Voyager Planetary Encounters |
The space environments that surround the giant planets, as well as that around Earth, are controlled largely by the magnetic fields generated within the interiors of the planets. This magnetic field carves out a bullet-shaped cavity within the solar wind, which is a supersonic ionized gas that blows away from the Sun at a speed of about 400 km/s. The cavity, called a planetary magnetosphere, extends in the solar direction to a distance of about 12 planetary radii for Earth, and to distances of 50 to 100 planetary radii for Jupiter. In the anti-solar direction, the "magnetotail" portions of these cavities have been observed (for Jupiter) to extend to many astronomical units (AU's -- 1 AU = 1.5 x 10^8 km).
An apparently fundamental characteristic of planetary magnetospheres is that they are prodigious accelerators of charged particles. Within the Earth's magnetosphere, the most well-known consequences of this process are the beautiful optical displays of the polar region called auroras (northern and southern lights) and the Van Allen radiation belts that surround the Earth, posing radiation hazards to both astronauts and sensitive equipment. The characterization of the processes that generate auroras and the Van Allen belts near giant outer planets is among the objectives of the Voyager LECP instruments. We present here color displays of the LECP data sampled at all of the giant gas planets (Jupiter, Saturn, Uranus, and Neptune), and of data obtained near Earth by the MEPI experiment on NASA's ISEE-1 spacecraft (courtesy of D. J. Williams). Both Ion and Electron data are shown in separated displays.
Based on the LECP data and other Voyager data, models of the magnetospheres of the planets are generated. Available for viewing here are schematics of the magnetospheres of Jupiter, Saturn, Uranus, and Neptune.