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Voyager 1 exited the solar wind at a distance of 85 au from the Sun


The outer limit of the Solar System is often considered to be at the distance from the Sun where the solar wind changes from supersonic to subsonic flow1. Theory predicts that a termination shock marks this boundary, with locations ranging2 from a few to over 100 au (1 au ≈ 1.5 × 108 km, the distance from Earth to the Sun). ‘Pick-up ions’ that originate3,4 as interstellar neutral atoms should be accelerated to tens of MeV at the termination shock, generating anomalous cosmic rays5,6,7. Here we report a large increase in the intensity of energetic particles in the outer heliosphere, as measured by an instrument on the Voyager 1 spacecraft. We argue that the spacecraft exited the supersonic solar wind and passed into the subsonic region (possibly beyond the termination shock) on about 1 August 2002 at a distance of 85 au (heliolatitude 34° N), then re-entered the supersonic solar wind about 200 days later at 87 au from the Sun. We show that the composition of the ions accelerated at the putative termination shock is that of anomalous cosmic rays and of interstellar pick-up ions.

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Figure 1: Intensity profiles at Voyager 1, Voyager 2 since late 2001.
Figure 2: Data from Voyager 1 LECP for 0.57–1.78 MeV protons.
Figure 3: Anisotropy plots of time-averaged sector rates for periods A, B and C noted in Fig. 1 and solar wind velocity fits thereof.
Figure 4: Composition spectra for the duration of Voyager 1's excursion into the heliosheath from LECP 2002/194 to 2003/044.


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

    Article  ADS  Google Scholar 

  2. Stone, E. C. News from the edge of interstellar space. Science 293, 55–56 (2001)

    Article  CAS  Google Scholar 

  3. Fisk, L. A., Kozlovsky, B. & Ramaty, R. An interpretation of the observed oxygen and nitrogen enhancements in low-energy cosmic rays. Astrophys. J. 190, L35–L37 (1974)

    Article  ADS  CAS  Google Scholar 

  4. Gloeckler, G. & Geiss, J. in AIP Conf. Proc. 598 Joint SOHO-ACE Workshop 2001 (ed. Wimmer-Schweinbruber, R.) 281–289 (AIP, Melville, NY, 2001)

    Google Scholar 

  5. Pesses, M. E., Jokipii, J. R. & Eichler, D. Cosmic ray drift, shock acceleration, and the anomalous component of cosmic rays. Astrophys. J. 246, L85–L88 (1981)

    Article  ADS  CAS  Google Scholar 

  6. Steenberg, C. D. & Moraal, H. Form of the anomalous cosmic ray spectrum at the solar wind termination shock. J. Geophys. Res. 104, 24879–24884 (1999)

    Article  ADS  Google Scholar 

  7. Fichtner, H. Anomalous cosmic rays: Messengers from the outer heliosphere. Space Sci. Rev. 95, 639–754 (2001)

    Article  ADS  CAS  Google Scholar 

  8. Krimigis, S. M. et al. The Low Energy Charged Particle (LECP) experiment on the Voyager spacecraft. Space Sci. Rev. 21, 329–354 (1977)

    Article  ADS  Google Scholar 

  9. McDonald, F. B. et al. Enhancements of energetic particles near the heliospheric termination shock. Nature 426 48–51 (2003)

    Article  ADS  CAS  Google Scholar 

  10. Decker, R. B., Krimigis, S. M., McNutt, R. L., Hamilton, D. C. & Collier, R. M. Latitude associated differences in the low energy charged particle activity at Voyagers 1 and 2 during 1991 to early 1994. Space Sci. Rev. 72, 347–352 (1995)

    Article  ADS  Google Scholar 

  11. Decker, R. B., Krimigis, S. M., Roelof, E. C. & Hill, M. E. Angular distributions and energy spectra of low-energy ions observed by Voyager 1 at 85–88 au. Geophys. Res. Abstr. 5, 03301 (2003).

