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Radio emissions observed by Galileo near Io
Author(s) -
Menietti J. D.,
Gurnett D. A.,
Kurth W. S.,
Groene J. B.,
Granroth L. J.
Publication year - 1998
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/97gl03442
Subject(s) - physics , plasma , torus , modulation (music) , radio frequency , whistler , waves in plasmas , energy flux , range (aeronautics) , spacecraft , computational physics , astronomy , materials science , telecommunications , geometry , mathematics , computer science , acoustics , composite material , quantum mechanics
The Galileo spacecraft observed spin modulation of radio wave emissions near Io in the frequency range from about 600 kHz to about 1.2 MHz. Assuming transverse EM radiation, we have used the modulation of the high‐frequency sweep‐frequency receiver signals of the electric dipole antenna over many spins to estimate the plane through the source. The emission has a range of frequencies close to the local upper hybrid frequency of the plasma near Io. We conclude that the emission may be associated with either the plasma torus or magnetic flux tubes in the wake of Io (the Alfvén current system). We postulate this emission may be associated with a free‐energy source such as density gradients, energetic plasma beams and/or an electron distribution with a temperature anisotropy. All of these free‐energy sources are observed or expected in the torus near Io. The observations are the first in the hectometric frequency range that have a source associated with Io or in the Io torus.