Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Article
  • Published:

Free-floating binary planets from ejections during close stellar encounters

Nature Astronomy (2024)Cite this article

Subjects

Abstract

The discovery of planetary systems beyond our Solar System has challenged established theories of planetary formation. Planetary orbits display a variety of unexpected architectures, and free-floating planets appear ubiquitous. The recently reported detection of candidate Jupiter-mass binary objects (JuMBOs) by the James Webb Space Telescope (JWST) has added another puzzling layer. Here, we demonstrate in direct few-body simulations that JuMBOs could arise from the ejection of two giant planets following a close encounter with a passing star, if the two planets are nearly aligned at closest approach. These ejected JuMBOs typically have an average semimajor axis approximately three times the orbital separation within their original planetary system and a high eccentricity, characterized by a superthermal distribution that sets them apart from those formed primordially. We estimate the JuMBO formation rate per planetary system in typical and densely populated clusters, revealing a significant environmental dependence. In dense clusters, this formation rate can reach a few percent for wide planetary systems. A comparative analysis of JuMBO rates and properties with current and forthcoming JWST observations across various environments promises to offer insights into the conditions under which these giant planets formed in protoplanetary disks, thereby imposing constraints on theories of giant planet formation.

This is a preview of subscription content, access via your institution

Access options

Buy this article

  • Purchase on Springer Link
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Fig. 1: Schematics of JuMBO production from stellar encounters.
Fig. 2: Angular dependency on JuMBO production cross-section, SMA and eccentricity.
Fig. 3: Cross sections for the production of JuMBOs and FFJs.
Fig. 4: Orbital parameters of the ejected JuMBO.
Fig. 5: Distributions of SMA and eccentricity for JuMBOs produced by stellar fly-bys.
Fig. 6: The upper limit for the number of JuMBOs produced per planetary system over 1 Myr due to stellar ejections.

Similar content being viewed by others

Data availability

Data are available at via figshare at https://doi.org/10.6084/m9.figshare.25331110.v2 (ref. 62).

Code availability

The code for SpaceHub is available via GitHub at https://github.com/YihanWangAstro/SpaceHub (ref. 63). The problem generator and data process script are available via GitHub at https://github.com/YihanWangAstro/JuMBO-code/tree/main (ref. 64).

References

  1. Christiansen, J. L. Five thousand exoplanets at the NASA Exoplanet Archive. Nat. Astron. 6, 516–519 (2022).

    Article  ADS  Google Scholar 

  2. Zhu, W. & Dong, S. Exoplanet statistics and theoretical implications. Annu. Rev. Astron. Astrophys. 59, 291–336 (2021).

    Article  ADS  Google Scholar 

  3. Pollack, J. B. et al. Formation of the giant planets by concurrent accretion of solids and gas. Icarus 124, 62–85 (1996).

    Article  ADS  Google Scholar 

  4. Ormel, C. W. & Klahr, H. H. The effect of gas drag on the growth of protoplanets. Analytical expressions for the accretion of small bodies in laminar disks. Astron. Astrophys. 520, A43 (2010).

    Article  ADS  Google Scholar 

  5. Lambrechts, M. & Johansen, A. Rapid growth of gas-giant cores by pebble accretion. Astron. Astrophys. 544, A32 (2012).

    Article  ADS  Google Scholar 

  6. Mayor, M. & Queloz, D. A Jupiter-mass companion to a solar-type star. Nature 378, 355–359 (1995).

    Article  ADS  Google Scholar 

  7. Winn, J. N. & Fabrycky, D. C. The occurrence and architecture of exoplanetary systems. Annu. Rev. Astron. Astrophys. 53, 409–447 (2015).

    Article  ADS  Google Scholar 

  8. Morales, J. C. et al. A giant exoplanet orbiting a very-low-mass star challenges planet formation models. Science 365, 1441–1445 (2019).

    Article  ADS  Google Scholar 

  9. Marois, C. et al. Direct imaging of multiple planets orbiting the star HR 8799. Science 322, 1348–1352 (2008).

    Article  ADS  Google Scholar 

  10. Lafrenière, D. et al. Discovery of an ~23 MJup brown dwarf orbiting ~700 au from the massive star HIP 78530 in Upper Scorpius. Astrophys. J. 730, 42 (2011).

    Article  ADS  Google Scholar 

  11. Deacon, N. R., Schlieder, J. E. & Murphy, S. J. A nearby young M dwarf with a wide, possibly planetary-mass companion. Mon. Not. R. Astron. Soc. 457, 3191–3199 (2016).

