The bubble-like shape of the heliosphere observed by Voyager and Cassini


For more than five decades, the shape and interactions of the heliosphere with the local interstellar medium have been discussed in the context of two competing models, posited in 19611: a magnetosphere-like heliotail and a more symmetric bubble shape. Although past models broadly assumed the magnetosphere-like concept, the accurate heliospheric configuration remained largely undetermined due to lack of measurements. In recent years, however, Voyagers 1 and 2 (V1 and V2) crossed the termination shock — the boundary where the solar wind drops — north and south of the ecliptic plane at 94 au2,3 and 84 au4 in 2004 and 2007, respectively, and discovered the reservoir of ions and electrons that constitute the heliosheath, while Cassini remotely imaged the heliosphere5 for the first time in 2003. Here we report 5.2–55 keV energetic neutral atom (ENA) global images of the heliosphere obtained with the Cassini/Ion and Neutral Camera (INCA). We compare them with 28–53 keV ions measured within the heliosheath by the low-energy charged particle (LECP) experiment onboard V1 and V2 over an 11-year period (2003–2014). We show that the heliosheath ions are the source of ENA. These observations also demonstrate that the heliosphere responds promptly, within ~2–3 years, to outward propagating solar wind changes in both the nose and tail directions. These results, together with the V1 measurement of a ~0.5 nT interstellar magnetic field6 and the enhanced ratio between particle pressure and magnetic pressure in the heliosheath7, strongly suggest a diamagnetic bubble-like heliosphere with few substantial tail-like features. Our results are consistent with recent modelling811.

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Figure 1: Conceptual models of the global heliosphere.
Figure 2: ENAs and ions in the heliosheath compared with SSN.
Figure 3: ‘Ground truth’ ENA-ion intensities in the heliosphere.


  1. 1

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

    ADS  Article  Google Scholar 

  2. 2

    Decker, R. B . et al. Voyager 1 in the foreshock, termination shock, and heliosheath. Science 309, 2020–2024 (2005).

    ADS  Article  Google Scholar 

  3. 3

    Stone, E. C . et al. Voyager 1 explores the termination shock region and the heliosheath beyond. Science 309, 2012–2020 (2005).

    ADS  Google Scholar 

  4. 4

    Decker, R. B. et al. Mediation of the solar wind termination shock by non-thermal ions. Nature 454, 67–70 (2008).

    ADS  Article  Google Scholar 

  5. 5

    Krimigis, S. M., Mitchell, D. G., Roelof, E. C., Hsieh, K. C. & McComas, D. J. Imaging the interaction of the heliosphere with the interstellar medium from Saturn with Cassini. Science 326, 971–973 (2009).

    ADS  Article  Google Scholar 

  6. 6

    Burlaga, L. F., Ness, N. F. & Stone, E. C. Magnetic field observations as Voyager 1 entered the heliosheath depletion region. Science 341, 147–150 (2013).

    ADS  Article  Google Scholar 

  7. 7

    Krimigis, S. M., Mitchell, D. G., Roelof, E. C. & Decker, R. B. ENA (E>5 keV) images from Cassini and Voyager “ground truth”: suprathermal pressure in the heliosheath AIP Conf. Proc. 1302, 79 (2010).

    ADS  Article  Google Scholar 

  8. 8

    Opher, M., Drake, J. F., Zieger, B. & Gombosi, T. I. Magnetized jets driven by the Sun: the structure of the heliosphere revisited. Astrophys. J. Lett. 800, 7 (2015).

    Article  Google Scholar 

  9. 9

    Drake, J. F., Swisdak, M. & Opher, M. A model of the heliosphere with jets. Astrophys. J. Lett. 808, 6 (2015).

    Article  Google Scholar 

  10. 10

    Kivelson, M. G. & Jia, X. An MHD model of Ganymede's mini-magnetosphere suggests that the heliosphere forms in a sub-Alfvénic flow. J. Geophys. Res. 118, 6839–6846 (2013).

    Article  Google Scholar 

  11. 11

    Izmodenov, V. V. & Alexashov, D. B. Three-dimensional kinetic-MHD model of the global heliosphere with the heliopause-surface fitting. Astrophys. J. Suppl. S. 220, 14 (2015).

    ADS  Article  Google Scholar 

  12. 12

    Dialynas, K., Krimigis, S. M., Mitchell, D. G., Roelof, E. C. & Decker, R. B. A three-coordinate system (ecliptic, galactic, ISMF) spectral analysis of heliospheric ENA emissions using Cassini/INCA measurements. Astrophys. J. 778, 13 (2013).

