Paper: astro-ph/0508486
Date: Tue, 23 Aug 2005 13:11:04 GMT (383kb)

Title: On the Orbital Evolution of Low Mass Protoplanets in Turbulent,
Magnetised Disks

Authors: Richard P. Nelson (Queen Mary, University of London)

Comments: 21 pages, 16 figures. Accepted for publication in Astronomy &
Astrophysics. A version with full resolution, colour figures is available
from: http://www.maths.qmul.ac.uk/~rpn/preprints
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(Abridged).We present the results of MHD simulations of low mass protoplanets
interacting with turbulent disks. We calculate the orbital evolution of
`planetesimals' and protoplanets with masses in the range 0 < m_p < 30 M_Earth.
Planetesimals and protoplanets undergo stochastic migration due to interaction
with turbulent density fluctuations. Over run times of ~ 150 planet orbits,
stochastic migration dominates over type I migration for many models. Fourier
analysis of the torques experienced by planets indicates that the torque
fluctuations contain components with significant power whose time scales of
variation are similar to the simulation run times. These low frequency
fluctuations partly explain the dominance of stochastic torques, and may
provide a powerful means of counteracting the type I migration of some planets
in turbulent disks. Turbulence is a source of eccentricity driving.
Planetesimals attained eccentricities in the range 0.02 < e < 0.14, m_p=1
M_Earth planets attained eccentricities 0.02 < e < 0.08, and m_p=10 M_Earth
protoplanets reached 0.02 < e < 0.03. This is in basic agreement with a model
in which turbulence drives e-growth, and interaction with disk material at
coorbital Lindblad resonances causes e-damping. These results are significant
for planet formation. Stochastic migration may prevent some planet cores
migrating into their star via type I before becoming gas giants. The growth of
planetary cores may be enhanced by preventing isolation. Eccentricity
excitation by turbulence, however, may reduce growth rates of planetary cores
during the runaway and oligarchic growth stages, and cause collisions between
planetesimals to become destructive.

\\ ( http://arXiv.org/abs/astro-ph/0508486 , 383kb)