Chapter 10:
Worlds of Gas and LiquidThe 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
Overall Planet Composition
by mass
•75% Hydrogen
•71% Hydrogen
•24% Helium
•24% Helium
•1% Other
•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 poles
Polar Rotation Period
9 hr 55 min 41 sec
Equatorial Rotation Period
9 hr 50 min 28 sec
Polar Rotation Period
10 hr 39 min 25 sec
Equatorial Rotation Period
10 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 Spot
is 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
comparison
of the
orientation
of the giant
planets
magnetic
fields