Capture of interstellar planetesimals in protoplanetary discs in binary star systems
- 1School of Physics and Astronomy, Monash University , Clayton, VIC 3800 ,
- 2OzGrav: Australian Research Council Centre of Excellence for Gravitational Wave Discovery , Clayton, VIC 3800 ,
Abstract
Planet formation requires growth over 12 orders of magnitude in size, from micron-sized dust grains to fully formed planets. The formation of ∼ km-sized planetesimals is the most challenging stage, where radial drift and fragmentation rapidly remove meter-sized solids from the protoplanetary disc. Overcoming this barrier requires favourable conditions for streaming instability to concentrate solids. These problems are exacerbated in binary star systems, where gravitational perturbations and disc truncation reduce the efficiency of planetesimal formation pathways. Planetesimal capture provides an alternative mechanism where unbound planetesimals are captured by the protoplanetary disc through gas drag, potentially bypassing the most restrictive growth stages. We investigate this process in circumstellar and circumbinary discs using over 3× 107 numerical experiments across a range of binary separations. For circumstellar discs, capture of large (≳ 50 m) planetesimals is suppressed below ∼ 50 au, with the strongest reduction at ∼ 10 au, broadly consistent with the observed decrease in planet occurrence in binaries. Tight (∼ 10 au) binaries can still capture 𝒪(1) km-sized planetesimals, increasing to 𝒪(10) km-sized in wider systems during the birth cluster’s lifetime. Circumbinary discs are much less efficient, with capture rates dropping to ∼ 1 per cent of the single-star case for binaries above ∼ 1 au and becoming negligible for large planetesimals at wider separations. Overall, planetesimal capture provides a supplementary channel for delivering solids to binary systems and mitigating inefficiencies in in situ planetesimal formation.
Versions
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BibTeX
@article{pollard2026capture,
title = {{Capture of interstellar planetesimals in protoplanetary discs in binary star systems}},
author = {Alia Pollard and Evgeni Grishin},
journal = {Monthly Notices of the Royal Astronomical Society},
year = {2026},
month = oct,
doi = {10.1093/mnras/stag1926},
url = {https://academic.oup.com/mnras/article/doi/10.1093/mnras/stag1926/8907359},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Capture of interstellar planetesimals in protoplanetary discs in binary star systems
AU - Alia Pollard
AU - Evgeni Grishin
PY - 2026
DA - 2026/10/10
JO - Monthly Notices of the Royal Astronomical Society
DO - 10.1093/mnras/stag1926
UR - https://academic.oup.com/mnras/article/doi/10.1093/mnras/stag1926/8907359
AB - Planet formation requires growth over 12 orders of magnitude in size, from micron-sized dust grains to fully formed planets. The formation of ∼ km-sized planetesimals is the most challenging stage, where radial drift and fragmentation rapidly remove meter-sized solids from the protoplanetary disc. Overcoming this barrier requires favourable conditions for streaming instability to concentrate solids. These problems are exacerbated in binary star systems, where gravitational perturbations and disc truncation reduce the efficiency of planetesimal formation pathways. Planetesimal capture provides an alternative mechanism where unbound planetesimals are captured by the protoplanetary disc through gas drag, potentially bypassing the most restrictive growth stages. We investigate this process in circumstellar and circumbinary discs using over 3× 10^7 numerical experiments across a range of binary separations. For circumstellar discs, capture of large (≳ 50 m) planetesimals is suppressed below ∼ 50 au, with the strongest reduction at ∼ 10 au, broadly consistent with the observed decrease in planet occurrence in binaries. Tight (∼ 10 au) binaries can still capture 𝒪(1) km-sized planetesimals, increasing to 𝒪(10) km-sized in wider systems during the birth cluster’s lifetime. Circumbinary discs are much less efficient, with capture rates dropping to ∼ 1 per cent of the single-star case for binaries above ∼ 1 au and becoming negligible for large planetesimals at wider separations. Overall, planetesimal capture provides a supplementary channel for delivering solids to binary systems and mitigating inefficiencies in in situ planetesimal formation.
SN - 0035-8711
SN - 1365-2966
ER -