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Saturn’s rings aren’t the same, Cassini finds

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Researchers at NASA have suggested through analysis of data on Saturn’s rings that one of the rings of the planet isn’t the same as the others and it seems that the ring could very well be geologically younger than the rest.

Saturn’s tilt provides a great opportunity to scientists to study its rings specifically when sun’s rays move from north to south over the planet and its rings, and back again. Scientists have been studying the planet’s rings making use of changing temperatures caused by changing sunlight and findings suggest that temperatures of the rings vary from season to season.

One particular period which Cassini mission scientists have been very keen on is the Equinox during the Saturnian year when the sun illuminates the planet’s enormous ring system edge-on providing scientists with an extraordinary opportunity to observe short-lived changes in the rings that reveal details about their nature through Cassini.

A team of scientists have revealed through a new study, published in the journal Icarus, that one particular section of the rings appears to have higher temperatures than rest of the rings. This higher-than-expected temperature provided a unique window into the interior structure of ring particles not usually available to scientists.

“For the most part, we can’t learn much about what Saturn’s ring particles are like deeper than 1 millimeter below the surface. But the fact that one part of the rings didn’t cool as expected allowed us to model what they might be like on the inside,” said Ryuji Morishima of NASA’s Jet Propulsion Laboratory, Pasadena, California, who led the study.

When researchers compared the actual data with those obtained for their model of temperature changes of Saturn’s rings, they were puzzled. They found that while the model predicted the cooling of the rings accurately, there was this one large section — the outermost of the large, main rings, called the A ring — which was much warmer than the models predicted. The temperature spike was especially prominent in the middle of the A ring.

To find answers to this discrepancy, researchers performed a detailed investigation of how ring particles with different structures would warm up and cool down during Saturn’s seasons.

Previous studies based on Cassini data have shown Saturn’s icy ring particles are fluffy on the outside, like fresh snow. This outer material, called regolith, is created over time, as tiny impacts pulverize the surface of each particle. The team’s analysis suggested the best explanation for the A ring’s equinox temperatures was for the ring to be composed largely of particles roughly 3 feet (1 meter) wide made of mostly solid ice, with only a thin coating of regolith.

“A high concentration of dense, solid ice chunks in this one region of Saturn’s rings is unexpected,” said Morishima. “Ring particles usually spread out and become evenly distributed on a timescale of about 100 million years.”

The accumulation of dense ring particles in one place suggests that some process either placed the particles there in the recent geologic past or the particles are somehow being confined there. The researchers suggest a couple of possibilities to explain how this aggregation came to be. A moon may have existed at that location within the past hundred million years or so and was destroyed, perhaps by a giant impact. If so, debris from the breakup might not have had time to diffuse evenly throughout the ring. Alternatively, they posit that small, rubble-pile moonlets could be transporting the dense, icy particles as they migrate within the ring. The moonlets could disperse the icy chunks in the middle A ring as they break up there under the gravitational influence of Saturn and its larger moons.

“This particular result is fascinating because it suggests that the middle of Saturn’s A ring may be much younger than the rest of the rings,” said Linda Spilker, Cassini project scientist at JPL and a co-author of the study. “Other parts of the rings may be as old as Saturn itself.”

During its final series of close orbits to Saturn, Cassini will directly measure the mass of the planet’s main rings for the first time, using gravity science. Scientists will use the mass of the rings to place constraints on their age.