Magnetosphere of Jupiter

Abstract The magnetosphere of Jupiter is a vast region (50 million times the volume of the planet, 70,000 times the volume of the Sun) that is dominated by the magnetic field of Jupiter. Towards the Sun, upstream in the solar wind, the magnetosphere extends 60-100 jovian radii, compressing and expanding in response to changes in the solar wind pressure. Downstream in the solar wind, the magnetosphere extends past the orbit of Saturn. The vast volume of the magnetosphere encompasses the ring system and many of Jupiter’s 95 moons, including the four Galilean moons. The innermost Galilean moon, Io, ejects about one ton per second of gases, derived from its sulfur dioxide (SO2) atmosphere, that are dissociated and ionized to produce a toroidal region of plasma comprising electrons plus S and O ions of multiple charge states. Plasma from the Io plasma torus spreads out into the magnetosphere, getting heated (by poorly understood processes) to form a plasma sheet. Some of the magnetospheric particles are accelerated and precipitate into Jupiter’s atmosphere, where they excite intense auroral emissions, spanning the spectrum from X-rays to radio. The plasma sheet extends well beyond the orbits of the Galilean moons. The plasma interaction with Europa induces electrical currents in the ocean below the moon’s ice crust. Ganymede is the only moon known to have its own internal magnetic dynamo, producing a magnetosphere within a magnetosphere. Electrical currents generated in the plasma interactions with Io, Europa, and Ganymede travel along the magnetic field to Jupiter, where localized auroral emissions are excited at the satellites’ magnetic footprints. Large-scale electrical currents flow along the magnetic field between Jupiter and the plasma sheet, coupling the plasma sheet to Jupiter’s ionosphere that rotates with the planet’s ~10-hour spin period. Thus, Jupiter’s angular momentum drives the dynamics of the magnetosphere out to ~50 jovian radii. Farther out, the solar wind begins to influence the magnetospheric dynamics, coupled by processes at the magnetospheric boundary. Ultimately, the Iogenic material is ejected as plasma blobs down the magnetotail, eventually mixing with the solar wind, similar to the plasma tail of a comet.