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Science 15 December 1989:
Vol. 246. no. 4936, pp. 1473 - 1478
DOI: 10.1126/science.246.4936.1473
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Articles

Magnetic Fields at Neptune

Norman F. Ness 1, Mario H. Acuña 2, Leonard F. Burlaga 2, John E. P. Connerney 2, Ronald P. Lepping 2, and Fritz M. Neubauer 3

1 Bartol Research Institute, University of Delaware, Newark, DE 19716
2 Laboratory for Extraterrestrial Physics, NASA Goddard Space Flight Center, Greenbelt, MD 20771
3 Institut für Geophysik und Meteorologie, Universität zu Koln, D-5000 Koln 41, Federal Republic of Germany

The National Aeronautics and Space Administration Goddard Space Flight Center-University of Delaware Bartol Research Institute magnetic field experiment on the Voyager 2 spacecraft discovered a strong and complex intrinsic magnetic field of Neptune and an associated magnetosphere and magnetic tail. The detached bow shock wave in the supersonic solar wind flow was detected upstream at 34.9 Neptune radii (RN), and the magnetopause boundary was tentatively identified at 26.5 RN near the planet-sun line (1 RN = 24,765 kilometers). A maximum magnetic field of nearly 10,000 nanoteslas (1 nanotesla = 10-5 gauss) was observed near closest approach, at a distance of 1.18 RN. The planetary magnetic field between 4 and 15 RN can be well represented by an offset tilted magnetic dipole (OTD), displaced from the center of Neptune by the surprisingly large amount of 0.55 RN and inclined by 47° with respect to the rotation axis. The OTD dipole moment is 0.133 gauss-RN3. Within 4 RN, the magnetic field representation must include localized sources or higher order magnetic multipoles, or both, which are not yet well determined. The obliquity of Neptune and the phase of its rotation at encounter combined serendipitously so that the spacecraft entered the magnetosphere at a time when the polar cusp region was directed almost precisely sunward. As the spacecraft exited the magnetosphere, the magnetic tail appeared to be monopolar, and no crossings of an imbedded magnetic field reversal or plasma neutral sheet were observed. The auroral zones are most likely located far from the rotation poles and may have a complicated geometry. The rings and all the known moons of Neptune are imbedded deep inside the magnetosphere, except for Nereid, which is outside when sunward of the planet. The radiation belts will have a complex structure owing to the absorption of energetic particles by the moons and rings of Neptune and losses associated with the significant changes in the diurnally varying magnetosphere configuration. In an astrophysical context, the magnetic field of Neptune, like that of Uranus, may be described as that of an "oblique" rotator.


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Ultraviolet Spectrometer Observations of Neptune and Triton.
A. L. Broadfoot, S. K. Atreya, J. L. Bertaux, J. E. Blamont, A. J. Dessler, T. M. Donahue, W. T. Forrester, D. T. Hall, F. Herbert, J. B. Holberg, et al. (1989)
Science 246, 1459-1466
   Abstract »    PDF »
Plasma Observations Near Neptune: Initial Results from Voyager 2.
J. W. Belcher, H. S. Bridge, F. Bagenal, B. Coppi, O. Divers, A. Eviatar, G. S. Gordon Jr., A. J. Lazarus, R. L. McNutt Jr., K. W. Ogilvie, et al. (1989)
Science 246, 1478-1483
   Abstract »    PDF »
Hot Plasma and Energetic Particles in Neptune's Magnetosphere.
S. M. Krimigis, T. P. Armstrong, W. I. Axford, C. O. Bostrom, A. F. Cheng, G. Gloeckler, D. C. Hamilton, E. P. Keath, L. J. Lanzerotti, B. H. Mauk, et al. (1989)
Science 246, 1483-1489
   Abstract »    PDF »
Energetic Charged Particles in the Magnetosphere of Neptune.
E. C. Stone, A. C. Cummings, M. D. Loooper, R. S. Selesnick, N. Lal, F. B. McDonald, J. H. Trainor, and D. L. Chenette (1989)
Science 246, 1489-1494
   Abstract »    PDF »
First Plasma Wave Observations at Neptune.
D. A. Gurnett, W. S. Kurth, R. L. Poynter, L. J. Granroth, I. H. Cairns, W. M. Macek, S. L. Moses, F. V. Coroniti, C. F. Kennel, and D. D. Barbosa (1989)
Science 246, 1494-1498
   Abstract »    PDF »
Voyager Planetary Radio Astronomy at Neptune.
J. W. Warwick, D. R. Evans, G. R. Peltzer, R. G. Peltzer, J. H. Romig, C. B. Sawyer, A. C. Riddle, A. E. Schweitzer, M. D. Desch, M. L. Kaiser, et al. (1989)
Science 246, 1498-1501
   Abstract »    PDF »


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