Ring World
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Mass
(x 1024 kg)
Earth
1
Saturn
95.2
5.97
568
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Size
Radius
Equatorial
Polar
Earth
1
6378
6357
Saturn
9.45
60,268
54,364
Oblateness
0.3%
9.8%
Look for the flattening in the next photo.
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Earth
Our Moon
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Density
kg/m3
Earth
100%
5515
Saturn
12.5
687
Saturn has the lowest density of all the
planets and moons.
Saturn would float in water!
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Large Magnetosphere
• Saturn’s magnetosphere is about 1/5th as
large as Jupiter’s.
– This is expected because Saturn has a
thinner conducting mantle of metallic H than
Jupiter has.
• It’s 20x weaker than Jupiter’s field.
– It’s actually only 68% as strong as Earth’s!
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Magnetosphere
• Jupiter’s magnetosphere is tipped slightly
to its rotation, and is complex in structure
• Saturn’s magnetosphere is aligned almost
perfectly with its rotation (axisymmetric),
and its structure is very simple.
• Interesting feature: a ring current.
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Evidence for Saturn’s Magnetic Field!
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Equatorial Ring Current
• Saturn’s moons Enceladus, Dione, and
Tethys are enclosed in a torus of ions (like
Jupiter’s Io).
• This torus is outside the major rings (but
inside the thin, tenuous E ring).
• A current of about 10 million amps flows
through this outer ring.
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Chemical Composition
• 96.3% H
3.25% He (by volume)
• Traces of methane (CH4), ammonia (NH3),
water, ammonium hydrosulfide (NH4SH)
• Like Jupiter, there is a mantle of metallic H
under a gaseous H envelope.
• Rocky / metallic core
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Saturn’s Orbit
• Average distance from the sun:
1.43 billion km (9.6 A.U.)
• Perihelion: 1.35 billion km
• Aphelion: 1.51 billion km
• Orbit Eccentricity: 0.056 (slightly more
eccentric than Jupiter’s orbit)
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Orbit (2)
• Orbital Period: 29.5 years
– Orbital Velocity: 9.7 km/s
• Inclination of orbit to ecliptic: 2.5o
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Saturn’s Rotation
• Rotational Period: 10.66 hours (10h 40m)
• Saturn has zonal winds, like Jupiter, but
the colors are more muted.
• The rotational axis is tilted 26.7o to the
ecliptic. This makes for a periodic tilt in
the rings as viewed from the earth.
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Notice the rotational storm.
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A red oval similar to Jupiter’s GRS.
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apod.nasa.gov/apod/ap090111.html
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The Rings !
• 2 (3) rings visible to the naked eye.
– separated by visible gaps.
• 3 more rings visible telescopically
• A new ring appears to be forming!
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Pan orbits within the Encke Division
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Movie
Dusty
ring
“spokes”
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Rings are Dynamic, not Static
• Dusty spokes indicate that the rings may
be able to change on a short time frame.
• There are also periodic “ripples” in part of
the rings…evidence of a collision between
the rings & a comet or asteroid.
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Braided
F ring
The ring
isn’t really
braided,
but has
spirals
around it.
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Here’s a site with more info about the spiral
around the F ring.
http://www.aim.ufr-physique.univ-paris7.fr/CHARNOZ/homepage/SPIRAL/spiral_uk.htm
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Shepherd Moons
• Collisions between ring particles should
remove kinetic energy from some
particles, transfer kinetic energy to others.
– Slower particles should fall into Saturn.
– Faster particles should leave the ring.
– Net: the rings should spread out and
dissipate.
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The gravity
of the
shepherd
moons
focuses the
rings.
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Barely
discernible
new ring
(with 2 new
tiny moons)
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The Larger Moons
• They’re all ice balls, but they’re not all the
same.
• Mimas
• Dione
• Iapetus
Enceladus
Rhea
Tethys
Titan
• All of these moons are in synchronous
rotation (leading vs. trailing hemisphere
differences)
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Mimas
with
Herschel
Crater
Mimas is
about the
size of
Ohio
1150 kg/m3
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Enceladus
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South Pole
Bluish “tiger stripes”
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Geysers of water & water vapor erupt from
Enceladus’ south pole region.
Hot spots have been discovered here by Cassini.
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Tethys has
a gigantic
canyon
which nearly
circles the
moon.
Ithaca Chasma
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Dione, leading hemisphere
at left, trailing at right.
Dione
Direction of
movement
through space.
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Rhea
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Rhea also has
those strange
lighter stripes
on its trailing
hemisphere.
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Atmosphere of N2
heavily laden with
hydrocarbons:
methane ethane
Very smoggy
Titan 5150 km diameter 1880 kg/m3
Ganymede 5262 km dia. 1940 kg/m3
How can Titan have a thick atmosphere, when
Ganymede doesn’t?
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Titan has
a complex
layered
atmosphere
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Titan’s atmosphere is 95% N2, 10X denser than
Earth’s, and extends 600 km above the surface.
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Some liquid
flows on
titan’s
surface.
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The shoreline of an ethane lake.
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The darker areas are lakes
of liquid methane and ethane.
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At Titan’s surface, the
Temperature is about
95K (-290oF)
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Iapetus
sooty leading hemisphere
bright trailing hemisphere
equatorial ridge
What’s the
source of
the soot?
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Hyperion – a captured comet?
apod.nasa.gov/apod/ap090118.html
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Missions to Saturn
• Pioneer 11
– Launched 1973, flyby 1979.
– Transmitted low-resolution photos of Saturn,
rings, moons.
• Voyager 1
– Launched 1977, flyby 1980
– Transmitted 900+ photos of the moons.
– Discovered complexity of rings & nature of
Titan’s atmosphere.
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Missions to Saturn (2)
• Voyager 2
– Launched 1977, flyby 1981
– 1150 photographs of the moons
• Cassini Orbiter with Huygens probe to
Titan’s surface.
– Launched 1997, arrived in orbit July 1, 2004.
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Cassini’s Mission
• Cassini is designed to photograph and
map Saturn & its moons in visible,
infrared, and ultraviolet wavelengths.
• It has a magnetometer, magnetic imager,
and plasma imager to closely study
Saturn’s magnetic field.
• Huygens probe landed on Titan on
January 14, 2005.
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http://nssdc.gsfc.nasa.gov/planetary/factsheet/saturnfact.html
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http://science.nasa.gov/headlines/y2002/images/rings/ringnames_big.gif
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http://www.universetoday.com/am/uploads/2004-0909ring-full.jpg
http://hal.physast.uga.edu/~jss/1010/ch11/
http://www.spaceflightnow.com/cassini/061011dring.html
http://www.aim.ufr-physique.univ-paris7.fr/CHARNOZ/homepage/SPIRAL/spiral_uk.htm
http://astrogeology.usgs.gov/Projects/BrowseTheSolarSystem/gifs/dione2.gif
http://esamultimedia.esa.int/images/Science/huygens31150.jpg
http://esamultimedia.esa.int/images/cassini_huygens/PIA06983_H.jpg
http://antwrp.gsfc.nasa.gov/apod/image/0501/landing_huygens_01_h3.jpg
http://antwrp.gsfc.nasa.gov/apod/ap060131.html
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http://saturn.jpl.nasa.gov/multimedia/images/image-details.cfm?imageID=1105
http://www.windows.ucar.edu/tour/link=/saturn/space_missions.html
http://saturn.jpl.nasa.gov/spacecraft/images/sc-components-litho.jpg
http://solarsystem.nasa.gov/multimedia/gallery/Cassini_Enc.jpg