The bouncing barrier revisited: Impact on key planet formation processes and observational signatures

Abstract

Context. A leading paradigm in planet formation is currently the streaming instability and pebble accretion scenario. For this scenario, dust must grow into sizes in a specific regime of Stokes numbers in order to make these processes viable and sufficiently effective. The dust growth models currently in use do not implement some of the growth barriers suggested to be relevant in the literature. Aims. We want to investigate if the bouncing barrier, when effective, has impact on the time scales and efficiencies of processes like the streaming instability and pebble accretion, as well as on the observational appearance of planet-forming disks. Methods. We implement a formalism for the bouncing barrier into the publicly available dust growth model DustPy and run a series of models to understand the impact. Results. We find that the bouncing barrier has significant effect on the dust evolution in planet-forming disks. It reduces in many cases the size of the typical or largest particles available in the disk, it produces a very narrow, almost mono-disperse size distribution and removes most micrometer-sized grains in the process, with impact on scattered light images. It modifies the settling and therefore the effectiveness of and timescales for the streaming instability and for pebble accretion. An active bouncing barrier may well have observational consequences. It may reduce the strength if signatures of small particles (e.g. the 10 micron silicate feature), and it may create additional shadowed regions visible in scattered light images. Conclusions. Modeling of planet formation leaning heavily on the streaming instability and on pebble accretion should take the bouncing barrier into account. The complete removal of small grains in our model is not consistent with observations. However, this could be resolved by incomplete vertical mixing or some level of erosion in collisions.