Although space is a virtual vacuum, this does not mean there is no sound in space. Sound does exist as electromagnetic vibrations. Through specially designed instruments the NASA Voyager, INJUN 1, ISEE 1, and HAWKEYE space probes used Plasma Wave antenna to record the vibrations all within the range of human hearing (20-20.000 Hz). The recorded sound sounds are the complex interactions of charged electromagnetic particles from the Solar Wind, ionisphere, and planetary magnetosphere.

(via soundscape explorations)