Magnetosphere of Jupiter
The magnetosphere of Jupiter is the cavity created in the solar wind by Jupiter'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.
False-color image of aurorae on the north pole of Jupiter, as viewed by the Hubble Space Telescope | |
| Discovery | |
|---|---|
| Discovered by | Pioneer 10 |
| Discovery date | December 1973 |
| Internal field | |
| Radius of Jupiter | 71,492 km |
| Magnetic moment | 2.83 × 1020 T·m3 |
| Equatorial field strength | 417.0 μT (4.170 G) |
| Dipole tilt | ~10° |
| Magnetic pole longitude | ~159° |
| Rotation period | 9h 55m 29.7 ± 0.1s |
| Solar wind parameters | |
| Speed | 400 km/s |
| IMF strength | 1 nT |
| Density | 0.4 cm−3 |
| Magnetospheric parameters | |
| Type | Intrinsic |
| Bow shock distance | ~82 RJ |
| Magnetopause distance | 50–100 RJ |
| Magnetotail length | up to 7000 RJ |
| Main ions | On+, Sn+ and H+ |
| Plasma sources | Io, solar wind, ionosphere |
| Mass loading rate | ~1000 kg/s |
| Maximum plasma density | 2000 cm−3 |
| Maximum particle energy | up to 100 MeV |
| Aurora | |
| Spectrum | radio, near-IR, UV and X-ray |
| Total power | 100 TW |
| Radio emission frequencies | 0.01–40 MHz |
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 internally driven, shaped primarily by Io's plasma and its own rotation, rather than by the solar wind as at 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.