Cassini Reports on an Evolving Saturn

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The Cassini spacecraft continues to send intriguing insights from up close to Saturn back to astronomers on Earth. The latest results from the mission, published online Friday by the journal Science, provide new clues into the icy nature of the planet's rings and how the planet has changed in recent years.

Larry W. Esposito of the University of Colorado at Boulder and his colleagues employed the ultraviolet imaging spectrometer (UVIS) onboard Cassini to measure the amount of hydrogen and oxygen present in the Saturnian system. The results suggest that the amount of oxygen present varies greatly. "A possible explanation for the fluctuation in oxygen is that small, unseen icy moons have been colliding with Saturn's E ring," Esposito posits. "The collisions may have produced small grains of ice, which yielded oxygen atoms when struck by energetic, charged particles in Saturn's magnetosphere." Each of Saturn's rings exhibits variations in brightness, which reveal varying degrees of meteorite pollution and thus age, the authors report. "The evidence indicates that in the last 10 million to 100 million years, fresh material probably was added to the ring system," Esposito says.

In a second paper, Donald A. Gurnett of the University of Iowa and his collaborators report that the gas giant has not stayed static over the past two decades since the flyby of space probe Voyager 1. Indeed, plasma and radio-wave instruments on Cassini detected lighting storms that were between 10 and 30 times more intense than those recorded 24 years ago. In addition, the team discovered that Saturn is slowing down: its current rotation period of 10 hours and 45 minutes is six minutes longer than the rotation Voyager measured. Next up for Cassini is the release of the Huygens probe, which will head for the surface of the moon Titan on December 24.

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