Chao-Chin Yang, Mordecai-Mark Mac Low, Kristen Menou
Due to the gravitational influence of density fluctuations driven by
magneto-rotational instability in the gas disk, planetesimals and protoplanets
undergo diffusive radial migration as well as changes in other orbital
properties. The magnitude of the effect on particle orbits can have important
consequences for planet formation scenarios. We use the local-shearing-box
approximation to simulate an ideal, isothermal, magnetized gas disk with
vertical density stratification and simultaneously evolve numerous massless
particles moving under the gravitational field of the gas and the host star. We
measure the evolution of the particle orbital properties, including mean
radius, eccentricity, inclination, and velocity dispersion, and its dependence
on the disk properties and the particle initial conditions. Although the
results converge with resolution for fixed box dimensions, we find the response
of the particles to the gravity of the turbulent gas correlates with the
horizontal box size, up to 16 disk scale heights. This correlation indicates
that caution should be exercised when interpreting local-shearing-box models
involving gravitational physics of magneto-rotational turbulence. Based on
heuristic arguments, nevertheless, the criterion L_h / R ~ O(1), where L_h is
the horizontal box size and R is the distance to the host star, is proposed to
possibly circumvent this conundrum. If this criterion holds, we can still
conclude that magneto-rotational turbulence seems likely to be ineffective at
driving either diffusive migration or collisional erosion under most
circumstances.
View original:
http://arxiv.org/abs/1103.3268
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