Astrophysics, abstract
astro-ph/0606237

From: Soko Matsumura [view email]

Date: Fri, 9 Jun 2006 16:11:57 GMT (510kb)

Saving Planetary Systems: Dead Zones & Planetary Migration

Authors: Soko Matsumura, Ralph E. Pudritz, Edward W. Thommes

Comments: 38 pages, 17 figures, submitted to ApJ

The tidal interaction between a disk and a planet leads to the planet's migration. It is widely believed that this mechanism explains the variety of orbital radii of extrasolar planets. A long-standing question regarding this mechanism is how to stop the migration before planets plunge into their central stars.

In this paper, we propose a new, simple mechanism to significantly slow down planet migration, and test the possibility by using a hybrid numerical integrator to simulate the disk-planet interaction. The key component of the scenario is a low viscosity region in a protostellar disk called a dead zone. The low viscosity affects the planet migration speed in two ways. First of all, it allows a smaller-mass planet to open a gap, and hence switch the faster type I migration (pre-gap-opening migration) to the slower type II migration (post-gap-opening migration). Secondly, a low viscosity slows down type II migration itself, because type II migration is directly proportional to the viscosity.

We show that, when a light-mass planet (e.g. 1 or 10 Earth masses) migrates from outside the dead zone, its migration gets reversed due to the mass accumulation inside the dead zone. When a light planet migrates from inside the dead zone, it opens a gap and slows down its migration. A heavy-mass planet like Jupiter, on the other hand, opens a gap and slows down inside the dead zone, independent of its initial orbital radius. Finally, we show that the observed percentage of planets which end up within the current observational limit of about 5 AU (5-25%) is well-explained by the existence of low viscosity regions (alpha<1e-4).

http://arxiv.org/abs/astro-ph/0606237