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Jupiter's
Puzzling Magnetosphere
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The
study of Jupiter's magnetosphere can help us understand our own
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The most intriguing aspect
of Jupiter's magnetosphere is its pulsar behavior, that is, a celestial
radio source with a well-defined modulation period, assumed to be the
spin period of the central object. For
Jupiter, this is 10 earth hours. Most planets, including Earth and Jupiter,
have an intrinsic magnetic field that deflects the solar wind, creating
a comet-shaped cavity called a magnetosphere.The
space between the planets is filled with a solar wind of ionized gas (plasma)
expanding supersonically outward from the Sun. Frictional coupling at
the magnetopause drives plasma circulation, known as convection,
within the magnetosphere, a dynamic process that gives rise, among other
things, to visible aurorae and planetary radio emissions.
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| How
do Scientists Study the Jovian Planets? |
Jupiter
emits more radio noise than any other object in the Solar System except
the Sun!
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For years, scientists have been measuring radio waves from Jupiter, which
emits radio waves in three wavelength bands: centimeter, decimeter, and
decameter. |
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The three distinct bands
of radio emission from Jupiter are recorded.
The very high frequency
(wavelengths shorter than 3 cm) is thermal radiation - it indicates Jupiter's
temperature of about -140 degrees Celcius!
Wavelengths between 3 cm
and 3 feet are produced by the motion of electrons in a magnetic field.
This radio noise from Jupiter gave the first indication that Jupiter has
an abnormally large magnetic field.
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| What
does this mean? |
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| Scientists
speculate some of Jupiter's decametric radiation, with wavelengths longer
than 3 meters is related to Jupiter's satellite, Io. Io orbits at a distance
of 6 Jupiter radii, deep within the magnetosphere, which extends as far
as 100 Jupiter radii. What does this have to do
with Jupiter's extraordinarily large magnetosphere?
Every second Jupiter's magnetic field strips from Io about one ton of material,
which becomes ionized and forms a thick ring of intense radiation. Ions
escaping the ring create aurora storms in Jupiter's atmosphere and inflate
the planet's magnetic field.
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As
Io passes through Jupiter's magnetic field, it becomes electrically charged,
negative on one end and positive on the other. This can produce a potential
of 400,000 volts across the satellite. At certain positions, an electric
current of 5 million amperes may flow between Jupiter's ionosphere and Io,
which would produce the tremendous radio bursts scientists record on earth. |
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| If
it were visible, Jupiter's magnetosphere would appear larger than the Sun
or Moon from earth. With a 10 hour day, Jupiter is the fastest rotator among
the planets. This rapid spin when imposed on a magnetosphere provides a
vast source of power for magnetospheric phenomena. To use this power however,
an internal source of plasma is required. The plasma is provided by Io,
as it is the most volcanically active body in the Solar System. The volcanic
emissions of sulphur dioxide escape Io's gravity and produce a plasma torus,
visible at left as two "balloons" at the centre of the magnetosphere.
These ions of oxygen and sulphur stream along Jupiter's magnetic field lines
and create spectacular auroras in the upper atmosphere. It is the ions that
escape from this torus that inflate Jupiter's magnetosphere to over twice
the size scientists would expect. |
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