viscous fluid. We have considered a range of planetary masses from 1 to 3 Jupiter masses (Mj) and a range of initial orbital eccentricities from 0 to 0.5. We have also performed calculations for various fluid viscosities and for two different disk temperatures. We found that orbital eccentricity growth can be sustained under certain disk conditions. For an alpha-viscosity of 0.004, the initially circular orbit of a 2Mj and a 3Mj planet gains an eccentricity larger than 0.1 within 2500 orbital periods. An eccentricity growth of almost 0.1 is observed for a 1Mj planet, over a 3000 orbit period, when the alpha-viscosity is 0.001. Colder disks seem to favor orbital eccentricity growth whereas higher viscosity values seem to suppress it. We also found that the inward radial migration of a giant planet can be drastically slower, and even reverse and be directed outwards, when the planet's orbit has gained significant eccentricity (larger than 0.1).- Publication:
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AAS/Division of Dynamical Astronomy Meeting #38
- Pub Date:
- July 2007
- Bibcode:
- 2007DDA....38.1312D