Narrator: What safeguards our solar system...

is our star.

The sun provides a shield, stretching beyond the last

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

rays."

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

outbursts called coronal mass ejections.

Want a vision of earth gone wrong?

Just look at what solar storms do our sister planet,

Venus. They strip away lighter

elements in its upper atmosphere, hydrogen, oxygen

and the molecule they form: water.

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

including thick sulfurous clouds.

How has Earth avoided the grim fate of Venus?

We can see the answer as the solar storm

approaches Earth.

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

A powerful magnetic field

generated deep within its core.

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

Much of the solar energy that gets through is reflected back

to space by clouds, ice, and snow.

The energy that Earth absorbs is just enough to power

a remarkable planetary engine: the climate.

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It's set in motion by the unevenness of solar

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

and the seasons that cause warm tropical winds

to blow toward the poles and cold polar air

toward the equator.

Wind currents drive surface ocean currents.

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This computer simulation shows the Gulf Stream winding its

way along the coast of North America.

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This great

ocean river carries enough heat energy to power the industrial

world a hundred times over.

It breaks down in massive world pools

that spread warm tropical waters over northern seas.

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Below the surface they mix with cold deep currents that swirl

around under sea ledges and mountains.

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Earth's climate engine

has countless moving parts: tides and terrain,

cross winds and currents-- all working to equalize temperatures

around the globe.

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