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Cosmic ray measurements from Voyager 2 as it crossed into interstellar space

Nature Astronomy volume 3, pages 1013–1018 (2019)Cite this article

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Abstract

The interaction of the interstellar and solar winds is complex, as revealed by differences in intensities and anisotropies of low-energy ions (>0.5 MeV per nucleon) originating inside the heliosphere and those of higher-energy Galactic cosmic rays (>70 MeV per nucleon) originating outside, in the Milky Way. On 5 November 2018, Voyager 2 observed a sharp decrease in the intensity of low-energy ions and a simultaneous increase in the intensity of cosmic rays, indicating that Voyager 2 had crossed the heliopause at 119 au and entered interstellar space about six years after Voyager 1. Unlike Voyager 1, which found that two interstellar flux tubes had invaded the heliosheath and served as precursors to the heliopause, Voyager 2 found no similar precursors. However, just beyond the heliopause Voyager 2 discovered a boundary layer, in which low-energy particles streamed outward along the magnetic field and cosmic ray intensities were only 90% of those further out.

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Fig. 1: Counting rates of different energetic particle species on Voyager 1 and Voyager 2 around the times of their crossings of the heliopause.
Fig. 2: Counting rates and particle pitch angles around the time of the Voyager 2 heliopause crossing.
Fig. 3: Voyager 2 counting rates, streaming index, magnetic field strength and particle pitch angles for the period from day 180 of 2018 to day 20 of 2019.
Fig. 4: Voyager 2 counting rates and particle pitch angles around the time of the particle anisotropy event.
Fig. 5: Rate of ~0.5–35 MeV protons from Voyager 2 averaged over three telescopes (LETs A, C and D) during a spacecraft roll manoeuvre on day 256 of 2018.
Fig. 6: Intensities of O nuclei with 5.4–13.9 MeV per nucleon in the vicinity of the Voyager 1 and Voyager 2 heliopause crossings.
Fig. 7: Energy spectra of electrons (e+ + e−), H nuclei and He nuclei observed by the CRS telescopes on Voyager 1 and Voyager 2.

Data availability

Most of the CRS data can be obtained by clicking on the DATA link at https://voyager.gsfc.nasa.gov/ and following other links to obtain rate and flux data. All data that were used in the figures can be provided by the corresponding author on request.

References

  1. Burlaga, L. F. & Ness, N. F. Voyager 1 observations of the interstellar magnetic field and the transition from the heliosheath. Astrophys. J. 784, 146–159 (2014).

    Article  ADS  Google Scholar 

  2. 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).

    Article  ADS  Google Scholar 

  3. 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).

    Article  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

  5. Stone, E. C. et al. Voyager 1 observes low-energy galactic cosmic rays in a region depleted of heliospheric ions. Science 341, 150–153 (2013).

    Article  ADS  Google Scholar 

  6. Florinski, V., Stone, E. C., Cummings, A. C. & le Roux, J. A. Energetic particle anisotropies at the heliospheric boundary. II. Transient features and rigidity dependence. Astrophys. J. 803, 47–54 (2015).

    Article  ADS  Google Scholar 

  7. Strumik, M., Czechowski, A., Grzedzielski, S., Macek, W. M. & Ratkiewicz, R. Small-scale local phenomena related to the magnetic reconnection and turbulence in the proximity of the heliopause. Astrophys. J. Lett. 773, L23–L27 (2013).

  8. Strumik, M., Grzedzielski, S., Czechowski, A., Macek, W. M. & Ratkiewicz, R. Advective transport of interstellar plasma into the heliosphere across the reconnecting heliopause. Astrophys. J. Lett. 782, L7–L11 (2014).

  9. Strauss, R. D., Potgieter, M. S., Ferreira, S. E. S., Fichtner, H. & Scherer, K. Cosmic ray modulation beyond the heliopause: a hybrid modeling approach. Astrophys. J. Lett. 765, L18–L23 (2013).

  10. Luo, X. et al. A numerical simulation of cosmic ray modulation near the heliopause. II. Some physical insights. Astrophys. J. 826, 182–191 (2016).

    Article  ADS  Google Scholar 

  11. Cummings, A. C. et al. Galactic cosmic rays in the local interstellar medium: Voyager 1 observations and model results. Astrophys. J. 831, 18–38 (2016).

