Scientists baffled by changes Cassini shows in Saturn's rings

LOS ANGELES — New observations by the international Cassini spacecraft reveal that Saturn's shimmering rings, which have dazzled astronomers since Galileo's time, have dramatically changed over just the past 25 years.

Among the most surprising findings is that parts of Saturn's innermost ring — the D ring — have grown dimmer since the Voyager spacecraft flew by the planet in 1981, and a piece of the D ring has moved 125 miles inward toward Saturn.

While scientists puzzle over what caused the changes, their observations could reveal something about the age and lifetime of the rings.

Cassini-related discoveries were discussed yesterday at a meeting of the American Astronomical Society's division of planetary sciences in Cambridge, England.

"I don't think Saturn's rings will disappear anytime soon, but this tells us how the rings are evolving and how long they might last," deputy project scientist Linda Spilker said from England.

Scientists are interested in Saturn's rings because they are a model of the disk of gas and dust that initially surrounded the sun. Studying them could yield important clues about how the planets formed from that disc 4.5 billion years ago.

The ring observations were made this summer. The $3.3 billion Cassini mission, funded by NASA and the European and Italian space agencies, launched in 1997.