Q: Why do we think Jupiter has a metallic fluid hydrogen layer deep inside the planet?
H: What special characteristic about the Earth is associated with Earth's iron-nickel liquid outer core?
A magnetosphere is the region around a planet where its magnetic field predominates over the magnetic field of the surrounding interplanetary region. Despite its name, Jupiter's magnetosphere is not spherical, but has a long "magnetotail" streaming away like a windsock from the Sun's solar wind . The solar wind itself is made mostly of protons and electrons. The magnetotail stretches beyond the orbit of Saturn! A shock wave (like the bow wave of a boat) is formed where the solar wind particles are slowed by the magnetic field causing a turbulent region to form ("magnetopause"). In the outer reaches of Jupiter's magnetosphere there is a disk-shaped region (“magnetodisk”) within which electric currents flow, carried by low-energy "plasma". Plasma is matter which is heated up enough not only to break the bonding forces between its molecules, but also to free the electrons from their atoms!
Arrows located on the magnetic field's "lines of force" show the direction that an Earth-made compass' "North" arrow would point. On Jupiter, the "North" arrow would point toward geographic SOUTH! On Earth, rocks with magnetic minerals show that the "polarity" of the magnetic field has changed throughout geologic time. This is probably also true for the magnetic fields of other planets... so if you're planning a trip to Jupiter in the future don't throw away your compass !!