    Article  Google Scholar 

  13. 13

    Dialynas, K ., Krimigis, S. M ., Mitchell, D. G ., Roelof, E. C & Decker, R. B. Energetic Neutral Atom (ENA) intensity gradients in the heliotail during year 2003, using Cassini/INCA measurements. J. Phys. Conf. Ser. 577, 012007 (2015).

    Article  Google Scholar 

  14. 14

    McComas, D. J. et al. Global observations of the interstellar interaction from the Interstellar Boundary Explorer (IBEX). Science 326, 959 (2009).

    ADS  Article  Google Scholar 

  15. 15

    Dayeh, M. A. et al. Spectral properties of regions and structures in the Interstellar Boundary Explorer (IBEX) sky maps. Astrophys. J. 734, 29 (2011).

    ADS  Article  Google Scholar 

  16. 16

    Reisenfeld, D. et al. Tracking the solar cycle through IBEX observations of energetic neutral atom flux variations at the heliospheric poles. Astrophys. J. 833, 2 (2016).

    Article  Google Scholar 

  17. 17

    Schwadron, N. et al. Separation of the Interstellar Boundary Explorer ribbon from the globally distributed Energetic Neutral Atom flux. Astrophys. J. 731, 22 (2011).

    Article  Google Scholar 

  18. 18

    Sokół, J. M., Swaczyna, P., Bzowski, M. & Tokumaru, M. Reconstruction of helio-latitudinal structure of the solar wind proton speed and density. Solar Phys. 290, 2589–2615 (2015).

    ADS  Article  Google Scholar 

  19. 19

    McComas, D. J. et al. Weakest solar wind of the space age and the current “mini” solar maximum. Astrophys. J. 779, 10 (2013).

    ADS  Article  Google Scholar 

  20. 20

    Krimigis, S. M., Roelof, E. C., Decker, R. B. & Hill, M. E. Zero outward flow velocity for plasma in a heliosheath transition layer. Nature 474, 359–361 (2011).

    ADS  Article  Google Scholar 

  21. 21

    McComas, D. J., Dayeh, M. A., Funsten, H. O., Livadiotis, G. & Schwadron, N. A. The heliotail revealed by the Interstellar Boundary Explorer. Astrophys. J. 771, 77 (2013).

    ADS  Article  Google Scholar 

  22. 22

    Livadiotis, G., McComas, D. J., Dayeh, M. A., Funsten, H. O. & Schwadron, N. A. First sky map of the inner heliosheath temperature using IBEX spectra. Astrophys. J. 734, 19 (2011).

    Article  Google Scholar 

  23. 23

    Zhang, J, Woch, J., Solanki, S. K. & Steiger, R. The Sun at solar minimum: north–south asymmetry of the polar coronal holes. Geophys. Res. Lett. 29, 1236 (2002).

    ADS  Google Scholar 

  24. 24

    Opher, M., Stone, E. C., Liewer, P. C. & Gombosi, T. Global asymmetry of the heliosphere. Phys. Inner Heliosheath 858, 45–50 (2006).

    ADS  Google Scholar 

  25. 25

    Roelof, E. C ., Krimigis, S. M ., Mitchell, D. G ., Decker, R. B & Dialynas, K. Cassini ENA images of the heliosheath and Voyager “ground truth”: thickness of the heliosheath. AIP Conf. Proc. 1436, 239 (2012).

    ADS  Article  Google Scholar 

  26. 26

    Heerikhuisen, J., Zirnstein, E. J., Funsten, H. O., Pogorelov, N. V. & Zank, G. P. The effect of new interstellar medium parameters on the heliosphere and energetic neutral atoms from the interstellar boundary. Astrophys. J. 784, 73 (2014).

    ADS  Article  Google Scholar 

  27. 27

    Burlaga, L. F. & Ness, N. F. Interstellar magnetic fields observed by Voyager 1 beyond the heliopause. Astrophys. J. Lett. 795, 5 (2014).

    Article  Google Scholar 

  28. 28

    Opher, M. et al. A strong, highly-tilted interstellar magnetic field near the Solar System. Nature 462, 7276 (2009).

    Article  Google Scholar 

  29. 29

    Gurnett, D. A., Kurth, W. S., Burlaga, L. F. & Ness, N. F. In situ observations of interstellar plasma with Voyager 1. Science 341, 1489–1492 (2013).

    ADS  Article  Google Scholar 

  30. 30

    Wood, B. E., Izmodenov, V. V., Alexashov, D. B., Redfield, S. & Edelman, E. A new detection of LYα absorption from the heliotail. Astrophys. J. 780, 12 (2014).

    Google Scholar 

  31. 31

    Galli, A. et al. The roll-over of heliospheric neutral hydrogen bellow 100 eV: observations and implications. Astrophys. J. 821, 10 (2016).

    Article  Google Scholar 

  32. 32

    McComas, D. J. et al. The heliosphere’s interstellar interaction: no bow shock. Science 336, 1291 (2012).