    Article  ADS  Google Scholar 

  12. Miret-Roig, N. et al. A rich population of free-floating planets in the Upper Scorpius young stellar association. Nat. Astron. 6, 89–97 (2022).

    Article  ADS  Google Scholar 

  13. Pearson, S. G. & McCaughrean, M. J. Jupiter mass binary objects in the Trapezium cluster. Preprint at https://arxiv.org/abs/2310.01231 (2023).

  14. Lin, D. N. C., Bodenheimer, P. & Richardson, D. C. Orbital migration of the planetary companion of 51 Pegasi to its present location. Nature 380, 606–607 (1996).

    Article  ADS  Google Scholar 

  15. Winn, J. N., Fabrycky, D., Albrecht, S. & Johnson, J. A. Hot stars with hot Jupiters have high obliquities. Astrophys. J. Lett. 718, L145–L149 (2010).

    Article  ADS  Google Scholar 

  16. Chatterjee, S., Ford, E. B., Matsumura, S. & Rasio, F. A. Dynamical outcomes of planet–planet scattering. Astrophys. J. 686, 580–602 (2008).

    Article  ADS  Google Scholar 

  17. Lee, E. J. The boundary between gas-rich and gas-poor planets. Astrophys. J. 878, 36 (2019).

    Article  ADS  Google Scholar 

  18. Lambrechts, M. & Johansen, A. Forming the cores of giant planets from the radial pebble flux in protoplanetary discs. Astron. Astrophys. 572, A107 (2014).

    Article  ADS  Google Scholar 

  19. Veras, D. & Raymond, S. N. Planet-planet scattering alone cannot explain the free-floating planet population. Mon. Not. R. Astron. Soc. 421, L117–L121 (2012).

    Article  ADS  Google Scholar 

  20. Boss, A. P. Giant planet formation by gravitational instability. Science 276, 1836–1839 (1997).

    Article  ADS  Google Scholar 

  21. Gammie, C. F. Nonlinear outcome of gravitational instability in cooling, gaseous disks. Astrophys. J. 553, 174–183 (2001).

    Article  ADS  Google Scholar 

  22. Rafikov, R. R. Can giant planets form by direct gravitational instability? Astrophys. J. Lett. 621, L69–L72 (2005).

    Article  ADS  Google Scholar 

  23. Boley, A. C. & Durisen, R. H. On the possibility of enrichment and differentiation in gas giants during birth by disk instability. Astrophys. J. 724, 618–639 (2010).

    Article  ADS  Google Scholar 

  24. Nayakshin, S. Formation of terrestrial planet cores inside giant planet embryos. Mon. Not. R. Astron. Soc. 413, 1462–1478 (2011).

    Article  ADS  Google Scholar 

  25. Zhu, Z., Hartmann, L., Nelson, R. P. & Gammie, C. F. Challenges in forming planets by gravitational instability: disk Irradiation and clump migration, accretion, and tidal destruction. Astrophys. J. 746, 110 (2012).

    Article  ADS  Google Scholar 

  26. Keppler, M. et al. Discovery of a planetary-mass companion within the gap of the transition disk around PDS 70. Astron. Astrophys. 617, A44 (2018).

    Article  Google Scholar 

  27. Haffert, S. Y. et al. Two accreting protoplanets around the young star PDS 70. Nat. Astron. 3, 749–754 (2019).

    Article  ADS  Google Scholar 

  28. Laughlin, G. & Adams, F. C. The modification of planetary orbits in dense open clusters. Astrophys. J. Lett. 508, L171–L174 (1998).

    Article  ADS  Google Scholar 

  29. Bonnell, I. A., Smith, K. W., Davies, M. B. & Horne, K. Planetary dynamics in stellar clusters. Mon. Not. R. Astron. Soc. 322, 859–865 (2001).

    Article  ADS  Google Scholar 

  30. Ford, E. B., Rasio, F. A. & Yu, K. Chaotic interactions in multiple planet systems. ISSI Sci. Rep. Ser. 6, 123–136 (2006).

    ADS  Google Scholar 

  31. Malmberg, D. et al. Close encounters in young stellar clusters: implications for planetary systems in the solar neighbourhood. Mon. Not. R. Astron. Soc. 378, 1207–1216 (2007).

    Article  ADS  Google Scholar 

  32. Fregeau, J. M., Chatterjee, S. & Rasio, F. A. Dynamical interactions of planetary systems in dense stellar environments. Astrophys. J. 640, 1086–1098 (2006).

