Saturn
Overall Properties
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Saturn was the outermost planet known to
ancient astronomers
Named after the father of Jupiter in Roman
mythology
Orbits the Sun at almost twice the distance
of Jupiter
Rotation Rate
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Rotates very rapidly and differentially
The rotation period at the equator is 10h
14m
Because of Saturn’s lower density, this
rapid rotation makes Saturn even more
flattened than Jupiter
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Saturn is the "flattest" planet in the solar system
Rings
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The rings lie in the equatorial plane
Their appearance from Earth changes seasonally
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Saturn’s rotation axis is significantly tilted with respect to
the planet’s orbit plane—the axial tilt is 27°
As Saturn orbits the Sun, the angles at which the rings are
illuminated and at which we view them vary
When the planet’s north or south pole is tipped toward the
Sun the highly reflective rings are at their brightest
When the rings are close to being edge-on they seem to
disappear altogether
The rings are very thin
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Their thickness is less than a few hundred meters
Appearance
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Saturn is much less colorful than Jupiter
Bands and storms do exist but the color
changes that distinguish them on Jupiter
are largely absent on Saturn
Atmosphere Composition
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Molecular hydrogen-92.4%
Helium-7.4 %
Methane-0.2%
Ammonia-0.02%
Saturn’s weaker gravity
results in thicker clouds
and a more uniform
appearance
Cloud Layers
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The total thickness of the three cloud layers in Saturn’s
atmosphere is roughly 200 km, compared with about 80 km
on Jupiter
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The reason for this difference is Saturn’s weaker gravity
Jupiter’s atmosphere is pulled much more powerfully toward the
center of the planet
Jupiter’s atmosphere is compressed more than Saturn’s, and
the clouds are squeezed more closely together
Because Saturn’s clouds are thicker, there are few holes and
gaps in the top layer, so we rarely glimpse the more colorful
levels below
We see only different levels in the topmost layer, which
accounts for Saturn’s rather uniform appearance
We see more structure in Saturn’s cloud cover when computer processing
and artificial color are used to enhance the image contrast
Weather
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The large-scale flows and
small-scale storm systems
are powered by convective
motion in Saturn’s interior
and the planet’s rapid
rotation
The zonal flow on Saturn
is considerably faster than
on Jupiter and shows
fewer east–west
alternations
Hexagon clouds
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North pole region
Storm
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In September 1990, amateur
astronomers detected a large
white spot in Saturn’s southern
hemisphere, just below the
equator
The spot developed into a band of
clouds completely encircling the
planet’s equator
Astronomers believe that the white
coloration arose from crystals of
ammonia ice formed when an
upwelling plume of warm gas
penetrated the cool upper cloud
layers
Interior
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Saturn has the same basic
internal parts as Jupiter, but
their relative proportions are
somewhat different:
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Saturn’s metallic hydrogen
layer is thinner, and its core is
larger
Because of its lower mass,
Saturn has a less extreme
core temperature, density,
and pressure than Jupiter
The central pressure is
around a tenth of Jupiter’s—
not too different from the
pressure at the center of
Earth
Temperature
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Saturn radiates almost three times more energy than it absorbs
Saturn has an internal energy source
In Saturn the helium doesn’t dissolve easily and tends to form
droplets instead because the temperature is low
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Saturn probably started out with a fairly uniform solution of helium
dissolved in hydrogen, but the helium tended to condense out of the
surrounding hydrogen
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The phenomenon is familiar to cooks, who know that it is generally much
easier to dissolve ingredients in hot liquids than in cold ones
The amount of helium condensation was greatest in the planet’s cool outer
layers, where the mist turned to rain about 2 billion years ago
A light shower of liquid helium has been falling through Saturn’s interior
ever since
As the helium sinks toward the center, the planet’s gravitational
field compresses it and heats it up
Magnetosphere
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Saturn’s electrically
conducting interior and
rapid rotation produce a
strong magnetic field and
an extensive
magnetosphere
Saturn’s magnetosphere
extends about 1 million km
toward the Sun and is
large enough to contain
the planet’s ring system
and the innermost 16
small moons
Ring System
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Astronomers now know that all the jovian planets have rings,
but Saturn’s are by far the brightest, the most extensive, and
the most beautiful
Galileo saw them first in 1610, but he did not recognize what
he saw as a planet with a ring
In 1659 the Dutch astronomer Christian Huygens realized
what the "bump" was—a thin, flat ring, completely encircling
the planet
In 1675 the French-Italian astronomer Giovanni Domenico
Cassini discovered the first ring feature, a dark band about
two-thirds of the way out from the inner edge
From Earth, the band looks like a gap in the ring
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This "gap" is named the Cassini Division
Ring System
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The inner "ring" is in reality
also composed of two rings
From the outside in, the three
rings are known as the A, B,
and C rings
The Cassini Division lies
between the A and B rings
The much narrower Encke gap
is found in the outer part of the
A ring
The B ring is brightest,
followed by the somewhat
fainter A ring, and then by the
almost translucent C ring
Rings
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In 1857 Scottish physicist James Clerk Maxwell, after
showing that a solid ring would become unstable and break
up, suggested that the rings are composed of a great number
of small particles, all independently orbiting Saturn
The rings reflect most (over 80 percent) of the sunlight
striking
Ice is the main component of the rings
The diameters of the particles range from fractions of a
millimeter to tens of meters, with most particles being about
the size (and composition) of a large snowball on Earth
Roche Limit
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The increasing tidal field of a planet
first distorts, and then destroys, a
moon that strays too close
For any given planet and any given
moon, the critical distance, inside of
which the moon is destroyed, is
known as the tidal stability limit, or the
Roche limit
 If our hypothetical moon is held
together by its own gravity and its
average density is comparable to
that of the parent planet, the
Roche limit is roughly 2.4 times
the radius of the planet
 For Saturn, no moon can survive
within a distance of 144,000 km of
the planet’s center
Origin of the Rings
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Rings must be quite young—perhaps no
more than 50 million years old, or 100
times younger than the solar system
They are probably the result of a relatively
recent, possibly catastrophic, event in the
planet’s system—perhaps a small moon
that was hit by a large comet, or even by
another moon
Moons
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Saturn has 18 named moons
Saturn has the most extensive, and in many ways the most complex, system of
natural satellites of all the planets
Most are covered with snow and ice
There are the many "small" moons—irregularly shaped chunks of ice, all less than
300 km across
There are six "medium-sized" moons—spherical bodies with diameters ranging from
about 400 to 1500 km
Saturn’s single "large" moon—Titan—which, at 5150 km in diameter, is the secondlargest satellite in the solar system
Saturn video
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Quiz to follow
QUIZ
#1
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1.Scientific data indicate that the lakes
on Saturn are composed of _____.
A.
B.
C.
D.
hot acids
bubbling lava
molten aluminum
liquid hydrocarbons
#2
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Approximately how many Earths could
fit into the volume of Saturn?
A.
B.
C.
D.
250
500
750
1,000
#3
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The density of Saturn is greater than the
density of water.
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true
false
#4
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Saturn bulges at the equator and is
squashed at the poles because the
planet _____.
A.
B.
C.
D.
spins very fast
has magnetic poles
has a low gravitational pull
is very dense along the equator
#5
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5.What is Saturn mainly composed
of?
A.
B.
C.
D.
radon
helium
nitrogen
hydrogen
#6
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Saturn’s rings are made up of _____.
A.
B.
C.
D.
dust and rocks
liquid ammonia
droplets of water
nitrogen and oxygen
#7
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7.Based on observations made so far,
scientists think that there are at least
_____ moons orbiting Saturn. [Pick the
closest number.]
A.
B.
C.
D.
10
20
30
40
#8

