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

Abstract

Context. The growth processes from protoplanetary dust to planetesimals are not fully understood. Laboratory experiments and theoretical models have shown that collisions among the dust aggregates can lead to sticking, bouncing, and fragmentation. However, no systematic study on the collisional outcome of protoplanetary dust has been performed so far, so that a physical model of the dust evolution in protoplanetary disks is still missing. Aims. We intend to map the parameter space for the collisional interaction of arbitrarily porous dust aggregates. This parameter space encompasses the dust-aggregate masses, their porosities and the collision velocity. With such a complete mapping of the collisional outcomes of protoplanetary dust aggregates, it will be possible to follow the collisional evolution of dust in a protoplanetary disk environment. Methods. We use literature data, perform laboratory experiments, and apply simple physical models to get a complete picture of the collisional interaction of protoplanetary dust aggregates. Results. We found four different kinds of sticking, two kinds of bouncing, and three kinds of fragmentation as possible outcomes in collisions among protoplanetary dust aggregates. Our best collision model distinguishes between porous and compact dust. We also differentiate between collisions among similar-sized and different-sized bodies. All in all, eight combinations of porosity and mass ratio can be discerned. For each of these cases, we present a complete collision model for dust-aggregate masses between 10 −12 and 10 2 g and collision velocities in the range of 10 −4 . . . 10 4 cm s −1 for arbitrary porosities. This model comprises the collisional outcome, the mass(es) of the resulting aggregate(s) and their porosities. Conclusions. We present the first complete collision model for protoplanetary dust. This collision model can be used for the determination of the dust-growth rate in protoplanetary disks.

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

“…The fragment masses follow a velocity-independent power law, with the largest fragment being a function of impact speed (Blum & Münch, 1993;Güttler et al, 2010). For the micrometer-sized spherical SiO 2 particles used in most of our experiments, the fragmentation boundary is at v c ≈ 1 m s −1 , remarkably close to the threshold velocity for sticking of the monomer grains (see Sect.…”

“…The interested reader is referred to Güttler et al (2010) for a detailed description and the complete set of formulae.…”

“…On top of that, the collision model requires quite a large number of physical parameters as input values (see Table 2 in Güttler et al (2010)). We carefully measured or estimated these values to complete the model.…”

“…The underlying PPD model was a MMSN model at 1 AU and in the midplane with α = 10 −4 . The dust-aggregate collision model was taken from Güttler et al (2010). The left graph shows the temporal evolution of the mass distribution of the aggregates, whereas the right graph denotes the temporal behavior of the enlargement parameter.…”

Facula, Faculae

“…However, dust particles encounter many barriers and bottlenecks in their growth toward planetesimals, as bouncing and fragmentation become increasingly likely with increased size (Zsom et al 2010). Particles of sizes from mm to several m are nevertheless concentrated in the turbulent flow of the gas, and the overdensities can become high enough for the collective gravity to be dominant (Johansen et al 2007).…”