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Evidence for a magnetosphere at Ganymede from plasma-wave observations by the Galileo spacecraft

Nature volume 384, pages 535537 (12 December 1996) | Download Citation

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Abstract

ON 27 June 1996 the Galileo spacecraft1,2 made the first of four planned close fly-bys of Ganymede, Jupiter's largest moon. Here we report measurements of plasma waves and radio emissions, over the frequency range 5 Hz to 5.6 MHz during the first encounter. Intense plasma waves were detected over a region of space nearly four times Ganymede's diameter, which is much larger than would be expected for a simple wake arising from Ganymede's passage through Jupiter's rapidly rotating magneto-sphere. The types of waves detected (whistler-mode emissions, upper hybrid waves, electrostatic electron cyclotron waves and escaping radio emission) strongly suggest that Ganymede has a large, extended magnetosphere of its own. The data indicate the presence of a strong (B > 400 nT) magnetic field, and show that Ganymede is surrounded by an ionosphere-like plasma with a maximum electron density of about 100 particles cm−3 and a scale height of about 1,000km.

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Author information

Affiliations

  1. Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA

    • D. A. Gurnett
    •  & W. S. Kurth
  2. Centre d'Etudes des Environnements Terrestre et Planetaires, Universite Versailles Saint Quentin, 10/12 Avenue de I'Europe, 78140 Velizy, France

    • A. Roux
  3. Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, California 91109, USA

    • S. J. Bolton
  4. Office of the Chancellor, UCLA, Los Angeles, California 90095, USA

    • C. F. Kennel

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https://doi.org/10.1038/384535a0

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