Magnetic
field arises when there is a conducting, convecting
medium in a rapidly rotating body. This makes a
“dynamo”; the same mechanism in the Sun, the
Earth and other contexts.
Jupiter has by
far the strongest field. Venus may be too slow a rotator – no field. The
magnetic fields trap high energy particles, making “radiation belts”.
Astronauts have to stay out of them, and spacecraft near Jupiter have to be
specially designed. Particles from Io are trapped in a doughnut or “torus”
around Jupiter. Note the off-center fields for Uranus and Neptune.
