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16. Star Watching and Saturn

Philip Nicholson and Matt HedmanPhilip D. Nicholson, Astronomy, and research colleagues, members of NASA’s Cassini-Huygens mission, found the most direct evidence to date of patterns within Saturn’s outer rings. These patterns—called gravitational wakes—are thin, parallel striations (small chunks of water ice) radiating outward like spokes on a pinwheel. Because of their small scale—328 feet wide—they are impossible to see with the spacecraft’s high-resolution camera. Nicholson’s team used Cassini’s visual and infrared mapping spectrometer (VIMS) to take spectra of the star Omicron Ceti as it passed behind Saturn’s outer rings during four three-hour intervals, or stellar occultations. With more than 100,000 spectra from each occultation, the researchers analyzed the data, plotting the amount of near-infrared light that filtered through the rings. The patterns have been theorized since the 1970s. This finding gives scientists new information about the rings’ microstructure and internal dynamics: how the ice chunks move as they are pulled toward each other and collide and as Saturn’s tidal force shears them apart. It also gives researchers a tool for judging the overall thickness of Saturn’s rings.

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