31st Annual Meeting of the DPS, October 1999
Session 57. Europa, Ganymede and Callisto Posters
Poster Group II, Thursday-Friday, October 14, 1999, , Kursaal Center

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[57.06] Plasma Density Distributions in the Ionosphere of Ganymede

A. Eviatar (Tel Aviv University, Ramat Aviv, Israel), V.M. Vasyli\={u}nas (Max-Planck-Institut f\"{u}r Aeronomie, Lindau, Germany)

We consider the distribution of plasma density in two separate regions of Ganymede, which has been found by {\em Galileo} to have an intrinsic magnetic field. The polar cap region, for which the latitude \lambda satisfies \begin{math} \lambda > 45\deg \end{math} is characterized by field lines which intersect Ganymede at one end and connect to Jupiter at the other. This region is subject to intense interaction with the energetic particles that populate the magnetosphere of Jupiter, undergoes intense sputtering and has been observed to emit an atmospheric air glow excited by electron impact. The plasma in this region will be lost by a polar wind, analogous to that of the Earth. The equatorial region, for which\begin{math} \lambda < 45\deg \end{math} has closed field lines to which low energy Jovian particles have no access. In this region, the density will depend on the local temperature and on the local magnetic field. In both regions, observations indicate that the ionosphere will be exospheric. We use existing models of flux and density distributions to estimate the loss rate of plasma, the equilibrium density and the decrease of density along a closed field line. We find that the loss rate is comparable with the source strength estimated from sputtering by the ions whose spectra have been obtained from the Galileo EPD observations.

The author(s) of this abstract have provided an email address for comments about the abstract: arkee@daphne.tau.ac.il

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