Astronomy and Astrophysics – Astronomy
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...210.3305j&link_type=abstract
American Astronomical Society Meeting 210, #33.05; Bulletin of the American Astronomical Society, Vol. 39, p.145
Astronomy and Astrophysics
Astronomy
Scientific paper
We explore a possible dynamical origin of the extrasolar planet eccentricity distribution through numerical integrations of ensembles of planetary systems in the 108 yr after planet formation.
We find that the final dynamical properties of simulated systems depend on the initial level of dynamical activity. In all dynamically active ensembles, the systems relax through numerous ejections, collisions, and the increase of median spacings between planets to final values of DH 12 mutual Hill radii. Their eccentricity distributions relax to an equilibrium distribution, well described by n(e)dn ∝ e\exp(e2 / (2 ċ 0.32))dn, irrespective of the details of the initial conditions.
The simulated eccentricity distribution agrees well with the one observed in extrasolar planets, excluding the circularized population of hot Jupiters. The resulting eccentricities have little or no correlation with mass or semimajor axis, consistent with the observations.
For this mechanism to be effective, the gas-giant planets in newly formed planetary systems must start in crowded configurations, followed by a period of large-scale dynamical instability and relaxation lasting 1--2 orders of magnitude longer than the 1 Myr interval in which gas-giant planets are assembled. Additionally, this mechanism predicts a likely numerous population of unbound planets, with counts at least on order of those of bound planets.
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