Saturn—God of Agriculture
Saturn: Son of Uranus and Gaia—
After castrating his father, his 6th
son, Jupiter, overthrew him and the
rest of the Titans and seized power
for the Olympian gods.
Saturn—As Seen From Earth
Saturn—Voyager 2 in 1981
Notice:
Internal Structure
Note: ‘liquid metallic
hydrogen’ on
Saturn, also.
How do we know
that Saturn has a
larger core to overall
mass ratio (10%)
compared to
Jupiter’s (2.6%)?
The core to overall mass ratio is about 2.6% for
Jupiter, but is much larger for Saturn … about
10%. An observation supporting this conclusion
is that _____.
A. Saturn is more massive than Jupiter and
its center is more gravitationally
compressed.
B. Saturn’s ring system is more extensive
than Jupiter’s
C. Saturn is less oblate than Jupiter, even
though it is more massive and rotates at
approximately the same speed.
D. Saturn is more oblate than Jupiter—but
not as oblate as it would be if it had the
same core to overall mass ratio as Jupiter
Saturn has lower
atmospheric temperature
than Jupiter.
Saturn has lower ‘g’ so
its cloud layers are
more spread out.
Jupiter
Saturn
Ultraviolet image superimposed on visible image
SATURN’S NORTH POLE
• First seen by
Voyager 1980
Saturn’s Hexagon
• 30 years later—Cassini
looks at north pole after
Saturn emerged from 15
years of winter.
• Hexagonal ‘jet stream’
is still there!
Saturn from Voyager
Rhea
Enceladus
Mimas
Dione
Tethys
Titan
Orbits of Saturn’s Moons
Inner, large moons
Outer, captured
moons
Hyperion
Notice inclined,
elliptical orbit
Views of Saturn’s Rings
Saturn’s Ring System
The Cassini division is _____.
A. an elite division of WWII Italian
soldiers that fought off the German
landing at Anzio
B. a major division in the rings of
Saturn that is visible from Earth
C. the division between terrestrial and
Jovian planets
D. a gap between two mountain
ranges on Saturn
Saturn’s Satellites and Rings
Saturn's Major Satellites
Diameter
Name Lunar Units Orbital Radius
Mimas
0.12
3.08
Enceladus 0.14
3.95
Tethys
0.30
4.89
Dione
0.32
6.26
Rhea
0.44
8.75
Titan 1.48 (0.75 Mars) 20.27
Hyperion 328×260×214 km 24.90
Iapetus
0.42
59.08
Phoebe 230×220×210 km 214.84
Period (days)
0.9
1.4
1.9
2.7
4.5
15.9
21.3
79.3
-545.1
Saturn’s Ring Structure
The Roche Limit
≈ 2.4 Planetary Radii
Planetary Rings and Roche Limit
A planet’s Roche limit is ______.
A. the distance beyond which matter
cannot be captured by the planet
B. the distance within which any solid
satellite (e.g., a fragment of rock) will be
pulled apart by tidal forces
C. the outer extent of the magnetic field of
the planet, or the magnetospheric
boundary
D. the distance within which tidal forces
will overcome the mutual gravitational
forces that hold a large object together in
a spherical shape and pull it apart into
small, irregularly fragments held together
primarily by molecular forces
Cassini Division and Encke Gap
View of Rings Away from Sun
Cassini Division is not empty
Ring Structure
Rings—Natural Color
Different chemical compositions?
Ring Spokes
Spokes—Close Up
Spokes rotate at
same rate as
Saturn’s
magnetic field
Clouds of
electrically
charged dust
raised from rings
by magnetic
forces
Cassini approaches Saturn
Cassini sees Prometheus &
Pandora
Prometheus and
Pandora are ‘shepherd’
satellites
F-Ring and Prometheus
Prometheus’ gravitation creates ‘drape’ in F-Ring
The F-Ring Shepherds
Prometheus
Pandora
Two tiny but significant satellites,
Prometheus and Pandora, that follow nearly
identical orbits around Saturn are called
shepherd satellites because they ______.
