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Galileo Observers Electromagnetically Coupled Dust in the Jovian Magnetosphere

To appear in the Journal of Geophysical Research, August 1998.

E. Grun(1), H. Kruger(1), A. L. Graps(2,1), D. P. Hamilton(3), A. Heck(1), G. Linkert(1), H. A. Zook(4), S. Dermott(5), H. Fechtig(1), B. A. Gustafson(5), M. S. Hanner(6), M. Horanyi(7), J. Kissel(1), B. A. Lindblad(8), D. Linkert(1), I. Mann(9), J. A. M. McDonnell(10), G. E. Morfill(11), C. Polanskey(6), G. Schwehm(12), R. Srama(1),

1Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany 2Stanford University, Center for Space Science and Astrophysics, Stanford, CA 94305-4085, USA 3University of Maryland, College Park, MD20742- 2421, USA 4NASA Johnson Space Center, Houston, TX77058, USA 5University of Florida, Gainesville, FL32611, USA 6Jet Propulsion Laboratory, Pasadena, CA91109, USA 7Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO80309, USA 8Lund Observatory, 221, Lund, Sweden 9Max-Planck-Institut für Aeronomie, 37191 Katlenburg-Lindau, Germany 10University of Kent, Canterbury, CT2 7NR, UK 11Max-Planck-Institut für Extraterrestrische Physik, 85740 Garching, Germany 12European Space Research and Technology Centre, 2200 AG Noordwijk, The Netherlands

Abstract:

Measurements of dust coupled to the Jovian magnetosphere have been obtained with the dust detector on board the Galileo spacecraft. We report on data obtained during the first four orbits about Jupiter that had flybys of the Galilean satellites: Ganymede (orbits 1 and 2), Callisto (orbit 3), and Europa (orbit 4). The most prominent features observed are highly time variable dust streams recorded throughout the Jovian system. The impact rate varied by up to 2 orders of magnitude with a 5 and 10 hour periodicity, which shows a correlation with Galileo's position relative to the Jovian magnetic field. Around 20 R_J (Jupiter radius, R_J = 71,492 km) in bound a dip in the impact rate has been found consistently. At the same times, reversals by 180 in impact direction occurred. This behavior can be qualitatively explained by strong coupling of nanometer-sized dust to the Jovian magnetic field. At times of satellite flybys, enhanced rates of dust impacts have been observed, which suggests that all Galilean satellites are sources of ejecta particles. Inside about 20 R_J impacts of micrometer-sized particles have been recorded that could be particles on bound orbits about Jupiter.