Image Caption:
NASA's Cassini spacecraft, approaching Jupiter, is detecting waves in the thin gas of charged particles that fills the space between the Sun and its planets. The waves are in low radio frequencies, which can be converted to sound waves to make the patterns audible.
Click here to listen to sound waves
The waves presented here were detected by Cassini's radio wave and plasma science instrument (RPWS) on Dec. 8, 2000, at a distance of about 23 million kilometers (14 million miles) from Jupiter. They are likely to have derived from an interaction of the magnetic field that surrounds Jupiter and the solar wind of particles speeding away from the Sun.
The oscillations discernible in the graph and in the audio file are from ion-acoustic waves, which result from electrons moving in non-random patterns driven by a flow of energy. In this case, the energy flow probably comes from the heat of Jupiter's bow shock. The bow shock is similar to a sonic boom from a supersonic jet flying through Earth's atmosphere, except that the bow shock is caused by the supersonic solar wind being diverted around Jupiter's magnetic field. The shock is a place where the solar wind is heated, slowed and deflected by the magnetic field surrounding Jupiter. Cassini has not reached the bow shock, but the shock is probably the source of energy driving the waves that are reaching the spacecraft.
The period represented in the graph and audio file lasted 30 seconds. In the process of presenting as sound waves what were originally electric waves, the frequency has been sped up and a few short gaps have been spliced out, resulting in a 10-second audio clip.