    ADS  Article  Google Scholar 

  33. 33

    Zieger, B., Opher, M., Schwadron, N. A., McComas, D. J. & Tóth, G. A slow bow shock ahead of the heliosphere. Geophys. Res. Lett. 40, 12 (2013).

    Article  Google Scholar 

  34. 34

    Fahr, H. J. Is the heliospheric interface submagnetosonic? Consequences for the LISM presence in the heliosphere. Adv. Space. Res. 6, 13– 25 (1986).

    ADS  Article  Google Scholar 

  35. 35

    Opher, M., Stone, E. C. & Gombosi, T. I. The orientation of the local interstellar magnetic field. Science 316, 875–878 (2007).

    ADS  Article  Google Scholar 

  36. 36

    Krimigis, S. M . et al. Search for the exit: Voyager 1 at heliosphere’s border with the Galaxy. Science 341, 144–147 (2013).

    ADS  Article  Google Scholar 

  37. 37

    Krimigis, S. M. et al. Magnetosphere Imaging Instrument (MIMI) on the Cassini mission to Saturn/Titan. Space Sci. Rev. 114, 233 (2004).

    ADS  Article  Google Scholar 

  38. 38

    Krimigis, S. M., Sergis, S., Mitchell, D. G., Hamilton, D. C. & Krupp, N. A dynamic, rotating ring current around Saturn. Nature 450, 1050–1053 (2007).

    ADS  Article  Google Scholar 

  39. 39

    Markwardt, C. B. Non-linear least squares fitting in IDL with MPFIT. In Proc. Astronomical Data Analysis Software and Systems XVIII (eds Bohlender, D., Dowler, P. & Durand, D.) 251–254 (ASP Conf. Series 411, 2009).

  40. 40

    Levenberg, K. A method for the solution of certain nonlinear problems in least squares. Quart. Appl. Math. 2, 164–168 (1944).

    MathSciNet  Article  Google Scholar 

  41. 41

    Marquardt, D. W. An algorithm for least squares estimation of nonlinear parameters. SIAM J. Appl. Math. 11, 431–441 (1963).

    MathSciNet  Article  Google Scholar 

  42. 42

    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 

  43. 43

    Burlaga, L. F. et al. Crossing the termination shock into the heliosheath: magnetic fields. Science 309, 2020–2024 (2005).

    ADS  Article  Google Scholar 

  44. 44

    Katushkina, O. A., Izmodenov, V. V., Quemerais, E. & Sokół, J. M. Heliolatitudinal and time variations of the solar wind mass flux: inferences from the backscattered solar Lyman-alpha intensity maps. J. Geophys. Res. 118, 2800–2808 (2013).

    Article  Google Scholar 

  45. 45

    Fahr, H.-J., Fichtner, H. & Scherer, K. Theoretical aspects of energetic neutral atoms as messengers from distant plasma sites with emphasis on the heliosphere. Rev. Geophys. 45, 4 (2007).

    Article  Google Scholar 

  46. 46

    Katushkina, O. A. & Izmodenov, V. V. Effect of the heliospheric interface on the distribution of interstellar hydrogen atom inside the heliosphere. Astron. Lett. 36, 297–330 (2010).

    ADS  Article  Google Scholar 

  47. 47

    Decker, R. B., Krimigis, S. M., Roelof, E. C. & Hill, M. E. No meridional plasma flow in the heliosheath transition region. Nature 489, 124–127 (2012).

    ADS  Article  Google Scholar 

  48. 48

    Richardson, J. D., Wang, C. & Paularena, K. I. The solar wind: from solar minimum to solar maximum. Adv. Space Res. 27, 471–479 (2001).

    ADS  Article  Google Scholar 

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This work was supported at JHU/APL by NASA under contract NAS5 97271 and NNX07AJ69G and by subcontract at the Office for Space Research and Technology. The authors are grateful to M. Kusterer for software development and assistance with the INCA data processing and Dogfish graphic designers ( for assistance with graphics in Fig. 1a.

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All authors were actively involved in all aspects of this manuscript. K.D. contributed most of the text and carried out most of the data analysis; S.M.K., D.G.M. and E.C.R. contributed to the text and provided most of the theory and interpretations; R.B.D. and S.M.K. performed the Voyager ion data analysis; D.G.M. oversaw the Cassini/INCA data.

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Correspondence to K. Dialynas.

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Supplementary Table 1, Supplementary Figures 1–3 and Supplementary References. (PDF 756 kb)

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Dialynas, K., Krimigis, S., Mitchell, D. et al. The bubble-like shape of the heliosphere observed by Voyager and Cassini. Nat Astron 1, 0115 (2017).

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