New observations by the international Cassini spacecraft reveal that Saturn's trademark shimmering rings, which have dazzled astronomers since Galileo's time, have dramatically changed over 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. A piece of the D ring also has shifted, moving 125 miles inward toward 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 planetary rings.
Scientists also are interested in Saturn and its magnificent 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 4 1/2 billion years ago.
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