WEBVTT

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A magnetosphere is the sphere of influence of a magnetic field. 

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So a planet that has a magnetic field has a magnetosphere when its sphere of influence

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extends beyond the planet out into space and affects the region around it.

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The presence of the Earth's magnetic field was recognized back in the 14th or 15th century. 

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And since the 17th century it's been a topic of active study. 
Yet we still don't know how magnetic fields are generated inside planets. 

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The magnetosphere of Jupiter is vast.

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So if you think of Jupiter being ten times the size of the Earth,
and the magnetosphere is a hundred times the size of Jupiter.

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So this is vast a big, big, big volume. 

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By measuring Jupiter's magnetic field from Juno we hope to do two things.

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One is to advance our understanding of how magnetic fields are generated in planets
and the other is to learn about the interior structure of Jupiter. 

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You might question why go 400 million miles to Jupiter to study its magnetic field
when the Earth has a perfectly good magnetic field which we can study.

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Jupiter's metallic hydrogen core is much closer to the surface. 

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So when we measure Jupiter's magnetic field from Juno,
we're much closer to where the field is generated

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and by looking at the magnetic field we should be able to tell whether Jupiter has
a solid inner core and that has profound consequences for how Jupiter formed

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for models of its interior, for understanding its gravity field.

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It's a sort of key observation we'd like to pin down for Jupiter.