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The Jovian Planets
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The Jovian planets aregas giants -
much larger than Earth
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Sizes of Jovian Planets• Planets get larger as
they get more massive• up to a point...
• Planets more massive than Jupiter are expected to shrink.
• There comes a point where gravity wins: adding more mass causes contraction.
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Jovian Planet Composition• Jupiter and Saturn
— Mostly H and He gas— these are the most common elements in the Universe
– “Gas Giants”
• Uranus and Neptune— Mostly hydrogen compounds: water (H2O),
methane (CH4), ammonia (NH3)— Some H, He, and rock— “Ice Giants”
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Interiors of Jovian Planets
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Inside Jupiter• High pressure inside
of Jupiter causes the phase of hydrogen to change with depth.
• Hydrogen acts like a metal at great depths because its electrons move freely.
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Inside Jupiter• The core is thought
to be made of rock, metals, and hydrogen compounds.
• The core is about the same size as Earth but 10 times as massive.
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Comparing Jovian Interiors
• Models suggest that cores of jovian planets have similar composition.
• Lower pressures inside Uranus and Neptune mean no metallic hydrogen.
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Jupiter’s Atmosphere• Hydrogen compounds in
Jupiter form clouds.
• Different cloud layers correspond to freezing points of different hydrogen compounds.
• Other jovian planets have similar cloud layers.
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Jupiter’s Colors
• Ammonium sulfide clouds (NH4SH) reflect red/brown.• Ammonia, the highest, coldest layer, reflects white.
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Saturn’s Colors
• Saturn’s layers are similar but are deeper in and farther from the Sun — more subdued.
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Methane on Uranus and Neptune• Methane gas on
Neptune and Uranus absorbs red light but transmits blue light.
• Blue light reflects off methane clouds, making those planets look blue.
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Weather on Jovian Planets
• All the jovian planets have strong winds and storms.
The great red spot on Jupiteris a storm larger than Earththat has persisted for centuries.
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• Big– massive and cold, they can retain light elements
like hydrogen and helium
Jovian planets are
Temperature
Esca
pe S
peed
Hydrogen retained
Oxygen retained
Jovian planets
Terrestrial planets
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Jovian planets are• Big
– massive and cold, they can retain light elements like hydrogen and helium
– their composition is like that of the stars– the smaller terrestrial planets are the abnormal
planets in terms of composition• Like miniature solar systems
– moons– rings
Temperature
Esca
pe S
peed
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The moons of the Jovian planets
Galilean moons of Jupiter(“Medici stars”)
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Sizes of Moons
• Small moons (< 300 km)— No geological activity
• Medium-sized moons (300–1,500 km)— Geological activity in past
• Large moons (> 1,500 km)— Ongoing geological activity
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Medium and Large Moons
• Enough self-gravity to be spherical
• Have substantial amounts of ice - as important as rock to overall composition
• Formed in orbit around jovian planets
• Circular orbits mostly in the same direction as planet rotation
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Small Moons
• Far more numerous than the medium and large moons
• Not enough gravity to be spherical: “potato-shaped”
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Some interesting cases:
• Io is the most volcanically active body in the solar system.
Io
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Tidal Heating
Io is squished and stretched as it orbits Jupiter.
Orbit is elliptical because of orbital resonances with other moons
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Orbital Resonances
Every 7 days, these three moons line up.
The tugs add up over time, making all three orbits elliptical.
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• Volcanic eruptions continue to change Io’s surface.
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Europa
• Icy surface– cracks driven
by some “geological” activity
• Liquid ocean beneath?– popular spot to
speculate about the potential for life
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Ganymede
• Largest moon in the solar system
• Clear evidence of geological activity
• Tidal heating plus heat from radio-active decay?
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Saturn’s large moon Titan
• Titan is the only moon in the solar system which has a thick atmosphere.
• It consists mostly of nitrogen with some argon, methane, and ethane.
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Titan’s Surface
• The Huygens probe provided a first look at Titan’s surface in early 2005.
• It had liquid methane, “rocks” made of ice.
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Neptune’s Moon Triton• Similar to Pluto, but
larger
• Evidence for past geological activity
• orbits retrograde– unique for such a
large moon
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Saturn’s rings
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What are Saturn’s rings like?
• They are made up of numerous, small, icy particles.
• They orbit over Saturn’s equator.• They are very thin.
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Artist’s Conception in Ring
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Elaborate structure in rings controlled by the gravity of “shepherd” moons
Pan Prometheus
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Newly discovered outer ring
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Iapetus
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actual data
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Jovian Ring Systems
• All four jovian planets have ring systems.• Others have smaller, darker ring particles than does Saturn.• Rings and moons ubiquitous around Jovian planets
– like small solar systems.