# Planets in Binaries: Formation and Dynamical Evolution

**Authors:** Francesco Marzari, Philippe Thebault  
**arXiv:** [2002.12006](https://arxiv.org/abs/2002.12006)  
**Date:** 2020-02-27  
**Summary page:** https://www.summarizepaper.com/en/arxiv-id/2002.12006v1/

## Key points

- The study explores the formation and evolution of planets in binary star systems.
- Binary systems with separations smaller than 100 au have fewer planets, suggesting that close companion stars hinder planet formation.
- The gravitational pull of the second star affects all stages of planet formation.
- Planetesimal accretion might be hampered due to increased impact velocities during the crucial accretion phase.
- Binary secular perturbations and mean motion resonances lead to unstable regions where planet formation is inhibited and massive bodies could be ejected from the system on a hyperbolic orbit.
- S and P type planets are affected differently by these effects, highlighting the influence of companion stars on planet formation.
- Long-term dynamical evolution influences final architecture in planetary systems in binaries for both S and P type systems.

## Summary

The study by Francesco Marzari and Philippe Thebault explores the formation and dynamical evolution of planets in binary star systems. While binary systems are common among field stars, there is statistical evidence that planets are less frequent in binaries with separations smaller than 100 au, suggesting that the presence of a close companion star has an adverse effect on planet formation. The gravitational pull of the second star can affect all stages of planet formation, from proto-planetary disk formation to dust accumulation into planetesimals, to the accretion of these planetesimals into large planetary embryos and eventually the final growth of these embryos into planets. The complex coupling between dynamical perturbations from the binary and friction due to gas in the protoplanetary disk suggests that planetesimal accretion might be hampered due to increased, accretion-hostile impact velocities during the crucial planetesimal accretion phase. Additionally, interplay between binary secular perturbations and mean motion resonances lead to unstable regions where not only is planet formation inhibited but also where a massive body would be ejected from the system on a hyperbolic orbit. The amplitude of these two main effects differs for S and P type planets; thus, a comparison between both populations could outline the influence of companion stars on the planet formation process. However, at present circumstellar or circumbinary populations are not equally known well enough for quantitative comparison due to different biases and uncertainties. The authors also highlight how long-term dynamical evolution influences final architecture in planetary systems in binaries for both S and P type systems. Overall, this study provides insights into how binary star systems affect planetary formation processes. It highlights potential challenges faced by such systems while forming planets as well as their long-term dynamics that ultimately shape their planetary architectures.