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Science 10 April 1981:
Vol. 212. no. 4491, pp. 217 - 224
DOI: 10.1126/science.212.4491.217
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Articles

Plasma Observations Near Saturn: Initial Results from Voyager 1

H. S. BRIDGE 1, J. W. BELCHER 1, A. J. LAZARUS 1, S. OLBERT 1, J. D. SULLIVAN 1, F. BAGENAL 1, P. R. Gazis 1, R. E. HARTLE 2, K. W. OGILVIE 3, J. D. SCUDDER 3, E. C. SITTLER 3, A. EVIATAR 4, G. L. SISCOE 4, C. K. GOERTZ 5, and V. M. VASYLIUNAS 6

1 Center for Space Research and Department of Physics, Massachusetts Institute of Technology, Cambridge 02139
2 Laboratory for Planetary Atmospheres, Goddard Space Flight Center, Greenbelt, Maryland 20771
3 Laboratory for Extraterrestrial Physics, Goddard Space Flight Center
4 Department of Atmospheric Sciences, University of California, Los Angeles 90024
5 Max-Planck-Institut für Aeronomie, D-3411, Katlenburg-Lindau 3, Federal Republic of Germany, and University of Iowa, Iowa City 52242
6 Max-Planck-Institut für Aeronomie, D-3411, Katlenburg-Lindau 3

Extensive measurements of low-energy plasma electrons and positive ions were made during the Voyager 1 encounter with Saturn and its satellites. The magnetospheric plasma contains light and heavy ions, probably hydrogen and nitrogen or oxygen; at radial distances between 15 and 7 Saturn-radii (Rs) on the inbound trajectory, the plasma appears to corotate with a velocity within 20 percent of that expected for rigid corotation. The general morphology of Saturn's magnetosphere is well represented by a plasma sheet that extends from at least 5 to 17 Rs, is symmetrical with respect to Saturn's equatorial plane and rotation axis, and appears to be well ordered by the magnetic shell parameter L (which represents the equatorial distance of a magnetic field line measured in units of Rs). Within this general configuration, two distinct structures can be identified: a central plasma sheet observed from L = 5 to L = 8 in which the density decreases rapidly away from the equatorial plane, and a more extended structure from L = 7 to beyond 18 Rs in which the density profile is nearly flat for a distance ± 1.8 Rs off the plane and falls rapidly thereafter. The encounter with Titan took place inside the magnetosphere. The data show a clear signature characteristic of the interaction between a subsonic corotating magnetospheric plasma and the atmospheric or ionospheric exosphere of Titan. Titan appears to be a significant source of ions for the outer magnetosphere. The locations of bow shock crossings observed inbound and outbound indicate that the shape of the Saturnian magnetosphere is similar to that of Earth and that the position of the stagnation point scales approximately as the inverse one-sixth power of the ram pressure.

Submitted on February 9, 1981


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
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Magnetic Field Studies by Voyager 1: Preliminary Results at Saturn.
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