13 research outputs found
Dust evolution and satellitesimal formation in circumplanetary disks
It is believed that satellites of giant planets form in circumplanetary
disks. Many of the previous contributions assumed that their formation process
proceeds similarly to rocky planet formation, via accretion of the satellite
seeds, called satellitesimals. However, the satellitesimal formation itself
poses a nontrivial problem as the dust evolution in the circumplanetary disk is
heavily impacted by fast radial drift and thus dust growth to satellitesimals
is hindered. To address this problem, we connected state-of-the-art
hydrodynamical simulations of a circumplanetary disk around a Jupiter-mass
planet with dust growth and drift model in a post-processing step. We found
that there is an efficient pathway to satellitesimal formation if there is a
dust trap forming within the disk. Thanks to the natural existence of an
outward gas flow region in the hydrodynamical simulation, a significant dust
trap arises at the radial distance of 85~R from the planet, where the
dust-to-gas ratio becomes high enough to trigger streaming instability. The
streaming instability leads to the efficient formation of the satellite seeds.
Because of the constant infall of material from the circumstellar disk and the
very short timescale of dust evolution, the circumplanetary disk acts as a
satellitesimal factory, constantly processing the infalling dust to pebbles
that gather in the dust trap and undergo the streaming instability.Comment: Accepted for publication in ApJ. Revised version addressing comments
from referee and communit
Planetesimal formation starts at the snow line
Planetesimal formation stage represents a major gap in our understanding of
the planet formation process. The late-stage planet accretion models typically
make arbitrary assumptions about planetesimals and pebbles distribution while
the dust evolution models predict that planetesimal formation is only possible
at some orbital distances. We want to test the importance of water snow line
for triggering formation of the first planetesimals during the gas-rich phase
of protoplanetary disk, when cores of giant planets have to form. We connect
prescriptions for gas disk evolution, dust growth and fragmentation, water ice
evaporation and recondensation, as well as transport of both solids and water
vapor, and planetesimal formation via streaming instability into a single,
one-dimensional model for protoplanetary disk evolution. We find that processes
taking place around the snow line facilitate planetesimal formation in two
ways. First, due to the change of sticking properties between wet and dry
aggregates, there is a "traffic jam" inside of the snow line that slows down
the fall of solids onto the star. Second, ice evaporation and outward diffusion
of water followed by its recondensation increases the abundance of icy pebbles
that trigger planetesimal formation via streaming instability just outside of
the snow line. Planetesimal formation is hindered by growth barriers and radial
drift and thus requires particular conditions to take place. Snow line is a
favorable location where planetesimal formation is possible for a wide range of
conditions, but still not in every protoplanetary disk model. This process is
particularly promoted in large, cool disks with low intrinsic turbulence and
increased initial dust-to-gas ratio.Comment: Accepted for publication in Astronomy & Astrophysic
Can dust coagulation trigger streaming instability?
Streaming instability can be a very efficient way of overcoming growth and
drift barriers to planetesimal formation. However, it was shown that strong
clumping, which leads to planetesimal formation, requires a considerable number
of large grains. State-of-the-art streaming instability models do not take into
account realistic size distributions resulting from the collisional evolution
of dust. We investigate whether a sufficient quantity of large aggregates can
be produced by sticking and what the interplay of dust coagulation and
planetesimal formation is. We develop a semi-analytical prescription of
planetesimal formation by streaming instability and implement it in our dust
coagulation code based on the Monte Carlo algorithm with the representative
particles approach. We find that planetesimal formation by streaming
instability may preferentially work outside the snow line, where sticky icy
aggregates are present. The efficiency of the process depends strongly on local
dust abundance and radial pressure gradient, and requires a super-solar
metallicity. If planetesimal formation is possible, the dust coagulation and
settling typically need ~100 orbits to produce sufficiently large and settled
grains and planetesimal formation lasts another ~1000 orbits. We present a
simple analytical model that computes the amount of dust that can be turned
into planetesimals given the parameters of the disk model.Comment: 12 pages, 6 figures, 1 table, accepted for publication in A&A (minor
corrections with respect to v1
Planetesimal formation during protoplanetary disk buildup
Models of dust coagulation and subsequent planetesimal formation are usually
computed on the backdrop of an already fully formed protoplanetary disk model.
At the same time, observational studies suggest that planetesimal formation
should start early, possibly even before the protoplanetary disk is fully
formed. In this paper, we investigate under which conditions planetesimals
already form during the disk buildup stage, in which gas and dust fall onto the
disk from its parent molecular cloud. We couple our earlier planetesimal
formation model at the water snow line to a simple model of disk formation and
evolution. We find that under most conditions planetesimals only form after the
buildup stage when the disk becomes less massive and less hot. However, there
are parameters for which planetesimals already form during the disk buildup.
This occurs when the viscosity driving the disk evolution is intermediate
() while the turbulent mixing of the dust is
reduced compared to that (), and with the assumption
that water vapor is vertically well-mixed with the gas. Such scenario could be expected for layered accretion, where the gas flow
is mostly driven by the active surface layers, while the midplane layers, where
most of the dust resides, are quiescent.Comment: 6 pages, 5 figures, accepted for publication in A&A, minor changes
due to language editio
From Dust to Planetesimals
It is now clear that on average every star in the Milky Way has at least one planet. Planet formation seems to be an inevitable side effect of the star formation process. However, there are several problems that make it difficult to understand how the primordial micrometer dust grains observed in protoplanetary disks are turned to planets. One of them is the formation of kilometer-sized planetesimals, which is the topic of this dissertation.
We first develop a new code for dust evolution in protoplanetary disks, which is based on the Monte Carlo approach. The code is then used to model several possible planetesimal formation scenarios. We test planetesimal formation by both dust coagulation and gravitational collapse of dense pebble clumps formed by the streaming instability. We examine what conditions are necessary for these scenarios to proceed and compare their planetesimal formation efficiencies. Our results suggest that planetesimal formation via dust coagulation is possible in the inner part of the protoplanetary disk, whereas the streaming instability may only be efficient beyond the snow line. Our predictions can be used to model the late stages of planet formation
Bifurcation of planetary building blocks during Solar System formation
Geochemical and astronomical evidence demonstrate that planet formation
occurred in two spatially and temporally separated reservoirs. The origin of
this dichotomy is unknown. We use numerical models to investigate how the
evolution of the solar protoplanetary disk influenced the timing of protoplanet
formation and their internal evolution. Migration of the water snow line can
generate two distinct bursts of planetesimal formation that sample different
source regions. These reservoirs evolve in divergent geophysical modes and
develop distinct volatile contents, consistent with constraints from accretion
chronology, thermo-chemistry, and the mass divergence of inner and outer Solar
System. Our simulations suggest that the compositional fractionation and
isotopic dichotomy of the Solar System was initiated by the interplay between
disk dynamics, heterogeneous accretion, and internal evolution of forming
protoplanets.Comment: Published 21 January 2021; authors' version; 30 pages, 18 figures;
summary available at http://bit.ly/BifurcationBlog (blog) and
https://bit.ly/BifurcationVideo (video