The
magnetosphere of Jupiter is the cavity created in the
solar wind by the planet's
magnetic field. Extending up to seven million kilometers in the Sun's direction and almost to the orbit of
Saturn in the opposite direction, Jupiter's
magnetosphere is the largest and most powerful of any planetary magnetosphere in the
Solar System, and by volume the largest known continuous structure in the Solar System after the
heliosphere. Wider and flatter than the
Earth's magnetosphere, Jupiter's is stronger by an
order of magnitude, while its
magnetic moment is roughly 18,000 times larger. The existence of Jupiter's magnetic field was first inferred from observations of radio emissions at the end of the 1950s and was directly observed by the
Pioneer 10 spacecraft in 1973.