Saturn
and its Moons
Printable
version
April
20, 2000
Announcements
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IN
CLASS EVALUATIONS SOON (COME TO LECTURE)
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Next
honors meeting April 26 OUTLINE DUE
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Homework
#6 due next week
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Think
about writing up observing project
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Extra
credit project posted on web
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Measuring
angle of sun at sunset
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Find
West relative to landmarks
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Use
streets, map, compass, etc
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Measure
angle from west to your landmarks
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to
the right (North) is plus
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to
the left (South) is minus
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Record
angles in graph
Saturn
and its Moons Preview
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Saturn
overview
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Outer
atmosphere
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3 layers
of clouds (like Jupiter)
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Internal
structure
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Solved
(?) puzzles of Saturn
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Chemical
composition
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Excess
heat source
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Titan
(largest moon)
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Other
moons
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Cassini
and Huygens probes
Saturn
Overview
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Saturn similar in size to
Jupiter but 1/3 the mass
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Average density is less than
water!
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Most oblate planet (diameter
at equator greater than diameter at poles)
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10% oblate vs 6.5% for Jupiter
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Differential rotation
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Poles rotate slower than
equator
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Inside rotates slower than
equator
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Similar to Jupiter
Saturn's
Outer Atmosphere
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Compare
to Jupiter
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Three
layers of clouds (like Jupiter)
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Ammonia
(NH3)
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Ammonium
hydrosulfide (NH4SH)
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Water
(H2O)
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Less
gravity on Saturn means clouds less compressed
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Larger
haze layer between cloud
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optical
telescopes can't see as deeply into Saturn's atmosphere
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Saturn
less colorful
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Saturn
has higher wind speeds see Solved Puzzles
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No
long-lived storms like Jupiter's Great Red Spot
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Saturn
also has belts and zones
Jupiter
Storm
on Saturn (white arrow shape)
Saturn's
Belts and Zones
Saturn's
Internal Structure
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Similar
to Jupiter
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Rocky
core larger than Jupiter's
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Liquid
metallic hydrogen layer smaller
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Outer
atmosphere much thicker
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why
more oblate and less dense
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Where
is Saturn's magnetic field generated?
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Liquid
metallic hydrogen layer
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Saturn
has Aurora
Aurora
on Saturn
Solved
(?) Puzzles of Saturn
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Outer atmosphere composition
different from Jupiter, Sun
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Jupiter, Sun: 80% hydrogen,
19% helium, 1% other
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Saturn: 88% hydrogen, 11%
helium, 1% other
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Generates 3 times more heat
than it receives from the Sun
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Jupiter generates twice as
much
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Why should Jupiter emit more
heat?
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Larger
bodies retain more he
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More
heat output contributes to higher wind speed
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Hypothesis:
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Saturn cold enough, dense
enough atmosphere to condense out liquid helium (like rain)
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Falling liquid helium rain
heated lower atmosphere by friction
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(potential energy lecture
demo)
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heat still escaping today
Titan
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Saturn's largest moon
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Cold enough and big enough
to have an atmosphere
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Absorption lines of CH4
(methane) seen from Earth
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Atmosphere too thick to see
the ground in optical wavelengths!
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Even thicker than Earth's
atmosphere!
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No other moon with a thick
atmosphere
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90% Nitrogen
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what other solar system body
has a nitrogen rich atmosphere?
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Earth!
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Nitrogen was originally bound
in ammonia (NH3)
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Sunlight broke up ammonia,
hydrogen floated away
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This effect dried out which
other solar system bodies?
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Venus
and Mars
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Lots of methane (CH4)
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Methane and sunlight make
hydrocarbons, in particular ethane
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ethane may have condensed
to make rivers and lakes
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Methane and hydrocarbons
combine to make long chain polymers (plastics)
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Some of the longer chains
fall out of the atmosphere
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probably gooey like melted
plastic
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Infrared images from Hubble
Space Telescope
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light areas may be water
and ammonia ice
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dark areas may be hydrocarbon
lakes
Titan from Voyager (optical)
Titan from HST (infrared)
Saturn's
Other Moons
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At least 18 moons in all
(similar to Jupiter)
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Only Titan is really big
(between Mercury and Mars)
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6 moderate sized moons
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Mimas
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Enceladus
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Recent geologic activity
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Source of heat mystery
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More reflective than new
snow
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Tethys
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Dione
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Leading hemisphere cratered
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Trailing hemisphere has weird
wisps
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Rhea
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Iapetus
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Leading hemisphere very dark
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Material may be from Phoebe
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trailing light
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Synchronous rotation, prograde
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Average densities 1200-1400
kg/m3 (ice)
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Several rock or ice fragments
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Pan (makes Encke Gap)
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Prometheus and Pandora (F-ring
shepherds)
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...
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Mimas
Enceladus
Tethys MPEG
movie of Tethys
Dione trailing hemisphere
Rhea
Iapetus
Cassini
and
Huygens
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Cassini
is a space probe that will orbit Saturn
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Huygens
currently attached to Cassini will fall into Titan's atmosphere
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Why
doesn't Cassini have any solar panels?
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Too
far from Sun
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Nuclear
powered
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Saturn
and its Moons Summary
-
Saturn
overview
-
Outer
atmosphere
-
3 layers
of clouds (like Jupiter)
-
Internal
structure
-
Solved
(?) puzzles of Saturn
-
Chemical
composition
-
Excess
heat source
-
Titan
(largest moon)
-
Other
moons
-
Cassini
and Huygens probes