Voyager plasma sounds

Recording by NASA. 

These melodious tones are created at a special frequency in a plasma with a magnetic field. The frequency is set by the number of electrons in a given volume (the electron density) and the strength of the magnetic field. Hence, the frequency of these waves, called upper hybrid waves, can provide a very accurate measure of the density of the plasma; a fundamental property of the Jovian environment of interest to scientists. These emissions were acquired by Voyager 2 as it passed through the outer magnetosphere in 1979.

Part of the Space is the Place project - for more information, see http://www.citiesandmemory.com/space