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.

  • Letter
  • Published:

Domination of heliosheath pressure by shock-accelerated pickup ions from observations of neutral atoms

Nature volume 454, pages 81–83 (2008)Cite this article

Abstract

The solar wind blows an immense magnetic bubble, the heliosphere, in the local interstellar medium (mostly neutral gas) flowing by the Sun1. Recent measurements by Voyager 2 across the termination shock, where the solar wind is slowed to subsonic speeds before entering the heliosheath, found that the shocked solar wind plasma2 contains only ∼20 per cent of the energy released by the termination shock, whereas energetic particles3 above ∼28 keV contain only ∼10 per cent; ∼70 per cent of the energy is unaccounted for, leading to speculation2,3 that the unmeasured pickup ions or energetic particles below 28 keV contain the missing energy. Here we report the detection and mapping of heliosheath energetic (∼4–20 keV) neutral atoms produced by charge exchange of suprathermal ions with interstellar neutral atoms. The energetic neutral atoms come from a source ∼60° wide in longitude straddling the direction of the local interstellar medium. Their energy spectra resemble those of solar wind pickup ions, but with a knee at ∼11 keV instead of ∼4 keV, indicating that their parent ions are pickup ions energized by the termination shock. These termination-shock-energized pickup ions contain the missing ∼70 per cent of the energy dissipated in the termination shock, and they dominate the pressure in the heliosheath.

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

Figure 1: The flow direction of energetic neutral atoms in the ecliptic plane.
Figure 2: The temporal variation of the 6.8 keV hydrogen ENA flux.
Figure 3: The map of the heliosheath source of ENAs versus ecliptic longitude.
Figure 4: Energy spectra of the particles.

Similar content being viewed by others

References

  1. Axford, W. I. et al. in Solar Wind (eds Sonett, G. P., Coleman, P. J. Jr & Wilcox, J. M.) 609–660 (Spec. Publ. 308, NASA, Washington DC, 1972)

    Google Scholar 

  2. Richardson, J. D., Kasper, J. C., Wang, C., Belcher, J. W. & Lazarus, A. J. Cool heliosheath plasma and deceleration of the upstream solar wind at the termination shock. Nature 10.1038/nature07024 (this issue)

  3. Decker, R. B. et al. Mediation of the solar wind termination shock by non-thermal ions. Nature 10.1038/nature07030 (this issue)

  4. Gruntman, M. et al. Energetic neutral atom imaging of the heliospheric boundary region. J. Geophys. Res. 106, 15767–15781 (2001)

    Article  CAS  ADS  Google Scholar 

  5. Lin, R. P. et al. The STEREO IMPACT Suprathermal Electron (STE) instrument. Space Sci. Rev. 10.1007/s11214-008-9330-7 (in the press)

  6. Luhmann, J. G. et al. STEREO IMPACT investigation goals, measurements, and data products overview. Space Sci. Rev. 10.1007/s11214-007-9170-x (in the press)

  7. Heerikhuisen, J. et al. The effects of global heliospheric asymmetries on energetic neutral atom sky maps. Astrophys. J. 655, L53–L56 (2007)

    Article  ADS  Google Scholar 

  8. Hilchenbach, M. et al. Detection of 55–80 keV hydrogen atoms of heliospheric origin by CELIAS/HSTOF on SOHO. Astrophys. J. 503, 916–922 (1998)

    Article  CAS  ADS  Google Scholar 

  9. Galli, A. et al. Direct measurements of energetic neutral hydrogen in the interplanetary medium. Astrophys. J. 644, 1317–1325 (2006)

    Article  CAS  ADS  Google Scholar 

  10. Wurz, P. et al. in Physics of the Inner Heliosheath (eds Heerikhuisen, J., Florinski, V., Zank, G. P. & Pogorelov, N. V.) 269–275 (AIP Conf. Proc. 858, AIP, New York, 2006)

    Google Scholar 

  11. Collier, M. R. et al. An unexplained 10–40° shift in the location of some diverse neutral atom data at 1 AU. Adv. Space Res. 34, 166–171 (2004)

    Article  CAS  ADS  Google Scholar 

  12. Witte, M. et al. Kinetic parameters of interstellar neutral helium: Final results from the ULYSSES/GAS Instrument. Adv. Space Res. 34, 61–65 (2004)

    Article  CAS  ADS  Google Scholar 

  13. Gloeckler, G. et al. Observations of the helium focusing cone with pickup ions. Astron. Astrophys. 426, 845–854 (2004)

    Article  CAS  ADS  Google Scholar 

  14. Decker, R. B. et al. in Physics of the Inner Heliosheath (eds Heerikhuisen, J., Florinski, V., Zank, G. P. & Pogorelov, N. V.) 73–78 (AIP Conf. Proc. 858, AIP, New York, 2006)

    Google Scholar 

  15. Gloeckler, G. & Fisk, L. A. in Physics of the Inner Heliosheath (eds Heerikhuisen, J., Florinski, V., Zank, G. P. & Pogorelov, N. V.) 153–158 (AIP Conf. Proc. 858, AIP, New York, 2006)

    Google Scholar 

  16. Fisk, L. A. et al. Acceleration of low-energy ions at the termination shock of the solar wind. Astrophys. J. 644, 631–637 (2006)

    Article  ADS  Google Scholar 

  17. Richardson, J. D., Paularena, K. I., Lazarus, A. J. & Belcher, J. W. Evidence for a solar wind slowdown in the outer heliosphere? Geophys. Res. Lett. 22, 1469–1472 (1995)

    Article  ADS  Google Scholar 

  18. Burlaga, L. F. et al. Magnetic fields at the solar wind termination shock. Nature 10.1038/nature07029 (this issue)

Download references

Acknowledgements

We thank R. Mewaldt for suggestions, G. Gloeckler and E. Roelof for discussions, D. Curtis for instrument development and explanations of calibration data, and the Voyager team for sharing their results before publication. This research was supported in part by the National Aeronautics and Space Administration.

Author Contributions L.W. analysed the data and wrote the paper with direction and help from R.P.L. R.P.L. designed the Suprathermal Electron instrument and is the co-investigator in charge. D.E.L. assisted with the experimental work. J.G.L. is the principal investigator of the IMPACT investigation on STEREO that includes STE.

Author information

Authors and Affiliations

  1. Physics Department, University of California, Berkeley, California 94720-7300, USA,

    Linghua Wang & Robert P. Lin

  2. Space Sciences Laboratory, University of California, Berkeley, California 94720-7450, USA ,

    Linghua Wang, Robert P. Lin, Davin E. Larson & Janet G. Luhmann

Authors
  1. Linghua Wang
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Robert P. Lin
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Davin E. Larson
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Janet G. Luhmann
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to Linghua Wang.

Supplementary information

Supplementary information

This file contains Supplementary Discussion; Supplementary Figure S1 with Legend; Supplementary Table 1 with Legend; and additional references. The Supplementary Discussion includes more detailed instrumentation for detection of energetic neutral atoms, data analysis methods and limitation. The Supplementary Figure S1 shows an example of energetic neutral atom observations by STE. The Supplementary Table 1 summarizes the changes in the energy densities and number densities of various plasma/energetic particle populations and magnetic fields across the termination shock. (PDF 258 kb)

PowerPoint slides

Rights and permissions

Reprints and permissions

About this article

Cite this article

Wang, L., Lin, R., Larson, D. et al. Domination of heliosheath pressure by shock-accelerated pickup ions from observations of neutral atoms. Nature 454, 81–83 (2008). https://doi.org/10.1038/nature07068

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nature07068

This article is cited by

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

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