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July 9, 2004: When the Cassini spacecraft reached Saturn on June 30th, it dashed through a gap in Saturn's rings ... and then did it again. The double ring crossing was part of a maneuver required to put Cassini in orbit.

Although the ring gaps appeared empty, they weren't. Innumerable bits of ring-dust were waiting for Cassini, and they plowed into the spacecraft at a relative speed of approximately 20 km/s. That's 45,000 mph!

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"When we crossed the ring plane, we had roughly 100,000 total dust hits in less than five minutes," says Cassini science team member Don Gurnett of the University of Iowa. Fortunately the particles were small--"comparable in size to particles in cigarette smoke," he says. And most of the hits were to the spacecraft's tough high-gain antenna.

No damage was done, but it sounded exciting.

Each time a dust particle hit Cassini, the impact produced a puff of plasma--a tiny cloud of ionized gas. Cassini's Radio and Plasma Wave Science (RPWS) instrument was able to count these clouds; there were as many as 680 puffs per second. "We converted these into audible sounds that resemble hail hitting a tin roof," says Gurnett, the intrument's principal investigator. Click to listen: 2 MB Quicktime file.

The spacecraft reported no unusual activity due to the hits and performed flawlessly, successfully going into orbit around Saturn--a thrilling start to Cassini's four-year mission of exploration. More thrills are coming: visit the Cassini home page for updates.

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Credits & Contacts
Author: Dr. Tony Phillips
Responsible NASA official: John M. Horack

Production Editor: Dr. Tony Phillips
Curator: Bryan Walls
Media Relations: Steve Roy

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