8.Observations taken with the Hubble
Space Telescope indicate that Saturns
moon Titan has _____ distinct
surfaces.
A.
B.
C.
D.
2
4
6
8
#9
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Cassini is aiming to put a lander on
_____.
A.
B.
C.
D.
Titan
Dione
Tethys
Phoebe
Answers
#1

1.Scientific data indicate that the lakes
on Saturn are composed of _____.
A.
B.
C.
D.
hot acids
bubbling lava
molten aluminum
liquid hydrocarbons
#2

Approximately how many Earths could
fit into the volume of Saturn?
A.
B.
C.
D.
250
500
750
1,000
#3

The density of Saturn is greater than the
density of water.


true
false
#4

Saturn bulges at the equator and is
squashed at the poles because the
planet _____.
A.
B.
C.
D.
spins very fast
has magnetic poles
has a low gravitational pull
is very dense along the equator
#5

What is Saturn mainly composed of?
A.
B.
C.
D.
radon
helium
nitrogen
hydrogen
#6

Saturn’s rings are made up of _____.
A.
B.
C.
D.
dust and rocks
liquid ammonia
droplets of water
nitrogen and oxygen
#7

Based on observations made so far,
scientists think that there are at least
_____ moons orbiting Saturn. [Pick the
closest number.]
A.
B.
C.
D.
10
20
30
40
#8

8.Observations taken with the Hubble
Space Telescope indicate that Saturns
moon Titan has _____ distinct
surfaces.
A.
B.
C.
D.
2
4
6
8
#9

Cassini is aiming to put a lander on
_____.
A.
B.
C.
D.
Titan
Dione
Tethys
Phoebe