Magnetosphere of Jupiter

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.A primary objective of the Juno mission is to explore the polar magnetosphere of Jupiter. While Ulysses briefly attained latitudes of ~48 degrees, this was at relatively large distances from Jupiter (~8.6 RJ). Hence, the polar magnetosphere of Jupiter is largely uncharted territory and, in particular, the auroral acceleration region has never been visited. ... 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. Jupiter's internal magnetic field is generated by electrical currents in the planet's outer core, which is composed of liquid metallic hydrogen. Volcanic eruptions on Jupiter's moon Io eject large amounts of sulfur dioxide gas into space, forming a large torus around the planet. Jupiter's magnetic field forces the torus to rotate with the same angular velocity and direction as the planet. The torus in turn loads the magnetic field with plasma, in the process stretching it into a pancake-like structure called a magnetodisk. In effect, Jupiter's magnetosphere is shaped by Io's plasma and its own rotation, rather than by the solar wind like Earth's magnetosphere. Strong currents in the magnetosphere generate permanent aurorae around the planet's poles and intense variable radio emissions, which means that Jupiter can be thought of as a very weak radio pulsar. Jupiter's aurorae have been observed in almost all parts of the electromagnetic spectrum, including infrared, visible, ultraviolet and soft X-rays. The action of the magnetosphere traps and accelerates particles, producing intense belts of radiation similar to Earth's Van Allen belts, but thousands of times stronger. The interaction of energetic particles with the surfaces of Jupiter's largest moons markedly affects their chemical and physical properties. Those same particles also affect and are affected by the motions of the particles within Jupiter's tenuous planetary ring system. Radiation belts present a significant hazard for spacecraft and potentially to human space travellers. Jupiter's magnetosphere is a complex structure comprising a bow shock, magnetosheath, magnetopause, magnetotail, magnetodisk, and other components. The magnetic field around Jupiter emanates from a number of different sources, including fluid circulation at the planet's core (the internal field), electrical currents in the plasma surrounding Jupiter and the currents flowing at the boundary of the planet's magnetosphere. The magnetosphere is embedded within the plasma of the solar wind, which carries the interplanetary magnetic field. The bulk of Jupiter's magnetic field, like Earth's, is generated by an internal dynamo supported by the circulation of a conducting fluid in its outer core. But whereas Earth's core is made of molten iron and nickel, Jupiter's is composed of metallic hydrogen. As with Earth's, Jupiter's magnetic field is mostly a dipole, with north and south magnetic poles at the ends of a single magnetic axis. However, on Jupiter the north pole of the dipole is located in the planet's northern hemisphere and the south pole of the dipole lies in its southern hemisphere, opposite to the Earth, whose north pole lies in the southern hemisphere and south pole lies in the northern hemisphere. Jupiter's field also has quadrupole, octupole and higher components, though they are less than one tenth as strong as the dipole component. The dipole is tilted roughly 10° from Jupiter's axis of rotation; the tilt is similar to that of the Earth (11.3°). Its equatorial field strength is about 417.0  μT (4.170 G), which corresponds to a dipole magnetic moment of about 2.83 × 1020 T·m3. This makes Jupiter's magnetic field about 20 times stronger than Earth's, and its magnetic moment ~20,000 times larger. Jupiter's magnetic field rotates at the same speed as the region below its atmosphere, with a period of 9 h 55 m. No changes in its strength or structure had been observed since the first measurements were taken by the Pioneer spacecraft in the mid-1970s, until 2019. Analysis of observations from the Juno spacecraft show a small but measurable change from the planet's magnetic field observed during the Pioneer era. Jupiter's internal magnetic field prevents the solar wind, a stream of ionized particles emitted by the Sun, from interacting directly with its atmosphere, and instead diverts it away from the planet, effectively creating a cavity in the solar wind flow, called a magnetosphere, composed of a plasma different from that of the solar wind. The Jovian (i.e. pertaining to Jupiter) magnetosphere is so large that the Sun and its visible corona would fit inside it with room to spare. If one could see it from Earth, it would appear five times larger than the full moon in the sky despite being nearly 1700 times farther away. As with Earth's magnetosphere, the boundary separating the denser and colder solar wind's plasma from the hotter and less dense one within Jupiter's magnetosphere is called the magnetopause. The distance from the magnetopause to the center of the planet is from 45 to 100 RJ (where RJ=71,492 km is the radius of Jupiter) at the subsolar point—the unfixed point on the surface at which the Sun would appear directly overhead to an observer. The position of the magnetopause depends on the pressure exerted by the solar wind, which in turn depends on solar activity. In front of the magnetopause (at a distance from 80 to 130 RJ from the planet's center) lies the bow shock, a wake-like disturbance in the solar wind caused by its collision with the magnetosphere. The region between the bow shock and magnetopause is called the magnetosheath. At the opposite side of the planet, the solar wind stretches Jupiter's magnetic field lines into a long, trailing magnetotail, which sometimes extends well beyond the orbit of Saturn. The structure of Jupiter's magnetotail is similar to Earth's. It consists of two lobes (blue areas in the figure), with the magnetic field in the southern lobe pointing toward Jupiter, and that in the northern lobe pointing away from it. The lobes are separated by a thin layer of plasma called the tail current sheet (orange layer in the middle).