Spacecraft "Cassini" finds Saturn's rings shifting

Saturn's mysterious rings, which have fascinated astronomers since Galileo's time, have radically changed over the past 25 years, according to unprecedented observations by the international Cassini spacecraft.

The planet's innermost ring - known as the D ring - has grown dimmer since the Voyager spacecraft flew by the planet in 1981. A piece of the D ring has also shifted 125 miles inwards, towards Saturn.

While scientists puzzle over what caused Saturn's D ring to change in such a short period, the observations could tell something about the age and lifetime of ringed planets.

Astronomers are also interested in Saturn and its rings because they are a model of the disc of gas and dust that initially surrounded the sun. Studying them could yield important clues about how the planets formed four-and-a-half billion years ago. The D ring finding was among several Cassini-related discoveries announced at a meeting of the American Astronomical Society's division of planetary sciences in Cambridge.

Scientists also found that ice particles which make up Saturn's main rings - the A, B, and C rings - were spinning much slower than expected.

Astronomers expected the denser A and B rings - where crowds of particles crash into one another like bumper cars - to rotate faster than the sparser C ring. The spin rates were determined by measuring the temperature of the particles.

Linda Spilker, a deputy project scientist working on the craft's results, said: "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", "Scotsman" reported.