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[silence]

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[music] Narrator: You're probably more familiar with magnetic fields than you realize.

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If you have a compass and a map, you can use the Earth's magnetic

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field to help you find your way. You've probably also seen what a magnetic field looks

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like. Drop iron filings around a bar magnet, and the field shows itself as a series

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of lines. If you take the filings away, you can still get an idea of what the field

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looks like by flying a tiny compass around the magnet. The compass points in the direction of

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the magnetic field, allowing you to draw its shape. But how do you find

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out what a planet's magnetic field looks like? You basically do the same thing.

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However, instead of flying a simple compass around the planet, NASA scientists

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use satellites carrying a much more sensitive device called a magnetometer. Mounted

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far away from the spacecraft, a magnetometer uses electric currents to measure the magnetic

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field of the planet. By flying this "electronic compass" around the planet, scientists

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can draw an accurate model of what its magnetic field looks like. And magnetometers

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have helped scientsts discover more than just the shape of the Earth's magnetic field. Other planets

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in our solar system, such as Jupiter, have magnetic fields that are similar to ours.

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The Sun also generates its own magnetic field that affects the entire solar system.

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But not every planet in our solar system has a magnetic field.

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For example, we've discovered that, unlike Earth, Mars doesn't have a global magnetic field at all.

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Instead, it has small pockets of local magnetic fields.

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But after all is said and done, even with all the advanced technology, the most

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amazing thing is that we've made all these discoveries using something that's essentially

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an upgraded compass.

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[music fading, beeping]

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[beeping]