Saturn is the sixth planet from the Sun , and the second largest in the solar system . Saturn's most distinctive feature is its ring system. The rings are named in order of their discovery, and from the planet outward they are known as the D, C, B, A, F, G, and E rings. These rings are now known to comprise more than 100,000 individual ringlets, each of which circles the planet. Rings A and B are easily visible from the Earth by a telescope. Other special feature is that Saturn (as well as Jupiter) is still settling gravitationally, following its original accretion from the gas and dust nebula from which the solar system was formed more than 4 billion years ago. This contraction generates heat, causing Saturn to radiate into space three times as much heat as it receives from the sun.
The Pioneer 11 probe flew by Saturn in September 1979, followed by Voyager 1 in November 1980 and Voyager 2 in August 1981. The CASSINI satellite will study the planet and the Titan moon further from 2004 onwards.
Saturn has an internal magnetic field with a dipole aligned with the rotation axis (Ness et al., 1982). Together with the ring current (Connerney et al., 1983) and the solar wind pressure it defines the position of the magnetopause (e.g., Maurice et al., 1996). Saturn's magnetic field is substantially weaker than that of Jupiter, and Saturn's magnetosphere a is about one-third the size of Jupiter's. Saturn's magnetosphere consists of a set of doughnut-shaped radiation belts in which electrons and atomic nuclei are trapped. The belts extend to more than 2 million km from the center of Saturn and even farther in the direction away from the Sun, although the size of the magnetosphere fluctuates, depending on the intensity of the solar wind. The solar wind and Saturn's rings and satellites supply the particles that are trapped in the radiation belts. The rotation period of 10 hr 39 min 25 sec for Saturn's interior was measured by Voyager 1 while passing through the magnetosphere, which rotates in synchrony with the interior of Saturn. The magnetosphere interacts with the ionosphere , the topmost layer of Saturn's atmosphere, causing auroral emissions of ultraviolet radiation.
More than 20 satellites have been discovered orbiting Saturn. Between the inner and outer satellites orbits Titan, Saturn's largest moon (larger than the planet Mercury). Titan has a nitrogen atmosphere with traces of methane, ethane, acetylene, ethylene, hydrogen cyanide, and carbon monoxide and dioxide. On the surface, the temperature is about -182 C, and methane or ethane may be present in the forms of rain, snow, ice, and vapor. The interior of Titan probably consists of equal amounts of rock and water ice. No magnetic fields have been detected.
Surrounding the Titan's orbit is an enormous toroidal cloud of neutral hydrogen atoms. A disk of plasma, composed of hydrogen and possibly oxygen ions, is located inside the orbit of Titan. The plasma rotates in nearly perfect synchrony with Saturn's magnetic field.
- Connerney, J. E. P., M. H. Acuna, and N. F. Ness, Currents in Saturn's magnetosphere, J. Geophys. Res., 88, 8779-8789, 1983.
- Maurice, S., I. M. Engle, M. Blanc, and S. Skubis, Geometry of Saturn's magnetopause model, J. Geophys. Res., 101, 27053-27059, 1996.
- Ness, N. F., M. H. Acuna, K. W. Behannon, L. F. Burlaga, J. E. P. Connerney, and R. P. Lepping, Magnetic field studies by Voyager 2: Preliminary results at Saturn, Science, 215, 558-563, 1982.
See also Wikipedia on Saturn.