SATURN’S RINGS “DISAPPEAR”—

In a celestial feat any magician would appreciate, the planet Saturn made its wide but thin ring system disappear from our view Aug. 11.

Saturn's rings, loaded with ice and mud, boulders and tiny moons, is 170,000 miles wide. But the shimmering setup is only about 30 feet thick. The rings harbor 35 trillion-trillion tons of ice, dust and rock, scientists estimate.

The rings shine because they reflect sunlight. But every 15 years, the rings turn edge on to the sun and reflect almost no sunlight.

"The light reflecting off this extremely narrow band is so small that for all intents and purposes the rings simply vanish," explained Linda Spilker, deputy project scientist for the Cassini Saturn mission at NASA's Jet Propulsion Laboratory.

The rings remain a bit of a mystery. Scientists are not sure when or how they formed, though likely a collision of other objects was involved.

Saturn's equator is tilted relative to its orbit around the sun by 27 degrees – similar to the 23-degree tilt of the Earth. As Saturn circles the sun, first one hemisphere and then the other is tilted sunward. This causes seasons on Saturn, just as Earth's tilt causes seasons on our planet.

While Earth goes around the sun once every 365 days or so, Saturn's annual orbit takes 29.7 years. So every 15 years, the attitude shift puts the gas giant planet's equator, and its ring plane, directly in line with sunlight. Scientists call it an equinox, and this one marks the arrival of spring to the giant planet's northern hemisphere. (On Earth, equinoxes occur in March and September.)

"Whenever equinox occurs on Saturn, sunlight will hit Saturn's thin rings, the ring plane, edge-on," Spilker said.

Exerpts from: www.space.com/scienceastronomy/090810-mm-saturn-rings-edge-on.html

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