THE GROWTH AND MIGRATION OF JOVIAN PLANETS IN EVOLVING PROTOSTELLAR DISKS WITH DEAD ZONES
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abstract
The growth of Jovian mass planets during migration in their protoplanetary
disks is one of the most important problems that needs to be solved in light of
observations of the exosolar planets. Studies of the migration of planets in
standard gas disk models routinely show that migration is too fast to form
Jovian planets, and that such migrating planetary cores generally plunge into
the central stars in less than a Myr. In previous work, we have shown that a
poorly ionized, less viscous region in a protoplanetary disk called a dead zone
slows down the migration of fixed-mass planets. In this paper, we extend our
numerical calculations to include dead zone evolution along with the disk, as
well as planet formation via accretion of rocky and gaseous materials. Using
our symplectic-integrator-gas dynamics code, we find that dead zones, even in
evolving disks wherein migrating planets grow by accretion, still play a
fundamental role in saving planetary systems. We demonstrate that Jovian
planets form within 2.5 Myr for disks that are ten times more massive than a
minimum mass solar nebula (MMSN) with an opacity reduction and without slowing
down migration artificially. Our simulations indicate that protoplanetary disks
with an initial mass comparable to the MMSN only produce Neptunian mass
planets. We also find that planet migration does not help core accretion as
much in the oligarchic planetesimal accretion scenario as it was expected in
the runaway accretion scenario. Therefore we expect that an opacity reduction
(or some other mechanisms) is needed to solve the formation timescale problem
even for migrating protoplanets, as long as we consider the oligarchic growth.
We also point out a possible role of a dead zone in explaining long-lived,
strongly accreting gas disks.
