Astronomers had thought Saturn's rings were cosmically young, likely born some 100 million years ago from leftovers of a meteoric collision with a moon, based on data by NASA's Voyager spacecraft in the 1970s.
However, new data from the orbiting international Cassini spacecraft suggest the rings existed as far back as 4.5 billion years ago, roughly the same time the sun and planets formed. The probe also found evidence that ring particles are constantly shattering and regrouping to form new rings.
"Recycling allows the rings to be as old as the solar system although continually changing,'' said Larry Esposito, a Cassini scientist from the University of Colorado.
The findings were presented at an American Geophysical Union meeting in San Francisco and will be published in the astronomical journal Icarus.
Saturn's trademark arcs have awed astronomers since Galileo's time. Scientists are interested in the rings because they are a model of the disk of gas and dust that initially enveloped the sun and studying them could yield clues about planet formation.
Saturn's ring system consists of seven major rings and thousands of ringlets, mostly made of orbiting ice mixed with dust and rock fragments.
The notion that Saturn's rings may be a permanent feature was based on observations by the ultraviolet spectrograph instrument on Cassini, which viewed the light reflected from the rings and watched stars passing behind them.
The Cassini mission, funded by NASA and the European and Italian space agencies, was launched in 1997 and reached Saturn in 2004. The mission is managed by NASA's Jet Propulsion Laboratory in Pasadena.