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Physics/Selected picture/October 2012
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Portal:Physics
Magnetosphere of Jupiter
edit
The
magnetosphere of Jupiter
is the cavity created in the
solar wind
by the planet's
magnetic field
. Extending up to seven million kilometers in the Sun's direction and almost to the orbit of
Saturn
in the opposite direction, Jupiter's
magnetosphere
is the largest and most powerful of any planetary magnetosphere in the
Solar System
, and by volume the largest known continuous structure in the Solar System after the
heliosphere
. Wider and flatter than the
Earth's magnetosphere
, Jupiter's is stronger by an
order of magnitude
, while its
magnetic moment
is roughly 18,000 times larger. The existence of Jupiter's magnetic field was first inferred from observations of radio emissions at the end of the 1950s and was directly observed by the
Pioneer 10
spacecraft in 1973.
The main driver of Jupiter's magnetosphere is the planet's rotation. In this respect Jupiter is similar to a device called a
Unipolar generator
. When Jupiter rotates, its ionosphere moves relatively to the dipole magnetic field of the planet. Because the dipole magnetic moment points in the direction of the rotation, the
Lorentz force
, which appears as a result of this motion, drives negatively charged electrons to the poles, while positively charged ions are pushed towards the equator. As a result, the poles become negatively charged and the regions closer to the equator become positively charged. Since the magnetosphere of Jupiter is filled with highly conductive plasma, the
electrical circuit
is closed through it.
The Io plasma torus is in yellow. Jupiter's volcanically active moon
Io
is a strong source of plasma in its own right, and loads Jupiter's magnetosphere with as much as 1,000 kg of new material every second. Strong volcanic eruptions on Io emit huge amounts of
sulfur dioxide
, a major part of which is
dissociated
into atoms and
ionized
by the solar
ultraviolet radiation
, producing ions of
sulfur
and
oxygen
: S
+
, O
+
, S
2+
and O
2+
. These ions escape from the satellite's atmosphere and form the
Io plasma torus
Io's interaction with Jupiter's magnetosphere. As a result of several processes, the plasma slowly leaks away from Jupiter
Bow shock