The above recording was made on 27 June 1996. It was made by the Galileo spacecraft as it passed Ganymede, a moon of Jupiter.
At about 8 seconds in, Galileo enters Ganymede’s magnetosphere (there is a sudden increase in noise, sounding like a clap of thunder). As the spacecraft passed through the magnetosphere, the noise rose in pitch to peak, then decreased again. The irregularities in the recording, such as the sudden drop in volume at 15 seconds, are caused by irregularities in the magnetosphere of Ganymede as it passes through the influence of the immense magnetic field of Jupiter.
An antenna on the spacecraft was picking up plasma waves, created by the unusually strong magnetosphere of Ganymede (about 3 times stronger Mercury). This was used to create an audio signal (below, the 45 minute signal is compressed into about 60 seconds), where the sound frequency corresponds to the frequency of the waves detected.
