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Tuesday, April 24, 2012

"Snowballs" Punch Through Saturn's Rings

The objects are actually snowballs created by some of Saturn’s 60 moons, like Prometheus.

They have been snapped punching through Saturn’s F ring, the outermost of the planet's main rings, with a radius of about 87,000 miles. 
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Scientists have known that relatively large objects like Prometheus (as long as 92 miles, or 148 kilometres, across) can create channels, ripples and snowballs in the F ring.

But scientists didn't know what happened to these snowballs after they were created, Murray said.

Some were surely broken up by collisions or tidal forces in their orbit around Saturn, but now scientists have evidence that some of the smaller ones survive, and their differing orbits mean they go on to strike through the F ring on their own.

These small objects appear to collide with the F ring at gentle speeds – something on the order of about 4mph (two metres per second).

The collisions drag glittering ice particles out of the F ring with them, leaving a trail typically 20 to 110 miles (40 to 180 kilometres) long.

Murray's group happened to see a tiny trail in an image from January 30, 2009 and tracked it over eight hours.

The long footage confirmed the small object originated in the F ring, so they went back through the Cassini image catalogue to see if the phenomenon was frequent.‘The F ring has a circumference of 550,000 miles (881,000 kilometres), and these mini-jets are so tiny they took quite a bit of time and serendipity to find,’ said Nick Attree, a Cassini imaging associate at Queen Mary. ‘We combed through 20,000 images and were delighted to find 500 examples of these rogues during just the seven years Cassini has been at Saturn.’

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