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Science 15 December 1989:
Vol. 246. no. 4936, pp. 1478 - 1483
DOI: 10.1126/science.246.4936.1478
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Articles

Plasma Observations Near Neptune: Initial Results from Voyager 2

J. W. Belcher 1, H. S. Bridge 1, F. Bagenal 2, B. Coppi 1, O. Divers 3, A. Eviatar 4, G. S. Gordon Jr. 1, A. J. Lazarus 1, R. L. McNutt Jr. 1, K. W. Ogilvie 5, J. D. Richardson 1, G. L. Siscoe 6, E. C. Sittler Jr. 5, J. T. Steinberg 1, J. D. Sullivan 1, A. Szabo 1, L. Villanueva 1, V. M. Vasyliunas 7, and M. Zhang 1

1 Massachusetts Institute of Technology, Cambridge, MA 02139
2 University of Colorado, Boulder, CO 80309
3 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109
4 Tel Aviv University, Tel Aviv, Israel
5 National Aeronautics and Space Administration Goddard Space Flight Center, Greenbelt, MD 20770
6 University of California, Los Angels, CA 90024
7 Max-Planck-Institüt für Aeronomie, Katlenburg-Lindau, Federal Republic of Germany

The plasma science experiment on Voyager 2 made observations of the plasma environment in Neptune's magnetosphere and in the surrounding solar wind. Because of the large tilt of the magnetic dipole and fortuitous timing, Voyager entered Neptune's magnetosphere through the cusp region, the first cusp observations at an outer planet. Thus the transition from the magnetosheath to the magnetosphere observed by Voyager 2 was not sharp but rather appeared as a gradual decrease in plasma density and temperature. The maximum plasma density observed in the magnetosphere is inferred to be 1.4 per cubic centimeter (the exact value depends on the composition), the smallest observed by Voyager in any magnetosphere. The plasma has at least two components; light ions (mass, 1 to 5) and heavy ions (mass, 10 to 40), but more precise species identification is not yet available. Most of the plasma is concentrated in a plasma sheet or plasma torus and near closest approach to the planet. A likely source of the heavy ions is Triton's atmosphere or ionosphere, whereas the light ions probably escape from Neptune. The large tilt of Neptune's magnetic dipole produces a dynamic magnetosphere that changes configuration every 16 hours as the planet rotates.


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Magnetic Fields at Neptune.
N. F. Ness, M. H. Acuna, L. F. Burlaga, J. E. P. Connerney, R. P. Lepping, and F. M. Neubauer (1989)
Science 246, 1473-1478
   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 »
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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