GALILEO PLASMA WAVE INVESTIGATION:
OBSERVATIONS AT EUROPA
Europa orbits Jupiter just at the outer edge of the Io plasma torus. The plasma wave observations show that there is an important interaction between the Jovian magnetosphere and this satellite, but the dominance of the Io torus likely overshadows some aspects of the interaction.
This electric field spectrogram shows an intense burst of broadband wave turbulence centered near the closest approach to Europa, most of which we interpret as a mode known as whistler-mode emissions. However the brief burst of noise extending above 10 kHz is probably electrostatic in nature and not related to the whistler mode. The UHR band running along near the top of the display at nearly constant frequency shows that there is not a large change in plasma density near Europa, unlike the situations at Io and Ganymede. However, it is interesting that this band intensifies significantly near Europa, suggesting the satellite has some influence over the production of this band of emission.
This is the magnetic spectrogram covering the same time interval as the electric spectrogram above. The primary feature is the magnetic component of the whistler-mode emissions.
Listen to sounds of Europa's plasma waves. The Galileo plasma wave receiver has a special mode which records the actual waveforms of the signals detected by the instrument's electric field antenna. In order to make it possible to "listen" to the ~45 minutes of signals around closest approach, we've had to shorten the recording by using very short slices of the waveform and cutting out relatively long periods between each pair of slices. We've also had to play back the waveform at about a factor of 10 slower since the original recording had a bandwidth of 80 kHz and the human ear can only hear sounds up to about 10 or 20 kHz.