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Planet Jupiter
The Bringer of Jollity
Diameter (km)
Diameter (Earth = 1)
Distance from Sun (x 106 )
Distance from Sun (AU)
Escape Velocity (km/s)
Mass (kg)
Mass (Earth = 1)
Density (g/cm3)
Density (Earth = 1)
Gravity (m/s2)
Average Surface Temperature (oC)
Rotational Period (days)
Orbital Period (years)
Number of Moons
Space Craft Missions
142,980
11.209
778.3
5.203
59.5
1.899 E+27
317.833
1.2463
0.22578
23.1
-150
0.4101
11.86
28
Pioneer 10 & 11, Voyager 1
& 2, Galileo, Cassini
The first of the gaseous giants and second of the superior planets, is the largest
planet in our solar system, Jupiter. Jupiter is over 11 times the diameter of the Earth
and has a mass 2.5 times that of all the other planets combined. This giant is
composed almost entirely of hydrogen (82%) and helium gas (17%). There is no
solid surface on Jupiter; instead, the surface consists of a dense atmosphere
topped with a layer of colourful clouds about 100 kilometres thick. The clouds are
made up of bands running parallel to the equator, ranging from white to dark
reddish brown, their colour arising within the clouds from complex chemical
reactions that are not fully understood by scientists. The bands are in constant
motion, and create an active surface of red belts and light-coloured zones which
rapidly rotate around the planet. Because Jupiter does not have a solid surface, it
experiences differential rotation, similar to the Sun. The bands of cloud rotate at
different speeds, but unlike the Sun, the bands also travel in opposing directions.
Two bands of gas traveling in opposite directions can create intricate circular
currents, also known as eddies, along their border which can become whirlwind
storms. While storms are constantly forming and dissipating on Jupiter, the Great
Red Spot is a huge storm that has been visible for hundreds of years. It is about
three times the size of the Earth and is the most recognizable feature on Jupiter,
visible even in amateur telescopes. The rotational rate of the equatorial region is
just under ten hours, which is extremely fast for a planet as large as Jupiter. As a
result, Jupiter is noticeably oblate, its equatorial diameter being 6.5% greater than
its polar diameter.
According to scientists, the interior of Jupiter is most likely composed of a small
metallic core surrounded by liquid hydrogen. Currents within the layer of liquid
hydrogen cause a strong magnetic field which shields Jupiter from the solar wind
and focuses the particles to the poles, causing aurora similar to the aurora on the
Earth. Had Jupiter been more massive during its formation, the internal pressure
would have generated a high enough temperature to ignite nuclear reactions within
the core, creating a sister star to the Sun. Instead, Jupiter’s core never ignited, but
has been steadily cooling since the planet’s formation, and is presently around 25
000K, compared to a temperature of only about 110K at its surface.
Four spacecraft have visited Jupiter, two Pioneer fly-bys in 1974 and two Voyager
probes in 1979. The probes obtained high-resolution images of Jupiter’s gaseous
surface and gave scientists valuable information about the planet and its intricate
atmosphere of clouds. One discovery that these probes made was the detection of
Jupiter’s thin and delicate ring structure, which is not visible from the Earth. The
probes also detected many new satellites, and along with recent discoveries we
now know of 52 moons in orbit around Jupiter, the most of any planet. Many of the
satellites are very small and resemble asteroids (the most recently discovered
moons are only a kilometre or two in diameter); however, four of its moons are
among the largest and most interesting in the solar system and were discovered by
Galileo Galilei in 1610.
The Galilean satellites had never been seen in any detail until the Voyager
spacecraft passed by them in 1979, increasing our knowledge of the four moons
tremendously. Io, Europa, Ganymede and Callisto are approximately the same size
as our Moon (Europa being slightly smaller) and are easily seen from the Earth with
binoculars or a telescope as star-like points of light along Jupiter’s equatorial plane.
Their alignment constantly changes on a nightly basis as the moons rapidly circle
around Jupiter and dance from one side to the other in a matter of hours. Io is
closest to Jupiter and is the most volcanically active body in the solar system with
numerous vents ejecting molten sulphur. The thin atmosphere and low gravity of
the moon cannot contain the material which can erupt hundreds of kilometres
above the surface. The gravity of Jupiter and the three outer Galilean satellites pull
Io in opposite directions and exert tidal forces which heat its interior, generating
pressure which is released by the eruption of the internal molten materials. Europa
is covered with a smooth tan coloured surface without mountains or craters,
suggesting a youthful surface with recent activity. The surface appears to be a layer
of frozen water with numerous cracks. Ganymede is larger than Mercury and is the
largest satellite in the solar system. Ganymede and Callisto are both dark in colour,
icy, and heavily cratered, Callisto being one of the most heavily cratered objects in
the solar system.