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Jupiter - King of the planets
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Jupiter weighs three times more than all the other planets 
combined. Its great mass causes it to act like an enormous cosmic 
vacuum cleaner.  Its gravitational influence attracted much of 
the debris in the early solar system. Without this thinning 
effect on the asteroid population the Earth would have suffered 
a much more severe bombardment from space during its history. 
Repeated catastrophic impacts would have almost certainly 
prevented the evolution of intelligent life. Without Jupiter 
guarding over us, we wouldn't exist!

The toxic atmosphere of Jupiter, formed from hydrogen, ammonia 
and methane, is whipped into a raging broth of cyclones and 
storms by the planet's rapid spin rate (just ten hours). The 
light and dark bands of colour are wrenched in opposite 
directions, resulting in continent-sized turbulent regions that 
can be stable for many centuries. The most famous feature, the 
Great Red Spot, is probably created as darker molecules from 
inside the planet are churned up to the surface by the violent 
storms.

Jupiter's rapid spin rate combined with its core of metallic 
hydrogen gives the planet an extremely strong magnetic field. 
This interacts with the Solar Wind to produce the largest 
enduring structure in the solar system.  Jupiter's magnetic 
cocoon stretches almost a billion kilometres, spanning the 
distance between the orbits of Jupiter and Saturn. A combination 
of the strong magnetic field and charged particles from the Sun 
results in currents as high as 5 million amps flowing between 
Jupiter and one of Jupiter's satellites, Io.  This natural power 
station generates a power of 2.5 trillion watts, vastly 
exceeding the energy we can produce on Earth.

Everyone is familiar with the majestic rings that encircle the 
planet Saturn, but it is not the only planet in our solar system 
that is surrounded by a disk of material. In 1977 astronomers 
were surprised to find faint and narrow rings surrounding the 
planet Uranus, and in 1979 Voyager 1 photographed a faint ring 
around the planet Jupiter.

Jupiter's rings are made from extremely small particles 
comparable in size to the particles in cigarette smoke. These 
objects are constantly falling into Jupiter's upper atmosphere 
and being replenished by dust that is sandblasted off Jupiter's 
two innermost moons by meteorites.

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Images
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1.  Jupiter from space
(http://www.solarsystem.f2s.com/jupiter/img1a.jpg)

This Hubble Space Telescope image provides a detailed look at 
the striped cloud patterns of Jupiter. The dark clouds are 
created by falling currents of gas while the light zones are 
formed when material rises to the surface.

Public domain image courtesy of NASA.

2.  A close look at Jupiter's Great Red Spot
(http://www.solarsystem.f2s.com/jupiter/img2a.jpg)

This dramatic view of Jupiter's Great Red Spot and its 
surroundings was obtained by Voyager 1 on Feb. 25, 1979, when 
the spacecraft was 9.2 million kilometres from Jupiter. Cloud 
details as small as 160 kilometres across can be seen here. The 
colorful, wavy cloud pattern to the left of the Red Spot is a 
region of extraordinarily complex and variable wave motion. 

Public domain image courtesy of NASA.

3.  Volcanoes on Io
(http://www.solarsystem.f2s.com/jupiter/img3a.jpg)

Io is Jupiter’s nearest moon, and also the most volcanically active body 
in the solar system. The Voyager I cameras recorded 8 major eruptions 
happening simultaneously! Io is so active because it is constantly 
squashed and stretched by the gravitational forces between Jupiter and 
the outer satellites.

© Calvin J. Hamilton.

4.  The rings of Jupiter
(http://www.solarsystem.f2s.com/jupiter/img4a.jpg)

Jupiter's ring was discovered by Voyager 1 in a single image that was 
targeted specifically to search for a faint ring system. Subsequently, 
Voyager 2 was reprogrammed to take a more complete set of images. 

© Calvin J. Hamilton.