Cassini Reveals Saturn's Eerie-sounding Radio Emissions

That's how University of Iowa researchers Bill Kurth and Don Gurnett describe their recent findings in the July 23 issue of the journal Geophysical Research Letters. Their paper is based on data from the Cassini spacecraft radio and plasma wave science instrument, which was built at the University of Iowa under Gurnett's direction. The study investigates sounds that are not just eerie, but also descriptive of a phenomenon similar to Earth's northern lights.

"All of the structures we observe in Saturn's radio spectrum are giving us clues about what might be going on in the source of the radio emissions above Saturn's auroras," says Kurth. "We believe that the changing frequencies are related to tiny radio sources moving up and down along Saturn's magnetic field lines."

The radio emissions, called Saturn kilometric radiation, are generated along with Saturn's auroras, or northern and southern lights. Because the Cassini instrument has higher resolution compared to a similar instrument on the Voyager spacecraft, it has provided more detailed information on the spectrum and its variability of the radio emissions. Samples of the resulting sounds can be found at http://www-pw.physics.uiowa.edu/cassini/ or at http://www-pw.physics.uiowa.edu/space-audio/.

The terrestrial cousins of Saturn's radio emissions were first reported in 1979 by Gurnett, who used an instrument onboard the International Sun Earth Exporer-1 spacecraft in Earth orbit. Kurth says that despite their best efforts, scientists still haven't agreed on a theory to fully explain the phenomenon. He adds that they will get another chance to solve the radio emission puzzle beginning in mid-2008 when Cassini will fly close to, or possibly even through, the source region at Saturn.

Commenting on the new observations, Gurnett says, "It is amazing that the radio emissions from Earth and Saturn sound so similar."

In addition to Kurth and Gurnett, other contributors include: UI scientists George Hospodarsky and Baptiste Cecconi; Mike Kaiser (currently at Goddard Space Flight Center and a former UI student); French scientists Philippe Louarn, Philippe Zarka and Alain Lecacheux; and Austrian scientists Helmut Rucker and Mohammed Boudjada.

Cassini, carrying 12 scientific instruments, on June 30, 2004, became the first spacecraft to orbit Saturn and begin a four-year study of the planet, its rings and its many moons. The $1.4 billion spacecraft is part of the $3.3 billion Cassini-Huygens Mission that includes the Huygens probe, a six-instrument European Space Agency probe that landed on Titan, Saturn's largest moon, in January 2005.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology, Pasadena, Calif. manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington, D.C.