A. trigger volcanoes or geysers on the
surfaces of larger moons by gravitational
interaction.
B. give off a sound like the ‘woof’ of a dog.
when ring particles try to move past them
C. concentrate particles in the narrow,
twisted F ring of Saturn.
D. clear out particles from the Cassini
division in Saturn's rings.
Daphnis and the Keeler Gap
in the A-Ring
As Daphnis orbits, its gravity
induces scalloping along the
edges of the Keeler gap
Outer Edge of B-Ring
Mimas
Mimas orbits Saturn in a 2:1 period resonance with
particles in the Cassini Division
Tethys…Telesto & Calypso not
shown
Size (km):
• Telesto: 29 x 22 x 20
• Calypso: 30 x 23 x 14
Diameter: 1066 km
Orbit of Tethys, Telesto, Calypso
Saturn's Major Satellites
Diameter
Name Lunar Units Orbital Radius
Mimas
0.12
3.08
Enceladus 0.14
3.95
Tethys
0.30
4.89
Dione
0.32
6.26
Rhea
0.44
8.75
Titan 1.48 (0.75 Mars) 20.27
Hyperion 328×260×214 km 24.90
Iapetus
0.42
59.08
Phoebe 230×220×210 km 214.84
Period (days)
0.9
1.4
1.9
2.7
4.5
15.9
21.3
79.3
-545.1
Phoebe
• Retrograde orbit in ecliptic
plane—not in Saturn’s
equatorial plane.
• Primitive object similar to Pluto
and Triton (ice and rock—very
dark) in composition.
• Ancient planetesimal which
accreted into cores of Jovian
planets—most were ‘thrown’
into Kuiper belt.
Iapetus
• Very dark, reddish ‘leading’
side
• Might be a thin layer of
organic material similar to
complex substances found in
primitive meteorites.
• Dark material might have
originated from Phoebe.
Micrometeor impacts could
kick dark matter off Phoebe
which is then swept up by
Iapetus.
Iapetus’ Equatorial Ridge
But…the dark material seems to
be concentrated in crater floors—
indicates an internal origin.
Iapetus is far from Saturn — might
have formed with methane or
ammonia ice in its interior. Dark
material explained by eruptions of
methane from its interior?
Hypothesis supported by a dark
ring of material about 100
kilometers (62 miles) in diameter
that straddles the border between
the leading and trailing
hemispheres of Iapetus.
Such rings formed on Moon
and Mars when dark volcanic
material flowed into impact
craters and filled around the
central peak.
Chaotic Hyperion
• Heavily cratered,
spongy-like reddish
surface
• Largest, irregularlyshaped satellite
• Tumbles chaotically in
eccentric orbit
Enceladus Orbits in E-Ring
Enceladu
s
The geologically youthful terrains came as a
great surprise to the scientific community,
because no theory was then able to predict
that such a small and cold moon compared
to Jupiter's highly active moon Io) could
exhibit signs of such activity.
Enceladus
Enceladus’ Surface
• Almost 100% reflective
• Areas where no craters
• Geological resurfacing—
liquid interior?
Ejection from Enceladus
Plume Vent
Model
Some astronomers suspect that Saturn's satellite
Enceladus is heated enough by tidal flexing, which
produces active geysers of water imaged by the Cassini
spacecraft flyby. This is similar to the mechanism that
causes Io’s ‘volcanoes.’ Which one of the following
observations supports this conjecture?
A. Enceladus orbits within Saturn’s faint E ring,
which lies outside Saturn’s Roche limit and
might be made up of ice particles ejected from
the geysers.
B. Enceladus is a “shepherd satellite” for Saturn’s
braided F ring, which could be made up of ice
particles from the geysers.
C. A strong electric current flows from Enceladus
to Saturn along Saturn's magnetic lines of force.
D. Enceladus lies within Saturn’s Roche limit and is
in the process of breaking up.
