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2019-01-25. How Long Is a Day on Saturn?

posted Jan 30, 2019, 7:56 PM by Alan Gould

By Nadia Drake, The New York Times. [https://www.nytimes.com/2019/01/25/science/saturn-day-length.html] For GSS A Changing Cosmos chapter 7. Excerpt: For decades, it was a nagging mystery — how long does a day last on Saturn? Earth pirouettes around its axis once every 24 hours or so, while Jupiter spins comparatively briskly, once in roughly 9.8 Earth-hours. And then there is Venus, a perplexingly sluggish spinner that takes 243 Earth-days to complete a full rotation. With Saturn, it turns out the answer rippled in plain view, in the planet’s lustrous rings. After reading small, spiraling waves in those bands, sculpted by oscillations from Saturn’s gravity, scientists reported this month in the Astrophysical Journal that one Saturnian day is a mere 10 hours, 33 minutes and 38 seconds long, measured in Earth time. ...Saturn has been stubbornly secretive about its days. Its buttery clouds don’t bear helpful markings that scientists might use to track the planet’s rotation, and they can't easily use its nearly vertical magnetic axis — as they have for Jupiter's more off-kilter alignment — to gather clues about the planet's interior. ... Not until the Cassini spacecraft swooped, flipped and twirled through the Saturn system did scientists realize that the answer was outside the planet itself, etched into its icy rings. As Saturn spins, its internal vibrations inscribe telltale signatures in its rings; studying those markings is now termed “kronoseismology,” from kronos, the Greek name for Saturn, and seismo, for quakes and vibrations....