Saturnâ€™s rings are older than we thought - December 13, 2007
Far from being youthful tykes, appearing only around the time of the dinosaurs, Saturnâ€™s rings actually date back to the start of our solar system some 4.5 billion years ago, according to data from the Cassini probe (press release, coverage on AP). However, thanks to a nifty anti-aging trick, they look younger than might be expected.
Previously it was thought that the distinctive rings were formed when a moon had a head-on disagreement with a comet. But Cassini found the ages of different rings varied considerably, suggesting one massive collision didnâ€™t cause the rings. Researchers also found 13 objects in the F ring of Saturn, ranging from 27 metres to 10 kilometres in size. Most of these objects were identified by the team as â€˜moonletsâ€™ of icy boulders aggregating then separating.
â€œThe evidence is consistent with the picture that Saturn has had rings all through its history. We see extensive, rapid recycling of ring material, in which moons are continually shattered into ring particles, which then gather together and re-form moons,â€ says Larry Esposito, principal investigator for Cassini's Ultraviolet Imaging Spectrograph (press release).
What Esposito has shown is not that the rings are as old as the solar system but they could have survived since the start of the solar system. If Saturnâ€™s rings were as old as Saturn, previous theories ran, they should have been darker due to infall of meteoric dust.
But the new observations show that the amount of ice and rock smashing around in the ring system is larger than previously thought. â€œThe more mass there is in the rings, the more raw material there is for recycling, which essentially spreads this cosmic pollution [of infall] around. If this pollution is being shared by a much larger volume of ring material, it becomes diluted and helps explain why the rings appear brighter and more pristine than we expected.",â€ says Esposito.
The BBC is focusing in on another aspect of the research â€“ not only are they old, the rings may â€œlast foreverâ€, it says.
Esposito and Miodrag Sremcevic are presenting these results at the American Geophysical Union meeting. Sremcevic recently featured on the Great Beyond with another Saturn story. In a paper published in Nature, Sremcevic detailed the discovery of â€˜moonletsâ€™ in Saturnâ€™s A ring. These were, he suggested, fragments from a collisional cascade triggered by the recent break up of a moon.
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