The Cassini spacecraft has collected the first high-resolution spectra of Saturn's sounds, astronomers report. The radio emissions, called kilometric radiation, vary widely in frequency and are closely related to the planet's auroras.

Cassini's radio and plasma wave science instrument picked up the signal--which translates into spooky audio with rising and falling tones that call to mind howling winds--as it approached Saturn. William S. Kurth of the University of Iowa and his colleagues analyzed more than 347 hours of data collected since April 2002, starting from a distance of 374 million kilometers, and describe their findings in the latest issue of Geophysical Research Letters. Earth emits similarly strange sounds, which study co-author Don Gurnett of the University of Iowa first reported in 1979. Exactly what causes the intense emission remains a mystery, although the new data are providing tantalizing hints. "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," Kurth says. "We believe that the changing frequencies are related to tiny radio sources moving up and down along Saturn's magnetic field lines."

The Cassini spacecraft also recently completed its closest flyby of a moon yet, gathering detailed images of the south pole of the moon Enceladus in the process. The new images, snapped just 109 miles above the surface, indicate that the southernmost region of the moon is remarkably smooth. The cameras detected almost no impact craters in the area but did reveal ice boulders the size of houses that are carved out by the moon's unique tectonic activity. "These tectonic features define a boundary that isolate the young, south polar terrains from older terrains on Enceladus," comments imaging team member Paul Helfenstein of Cornell University. "Their placement and orientation may tell us a very interesting story about the way the rotation of Enceladus has evolved over time and what might have provided the energy to power the geologic activity that has wracked this moon."