Nature 325, 418 - 419 (29 January 1987); doi:10.1038/325418a0

The formation of a magnetic-field-free cavity at comet Halley

W.-H. Ip & W. I. Axford

Max-Planck-Institut für Aeronomie, D-3411 Katlenburg-Lindau, FRG

One of the most important results of the Giotto mission to comet Halley was the discovery of a magnetic cavity surrounding the nucleus in which the magnetic field strength was apparently zero¹. The boundary of the cavity, the ionopause, occurred at 4,760 km (3,840 km) and the maximum magnetic field strength was 55 nT (65 nT), thousands of km outside the rather sharply defined transition to zero field on the inbound (outbound) part of the trajectory, respectively. We show here with the aid of a simple model that such a magnetic field structure can be explained as being largely the result of ion-neutral friction² rather than simple pressure-balance alone^3,4.

References

1.	Neubauer, F. M. et al. Nature 321, 352−355 (1986). | Article | ISI | ChemPort |
2.	Ip, W.-H. & Axford, W. I. in Comets (ed. Wilkening, L. L.) 588−634 (University of Arizona Press, Tucson, 1982). | ChemPort |
3.	Schmidt, H. U. & Wegman, R. in Comets (ed. Wilkening, L. L.) 538−560 (University of Arizona Press, Tucson, 1982). | ChemPort |
4.	Wallis, M. K. & Dryer, M. Astrophys. J. 205, 895−899 (1976). | Article | ISI |
5.	Axford, W. I., Cunnold, D. M. & Gleeson, L. J. Planet. Space Sci. 14, 909−919 (1966). | Article |
6.	Riedler, W., Schwingenschuh, K., Yeroshenko, Ye. G., Styashkin, V. A. & Russell, C. T. Nature 321, 288−299 (1986). | Article | ISI | ChemPort |
7.	Balsiger, H. et al. Nature 321, 330−334 (1986). | Article | ISI | ChemPort |
8.	Krankowsky, D. et al. Nature 321, 326−329 (1986). | Article | ISI | ChemPort |
9.	Mendis, D. A., Houpis, H. L. F. & Marconi, M. L. Fundamentals cosm. Phys. 10, 1−380 (1985). | ChemPort |
10.	Elphic, R. C. et al. J. geophys. Res. 85, 7679 (1980).
11.	Galeev, A. A. & Lipatov, A. S. Adv. Space Res. 4, 229−257 (1984).
12.	Ershkovich, A. I. & Mendis, D. A. Astrophys. J. 302, 849 (1986). | Article |