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Chapter 10:Worlds of Gas and
Liquid-The Giant Planets
The Giant Planets: Jupiter, Saturn, Uranus and
Neptune
Some numbers on the giant planets
Uranus & Neptune are discovered worlds
Near IR and visible light images taken with
the Keck telescope using adaptive optics
William Herschel discovered Uranus in 1781
He tried to name it Georgium Sidus after King George III (yes, it’s the same King George the American colonist called a tyrant).
No one outside England liked the name so it became Uranus
The discovery of Neptune is wrapped up in political
intrigue
John Couch Adams (England) & Urbain Le Verrier (France)
independently predicted Neptune in 1846 based on the orbit of Uranus
After receiving the predicted position from Le Verrier, Johann
Galle actually discovered Neptune on September 23,
1846
Jupiter and Saturn are mostly Hydrogen & Helium with other stuff deep in their
interior
Atmospheric Composition
by mass
• 75% Hydrogen
• 24% Helium
• 1% Other
Overall Planet Compositionby mass
• 71% Hydrogen
• 24% Helium
• 5% Heavier elements
Uranus and Neptune have much more heavy
elements
While the atmosphere is similar in composition to Jupiter and Saturn. The interior is much different. Both have a “rocky” core with a mass about that of Earth and an “icy” mantle with about 10 Earth masses. That makes the overall amount of hydrogen only about 15% of the total mass with helium being only a few percent
Jupiter and Saturn rotate faster at the equator than at
the polesPolar Rotation Period 9 hr 55 min 41 sec
Equatorial Rotation Period 9 hr 50 min 28 sec
Polar Rotation Period10 hr 39 min 25 sec
Equatorial Rotation Period10 hr 13 min 59 sec
Differential Rotation
Uranus and Neptune probably have differential rotation too but we haven’t been able to measure it
When we look at giant planets all we see are the
cloud tops
The wind patterns on Jupiter are extremely complex
The Great Red Spotis a huge
anticyclone
Saturn’s Atmosphere: Similar to Jupiter but
different
Saturn’s polar
vortex storm is
very unusual
The weather on Uranus and Neptune is best seen in IR
Uranus, especially, has very few clouds and they are deep in the atmosphere. Neptune is more active.
Neptune’s Great Dark Spot was actually a hole in the
clouds
The clouds on Jupiter and Saturn are not just water
Because Saturn is colder, the layers are deeper down
Uranus and Neptune have similar cloud layers
Uranus and Neptune are colder than Saturn so you have to go even deeper down to find the
clouds
The winds on Saturn are actually stronger than those on
Jupiter
The strongest winds of all are found on Neptune
The zonal winds on Jupiter are driven by strong storm vortexes
Similar processes may drive the winds on Saturn
Much of the internal heat comes from ongoing
differentiation
This is especially true for Saturn and Neptune
Differentiation in Jupiter and Saturn has resulted in a layered
interior structure
Liquid metallic hydrogen requires extreme pressure and high temperatures
Uranus & Neptune have more “icy” interiors
The pressure inside Uranus and Neptune is never high enough to form liquid metallic hydrogen
The result of all that liquid metallic hydrogen in Jupiter is an
enormous magnetosphere
Jupiter’s magnetic field creates radio waves by synchrotron emission
The “donut” in the magnetosphere is created by
particle spewed out of volcanoes on Io
Io’s movement through Jupiter’s magnetic field creates a 5 million amp current
Saturn’s Magnetosphere is not as strong as Jupiter’s
Saturn’s liquid metallic hydrogen layer is smaller than Jupiter’s but it still creates a huge magnetic
field
Uranus & Neptune don’t have liquid metallic hydrogen
The highly compressed liquid water and ammonia layer is a good conductor so it can create a magnetic
field
Uranus and Neptune have very unusual
magnetospheres
Their magnetic fields are tilted at an extreme angle from their rotation axis. They are also
offset from the center of the planet
A compariso
n of the orientation
of the giant
planets magnetic
fields