size of Saturn's magnetosphere is determined by external
pressure of the solar wind. When Voyager 2 entered the magnetosphere,
the solar-wind pressure was high and the magneto- sphere
extended only 19 Saturn radii (1.1 million kilometers or
712,000 miles) in the Sun's direction. Several hours later,
however, the solar-wind pressure dropped and Saturn's magneto-
sphere ballooned outward over a six-hour period. It apparently
remained inflated for at least three days, since it was
70 percent larger when Voyager 2 crossed the magnetic boundary
on the outbound leg.
all the other planets whose magnetic fields have been measured,
Saturn's field is tipped less than one degree relative to
the rotation poles. That rare alignment was firstmeasured
by Pioneer 11 in 1979 and was later confirmed by Voyagers
1 and 2.
distinct regions have been identified within Saturn's magnetosphere.
Inside about 400,000 kilometers (250,000 miles) there is
a torus of H+ and O+ ions, probably originating from water
ice sputtered from the surfaces of Dione and Tethys. (The
ions are positively charged atoms of hydrogen and oxygen
that have lost one electron.) Strong plasma-wave emissions
appear to be associated with the inner torus.
the outer regions of the inner torus some ions have been
accelerated to high velocities. In terms of temperatures,
such velocities correspond to 400 million to 500 million
Kelvins (700 to 900 million degrees Fahrenheit).
the inner torus is a thick sheet of plasma that extends
out to about 1 million kilometers (600,000 miles). The source
for material in the outer plasma sheet is probably Saturn's
ionosphere, Titan's atmosphere, and the neutral hydrogen
torus that surrounds Titan between 500,000 kilometers (300,000
miles) and 1.5 million kilometers (1 million miles).
emissions from Saturn had changed between the encounters
of Voyager 1 and 2. Voyager 2 detected Jupiter's magnetotail
as the spacecraft approached Saturn in the winter and early
spring of 1981. Son afterward, when Saturn was believed
to be bathed in the Jovian magnetotail, the ringed planet's
kilometric radio emissions were undetectable.
portions of Voyager 2's Saturn encounter, kilometric radio
emissions again were not detected. The observations are
consistent with Saturn's being immersed in Jupiter's magnetotail,
as was also the apparent reduction in solar-wind pressure
mentioned earlier, although Voyager scientists say they
have no direct evidence that those effects were caused by