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An asymmetric solar wind termination shock

Abstract

Voyager 2 crossed the solar wind termination shock at 83.7 au in the southern hemisphere, 10 au closer to the Sun than found by Voyager 1 in the north1,2,3,4. This asymmetry could indicate an asymmetric pressure from an interstellar magnetic field5,6, from transient-induced shock motion7, or from the solar wind dynamic pressure. Here we report that the intensity of 4–5 MeV protons accelerated by the shock near Voyager 2 was three times that observed concurrently by Voyager 1, indicating differences in the shock at the two locations. (Companion papers report on the plasma8, magnetic field9, plasma-wave10 and lower energy particle11 observations at the shock.) Voyager 2 did not find the source of anomalous cosmic rays at the shock, suggesting that the source is elsewhere on the shock12,13,14 or in the heliosheath15,16,17,18,19. The small intensity gradient of Galactic cosmic ray helium indicates that either the gradient is further out in the heliosheath20 or the local interstellar Galactic cosmic ray intensity is lower than expected21.

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$32.00 All prices are NET prices. References 1. Stone, E. C. et al. Voyager 1 explores the termination shock region and the heliosheath beyond. Science 309, 2017–2020 (2005) 2. Burlaga, L. F. et al. Crossing the termination shock into the heliosheath: Magnetic fields. Science 309, 2027–2029 (2005) 3. Decker, R. B. et al. Voyager 1 in the foreshock, termination shock, and heliosheath. Science 309, 2020–2024 (2005) 4. Gurnett, D. A. & Kurth, W. S. Electron plasma oscillations upstream of the solar wind termination shock. Science 309, 2025–2027 (2005) 5. Opher, M., Stone, E. C. & Liewer, P. C. The effects of a local interstellar magnetic field on Voyager 1 and 2 observations. Astrophys. J. 640, L71–L74 (2006) 6. Pogorelov, N. V., Stone, E. C., Florinski, V. & Zank, G. P. Termination shock asymmetries as seen by the Voyager spacecraft: The role of the interstellar magnetic field and neutral hydrogen. Astrophys. J. 668, 611–624 (2007) 7. Washimi, H., Zank, G. 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Astrophys. J. 611, L141–L144 (2004) Download references Acknowledgements This work was supported by NASA (NAS7-03001). Author information Authors and Affiliations Authors Corresponding author Correspondence to Edward C. Stone. PowerPoint slides PowerPoint slide for Fig. 1 PowerPoint slide for Fig. 2 PowerPoint slide for Fig. 3 Rights and permissions Reprints and Permissions About this article Cite this article Stone, E., Cummings, A., McDonald, F. et al. An asymmetric solar wind termination shock. Nature 454, 71–74 (2008). https://doi.org/10.1038/nature07022 Download citation • Received: • Accepted: • Issue Date: • DOI: https://doi.org/10.1038/nature07022 This article is cited by • Backscattered Solar Lyman-$\alpha \$ Emission as a Tool for the Heliospheric Boundary Exploration

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