The outcome of protoplanetary dust growth: pebbles, boulders, or planetesimals?

Abstract

Context. The sticking of micron-sized dust particles caused by surface forces within circumstellar disks is the first stage in the production of asteroids and planets. The key components describing this process are the relative velocity between the dust particles in this environment and the complex physics of dust aggregate collisions. Aims. We present the results of a collision model based on laboratory experiments of these aggregates. We investigate the maximum aggregate size and mass that can be reached by coagulation in protoplanetary disks. Methods. We use the results of laboratory experiments to establish the collision model previously published by Güttler et al. The collision model is based on the assumptions that we model the aggregates as spheres with compact and porous "phases" and that there is a continuous transition between these two. We apply this collision model to the Monte Carlo method developed previously by Zsom & Dullemond and include Brownian motion, radial drift, and turbulence as contributors of relative velocity between dust particles. Results. We model the growth of dust aggregates at 1 AU in the midplane for three different gas densities. We find that the evolution of the dust does not follow the previously assumed growth-fragmentation cycles. Catastrophic fragmentation hardly occurs in the three disk models. Furthermore, we see long-lived, quasi-steady states in the distribution function of the aggregates caused by bouncing. We explore how the mass and the porosity depend on both the turbulence parameter and the critical mass ratio of dust particles. Upon varying the turbulence parameter, the system behaves in a non-linear way, and we find that the critical mass ratio has a strong effect on the particle sizes and masses. Particles reach Stokes numbers of roughly 10 −4 during the simulations. Conclusions. The particle growth is stopped by bouncing rather than fragmentation in these models. The final Stokes number of the aggregates is rather insensitive to the variations in the gas density and the strength of turbulence. The maximum mass of the particles is limited to ≈1 g (chondrule-sized particles). Planetesimal formation can proceed by the means of the turbulent concentration of these aerodynamically size-sorted, chondrule-sized particles.

High-resolution simulations of planetesimal formation in turbulent protoplanetary discs

“…The first can be studied in the simulations that we present in this paper, while the actual masses and radii of planetesimal that form in the bound clumps will require the inclusion of particle shattering and particle sticking. Zsom & Dullemond (2008) and Zsom et al (2010) used a representative particle approach to model interaction between superparticles in a 0-D particle-inbox approach, based on a compilation of laboratory results for the outcome of collisions depending on particle sizes, composition and relative speed . We plan to implement this particle interaction scheme in the Pencil Code and perform simulations that include the concurrent action of hydrodynamical clumping and particle interaction.…”

Disk Dispersal: Theoretical Understanding and Observational Constraints

“…Formation of planetesimals due to dust coagulation is presently very uncertain due to several barriers to planetesimal growth: the bouncing barrier (Zsom et al 2010), the charge barrier (Okuzumi et al 2009), and the meter-size barrier (due to drift and fragmentation) (Blum & Wurm 2000). New approaches, such as formation in pressure maxima (Lyra et al 2009), particle concentration due to streaming instability and gravoturbulent planetesimal formation (Johansen et al 2014), have attempted to clarify these issues.…”

Dust growth in protoplanetary disks — a comprehensive experimental/theoretical approach

“…Results of the Monte-Carlo simulation of the dust evolution in PPDs (adapted from Zsom et al (2010)). The underlying PPD model was a MMSN model at 1 AU and in the midplane with α = 10 −4 .…”