Highly inclined and eccentric massive planets
I. Planet-disc interactions
1 University of Nice-Sophia Antipolis / CNRS / Observatoire de la Côte d’Azur, Laboratoire Lagrange UMR 7293, Boulevard de l’Observatoire, BP4229, 06304 Nice Cedex 4, France
2 NaXys, Department of Mathematics, University of Namur, 8 rempart de la Vierge, 5000 Namur, Belgium
3 Observatoire de Lille (LAL-IMCCE), CNRS-UMR 8028, 1 impasse de l’Observatoire, 59000 Lille, France
Received: 30 August 2012
Accepted: 11 May 2013
Context. In the solar system, planets have a small inclination with respect to the equatorial plane of the Sun, but there is evidence that in extrasolar systems the inclination can be very high. This spin-orbit misalignment is unexpected, as planets form in a protoplanetary disc supposedly aligned with the stellar spin. It has been proposed that planet-planet interactions can lead to mutual inclinations during migration in the protoplanetary disc. However, the effect of the gas disc on inclined giant planets is still unknown.
Aims. In this paper we investigate planet-disc interactions for planets above 1 MJup. We check the influence of three parameters: the inclination i, eccentricity e, and mass Mp of the planet. This analysis also aims at providing a general expression of the eccentricity and inclination damping exerted on the planet by the disc.
Methods. We perform three-dimensional numerical simulations of protoplanetary discs with embedded high-mass planets on fixed orbits. We use the explicit/implicit hydrodynamical code NIRVANA in 3D with an isothermal equation of state.
Results. We provide damping formulae for i and e as a function of i, e, and Mp that fit the numerical data. For highly inclined massive planets, the gap opening is reduced, and the damping of i occurs on time-scales of the order of 10-4 deg/year·Mdisc/(0.01 M⋆) with the damping of e on a smaller time-scale. While the inclination of low planetary masses (<5 MJup) is always damped, large planetary masses with large i can undergo a Kozai-cycle with the disc. These Kozai-cycles are damped through the disc in time. Eccentricity is generally damped, except for very massive planets (Mp ~ 5 MJup) where eccentricity can increase for low inclinations. So the dynamics tends to a final state: planets end up in midplane and can then, over time, increase their eccentricity as a result of interactions with the disc.
Conclusions. The interactions with the disc lead to damping of i and e after a scattering event of high-mass planets. If i is sufficiently reduced, the eccentricity can be pumped up because of interactions with the disc. If the planet is scattered to high inclination, it can undergo a Kozai-cycle with the disc that makes it hard to predict the exact movement of the planet and its orbital parameters at the dispersal of the disc.
Key words: accretion, accretion disks / planets and satellites: formation / hydrodynamics / planet-disk interactions
© ESO, 2013