Observations by the Galileo plasma wave receiver during the first two flybys of Ganymede revealed that this Jovian moon is the source of narrowband electromagnetic radio waves, making it the only satellite in the solar system known to generate non-thermal radio emissions. The emissions are the result of mode-coupling from electrostatic electron cyclotron emissions near the upper hybrid resonance frequency, similar to non-thermal continuum radiation found at the known magnetized planets.¿ 1997 American Geophysical Union