Abstract Jupiter's innermost Galilean satellite Io is regarded as a fairly good conductor ( σ > 10 −5 Ω −1 m −1 ). The trapping of magnetic field lines by Io and their deformation is described. A neutral point forms in the vicinity of the satellite. The magnetic field annihilation in the neutral point is enhanced by the emission of low frequency hmd waves. The power carried away by these waves may be as high 10 15 W. The characteristic frequency of the wave and its variation while Io orbits around Jupiter is determined.