Fragmentation-limited dust filtration in 2D simulations of planet-disk systems with dust coagulation. Parameter study and implications for the inner disk's dust mass budget and composition

TL;DR

This work uses 2D multifluid hydrodynamics with the TriPoD coagulation/fragmentation model in Athena++ to study how planet-induced gaps filter dust and shape the inner disk's mass budget and composition. By varying planetary mass $M_p$, fragmentation velocity $v_{frag}$, and viscosity parameter $\alpha$, the authors quantify when gap filtration is effective and how much outer-disk material contaminates the inner disk. The results reveal that filtration is efficient only for high $M_p$, high $v_{frag}$, and low $\alpha$, but even then small grains replenish through fragmentation and diffuse inward, challenging strict compositional separation. The findings highlight the need for multi-dimensional, coagulation-fragmentation–aware modeling to interpret dust transport and isotopic records in forming planetary systems, and suggest that Solar System–like dichotomies require particular disk conditions or additional mechanisms.

Abstract

Super-thermal gas giant planets or their progenitor cores are known to open deep gaps in protoplanetary disks, which stop large, drifting dust particles on their way to the inner disk. The possible separation of the disk into distinct reservoirs and the resulting dust depletion interior to the gap have important implications for planetesimal formation and the chemical and isotopic composition of the inner regions of protoplanetary disks. Dust fragmentation, however, maintains a reservoir of small grains which can traverse the gap. Dust evolution models are thus instrumental for studies of a gap's filtration efficiency. We present 2D multifluid hydrodynamic simulations of planet-disk systems with dust coagulation and fragmentation. For the first time, we evolve a series of 2D simulation with dust coagulation over 45000 planetary orbits and track the dust's size evolution and origin by using the TriPoD dust coagulation method. We investigate the effects of different planetary masses, fragmentation velocities, and viscosities on the inner disk's dust mass budget and composition, and highlight the advantages of multi-dimensional simulations over 1D models. Filtering can only be efficient for high planetary masses, high fragmentation velocities, and low diffusivities. Clear compositional distinctions between the inner and outer disk could not have been maintained by Jupiter's core if the fragmentation velocity was low, even if $α\lesssim 5 \times 10^{-4}$. Significant "contamination" of the inner disk by outer-disk dust occurs in much less than $2 \times 10^5$ yr in this case and even for more massive objects. This either places tight constraints on the physical conditions in the Solar nebula or mandates consideration of alternative explanations for the NC-CC dichotomy. Astrophysical constraints on the parameters could discriminate between these possibilities.

Figures (24)

• Figure 1: Initial distribution of the passive scalar for both dust fluids. This quantity represents the initial distribution of outer-disk material in our simulations.
• Figure 2: Snapshot of our fiducial simulation with $M_\mathrm{p}=0.4\Mjup$, $v_\mathrm{frag}=400cm\per s$ and $\alpha=10^{-3}$ after 45000 planetary orbits. We employ damping zones in the boundary layers, marked my the thin dashed lines.
• Figure 3: Azimuthally averaged dust size distribution of our fiducial simulation after 45000 planetary orbits. The maximum particle size is shown in white. The planet is located at 5.2. We employ damping zones in the boundary layers, marked by the thin dashed lines.
• Figure 4: Comparison between the azimuthally averaged dust density and particle size profiles of our two-dimensional fiducial simulation (solid lines) and two one-dimensional models. Dashed lines show the one-dimensional DustPy model in which the gas column density was interpolated from the two-dimensional simulation results. Dotted lines correspond to a one-dimensional DustPy model for which the gas density was evolved based on a viscosity profile with in inverse Duffell2020 gap.
• Figure 5: Streamlines of dust in the vicinity of the planet in our fiducial simulation. Azimuthal velocities are calculated in the planet's frame of reference. The color of the streamlines indicates the radial component of the flux. The white circles indicate the planet's Hill radius (outer circle) and the gravitational smoothing length (inner circle). Most of the mass flow between the inner and outer disk occurs via the flows past the planet.