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Science 10 April 1981:
Vol. 212. no. 4491, pp. 225 - 231
DOI: 10.1126/science.212.4491.225
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Articles

Low-Energy Charged Particles in Saturn's Magnetosphere: Results from Voyager 1

S. M. KRIMIGIS 1, T. P. ARMSTRONG 2, W. I. AXFORD 3, C. O. BOSTROM 4, G. GLOECKLER 5, E. P. KEATH 4, L. J. LANZEROTTI 6, J. F. CARBARY 4, D. C. HAMILTON 7, and E. C. ROELOF 4

1 Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland 20810
2 Department of Physics, University of Kansas, Lawrence 66044
3 Max-Planck Institute for Aeronomy, D-3411 Katlenburg-Lindau 3, West Germany
4 Applied Physics Laboratory, Johns Hopkins University
5 Department of Physics and Astronomy, University of Maryland, College Park 20742
6 Bell Laboratories, Murray Hill, New Jersey 07974
7 Department of Physics and Astronomy, University of Maryland

The low-energy charged particle instrument on Voyager 1 measured low-energy electrons and ions (energies ge 26 and ge 40 kiloelectron volts, respectively) in Saturn's magnetosphere. The first-order ion anisotropies on the dayside are generally in the corotation direction with the amplitude decreasing with decreasing distance to the planet. The ion pitch-angle distributions generally peak at 90°, whereas the electron distributions tend to have field-aligned bidirectional maxima outside the L shell of Rhea. A large decrease in particle fluxes is seen near the L shell of Titan, while selective particle absorption (least affecting the lowest energy ions) is observed at the L shells of Rhea, Dione, and Tethys. The phase space density of ions with values of the first invariant in the range sim 300 to 1000 million electron volts per gauss is consistent with a source in the outer magnetosphere. The ion population at higher energies (ge 200 kiloelectron volts per nucleon) consists primarily of protons, molecular hydrogen, and helium. Spectra of all ion species exhibit an energy cutoff at energies ge 2 million electron volts. The proton-to-helium ratio at equal energy per nucleon is larger (up to sim 5 x 103) than seen in other magnetospheres and is consistent with a local (nonsolar wind) proton source. In contrast to the magnetospheres of Jupiter and Earth, there are no lobe regions essentially devoid of particles in Saturn's nighttime magnetosphere. Electron pitch-angle distributions are generally bidirectional andfield-aligned, indicating closed field lines at high latitudes. Ions in this region are generally moving toward Saturn, while in the magnetosheath they exhibit strong antisunward streaming which is inconsistent with purely convective flows. Fluxes of magnetospheric ions downstream from the bow shock are present over distances ge 200 Saturn radii from the planet. Novel features identified in the Saturnian magnetosphere include a mantle of low-energy particles extending inward from the dayside magnetopause to sim 17 Saturn radii, at least two intensity dropouts occurring sim 11 hours apart in the nighttime magnetosphere, and a pervasive population of energetic molecular hydrogen.

Submitted on February 9, 1981


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Dynamics of Saturn's Magnetosphere from MIMI During Cassini's Orbital Insertion.
S. M. Krimigis, D. G. Mitchell, D. C. Hamilton, N. Krupp, S. Livi, E. C. Roelof, J. Dandouras, T. P. Armstrong, B. H. Mauk, C. Paranicas, et al. (2005)
Science 307, 1270-1273
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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
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Fast Ion Bombardment of Ices and Its Astrophysical Implications.
W. L. Brown, L. J. Lanzerotti, and R. E. Johnson (1982)
Science 218, 525-531
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Plasma Observations Near Saturn: Initial Results from Voyager 2.
H. S. BRIDGE, F. BAGENAL, J. W. BELCHER, A. J. LAZARUS, R. L. McNUTT, J. D. SULLIVAN, P. R. GAZIS, R. E. HARTLE, K. W. OGILVIE, J. D. SCUDDER, et al. (1982)
Science 215, 563-570
   Abstract »    PDF »
Low-Energy Hot Plasma and Particles in Saturn's Magnetosphere.
S. M. KRIMIGIS, T. P. ARMSTRONG, W. I. AXFORD, C. O. BOSTROM, G. GLOECKLER, E. P. KEATH, L. J. LANZEROTTI, J. F. CARBARY, D. C. HAMILTON, and E. C. ROELOF (1982)
Science 215, 571-577
   Abstract »    PDF »


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