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A small and round heliosphere suggested by magnetohydrodynamic modelling of pick-up ions

A Publisher Correction to this article was published on 05 May 2020

This article has been updated


As the Sun moves through the surrounding partially ionized medium, neutral hydrogen atoms penetrate the heliosphere, and through charge exchange with the supersonic solar wind, create a population of hot pick-up ions (PUIs). Until recently, the consensus was that the shape of the heliosphere is comet-like. The termination shock crossing by Voyager 2 demonstrated that the heliosheath (the region of shocked solar wind) pressure is dominated by PUIs; however, the impact of the PUIs on the global structure of the heliosphere has not been explored. Here we use a novel magnetohydrodynamic model that treats the PUIs as a separate fluid from the thermal component of the solar wind. The depletion of PUIs, due to charge exchange with the neutral hydrogen atoms of the interstellar medium in the heliosheath, cools the heliosphere, ‘deflating’ it and leading to a narrower heliosheath and a smaller and rounder shape, confirming the shape suggested by Cassini observations. The new model reproduces both the properties of the PUIs, based on the New Horizons observations, and the solar wind ions, based on the Voyager 2 spacecraft observations as well as the solar-like magnetic field data outside the heliosphere at Voyager 1 and Voyager 2.

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Fig. 1: TS crossing at V2.
Fig. 2: Meridional cuts showing the difference when PUIs and thermal ions are treated as separate fluids or not.
Fig. 3: Density of PUIs and solar wind.
Fig. 4: The new heliosphere.
Fig. 5: Pressures in the HS.
Fig. 6: Magnetic field outside the HP at V1 and V2.

Data availability

Our model is the OH module of SWMF and is available at The data produced by the model that support the findings of this study are available from the corresponding author upon reasonable request.

Change history

  • 05 May 2020

    An amendment to this paper has been published and can be accessed via a link at the top of the paper.


  1. 1.

    Davis, L. Interplanetary magnetic fields and cosmic rays. Phys. Rev. 100, 1440–1444 (1955).

    ADS  Article  Google Scholar 

  2. 2.

    Parker, E. N. The stellar-wind regions. Astrophys. J. 134, 20–27 (1961).

    ADS  Article  Google Scholar 

  3. 3.

    Axford, W. I. in The Interaction of the Solar Wind with the Interstellar Medium (eds Sonett, C. P. et al.) 609–660 (Scientific and Technical Information Office, NASA, 1972).

  4. 4.

    Baranov, V. B. & Malama, Y. G. Model of the solar wind interaction with the local interstellar medium: numerical solution of self-consistent problem. J. Geophys. Res. 98, 15157–15163 (1993).

  5. 5.

    Opher, M., Drake, J. F., Zieger, B. & Gombosi, T. I. Magnetized jets driven by the Sun: the structure of the heliosphere revisited. Astrophys. J. 800, L28 (2015).

    ADS  Article  Google Scholar 

  6. 6.

    Drake, J. F., Swisdak, M. & Opher, M. A model of the heliosphere with jets. Astrophys. J. 808, L44 (2015).

    ADS  Article  Google Scholar 

  7. 7.

    Dialynas, K., Krimigis, S. M., Mitchell, D. G., Decker, R. B. & Roelof, E. C. The bubble-like shape of the heliosphere observed by Voyager and Cassini. Nat. Astron. 1, 0115 (2017).

    ADS  Article  Google Scholar 

  8. 8.

    Izmodenov, V. V. & Alexashov, D. B. Three-dimensional kinetic-MHD model of the global heliosphere with the heliopause-surface fitting. Astrophys. J. Suppl. Ser. 220, 32 (2015).

    ADS  Article  Google Scholar 

  9. 9.

    Pogorelov, N. V., Borovikov, S. N., Heerikhuisen, J. & Zhang, M. The heliotail. Astrophys. J. 812, L6 (2015).

    ADS  Article  Google Scholar 

  10. 10.

