Galileo Energetic Particle Detector (EPD) anisotropies during plasma sheet crossings at Jupiter

L.S. Waldrop (Boston University), N. Krupp (Max Planck Institute for Aeronomy), T.A. Fritz, M. Mendillo (Boston University), D.J. Williams (JHU Applied Physics Laboratory), M.G. Kivelson (UCLA)

Although the Energetic Particles Detector (EPD) experiment on the Galileo spacecraft was not designed specifically for the detection of neutral particles, analysis of energetic particle anisotropies and spectra has revealed possible energetic neutral atom (ENA) signatures. Similar analysis using the Low Energy Charged Particle detector (LECP) on Voyager I near Jupiter has suggested the presence of energetic neutral particles escaping from its magnetosphere. These energetic neutrals are created in charge exchange reactions between ambient neutrals near Io associated with volcanic eruptions on the moon and energetic charged particles trapped in Jupiter's massive magnetosphere. Time variations in the size of the neutral cloud around Io, as previously reported by Mendillo et al (1992), could be associated with possible variations in the frequency of ENA's measured by the satellite. We will present initial results of an analysis of the particle anisotropies as Galileo passes back-and-forth through the plasma sheet into a lobe-like environment at approximately 100 tex2html_wrap_inline12 . We have observed anisotropies that can be associated with (1) the corotational direction of the motion of the magnetosphere, (2) enhanced fluxes flowing in the direction of the magnetic field, and (3) significantly, increased fluxes from the direction of the planet itself. We will report on the association of these anisotropies with the position of the Galileo spacecraft with respect to the plasma sheet by using the measured magnetic field kindly supplied by Dr. Margaret Kivelson of UCLA, Principle Investigator of the Magnetometer (MAG) experiment.