Size and density sorting of dust grains in SPH simulations of protoplanetary disc II: Fragmentation

TL;DR

This study uses 3D SPH simulations to explore how dust grain growth, fragmentation, and chemical sorting influence planetesimal formation in protoplanetary discs, revealing rapid growth and potential to overcome radial drift barriers.

Contribution

It introduces a detailed multi-phase dust model with fragmentation thresholds, showing how fragmentation and growth interplay affect dust composition and size distribution in evolving discs.

Findings

Disc transitions from fragmentation to growth regime in a few thousand years

Fragmentation influences chemical ratios like Fe/Si and rock/ice in dust

Dust can grow larger in fragmenting zones, overcoming radial drift barrier

Abstract

Grain growth and fragmentation are important processes in building up large dust aggregates in protoplanetary discs. Using a 3D two-phase (gas-dust) SPH code, we investigate the combined effects of growth and fragmentation of a multi-phase dust with different fragmentation thresholds in a time-evolving disc. We find that our fiducial disc, initially in a fragmentation regime, moves toward a pure-growth regime in a few thousands years. Timescales change as a function of the disc and dust properties. When fragmentation is efficient, it produces, in different zones of the disc, Fe/Si and rock/ice ratios different from those predicted when only pure growth is considered. Chemical fractionation and the depletion/enrichment in iron observed in some chondrites can be linked to the size-density sorting and fragmentation properties of precursor dusty grains . We suggest that aggregation of chondritic components could have occurred where/when fragmentation was not efficient if their aerodynamical sorting has to be preserved. Chondritic components would allow aerodynamical sorting in a fragmentation regime only if they have similar fragmentation properties. We find that, in the inner disc, and for the same interval of time, fragmenting dust can grow larger when compared to the size of grains predicted by pure growth. This counter-intuitive behaviour is due to the large amount of dust which piles up in a fragmenting zone followed by the rapid growth that occurs when this zone transitions to a pure growth regime. As an important consequence, dust can overcome the radial-drift barrier within a few thousands years.