Monday, August 10, 2009

Saturn to Pull Celestial Houdini

In 1918, magician extraordinaire Harry Houdini created a sensation when he made a 10,000 pound elephant disappear before a mystified audience of over 5,200 at New York's famed Hippodrome theatre. But a vanishing pachyderm is nothing compared to the magnificent illusion to be performed by our solar system's own sixth rock from the sun on Aug. 11. On that day, ladies and gentlemen, boys and girls, children of all ages, the planet Saturn, with no help from either Jupiter or Uranus, will make its 170,000-mile-wide ring system disappear.

How does a mere gas giant planet, without the benefit of a magic wand, smoke and mirrors, or even sleeves for that matter, manage to hide an estimated 35 trillion-trillion tons of ice, dust and rock fragments? Saturn itself, perhaps adhering to the magician's code never to reveal how a trick is performed, is not talking. But fortunately for us, dear friends, Linda Spilker, deputy project scientist for the Cassini Saturn mission at NASA's Jet Propulsion Laboratory in Pasadena, Calif., is not in the magician's guild.

"Saturn has been performing the "ring plane crossing" illusion about every 15 years since the rings formed, perhaps as long as 4.5 billion years ago, so by now it is pretty good at it," said Spilker. "The magician's tools required to perform this trick are pure sunlight, a planet that wobbles, and a main ring system that may be almost 200-thousand miles wide, but only 30 feet thick." All planets in our solar system wobble on their axes to some extent.

This change of attitude eventually places a planet's equator directly in line with the photons of light streaming in from the sun. This is called "equinox," and on Earth it occurs every year about March 21 (spring equinox) and September 22 (autumnal equinox). On Saturn, it occurs twice during each 29 Earth-year-long orbit around the sun (about every 15 years).

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