Just as the static on an AM radio grows louder with the approach of a summer lightning storm, strong radio emissions accompany bright auroral spots -- similar to Earth's northern lights -- on the planet Saturn, according to a research paper published in the Thursday, Feb. 17 issue of the journal Nature.
William Kurth, research scientist in the University of Iowa College of Liberal Arts and Sciences Department of Physics and Astronomy, says that the data was collected in early 2004, with NASA's Cassini spacecraft measuring the strength of Saturn's solar wind and radio emissions and the Hubble Space Telescope taking pictures of Saturn's aurora, or southern lights. The results also indicated that strong radio emissions grow stronger when the solar wind blows harder.
"We had expected that this might be the case, based on our understanding of auroral radio signals from Earth's auroras, but this is the first time we've been able to compare Saturn's radio emissions with detailed images of the aurora," Kurth says. "This is important to our on-going Cassini studies because this association allows us to have some idea of what the aurora are doing throughout the mission from our continuous radio observations."
Co-author Don Gurnett, Cassini Radio and Plasma Wave Science (RPWS) instrument principal investigator, says the finding means that radio emissions from Saturn's aurora are very similar to radio emissions from the Earth's aurora.
Kurth says that one of Cassini's objectives is to understand how the magnetic field around Saturn, called its magnetosphere, responds to the influence of the solar wind, a hot gas composed of electrons and ions that originates at the Sun and blows past the planets at speeds around one million miles per hour.
Two related papers published by other researchers in Thursday's issue of Nature show that, like a flaming log in a campfire, Saturn's aurora become brighter and more expansive when the solar wind blows harder. However, the distribution of auroras on Saturn differs from those on Earth.
Other discoveries made by UI researchers using the RPWS instrument have included finding that lightning on Saturn is roughly one million times stronger than lightning on Earth; observing that Cassini impacted dust particles as it traversed Saturn's rings; and learning that Saturn's radio rotation rate varies.
The radio sounds of Saturn's rotation -- resembling a heartbeat -- and other sounds of space can be heard by visiting http://www-pw.physics.uiowa.edu/space-audio.
Cassini, carrying 12 scientific instruments, on June 30, 2004 became the first spacecraft to orbit Saturn and began a four-year study of the planet, its rings and its 31 known moons. The $1.4 billion spacecraft is part of the $3.3 billion Cassini-Huygens Mission that includes the European Space Agency's Huygens probe that landed on Saturn's moon Titan in January. 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 Office of Space Science, Washington, D.C. JPL designed, developed and assembled the Cassini orbiter. For the latest images and information about the Cassini-Huygens mission, visit: http://www.nasa.gov/cassini
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