A magnetosphere is the sphere of influence of a magnetic field.
So a planet that has a magnetic field has a magnetosphere when its sphere of influence
extends beyond the planet out into space and affects the region around it.
The presence of the Earth's magnetic field was recognized back in the 14th or 15th century.
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.
The magnetosphere of Jupiter is vast.
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.
So this is vast a big, big, big volume.
By measuring Jupiter's magnetic field from Juno we hope to do two things.
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.
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.
Jupiter's metallic hydrogen core is much closer to the surface.
So when we measure Jupiter's magnetic field from Juno, we're much closer to where the field is generated
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
for models of its interior, for understanding its gravity field.
It's a sort of key observation we'd like to pin down for Jupiter.