Saturn has lightning, apparently deep in its atmosphere, which generates strong radio emissions, similar to the cracks and pops one hears on an AM radio during a thunderstorm. First discovered by Voyager 1, these radio emissions are the only direct evidence of lightning at Saturn, so far.
The Cassini Radio and Plasma Wave Science (RPWS) instrument sweeps in frequency up to 16 MHz. Since the lightning-related radio emissions are emitted over a broad range of frequencies but last only about one thirtieth of a second, a burst appears at whatever frequency the instrument happens to be tuned to at the moment of the burst.
In this representation of RPWS observations (called a spectrogram) of a strong thunderstorm, the radio emissions appear as speckles at random frequencies above about 2 MHz. These data were converted to sound by using the amplitude and duration of the bursts to create an audio signal. [The Quicktime movie included here features a cursor moving across the spectrogram, synchronized with the audio, to indicate time.]
This storm occurred on January 23 and 24, 2006. The clip compresses two hours of observations into about 28 seconds. Therefore, every second of the audio clip corresponds to about 4 minutes, 18 seconds. The actual occurrence rate of the flashes during the peak of this storm is about one every two seconds.
These data represent a similar, but earlier, Saturn electrical storm than the one discussed in PIA08410 and PIA08411.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The radio and plasma wave science team is based at the University of Iowa, Iowa City.