Jupiter's Magnetic Field and Radiation Belts
Jupiter is surrounded by an enormous magnetic field called the magnetosphere, which has a million times the volume of Earth's magnetosphere.
Charged particles are trapped in the magnetosphere and form intense radiation belts. These belts are similar to the Earth's Van Allen belts, but are many millions of times more intense.
The Inner Magnetosphere
Jupiter's inner magnetosphere is shaped like a doughnut with Jupiter filling the hole. The magnetosphere rotates very rapidly with the planet.
The Outer Magnetosphere
At distances of more than about 20 times the radius of Jupiter, the magnetic field becomes flattened. On the sunward side of the planet, the magnetosphere is blunted by the solar wind. The size of the outer magnetosphere varies depending on the intensity of the solar wind.
For years, scientists have been measuring radio waves from Jupiter, which emits radio waves in three wavelength bands: centimeter, decimeter, and decameter. Jupiter emits more radio noise than any other object in the solar system except the Sun.
Jupiter's Radio Spectrum
The three distinct bands of radio emission from Jupiter are shown here. The very high frequency — wavelengths shorter than 3 centimeters (1.2 inches) — or thermal radiation, indicates a temperature of about -140 degrees Celsius (-255 Fahrenheit) for Jupiter. This radiation is produced by the motion of molecules in Jupiter's atmosphere.
Decimetric radiation, with wavelengths between 3 centimeters (1.2 inches) and 3 meters (10 feet), is produced by the motion of electrons in a magnetic field. Radio noise from Jupiter gave the first indication that the planet has a large magnetic field.
Radio Bursts From Io
Some of Jupiter's decametric radiation, with wavelengths longer than 3 meters (10 feet), appears to be related to the Jovian satellite Io. As Io passes through Jupiter's magnetic field, it may become electrically charged, negative on one side and positive on the other. This can produce a potential of 400,000 volts accross the satellite.
When Io reaches certain positions, an electric current of five million amps may flow between Jupiter's ionosphere and Io, which would produce the tremendous radio bursts.