Nature 386, 374 - 377 (27 March 1997); doi:10.1038/386374a0

Anomalously small magnetic field in the local interstellar cloud

George Gloeckler^*†, L. A. Fisk^† & Johannes Geiss^‡

^* Department of Physics, University of Maryland, College Park, Maryland 20742, USA
^† Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA
^‡ International Space Science Institute, Hallerstrasse 6, CH-3012 Bern, Switzerland

The solar wind carves out a cavity, known as the heliosphere, in the warm local interstellar cloud, which is itself embedded in a larger hot cloud. It is generally assumed that there is an overall pressure balance between these three regions. Thermal pressure and magnetic field pressure in the local interstellar cloud should therefore balance the inward pressure from the hot cloud^1–3, and determine the size of the heliosphere. Here we present direct measurements of the density and speed of interstellar hydrogen and helium ions deep inside the Solar System, from which we derive the thermal pressure in the local interstellar cloud. Combined with the fact that the magnetic field strength in the local cloud is constrained to be less than 4.3 G (to be compatible with the fact that the Voyager 1 spacecraft has yet to encounter the heliosphere termination shock), the total pressure that we infer is insufficient to balance the inward pressure from the hot cloud. We conclude that either the magnetic field in the local cloud is inhomogeneous, or there is a significant, as yet undetected, non-thermal component to the pressure in the local cloud.

1. Bowyer, S., Lieu, R., Sidher, S. D., Lampton, M. & Kunde, J. Nature 375, 212−214 (1995). | Article | ChemPort |
2. Cox, D. Nature 375, 185−186 (1995). | Article | ChemPort |
3. Cox, D. P. & Reynolds, R. J. Annu. Rev. Astron. Astrophys. 25, 303−344 (1987). | Article | ISI | ChemPort |
4. Möbius, E. et al. Nature 318, 426−429 (1985). | Article | ISI |
5. Gloeckler, G. et al. Science 261, 70−73 (1993). | ISI | ChemPort |
6. Gloeckler, G. & Geiss, J. Nature 381, 210−212 (1996). | Article | ChemPort |
7. Gloeckler, G. in Proc. 1st ISSI Workshop (eds von Steiger, R., Lallement, R. & Lee, M. A.) Space Sci. Rev. 78, 335−346 (1996). | Article | ChemPort |
8. Holzer, T. E. Annu. Rev. Astron. Astrophys. 27, 199−234 (1989). | Article | ChemPort |
9. Baranov, V. B. & Malama, Y. G. J. Geophys. Res. 100, 755−761 (1995).
10. Williams, L. L., Hall, D. T., Pauls, H. L. & Zank, G. P. Astrophys. J. (submitted).
11. Steinolfson, R. S. & Gurnett, D. A. Geophys. Res. Lett. 22, 651−654 (1995). | Article |
12. Gloeckler, G. et al. Astron. Astrophys. Suppl. Ser. 92, 267−289 (1992). | ISI | ChemPort |
13. Witte, M., Rosenbauer, H., Banaskiewicz, M. & Fahr, H. J. Adv. Space Res. 13, 121−126 (1993). | ChemPort |
14. Thomas, G. E. Annu. Rev. Earth Planet. Sci. 6, 173−204 (1978). | Article | ChemPort |
15. Quemerais, E., Bertaux, J.-L., Sandel, B. R. & Lallement, R. Astron. Astrophys. 290, 941−954 (1996).
16. Vallerga, J. in Proc. 1st ISSI Workshop (eds von Steiger, R., Lallement, R. & Lee, M. A.) Space Sci. Rev. 78, 277−288 (1996). | Article | ChemPort |
17. Frisch, P. C. Space Sci. Rev. 72, 499−592 (1995). | Article | ChemPort |
18. Siscoe, G. L. in Solar System Magnetohydrodynamics: Concepts and Basic Equations in Solar Terrestrial Physics (eds Carovillano, R. L. & Forbes, J. M.) 74−76 (Reidel, Dordrecht, 1983).
19. Stone, E. C., Cummings, A. C. & Webber, W. R. J. Geophys. Res. 101, 11017−11025 (1996). | Article |
20. Frisch, P. C. in Cosmic Winds and the Heliosphere (eds Jokipii, J. R., Sonett, C. P. & Giampapa, M. S.) (Univ. Arizona Press, Tucson, in the press).
21. Dupuis, J., Vennes, S., Bowyer, S., Pradhan, A. K. & Thejll, P. Astrophys. J. 455, 574−589 (1995). | Article | ChemPort |
22. Cheng, K.-P. & Bruhweiler, F. C. Astrophys. J. 364, 573−581 (1990). | Article | ChemPort |
23. Burlaga, L. F., Ness, N. F., Belcher, J. W., Lazarus, A. J. & Richardson, J. D. in Proc. 1st ISSI Workshop (eds von Steiger, R., Lallement, R. & Lee, M. A.) Space Sci. Rev. 78, 33−42 (1996). | Article |
24. Geiss, J. & Witte, M. in Proc. 1st ISSI Workshop (eds von Steiger, R., Lallement, R. & Lee, M. A.) Space Sci. Rev. 78, 229−238 (1996). | Article | ChemPort |
25. Anders, E. & Grevesse, N. Geochim. Cosmochim. Acta. 53, 197−214 (1988). | Article | ISI |
26. Fite, W. L., Smith, A. C. H. & Stebbings, R. F. Proc. R. Soc. Land. A 268, 527−534 (1962). | ChemPort |
27. Lallement, R., Bertaux, J.-L. & Clarke, J. T. Science 260, 1095−1098 (1993). | ChemPort |
28. Janev, R. K., Langer, W. D., Evans, K. Jr & Post, D. E. Elementary Processes in Hydrogen-Helium Plasmas (Cross Sections and Reaction Rate Coefficients) (Springer, Berlin, 1987).
29. Gloeckler, G., Schwadron, N. A., Fisk, L. A. & Geiss, J. Geophys. Res. Lett. 22, 2665−2668 (1995). | Article | ChemPort |
30. Fisk, L. A., Schwadron, N. A. & Gloeckler, G. Geophys. Res. Lett. 24, 93−96 (1997). | Article |
31. Rucinski, D. et al. Proc. 1st ISSI Workshop (eds von Steiger, R., Lallement, R. & Lee, M. A.) Space Sci. Rev. 78, 73−84 (1996). | ChemPort |