    Article  ADS  Google Scholar 

  33. Malmberg, D., Davies, M. B. & Heggie, D. C. The effects of fly-bys on planetary systems. Mon. Not. R. Astron. Soc. 411, 859–877 (2011).

    Article  ADS  Google Scholar 

  34. Hao, W., Kouwenhoven, M. B. N. & Spurzem, R. The dynamical evolution of multiplanet systems in open clusters. Mon. Not. R. Astron. Soc. 433, 867–877 (2013).

    Article  ADS  Google Scholar 

  35. Shara, M. M., Hurley, J. R. & Mardling, R. A. Dynamical interactions make hot Jupiters in open star clusters. Astrophys. J. 816, 59 (2016).

    Article  ADS  Google Scholar 

  36. Cai, M. X., Kouwenhoven, M. B. N., Portegies Zwart, S. F. & Spurzem, R. Stability of multiplanetary systems in star clusters. Mon. Not. R. Astron. Soc. 470, 4337–4353 (2017).

    Article  ADS  Google Scholar 

  37. Flammini Dotti, F., Kouwenhoven, M. B. N., Cai, M. X. & Spurzem, R. Planetary systems in a star cluster. I. The Solar System scenario. Mon. Not. R. Astron. Soc. 489, 2280–2297 (2019).

    Article  ADS  Google Scholar 

  38. Fragione, G. Dynamical origin of S-type planets in close binary stars. Mon. Not. R. Astron. Soc. 483, 3465–3471 (2019).

    Article  ADS  Google Scholar 

  39. Li, D., Mustill, A. J. & Davies, M. B. Fly-by encounters between two planetary systems. I. Solar System analogues. Mon. Not. R. Astron. Soc. 488, 1366–1376 (2019).

    Article  ADS  Google Scholar 

  40. Wang, Y.-H., Perna, R. & Leigh, N. W. C. Planetary architectures in interacting stellar environments. Mon. Not. R. Astron. Soc. 496, 1453–1470 (2020).

    Article  ADS  Google Scholar 

  41. Wang, Y.-H., Perna, R. & Leigh, N. W. C. Giant planet swaps during close stellar encounters. Astrophys. J. Lett. 891, L14 (2020).

    Article  ADS  Google Scholar 

  42. Li, D., Mustill, A. J. & Davies, M. B. Flyby encounters between two planetary systems. II. Exploring the interactions of diverse planetary system architectures. Mon. Not. R. Astron. Soc. 496, 1149–1165 (2020).

    Article  ADS  Google Scholar 

  43. Moore, N. W. H., Li, G. & Adams, F. C. Inclination excitation of Solar System debris disk due to stellar flybys. Astrophys. J. 901, 92 (2020).

    Article  ADS  Google Scholar 

  44. Wang, Y.-H., Leigh, N. W. C., Perna, R. & Shara, M. M. Hot Jupiter and ultra-cold Saturn formation in dense star clusters. Astrophys. J. 905, 136 (2020).

    Article  ADS  Google Scholar 

  45. Carter, E. J. & Stamatellos, D. On the survivability of a population of gas giant planets on wide orbits. Mon. Not. R. Astron. Soc. 525, 1912–1921 (2023).

    Article  ADS  Google Scholar 

  46. Chen, C., Martin, R. G., Lubow, S. H. & Nixon, C. J. Tilted circumbinary planetary systems as efficient progenitors of free-floating planets. Astrophys. J. Lett. 961, L5 (2024).

    Article  ADS  Google Scholar 

  47. Heggie, D. C. Binary evolution in stellar dynamics. Mon. Not. R. Astron. Soc. 173, 729–787 (1975).

    Article  ADS  Google Scholar 

  48. Hut, P. & Bahcall, J. N. Binary-single star scattering. I. Numerical experiments for equal masses. Astrophys. J. 268, 319–341 (1983).

    Article  ADS  Google Scholar 

  49. Sigurdsson, S. & Phinney, E. S. Binary-single star interactions in globular clusters. Astrophys. J. 415, 631–651 (1993).

    Article  ADS  Google Scholar 

  50. Mathieu, R. D. Pre-main-sequence binary stars. Annu. Rev. Astron. Astrophys. 32, 465–530 (1994).

    Article  ADS  Google Scholar 

  51. Raghavan, D. et al. A survey of stellar families: multiplicity of solar-type stars. Astrophys. J. Suppl. Ser. 190, 1 (2010).

