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Narrator: What safeguards our solar system...

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is our star.

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The sun provides a shield, stretching beyond the last

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planet in its orbit: a force field that deflects these "cosmic

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rays."

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But these "solar winds" can be dangerous too, especially during

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outbursts called coronal mass ejections.

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Want a vision of earth gone wrong?

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Just look at what solar storms do our sister planet,

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Venus. They strip away lighter

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elements in its upper atmosphere, hydrogen, oxygen

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and the molecule they form: water.

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What's left is a witch's brew of noxious chemicals

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including thick sulfurous clouds.

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How has Earth avoided the grim fate of Venus?

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We can see the answer as the solar storm

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approaches Earth.

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Our planet has a protective shield all it's own--

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A powerful magnetic field

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generated deep within its core.

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In fact, that's just our first line of defense.

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Much of the solar energy that gets through is reflected back

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to space by clouds, ice, and snow.

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The energy that Earth absorbs is just enough to power

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a remarkable planetary engine: the climate.

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It's set in motion by the unevenness of solar

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heating, due in part to the cycles of day and night,

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and the seasons that cause warm tropical winds

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to blow toward the poles and cold polar air

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toward the equator.

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Wind currents drive surface ocean currents.

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This computer simulation shows the Gulf Stream winding its

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way along the coast of North America.

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This great

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ocean river carries enough heat energy to power the industrial

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world a hundred times over.

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It breaks down in massive whirl pools

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that spread warm tropical waters over northern seas.

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Below the surface they mix with cold deep currents that swirl

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around under sea ledges and mountains.

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Earth's climate engine

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has countless moving parts: tides and terrain,

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cross winds and currents-- all working to equalize temperatures

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around the globe.

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