Jupiter and Saturn

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Jupiter and Saturn
Jupiter and Saturn are the two largest and best
known Jovian planets. Others include Uranus and
Neptune. Pluto is considered as a separate
object.
Great Red Spot
a) Earth Based View b)View from Hubble
The four brightest moons are called the Galilean
satellites after Galileo
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While Jupiter is known for its four brightest
moons and the red spot, Saturn is known for its
extensive ring system.
a) Earth Based View b)View from Hubble
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Space Missions to the Jovian Planets

• Voyager I 1977 to Jupiter
• Voyager II 1977 to Jupiter, Saturn, Uranus,
  Neptune measured magnetoshperes, magnetic fields
  and radio, visible light and IR emissions.
• Galileo 1989 to Jupiter (in 1995) with gravity
  assists deployed atmospheric probe as of
  mid-2000 was still orbiting.
• Cassini to Saturn will arrive 2004 to send
  atmospheric probe into Titan and then orbit among
  moons for next 4 years.

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Discovery of Uranus
Uranus was discovered by William Herschel while
cataloging stars. Uranus slowly moved among the
stars proving it was a planet. Herschel wanted
to name the planet George but was talked into
Uranus by Johann Bode.
a) Earth view b) Voyager 2 view
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Discovery of Neptune
a) Earth view
The orbit of Uranus was being gravitationally
perturbed by another unknown planet. After two
years of searching, they found the planet within
2 degrees of its predicted position.
b) Voyager 2 view
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Physical Properties
Notice for example that Jupiter is 315 times more
massive than the Earth and 11 times bigger while
being less dense.
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It is difficult to measure the rotation rates of
the Jovian planets because they have no surface
to watch as they rotate. With nothing to tie
them down different parts of the atmosphere
rotate at different speeds (differential
rotation).
The Jovian planets are also known as the gas
giants.
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Jupiters Atmosphere
Because of its high escape velocity, Jupiter has
been able to retain all the lighter gasses
including hydrogen and has the same chemical
proportions as when it was created 4.6 billion
years ago. It consists of 86 hydrogen, 14
helium, traces of methane, ammonia, and water
vapor.
After its four bright moons, Jupiter is best
known for its cloud bands. The bands are the
result of convection currents in the atmosphere.
Lighter warmer gasses tend to ride on top
(ammonia) and the cooler heavier gasses sink down
(ammonium hydrosulfide) giving a light/dark
pattern on the surface.
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Weather on Jupiter
In addition to the large scale band structures on
Jupiter there are smaller structures. The most
famous being the great red spot which is a
hurricane storm which has been raging for over
300 years. Spacecraft have detected lightening
and aurora.
Show Fix laser disk video side 2, at 15559
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Saturns Atmosphere
Saturn is not as colorful or turbulent as
Jupiter. This may be due to the fact that Saturn
is cooler because it is further away from the
Sun. It does not contain as large storms, nor
are they permanet. It also has enough gravity to
hold on to all the gasses and consists of 92.4
hydrogen, 7.4 helium, and traces of methane and
ammonia.
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Some storms on Saturn actually encircle the
planet.
Sequence of images from Hubble
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The most noticeable thing about Saturn is its
rings.
Real color
Color enhanced to show structure.
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Atmospheres of Uranus and Neptune
Both planets have similar makeup to Jupiter and
Saturn Uranus 84 hydrogen, 14 helium, 2
methane Neptune 84 hydrogen, 14 helium, 3
methane Ammonia is not significant in either of
the planets. Their blue-green color is due to
the fact that methane absorbs in the red and thus
the planets only reflect the blue-green.
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Weather on Uranus and Neptune
Uranus as few cloud structures and those can only
be seen with the aid of computer enhancements.
a) True color b-d) computer enhanced
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Neptune shows more distinct cloud features than
does Uranus. It even has giant storms that last
a while (few years) much like Jupiter. Neptune
had the Great Dark spot from 1989 to 1994.
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Interior Structure
Since there is no surface to the Jovian planets
we cant set up seismic observations, how do we
know about their interiors? We use computer
modeling. Since the Jovian planets are made
mostly of the simple gasses of hydrogen and
helium, we think we understand how they behave.
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It is the combination of a metallic hydrogen
interior and high rotation rates that give the
Jovian planets (especially Jupiter) their strong
magnetic fields. This magnetic field channels
the solar wind around the planet and spacecraft
can measure its effects far from the planet.
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The one bad thing about being the largest planet
in the solar system is that you tend to attract a
lot of comets and meteors.
Visible Scar
Infrared Image
Breakup of comet Shoemaker-Levy 9
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Resources

• For current (and past) info on planetary probes
  and missions see
• http//www.windows.ucar.edu/tour/link/space_miss
  ions/
• space_missions.html
• Or http//dmoz.org/Science/Technology/Space/Miss
  ions/