    Article  ADS  Google Scholar 

  52. Hillenbrand, L. A. & Hartmann, L. W. A preliminary study of the Orion nebula cluster structure and dynamics. Astrophys. J. 492, 540–553 (1998).

    Article  ADS  Google Scholar 

  53. Nielsen, E. L. et al. The Gemini Planet Imager Exoplanet Survey: giant planet and brown dwarf demographics from 10 to 100 au. Astron. J. 158, 13 (2019).

    Article  ADS  Google Scholar 

  54. Vigan, A. et al. The SPHERE infrared survey for exoplanets (SHINE). III. The demographics of young giant exoplanets below 300 au with SPHERE. Astron. Astrophys. 651, A72 (2021).

    Article  Google Scholar 

  55. Zwart, S. P. & Hochart, E. The origin and evolution of wide Jupiter mass binary objects in young stellar clusters. Preprint at https://arxiv.org/abs/2312.04645 (2023).

  56. Wang, Y.-H., Leigh, N. W. C., Liu, B. & Perna, R. SpaceHub: a high-performance gravity integration toolkit for few-body problems in astrophysics. Mon. Not. R. Astron. Soc. 505, 1053–1070 (2021).

    Article  ADS  Google Scholar 

  57. Chambers, J. E., Wetherill, G. W. & Boss, A. P. The stability of multi-planet systems. Icarus 119, 261–268 (1996).

    Article  ADS  Google Scholar 

  58. Adams, F. C. The birth environment of the Solar System. Annu. Rev. Astron. Astrophys. 48, 47–85 (2010).

    Article  ADS  Google Scholar 

  59. Boley, A. C. The two modes of gas giant planet formation. Astrophys. J. Lett. 695, L53–L57 (2009).

    Article  ADS  Google Scholar 

  60. Vicente, S. M. & Alves, J. Size distribution of circumstellar disks in the Trapezium cluster. Astron. Astrophys. 441, 195–205 (2005).

    Article  ADS  Google Scholar 

  61. Mann, R. K. & Williams, J. P. The circumstellar disk mass distribution in the Orion Trapezium cluster. Astrophys. J. Lett. 694, L36–L40 (2009).

    Article  ADS  Google Scholar 

  62. Wang, Y. jumbo dataset 1. figshare https://doi.org/10.6084/m9.figshare.25331110.v2 (2024).

  63. Wang, Y. SpaceHub: a high-performance gravity integration toolkit for few-body problems in astrophysics. GitHub https://github.com/YihanWangAstro/SpaceHub (2019).

  64. Wang, Y. Free-floating binary planets from ejections during close stellar encounters. GitHub https://github.com/YihanWangAstro/JuMBO-code/tree/main (2013).

Download references

Acknowledgements

R.P. acknowledges support from the National Science Foundation (Award No. AST-2006839). Y.W. and Z.Z. acknowledge support from NASA (Grant No. 80NSSC23M0104) and the Nevada Center for Astrophysics.

Author information

Author notes

  1. These authors contributed equally: Yihan Wang, Rosalba Perna.

Authors and Affiliations

  1. Nevada Center for Astrophysics, University of Nevada, Las Vegas, NV, USA

    Yihan Wang & Zhaohuan Zhu

  2. Department of Physics and Astronomy, University of Nevada, Las Vegas, NV, USA

    Yihan Wang & Zhaohuan Zhu

  3. Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY, USA

    Rosalba Perna

  4. Center for Computational Astrophysics, Flatiron Institute, New York, NY, USA

    Rosalba Perna

Authors
  1. Yihan Wang
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Rosalba Perna
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Zhaohuan Zhu
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

R.P. proposed the model idea. Y.W. devised the numerical experiments, processed the data and performed the calculations. Z.Z. provided input on the models of planetary formation. R.P. and Y.W. drafted the first version of the manuscript. All authors contributed to the analysis and interpretation of the data, as well as to the final version of the manuscript.

Corresponding author

Correspondence to Yihan Wang.

Ethics declarations

Competing interests

The authors declare no competing interests.

Peer review

Peer review information

Nature Astronomy thanks Nathan Kaib, Sean Raymond and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Rights and permissions

Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Wang, Y., Perna, R. & Zhu, Z. Free-floating binary planets from ejections during close stellar encounters. Nat Astron (2024). https://doi.org/10.1038/s41550-024-02239-2

Download citation

  • Received:

  • Accepted:

  • Published:

  • DOI: https://doi.org/10.1038/s41550-024-02239-2

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing