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Saturn

Larger than thirty planet Earths. Faster than the speed of sound (really). Look, up on Saturn, it's...

Superstorm!

If you could tune in to the "Interplanetary Weather Channel," here's what you would have heard one day last fall: "And now for tomorrow's forecast. Saturn: swirling clouds, with winds gusting to 1,000 miles per hour."

And if IWC had "gone to the videotape," the pictures would have blown your socks off. A huge storm was sweeping across the Northern Hemisphere of our solar system's second largest planet.

When we say huge, we mean it. No mere Earthlike hurricane or cyclone, Saturn's storm started as a mass of clouds "the size of Earth." Then it grew...and grew...and grew... Within days, the storm circled the entire planet. The twisted garland of clouds was as big as thirty-one Earths laid side by side. Saturn must be some big planet, eh?

Great Spot!

Astronomers could hardly believe their telescopes — or eyes. Describing the storm in a letter to "Sky and Telescope" magazine, solar system photographer Donald Parker said, "It's the brightest thing I've ever seen on the planet." The storm looked bright because all those clouds reflected lots of sunlight — so much that they outshone Saturn's normally brilliant rings.

And there was lots of sunlight to reflect because, at the time the storm formed, it was summer in Saturn's Northern Hemisphere (an event that happens only once every 30 years). The planet's North Pole was tilted toward the Sun, so the rays were striking the hemisphere directly. If that sounds familiar, it's because the same kind of tilt causes our seasons on Earth.

The Sun Did It

Could this direct summer sun have had something to do with how Saturn's storm formed? Astronomers suspect it did. They say the rays penetrated the outer layers of the planet's thick atmosphere, heating up gases down below. What do you think happened then? Right, the warm gases rose, just as heated gases do on Earth.

And when the relatively warm gases hit Saturn's extremely cold upper atmosphere — zap! Ammonia, one of the gases in the mixture, froze into countless icelike crystals. Astronomers believe these white crystals formed the clouds of the Great White Spot...which were then whipped around the planet by Saturn's ever-present superfast winds.

Those same winds eventually tore the storm apart. But don't worry. Saturn's great storm will probably be back. To find out why — and when — read on.

Reaction Time:

1. Saturn has had similar "white-spot" storms in 1876, 1903, 1933 and 1960. Do you notice a pattern here? When do you think the next storm will strike?

2. Saturn's storm circled the entire planet. In order for a storm to circle Earth, it would have to be 40,000 kilometers wide — that's our planet's circumference. The average Earth hurricane measures only about 400 kilometers across. How many of these big, powerful storms would it take to circle Earth?

 

November 1, 1991

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