Researchers using data from NASA's Cassini spacecraft have found that Saturn's rings formed around 4.4 billion years ago, shortly after the planet itself took shape.
The origin of Saturn's ring system remains hotly debated, with some researchers arguing that it's a relatively young structure and others holding that it coalesced long ago, at roughly the same time as the gas giant's many satellites.
The new study, using data gathered by NASA's Saturn-orbiting Cassini spacecraft, strongly supports the latter scenario, researchers said.
Cassini's measurements suggest that "the main rings would be [extremely] old, rather than hundreds of millions of years old," said Sascha Kempf, of the University of Colorado in Boulder.
Saturn's main ring system is huge but razor-thin, measuring about 280,000 kilometres across but just 33 feet or so in the vertical direction.
The rings are composed primarily of water ice, but they contain small amounts of rocky material contributed by micrometeoroid bombardment, 'LiveScience' reported.
Kempf and his colleagues used Cassini's Cosmic Dust Analyzer instrument to measure just how frequently such tiny particles cruise through the Saturn system.
They found that a surprisingly small amount of dusty material comes into contact with the rings.
After measuring the low rate of dust recruitment, the team calculated that the rings have likely existed for about 4.4 billion years.
"It would be consistent with an old ring system," Kempf said.
The study was presented at the annual meeting of the American Geophysical Union.