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.

STORY SOURCE: University of Iowa News Services, 300 Plaza Centre One, Suite 301, Iowa City, Iowa 52242-2500.