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Ch 7--The Outer Planets
05 Oct 2000
ASTR103, GMU, Dr. Correll
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What Do You Think
• Is Jupiter a “failed star” or almost a star?
• What is Jupiter’s Great Red Spot?
• Does Jupiter have continents and oceans?
• Is Saturn the only planet with rings?
• Are the rings of Saturn solid ribbons?
05 Oct 2000
ASTR103, GMU, Dr. Correll
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Astronomical Telescopes
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ASTR103, GMU, Dr. Correll
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Jupiter
05 Oct 2000
ASTR103, GMU, Dr. Correll
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Jupiter Outer Layer
• Rapid rotation
generates dynamic
atmosphere
• The great red spot
– a “hurricane” lasting for
centuries
• Differential rotation at
different latitudes
causes colored cloud
bands
05 Oct 2000
ASTR103, GMU, Dr. Correll
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Jupiter’s Atmosphere
• Spectroscopy
from earth and
spacecraft reveal
– 86% hydrogen
– 13% helium
– traces of other
simple compounds
• methane
• ammonia
• water vapor
05 Oct 2000
ASTR103, GMU, Dr. Correll
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Jupiter’s Atmosphere
• Convection-movement of
material from
hotter to cooler
regions
– just as we saw
in the Earth’s
mantle
– and we’ll see
later in the Sun
05 Oct 2000
ASTR103, GMU, Dr. Correll
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Jupiter’s Interior
• Atmosphere--about 150 km of hydrogen, helium
and trace gases
• Liquid Hydrogen mantle--60,000 km
– lower 40,000 km is liquid metallic hydrogen which is
electrically conductive, generating the planet’s magnetic
field--about 20,000 time stronger than Earth’s
• Terrestrial protoplanet core--inner 10,000 km
radius, about 50% larger than the Earth!
05 Oct 2000
ASTR103, GMU, Dr. Correll
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Jupiter’s Moons
• Jupiter has at least 16 moons--typical for a large
planet
• Four largest were discovered by Galileo--the
Gallilean moons
–
–
–
–
Io
Europa
Ganymede
Callisto
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ASTR103, GMU, Dr. Correll
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Jupiter’s Moons
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ASTR103, GMU, Dr. Correll
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Io
• Tidal forces
generate heat and
volcanic activity
• Rich in sulfur and
sulfur dioxide,
hence the
yellowish color
05 Oct 2000
ASTR103, GMU, Dr. Correll
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Europa
• Ice and rock crust
• Tidal forces heat
the moon, making
it likely that liquid
water is abundant
under the ice crust
– fracture lines in
crust support this
theory
05 Oct 2000
ASTR103, GMU, Dr. Correll
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Ganymede
• Largest Jovian
moon
• Iron-rich core
• ice and rock
mantle
• week magnetic
field
• thin atmosphere
05 Oct 2000
ASTR103, GMU, Dr. Correll
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Callisto
• Similar to
Ganymede--icy
and rocky
• But, no iron-rich
core
• Geologically
inactive
05 Oct 2000
ASTR103, GMU, Dr. Correll
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Jupiter’s Rings
• Rings comprised of small particles of dust and ice
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ASTR103, GMU, Dr. Correll
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Saturn
05 Oct 2000
ASTR103, GMU, Dr. Correll
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Saturn
• Very similar to
Jupiter in
elemental makeup
and dynamic
structure
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ASTR103, GMU, Dr. Correll
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Saturn
• Strong magnetic
field creates
auroral activity as
on Earth and
Jupiter
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ASTR103, GMU, Dr. Correll
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Saturn’s Rings
• Composed of ice,
dust and rock
• Different rings
separated by gaps
– due to resonances
with gravity of
Saturn’s moons
– first discovered by
Cassini in 1675
05 Oct 2000
ASTR103, GMU, Dr. Correll
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Saturn’s Moons
• Of Saturn’s 22
known moons,
only 7 are
spherical
– the rest probably
captured asteroids
• Has a dense
atmosphere of
nitrogen gas
– 4 times denser
than Earth’s
– rich in primitive
organic molecules
05 Oct 2000
ASTR103, GMU, Dr. Correll
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Uranus and Neptune
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ASTR103, GMU, Dr. Correll
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Uranus and Neptune--Interiors
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ASTR103, GMU, Dr. Correll
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Planetary Magnetic Fields
• Planetary magnetic fields don’t always line up with
rotation axis--and probably change orientation with time
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ASTR103, GMU, Dr. Correll
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Rings and Moons of Uranus
• A common feature
of large planets
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ASTR103, GMU, Dr. Correll
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Neptune’s Discovery
• 1781--Uranus discovered
• 1840--Uranus orbit not following predicted path
according to Newtonian gravity
• 1840-1846--John Adams and Erbain Leverrier
predicted the location of an undiscovered planet
• 1846--Neptune discovered by Johann Galle at
predicted location
– Newton’s theory of gravity vindicated!
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Pluto
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Pluto and Charon
• Pluto is about 8 times
as massive as its
moon Charon
• Similar in composition
– rock and ice
• No discernable
features
• Mutually synchronous
rotation!
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ASTR103, GMU, Dr. Correll
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What Do You Think
• Is Jupiter a “failed star” or almost a star?
– Jupiter has 75 times too little mass to shine as a star
• What is Jupiter’s Great Red Spot?
– The great red spot is a long-lived, oval cloud circulation similar to
a hurricane on Earth
• Does Jupiter have continents and oceans?
– No, Jupiter is comprised mainly of a dense mantle of liquid
hydrogen and helium. There is a solid core at it’s center.
• Is Saturn the only planet with rings?
– No, Four planets (Jupiter, Saturn, Uranus, and Neptune) have
rings
• Are the rings of Saturn solid ribbons?
– Saturn’s rings are all comprised of thin, closely spaced ringlets of
ice and dust particles
05 Oct 2000
ASTR103, GMU, Dr. Correll
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Questions for review
• Describe the planet Jupiter, it’s cloud tops, interior
layers, magnetic fields and moons.
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