Collisional evolution from dust to planets
Speaker: Hiroshi Kobayashi (Nagoya University)
Abstract:
Planets were believed to form via the accretion of planetesimals
generated from dust grains in protoplanetary disks. However, the
growth of planets is much slower than their migration due to
disk-planet interaction. Comparably rapid growth via pebble
accretion was then proposed, which requires very massive
protoplanetary disks because most pebbles fall into the central
star. Although planetesimal formation, planetary migration, and
planetary growth have been studied with much effort, the full
evolution path from dust to planets was uncertain. We have
investigated full collisional evolution from dust to planets.
For collisional evolution, collisional outcomes are not simply
characterized as fragmentation, bouncing, etc. The impact
simulations for dust aggregates showed the detailed
outcomes. According to the outcome model, the growth of dust
grains are not prevent from collisional fragmentation. We thus
perform the full simulations (DTPSs) for collisional evolution
from dust to planet in whole protoplanetary disks. Dust growth
with high porosity allows the formation of icy planetesimals in
the inner disk (< 10 au), while pebbles formed in the outer
disk drift to the inner disk and there grow to planetesimals.
The growth of those pebbles to planetesimals suppresses their
radial drift and supplies small planetesimals sustainably in the
vicinity of cores. This enables rapid formation of sufficiently
massive planetary cores within 0.2-0.4 million years, prior to
the planetary migration. However, such porous pebbles are
unlikely to reproduce the polarized millimeter wavelength light
observed from protoplanetary disks. We thus investigate gas-giant
core formation with non-porous pebbles via DTPSs. Even non-porous
bodies can grow into planetesimals and massive cores to be gas
giants are also formed in several 100 thousand years. The rapid core
formation is mainly via the accretion of planetesimals produced
by collisional coagulation of pebbles drifting from the outer
disk. The formation mechanism is similar to the case with porous
pebbles, while core formation occurs in a wider
region (5-10 au) than that with porous pebbles. Although
pebble growth and core formation depends on the disk temperature,
core formation is likely to occur with disk temperatures in
typical optical thick disks around protostars.