    Glocer, A. et al. Multifluid block-adaptive-tree solar wind roe-type upwind scheme: magnetospheric composition and dynamics during geomagnetic storms—initial results. J. Geophys. Res. 114, A12203 (2009).

    ADS  Google Scholar 

  11. 11.

    McComas, D. et al. Interstellar pickup ion observations to 38 au. Astrophys. J. Suppl. Ser. 233, 8 (2017).

    ADS  Article  Google Scholar 

  12. 12.

    Lee, M. et al. Physical processes in the outer heliosphere. Space Sci. Rev. 146, 275–294 (2009).

    ADS  Article  Google Scholar 

  13. 13.

    Zieger, B., Opher, M., Toth, G., Decker, R. B. & Richardson, J. D. Constraining the pickup ion abundance and temperature through the multifluid reconstruction of the Voyager 2 termination shock crossing. J. Geophys. Res. 120, 7130–7153 (2015).

    Article  Google Scholar 

  14. 14.

    Zirnstein, E. J. et al. Local interstellar magnetic field determined from the interstellar boundary explorer Ribbon. Astrophys. J. 818, L18 (2016).

    ADS  Article  Google Scholar 

  15. 15.

    Richardson, J. D. et al. Cool heliosheath plasma and deceleration of the upstream solar wind at the termination shock. Nature 454, 63–66 (2008).

    ADS  Article  Google Scholar 

  16. 16.

    Smith, C. W., Isenberg, P. A., Mathaeus, W. H. & Richardson, J. D. Turbulent heating of the solar wind by newborn interstellar pickup protons. Astrophys. J. 638, 508–517 (2006).

    ADS  Article  Google Scholar 

  17. 17.

    Isenberg, P. A., Smith, C. W. & Matthaeus, W. H. Turbulent heating of the distant solar wind by interstellar pickup protons. Astrophys. J. 592, 564–573 (2003).

    ADS  Article  Google Scholar 

  18. 18.

    Fahr, H. J. & Chalov, S. V. Supersonic solar wind ion flows downstream of the termination shock explained by a two-fluid shock model. Astron. Astrophys. 490, L35–L38 (2008).

    ADS  Article  Google Scholar 

  19. 19.

    Zank, G. P. et al. Microstructure of the heliospheric termination shock: implications for energetic neutral atom observations. Astrophys. J. 708, 1092–1106 (2010).

    ADS  Article  Google Scholar 

  20. 20.

    Guo, X., Florinski, V. & Wang, C. Effects of anomalous cosmic rays on the structure of the outer heliosphere. Astrophys. J. 859, 157 (2018).

    ADS  Article  Google Scholar 

  21. 21.

    Richardson, J. D., Belcher, J. W., Garcia-Galindo, P. & Burlaga, L. F. Voyager 2 plasma observations of the heliopause and interstellar medium. Nat. Astron. 3, 1019–1023 (2019).

    ADS  Article  Google Scholar 

  22. 22.

    Grygorczuk, J., Czechowski, A. & Grzedzielski, S. Why are the magnetic field directions measured by voyager 1 on both sides of the heliopause so similar? Astrophys. J. 789, L43 (2014).

    ADS  Article  Google Scholar 

  23. 23.

    Pogorelov, N. V. et al. Heliosheath processes and the structure of the heliopause: modeling energetic particles, cosmic rays, and magnetic fields. Space Sci. Rev. 212, 193–248 (2017).

    ADS  Article  Google Scholar 

  24. 24.

    Burlaga, L. F. et al. Magnetic field and particle measurements made by Voyager 2 at and near the heliopause. Nat. Astron. 3, 1007–1012 (2019).

    ADS  Article  Google Scholar 

  25. 25.

    Burlaga, L. F., Florinski, V. & Ness, N. F. Turbulence in the outer heliosheath. Astrophys. J. 854, 10 (2018).

    Article  Google Scholar 

  26. 26.

    Opher, M., Drake, J. F., Swisdak, M., Zieger, B. & Toth, G. The twist of the draped interstellar magnetic field ahead of the heliopause: a magnetic reconnection driven rotational discontinuity. Astrophys. J. 839, L12 (2017).

