Although no major electrical problems have yet resulted from the current series of solar flares bombarding the Earth, University of Iowa Professor and Space Physicist Don Gurnett, recently used NASA's Cassini spacecraft to record the sound of one of the largest solar flares seen in decades as it moved outward from the sun.

The radio wave burst, resembling the clicking of an old-fashioned telegraph machine followed by the rush of a jet engine, was recorded Tuesday, Oct. 28 by Cassini while on its way to a July 1, 2004 encounter with Saturn and its moons and rings. Gurnett noted that the radio waves -- moving at the speed of light -- took just 69 minutes to reach the spacecraft, currently some 8.7 AU distant from the Earth. (One AU, or astronomical unit, is the distance from the Earth to the sun -- about 93 million miles.)

"This is one of the biggest events of its kind ever seen," said Gurnett, a veteran of more than 25 major spacecraft projects, including the Voyager 1 and Voyager 2 flights to the outer planets, the Galileo mission to Jupiter, and the Cassini mission to Saturn. The event, described as a "type III" radio burst, was detected using the 86-pound Cassini radio and plasma wave instrument, largely built at the UI and for which Gurnett serves as principal investigator. (The sound can be heard on-line by visiting Gurnett's Web site at: http://www-pw.physics.uiowa.edu/space-audio/)

"The sound is produced by electrons moving out from the solar flare, beginning at a high frequency before dropping to a lower frequency," Gurnett said. Scientists monitoring the solar flare said that the massive cloud -- composed of billions of tons of electrically charged particles -- reached the Earth on Thursday, Oct. 29, but no major power outages were reported.

Gurnett is also part of a NASA-funded, Italian-U.S. project called MARSIS (Mars Advanced Radar for Subsurface and Ionospheric Sounding) to search for underground water on Mars, a project whose radar instrument is aboard the European Space Agency's (ESA) Mars Express spacecraft. A member of the National Academy of Sciences, Gurnett has seen his 40 years of collected space sounds serve as the inspiration for the NASA-commissioned and critically acclaimed music and visual composition "Sun Rings," composed by Terry Riley and performed around the world by the famed Kronos Quartet.