Revisiting planetesimal formation from mm-sized grains in pressure bumps
Abstract
We present evidence that the streaming instability (SI) can form planetesimals from millimeter grains inside axisymmetric pressure bumps, provided the bump is not too strongly reinforced. We conducted three-dimensional local shearing-box simulations of millimeter grains in a Gaussian pressure bump of amplitude A = 0.6, at a resolution of 160/H. We varied only the Newtonian reinforcement timescale treinf, the timescale on which the imposed bump is restored against particle back-reaction. Our reference run T1 uses treinf = 1 Ω−1. Particles pile up in a narrow axisymmetric band at the minimum-headwind point, cross the Roche density, and collapse through direct gravitational instability (GI). In our weakly reinforced run T100 with treinf = 100 Ω−1, the outcome is different. Particles drift through the bump roughly three times more slowly, and dense SI-like filaments develop across a wide radial region well before the Roche density is reached. These results are consistent with a residence-time criterion, which states that for the SI to grow, tcross > tgrow, where tcross is the time a particle spends inside the region where the ratio Z/Π of the solid abundance Z = Σp/Σg to the headwind parameter Π= Δv/cs is high enough for strong clumping, and tgrow is the SI growth time. T1 violates this criterion, and T100 satisfies it. Our results suggest that the reinforcement timescale matters for millimeter grains because it helps set the crossing time, and therefore whether the SI has time to grow. We caution, however, that our reinforcement scheme is an idealised numerical construction rather than a physical bump-forming mechanism such as a planet, and a more definitive test of this picture will require simulations with a more physically motivated bump.
Related
- Formation of Micron-sized Presolar Graphite Grains in Low-energy Supernova Ejecta
- Carbonaceous Chondrites Provide Evidence for Late-stage Planetesimal Formation in a Pressure Bump
- Planetesimal formation facilitated by streaming instability in weak pressure bumps
- Planet formation at the inner edge of the dead zone. II. Outbursts, rings, vortices, and planetesimal formation
- Planetesimal Formation under Realistic Gas Dynamics: Dust Concentration in Turbulent and Windy Protoplanetary Disks
BibTeX
@misc{tanvir2026revisiting,
title = {{Revisiting planetesimal formation from mm-sized grains in pressure bumps}},
author = {Tabassum S Tanvir and Jacob B Simon and Daniel Carrera and Jeonghoon Lim},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.27025},
eprint = {2609.27025},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.27025},
}
RIS
TY - UNPB
TI - Revisiting planetesimal formation from mm-sized grains in pressure bumps
AU - Tabassum S Tanvir
AU - Jacob B Simon
AU - Daniel Carrera
AU - Jeonghoon Lim
PY - 2026
DA - 2026/09/22
PB - arXiv
DO - 10.48550/arxiv.2609.27025
UR - https://arxiv.org/abs/2609.27025
AB - We present evidence that the streaming instability (SI) can form planetesimals from millimeter grains inside axisymmetric pressure bumps, provided the bump is not too strongly reinforced. We conducted three-dimensional local shearing-box simulations of millimeter grains in a Gaussian pressure bump of amplitude A = 0.6, at a resolution of 160/H. We varied only the Newtonian reinforcement timescale t_reinf, the timescale on which the imposed bump is restored against particle back-reaction. Our reference run T1 uses t_reinf = 1 Ω^−1. Particles pile up in a narrow axisymmetric band at the minimum-headwind point, cross the Roche density, and collapse through direct gravitational instability (GI). In our weakly reinforced run T100 with t_reinf = 100 Ω^−1, the outcome is different. Particles drift through the bump roughly three times more slowly, and dense SI-like filaments develop across a wide radial region well before the Roche density is reached. These results are consistent with a residence-time criterion, which states that for the SI to grow, t_cross > t_grow, where t_cross is the time a particle spends inside the region where the ratio Z/Π of the solid abundance Z = Σ_p/Σ_g to the headwind parameter Π= Δv/c_s is high enough for strong clumping, and t_grow is the SI growth time. T1 violates this criterion, and T100 satisfies it. Our results suggest that the reinforcement timescale matters for millimeter grains because it helps set the crossing time, and therefore whether the SI has time to grow. We caution, however, that our reinforcement scheme is an idealised numerical construction rather than a physical bump-forming mechanism such as a planet, and a more definitive test of this picture will require simulations with a more physically motivated bump.
ER -