    ADS  Article  Google Scholar 

  27. 27.

    Malama, Y. G., Izmodenov, V. V. & Chalov, S. V. Modeling of the heliospheric interface: multi-component nature of the heliospheric plasma. Astron. Astrophys. 445, 693–701 (2006).

    ADS  Article  Google Scholar 

  28. 28.

    Opher, M. et al. A strong, highly-tilted interstellar magnetic field near the Solar System. Nature 462, 1036–1038 (2009).

    ADS  Article  Google Scholar 

  29. 29.

    Izmodenov, V., Malama, Y. G. & Ruderman, M. S. Modeling of the outer heliosphere with the realistic solar cycle. J. Adv. Space Res. 41, 318–324 (2008).

    ADS  Article  Google Scholar 

  30. 30.

    Izmodenov, V. V., Alexashov, D. B. & Ruderman, M. S. Electron thermal conduction as a possible physical mechanism to make the inner heliosheath thinner. Astrophys. J. 795, L7 (2014).

    ADS  Article  Google Scholar 

  31. 31.

    Gloeckler, G. & Fisk, L. A. Proton velocity distributions in the inner heliosheath derived from energetic hydrogen atoms measured with Cassini and IBEX. AIP Conf. Proc. 1302, 110–116 (2010).

    ADS  Article  Google Scholar 

  32. 32.

    McComas, D. J. et al. Interstellar mapping and acceleration probe (IMAP): a new NASA mission. Space Sci. Rev. 214, 116 (2018).

    ADS  Article  Google Scholar 

  33. 33.

    Toth, G. et al. Adaptive numerical algorithms in space weather modeling. J. Comput. Sci. 231, 870–903 (2012).

    ADS  MathSciNet  Google Scholar 

  34. 34.

    McNutt, R. L., Lyon, J. & Goodrich, C. C. Simulation of the heliosphere: model. J. Geophys. Res. 103, 1905–1912 (1988).

    ADS  Article  Google Scholar 

  35. 35.

    Zieger, B., Opher, M., Schwadron, N. A., McComas, D. J. & Toth, G. A slow bow shock ahead of the heliosphere. Geophys. Res. Lett. 40, 2923–2928 (2013).

    ADS  Article  Google Scholar 

  36. 36.

    Lindsay, B. G. & Stebbings, R. F. Charge transfer cross sections for energetic neutral atom data analysis. J. Geophys. Res. 110, A12213 (2005).

    ADS  Article  Google Scholar 

  37. 37.

    Heerikhuisen, J., Zirnstein, E. J., Pogorelov, N. V., Zank, G. P. & Desai, M. Effects of suprathermal protons in the heliosheath on the global structure of the heliosphere and heliotail. Astrophys. J. 874, 76 (2019).

    ADS  Article  Google Scholar 

  38. 38.

    Lallement, R. et al. Deflection of the interstellar neutral hydrogen flow across the heliospheric interface. Science 307, 1447–1449 (2005).

    ADS  Article  Google Scholar 

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We thank the staff at NASA Ames Research Center for the use of the Pleiades supercomputer under the award SMD-16-7616 and SMD-18-1875 and especially N. Carney. M.O. acknowledge discussions with A. Michael and M. Kornbleuth. M.O. and J.D. were partially supported by NASA grants NNH13ZDA001N-GCR and NNX14AF42G. A.L. acknowledges support from the Breakthrough Prize Foundation.

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M.O. performed the numerical simulations with guidance and collaboration from G.T. The scientific analysis and discussion of the results were done by all authors. The manuscript was reviewed and edited by all authors.

Corresponding author

Correspondence to Merav Opher.

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Supplementary Information

Supplementary Figs. 1–5 and Table 1.

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Opher, M., Loeb, A., Drake, J. et al. A small and round heliosphere suggested by magnetohydrodynamic modelling of pick-up ions. Nat Astron 4, 675–683 (2020).

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