Titan
• 2nd largest moon in Solar System—larger than Mercury
and Pluto
• Why so smoggy?
Interpreting Titan’s Spectrum
Titan Haze
Titan's air is predominantly made up of nitrogen with other
hydrocarbon elements which give Titan its orange hue. These
hydrocarbon rich elements are the building blocks for amino
acids necessary for the formation of life. Titan's environment
may be similar to that of the Earth's before life began putting
oxygen into the atmosphere.
Huygens Probe at ESA
Descent of Huygens Probe
Titan’s Lakes
Huygens image—visible light
Cassini image—infrared
North Pole lakes—
Larger than Lake Superior
Titan’s River Channels and
Coastline
Exposing Titan’s Surface
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If you want to see this on your own time … go to →
http://saturn.jpl.nasa.gov/multimedia/flash/Titan/index.
html
QUESTION
If interplanetary travel were possible,
how would a company in the business
advertise a holiday on Titan?
A. The largest number of volcanoes for your travel
dollar anywhere in the solar system!
B. Exquisite methane/ethane lakes, hydrocarbons
beyond your wildest dreams!
C. Glaciers galore for your hiking pleasure under
star-studded skies!
D. Hot and dry—never rains—beautiful crystal
clear skies!
Key Ideas
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Composition and Structure: Saturn much larger than
Earth.
Saturn’s internal structure is similar to that of Jupiter
(composed of 71% hydrogen, 24% helium, and 5% all
other elements by mass), but its core makes up a
larger fraction of its volume and its liquid metallic
hydrogen mantle is shallower than that of Jupiter.
Saturn rotates so rapidly that it is noticeably
flattened, more so than Jupiter. Rotation of interior
revealed by variations in radio emission.
Saturn emits more energy than it receives from the
Sun. Planet is still cooling and helium rain contributes.
Key Ideas
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Atmosphere: Visible “surface” of Saturn actually the
tops of clouds. Rapid rotation twists the clouds into
dark belts and light zones that run parallel to the
equator. Strong zonal winds run along the belts and
zones.
The outer layers show differential rotation: The
equatorial regions rotate slightly faster than the polar
regions. Polar rotation rate is nearly the same as the
internal rotation rate.
The colored ovals visible in the Saturnian atmosphere
represent gigantic storms. Storms in Saturn’s
atmosphere seem to be shorter-lived than Jupiter’s.
Key Ideas
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There are three cloud layers in the atmosphere. The
cloud layers in Saturn’s atmosphere are spread out
over a greater range of altitude than those of Jupiter,
giving Saturn a more washed-out appearance.
Saturn’s atmosphere contains less helium than Jupiter’s
atmosphere. This lower abundance may be the result of
helium raining downward into the planet. Helium
“rainfall” may also account for Saturn’s surprisingly
strong heat output.
Key Ideas
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Magnetic Field and Magnetosphere: Saturn’s
magnetic field and magnetosphere are much less
extensive than Jupiter’s.
Rings: Saturn is circled by a system of thin, broad
rings lying in the plane of the planet’s equator. This
system is tilted away from the plane of Saturn’s orbit,
which causes the rings to be seen at various angles by
an Earth-based observer over the course of a Saturnian
year.
Structure of the Rings: Saturn has three major,
broad rings (A, B, and C) that can be seen from
Earth. Other, fainter rings were found by the Voyager
spacecraft.
Key Ideas
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Principal rings of Saturn composed of particles of
ice and ice-coated rock ranging in size from a few
micrometers to about 10 m. Most rings exist inside
the Roche limit of Saturn, where disruptive tidal
forces are stronger than the gravitational forces
attracting the ring particles to each other.
Each of Saturn’s major rings composed of a great
many narrow ringlets. The faint F ring, which is just
outside the A ring, is kept narrow by the gravitational
pull of shepherd satellites.
Jupiter’s faint rings are composed of a relatively
small amount of small, dark, rocky particles that
reflect very little light.