The propeller-blade streaks indicate moonlets, probably only 330 feet (100 meters) in diameter.
That's too small to be seen even the Cassini photos, which are the highest resolution images ever taken of Saturn's rings. But it's large enough for the moonlets' gravitational pulls to visibly affect the particles around them.
Amazingly, the Cassini team found four of these propeller-like structures, even though only a few photos were detailed enough to depict such small features.
Since these photos covered only a tiny fraction of the ring, there may potentially be millions of moonlets yet to be found in the A ring alone.
Origin of the Rings
The finding supports the theory that Saturn's rings are formed of debris from one or more large objects that broke into pieces, rather than from matter that never quite managed to fuse together to form a moon.
It's unlikely that moonlets this large were formed through gradual buildup of space material, says Matthew Tiscareno of Cornell University in Ithaca, New York, who led the international study team.
"It's much easier if you start with a solid icy core, like a shard from a breakup [of a large object], which can then grow by sweeping up additional particles," Tiscareno said.
The discovery also helps explain how all of Saturn's moons and ring particles interact—useful not only for understanding the rings but for understanding how planets form from matter circling young stars.
"Everything we do in studying the rings gives us insight into how planets form, because the processes we see occurring today in Saturn's rings are the same as those occurring in the disk of material that eventually formed the solar system and the planets within it," Porco, of the Space Science Institute, said.
The discovery also increases understanding of how Pan and Daphnis create gaps in the ring system.
The propeller-like streaks, Porco says, are wannabe gaps.
If the bodies that created the streaks got bigger and bigger, she said, the "blades" would get longer and longer.
"Finally, they would meet, all the way around the ring," she said.
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