More Moon and Jupiter

StarDate: January 18, 2010

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The biggest weather feature in the solar system isn't quite as big as it used to be. Its shape has changed, too -- and it may continue to change over the next few decades.

The Great Red Spot is the most prominent feature of the planet Jupiter, which looks like a brilliant star below the Moon at nightfall this evening. The Spot is a giant high-pressure system -- the opposite of the low-pressure systems that form hurricanes and other storms here on Earth. It's been around for centuries.

Even though it's pretty stable, the Great Red Spot does change. Its color -- perhaps the result of reactions between sunlight and chemical compounds dredged from deep within the planet's atmosphere -- varies from bright red to pale orange, for example.

And last year, planetary scientists reported that the spot is getting smaller. From 1996 to 2006, it shrank by about 15 percent. Considering that it's about twice as wide as Earth, that's quite a change.

The spot is also getting rounder. When astronomers first spotted it, it was much longer than it was tall. Today, it's oval shaped. And by the middle of the century, it may be a circle.

Scientists aren't sure why the Great Red Spot is changing -- although to be honest, they aren't sure how it formed, why it's been around so long, or even why it's red, either. But they're fairly sure that more changes are on the way for this shrinking giant.

Tomorrow: an expanding giant.

Script by Damond Benningfield, Copyright 2009

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