The Cassini spacecraft crossed the bow shock of Saturn at 09 hr 45 min Universal Time on June 27, 2004, at a radial distance of 49.2 RS (Saturn Radii) from Saturn. The bow shock is a discontinuity that forms in the solar wind when the supersonic solar wind encounters the magnetic field of a planet, very similar to the shock wave that forms upstream of an aircraft moving at a supersonic speed. The color frequency-time spectrogram in the above illustration shows the electric field intensities detected by the Cassini Radio and Plasma Wave Science (RPWS) instrument. The bow shock crossing is indicated by the abrupt burst of electric field noise at the time marked by the arrow. The electric field noise is caused by electrical currents that flow in the shock.
The sound of the bow shock crossing can be heard by clicking on the button labeled "Audio" or in an animated version (which shows a cursor that indicates time on the spectrogram) by clicking on "Animate." Time on this recording has been compressed such that 10 seconds corresponds to 28 minutes.Don Gurnett
RPWS Principal Investigator
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The Radio and Plasma Wave Group, Department of Physics & Astronomy, College of Liberal Arts & Sciences.