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Tracking the Planets

Would you want to live on Saturn, where summer comes but once every 30 years? The good news is you'd have 30-year breaks between Saturn's raging summer storms. The bad news is you'd have to weather a giant storm every year. What's the deal?

The trouble is with the word "year." We normally think of a year as the time it takes Earth to travel once around the Sun. But that's only an Earth year. Each of the other eight planets takes a different amount of time to make it once around the Sun; they're racing in different lanes on the giant solar system "track."

Earth is relatively close to the center of the track. But Saturn is more than a billion kilometers farther out. Saturn takes about 30 times longer than Earth to make it once around the Sun. So there is a span of 30 Earth years between Saturn's storms. But if you measure in Saturn years, the storms strike each summer.

How did Saturn get stuck in its outside lane? Scientists say it has something to do with how the solar system formed.

According to one theory, it happened about 4.5 billion years ago, when an enormous cloud of gas and dust collapsed and began to spin around its center. The center formed a star — the Sun. The leftover gas and dust in the spinning cloud gradually stuck together in bigger and bigger clumps. These clumps eventually became the nine planets.

When the Sun began producing energy, it threw off powerful winds. These winds blasted the planets closest to the Sun; blowing away most of their light materials, such as hydrogen and helium gas. The result? The inner planets — Mercury, Venus, Earth and Mars — were left with dense metal cores, rocky surfaces and little or no atmospheres.

The clumps far from the Sun, however, were able to collect and hold onto huge envelopes of superlight hydrogen and helium gas. They grew to great size. Their incredibly thick atmospheres have earned the outer planets — Jupiter, Saturn, Uranus and Neptune — the collective name "gas giants." (Pluto, which remains a tiny, icy world, is an exception).

And the more atmosphere a planet has, the bigger its storms can grow. In addition to Saturn's "yearly" tempest, you've probably heard of Jupiter's Great Red Spot — a storm three times the size of Earth that has been raging for more than 300 Earth years. Neptune has a similar dark spot, an Earth-size storm with some of the fastest winds in the solar system. Are there giant storms on Uranus? ] Scientists haven't detected any yet, but keep your telescopes peeled!

 

November 1, 1991

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