  12. Roelof, E. C., Simnett, G. M., Sanderson, T. R. & Kunow, H. Corotating interaction regions at high latitudes. Space Sci. Rev. 89, 225–233 (1999)

    Google Scholar 

  13. Decker, R. B., Roelof, E. C. & Krimigis, S. M. in Acceleration and Transport of Energetic Particles in the Heliosphere (eds Mewaldt, R. A., Zurbuchen, T. H. & Cummings, A. C.) AIP Conf. Proc 528, 161–165 (AIP, Melville, NY, 2000)

    Google Scholar 

  14. Decker, R. B. The role of magnetic loops in particle acceleration at nearly perpendicular shocks. J. Geophys. Res. 98, 33–46 (1993)

    Article  ADS  Google Scholar 

  15. Sarris, E. T. & Krimigis, S. M. Quasi-perpendicular shock acceleration of ions to 200 MeV and electrons to 2 MeV observed by Voyager-2. Astrophys. J. 298, 676–683 (1985)

    Article  ADS  CAS  Google Scholar 

  16. Kane, M., Decker, R. B., Mauk, B. H. & Krimigis, S. M. The solar wind velocity determined from Voyager 1 and 2: Low Energy Charged Particle measurements in the outer heliosphere. J. Geophys. Res. 103, 267–276 (1998)

    Article  ADS  Google Scholar 

  17. Hill, M. E., Hamilton, D. C. & Krimigis, S. M. Evolution of anomalous cosmic-ray oxygen and helium energy spectra during the solar cycle 22 recovery phase in the outer heliosphere. Astrophys. J. 572, L169–L172 (2002)

    Article  ADS  Google Scholar 

  18. Burlaga, L. F. et al. Search for the heliosheath with Voyager 1 magnetic field measurements. Geophys. Res. Lett. (in the press)

  19. Fisk, L. A. Motion of the footpoints of heliospheric magnetic field lines at the sun: Implications for recurrent energetic particle events at high heliographic latitudes. J. Geophys. Res. 101, 15547–15553 (1996)

    Article  ADS  CAS  Google Scholar 

  20. Schwadron, N. A. & McComas, D. J. Heliospheric “FALTS”: Favored acceleration locations at the termination shock. Geophys. Res. Lett. 30, doi: 10.1029/2002GL016499 (2003)

  21. Izmodenov, V. V., Gloeckler, G. & Malama, V. When will Voyager 1 and 2 cross the termination shock? Geophys. Res. Lett. 30, 3–14 (2003)

    Article  Google Scholar 

  22. Fahr, H. J. & Rucinski, D. Neutral interstellar gas atoms reducing the solar wind Mach number and velocity. Astron. Astrophys. 350, 1071–1078 (1999)

    ADS  CAS  Google Scholar 

  23. Fahr, H. J., Kausch, T. & Scherer, H. A five fluid hydrodynamic approach to model the solar system-interstellar medium interaction. Astron. Astrophys. 357, 268–282 (2000)

    ADS  Google Scholar 

  24. Neugebauer, M. Spacecraft observations of the interaction of active comets with the solar wind. Rev. Geophys. 28, 231–252 (1990)

    Article  ADS  Google Scholar 

  25. Cargill, P. J., Hizanidis, K. & Papadopoulos, K. in Cometary and Solar Plasma Physics (ed. Buti, B.) (World Scientific, New York, 1988)

    Google Scholar 

  26. Gleeson, L. J. & Axford, W. I. The Compton-Getting effect. Astrophys. Space Sci. 2, 431–437 (1968)

    Article  ADS  Google Scholar 

  27. Roelof, E. C. in Lectures in High Energy Astrophysics (eds Ogelman, H. & Wayland, J. R.) Ch. VII (NASA SP-199, 1969)

    Google Scholar 

  28. Zwickl, R. D. & Roelof, E. C. Interplanetary propagation of <1 MeV protons in non-impulsive energetic particle events. J. Geophys. Res. 86, 5449 (1981)

    Article  ADS  CAS  Google Scholar 

  29. Parker, E. N. The passage of energetic charged particles through interplanetary space. Planet. Space Sci. 13, 9–49 (1965)

    Article  ADS  Google Scholar 

  30. Le Roux, J. A., Fichtner, H., Zank, G. P. & Ptuskin, V. S. Self-consistent injection and acceleration of pickup ions at the solar wind termination shock. Geophys. Res. Lett. 27, 2873–2876 (2000)

    Article  ADS  CAS  Google Scholar 

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This work was supported by a NASA grant to the Johns Hopkins University and by subcontracts at the University of Maryland and Fundamental Technologies.

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Correspondence to S. M. Krimigis.

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Krimigis, S., Decker, R., Hill, M. et al. Voyager 1 exited the solar wind at a distance of 85 au from the Sun. Nature 426, 45–48 (2003).

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