Jupiter,
with satellites Io and Europa (Click on the image
for a larger view)
An
electric current of 5 million amperes was detected in the
flux tube that flows between Jupiter and Io, five times
stronger than predicted. Voyager did not fly through the
flux tube, as planned, since the stronger current had twisted
the tube 7,000 kilometers (4,300 miles) from the predicted
location.
The
Voyagers saw ultraviolet emissions from doubly and triply
ionized sulfur and doubly ionized oxygen. Pioneers 10 and
11 did not detect them, so hot plasma evidently was not
present in 1973 and 74. The sulfur comes from Io's volcanoes.
Plasma-electron
densities in some regions of the Io torus (an inner-tube-shaped
ring of matter in the region of Io's orbit) exceeded 4,500
per cubic centimeter.
A
cold plasma, rotating with Jupiter, lies inside six Jupiter
radii (430,000 kilometers or 270,000 miles) from the planet.
Ions of sulfur, oxygen, and sulfur dioxide were found.
High-energy
trapped particles were also detected near Jupiter, with
enhanced abundances of oxygen, sodium, and sulfur.
Kilometric radio emissions were coming
from Jupiter. The emissions, in the frequency range from
10 kilohertz to 1 megahertz, may result from plasma oscillations
in the Io torus.
Plasma
flows in the dayside outer magnetosphere; the plasma rotates
with the planet every 10 hours.
Voyager
1 saw evidence of a transition from closed magnetic field
lines to a magnetotail on the antisolar side ofJupiter.
Although such a magnetotail was never in serious doubt,
its existence had not been confirmed before.
Voyager
2 observations during its Jupiter-to-Saturn cruise showed
the magnetotail extends at least to the orbit of Saturn,
650 million kilometers (400 million miles) away.
Scientists
interpreted whistler emissions as lightning whistlers in
the atmosphere. Lightning was suspected, and it has been
proven, from the emissions and detection of bolts; lightning
is a major energy source for many activities on Jupiter.
Voyager
also measured radio spectral arcs (from about 1 megahertz
to more than 30 megahertz) in patterns that correlate with
Jovian longitude.
Both
Voyagers continued on to encounters with Saturn. Voyager
1 is bound out of the solar system. Voyager 2 completed
encounters with Uranus (in January 1986) and Neptune (in
August 1989). It is now also leaving the solar system.