    Article  ADS  Google Scholar 

  12. Washimi, H., Tanaka, T. & Zank, G. P. Time-varying heliospheric distance to the heliopause. Astrophys. J. 846, L9–L14 (2017).

    Article  ADS  Google Scholar 

  13. Burlaga, L. F. et al. Magnetic field and particle measurements made by Voyager 2 at and near the heliopause. Nat. Astron. https://doi.org/10.1038/s41550-019-0920-y (2019).

  14. Gurnett, D. A. & Kurth, W. S. Plasma densities near and beyond the heliopause from the Voyager 1 and 2 plasma wave instruments. Nat. Astron. https://doi.org/10.1038/s41550-019-0918-5 (2019).

  15. Krimigis, S. M. et al. Energetic charged particle measurements from Voyager 2 at the heliopause and beyond. Nat. Astron. https://doi.org/10.1038/s41550-019-0927-4 (2019).

  16. Richardson, J. D., Belcher, J. W., Garcia-Galindo, P. & Burlaga, L. F. Voyager 2 plasma observations of the heliopause and interstellar medium. Nat. Astron. https://doi.org/10.1038/s41550-019-0929-2 (2019).

  17. Stone, E. C. et al. Cosmic ray investigation for the Voyager missions: energetic particle studies in the outer heliosphere—and beyond. Space Sci. Rev. 21, 355–376 (1977).

    ADS  Google Scholar 

  18. Fisk, L. A., Kozlovsky, B. & Ramaty, R. An interpretation of the observed oxygen and nitrogen enhancements in low-energy cosmic rays. Astrophys. J. Lett. 190, L35–L38 (1974).

    Article  ADS  Google Scholar 

  19. Pesses, M. E., Jokipii, J. R. & Eichler, D. Cosmic ray drift, shock wave acceleration, and the anomalous component of cosmic rays. Astrophys. J. Lett. 246, L85–L89 (1981).

    Article  ADS  Google Scholar 

  20. Strauss, R. D. & Fichtner, H. Cosmic ray anisotropies near the heliopause. Astron. Astrophys. 572, L3–L6 (2014).

    Article  ADS  Google Scholar 

  21. Potgieter, M. S., Vos, E. E., Munini, R., Boezio, M. & Di Felice, V. Modulation of galactic electrons in the heliosphere during the unusual solar minimum of 2006-2009: a modeling approach. Astrophys. J. 810, 141–150 (2015).

    Article  ADS  Google Scholar 

  22. Aguilar, M. et al. Precision measurement of the (e + + e −) flux in primary cosmic rays from 0.5 GeV to 1 TeV with the Alpha Magnetic Spectrometer on the International Space Station. Phys. Rev. Lett. 113, 221102 (2014).

    Article  ADS  Google Scholar 

  23. Shikaze, Y. et al. Measurements of 0.2–20 GeV/n cosmic-ray proton and helium spectra from 1997 through 2002 with the BESS spectrometer. Astropart. Phys. 28, 154–167 (2007).

    Article  ADS  Google Scholar 

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Acknowledgements

We thank L. Burlaga for providing magnetic field data before publication. A.C.C. acknowledges support from the International Space Sciences Institute in Bern, Switzerland, to participate in the international team The Physics of the Very Local Interstellar Medium in the autumn of 2018. This work was supported by NASA under grant NNN12AA01C.

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Authors and Affiliations

  1. California Institute of Technology, Pasadena, CA, USA

    Edward C. Stone & Alan C. Cummings

  2. NASA/Goddard Space Flight Center, Greenbelt, MD, USA

    Bryant C. Heikkila & Nand Lal

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  1. Edward C. Stone
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Contributions

All authors contributed to the production of this manuscript. A.C.C. and E.C.S. wrote the text. A.C.C., B.C.H. and N.L. performed the data analysis and A.C.C. and B.C.H. prepared the figures. All authors participated in reviewing and commenting on the paper and on the editor’s and referees’ comments.

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Correspondence to Edward C. Stone.

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Peer review information Nature Astronomy thanks Horst Fichtner and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Stone, E.C., Cummings, A.C., Heikkila, B.C. et al. Cosmic ray measurements from Voyager 2 as it crossed into interstellar space. Nat Astron 3, 1013–1018 (2019). https://doi.org/10.1038/s41550-019-0928-3

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