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Chapter 11
Jovian Planet Systems
11.1 A Different Kind of Planet
Our goals for learning:
- Are jovian planets all alike?
- What are jovian planets like on the inside?
- What is the weather like on jovian planets?
- Do jovian planets have magnetospheres like
Earth’s?
Are jovian planets all alike?
Jovian Planet Composition
- Jupiter and Saturn
- Uranus and Neptune
- Mostly hydrogen compounds: water (H 2 O), methane (CH 4 ), ammonia (NH 3 )
- Some H, He, and rock
Density Differences
- Uranus and Neptune are denser than Saturn because they have less (^0) H/He, proportionately
Jupiter^ SaturnUranus Neptune
Density (g/cc)
Density Differences
Jupiter^ SaturnUranus Neptune
Density (g/cc)
- But that explanation doesn’t work for Jupiter….
What are jovian planets like on
the inside?
Interiors of Jovian Planets
- No solid surface.
- Layers under high pressure and
temperatures.
- Cores (~10 Earth masses) made of hydrogen
compounds, metals & rock
- The layers are different for the different
planets. WHY?
Inside Jupiter
- High pressures inside Jupiter cause phase of hydrogen to change with depth
- Hydrogen acts like a metal at great depths because its electrons move freely
Inside Jupiter
- Core is thought to be made of rock, metals, and hydrogen compounds
- Core is about same size as Earth but 10 times as massive
Comparing Jovian Interiors
- Models suggest cores of jovian planets have similar composition
- Lower pressures inside Uranus and Neptune mean no metallic hydrogen
Jupiter’s Internal Heat
- Jupiter radiates twice as much energy it receives from Sun
- Energy probably comes from slow contraction of interior (releasing potential energy)
Jovian Planet Atmospheres
- Other jovian planets have cloud layers similar to Jupiter’s
- Different compounds make clouds of different colors
Jupiter’s
colors
- Ammonium sulfide clouds (NH 4 SH) reflect red/brown.
- Ammonia, the highest, coldest layer, reflects white.
Saturn’s
colors
- Saturn’s layers are similar, but deeper in and farther from the Sun --- more subdued.
Methane on Uranus and Neptune
- Methane gas of Neptune and Uranus absorb red light but transmit blue light
- Blue light reflects off methane clouds, making those planes look blue
Jupiter’s Bands
White ammonia clouds form where air rises
Coriolis effect changes N-S flow to E-W winds Between white clouds we see deeper reddish clouds of NH 4 SH
Warmer red bands are brighter in IR
Jupiter’s
Great
Red
Spot
- A storm twice as wide as Earth
- Has existed for at least 3 centuries
Other Magnetospheres
- All the jovian planets have substantial magnetospheres, but Jupiter’s is largest by far
Thought Question
Jupiter does not have a large metal core like the
Earth. How can it have a magnetic field?
a) The magnetic field is left over from when Jupiter accreted b) Its magnetic field comes from the Sun c) It has metallic hydrogen inside, which circulates and makes a magnetic field d) That’s why its magnetic field is weak
What have we learned?
- Are jovian planets all alike?
- Jupiter and Saturn are mostly H and He gas
- Uranus and Nepture are mostly H compounds
- What are jovian planets like on the inside?
- Layered interiors with very high pressure and cores made of rock, metals, and hydrogen compounds
- Very high pressure in Jupiter and Saturn can produce metallic hydrogen
What have we learned?
- What is the weather like on jovian planets?
- Multiple cloud layers determine colors of jovian planets
- All have strong storms and winds
- Do jovian planets have magnetospheres
like Earth’s?
- All have substantial magnetospheres
- Jupiter’s is largest by far
11.2 A Wealth of Worlds: Satellites of
Ice and Rock
Our goals for learning:
- What kinds of moons orbit jovian planets?
- Why are Jupiter’s Galilean moons so
geologically active?
- What is remarkable about Titan and other
major moons of the outer solar system?
- Why are small icy moons more geologically
active than small rocky planets?
What kinds of moons orbit the
jovian planets?
Small
Moons
- Captured asteroids or comets, so orbits do
not follow usual patterns.
Why are Jupiter’s Galilean
moons so geologically active?
Io’s Volcanic Activity
- Io is the most volcanically active body in the
solar system, but why?
Io’s Volcanoes
- Volcanic eruptions continue to change Io’s surface
Tidal Heating
Io is squished and
stretched as it orbits
Jupiter But why is its
orbit so
elliptical?
Orbital
Resonances
Every 7 days,
these 3 moons
line up.
The tugs add up over
time, making all 3
orbits elliptical.
Ganymede
solar system
geological activity
heat from radio-
active decay?
Callisto
iceball.
no orbital
resonances.
magnetic field !?
Thought Question
How does Io get heated by Jupiter?
a) Auroras b) Infrared Light c) Jupiter pulls harder on one side than the other d) Volcanoes
What is remarkable about Titan
and other major moons of the
outer solar system?
Titan’s Atmosphere
- Titan is the only moon in the solar system to have a thick atmosphere
- It consists mostly of nitrogen with some argon, methane, and ethane
Titan’s Surface
- Huygens probe provided first look at Titan’s surface in early 2005
- Liquid methane, “rocks” made of ice
Why are small icy moons more
geologically active than small
rocky planets?
Rocky Planets vs. Icy Moons
- Rock melts at higher temperatures
- Only large rocky planets have enough heat for activity - Ice melts at lower temperatures - Tidal heating can melt internal ice, driving activity
What have we learned?
- What kinds of moons orbit jovian planets?
- Moons of many sizes
- Level of geological activity depends on size
- Why are Jupiter’s Galilean moons so
geologically active?
- Tidal heating drives activity, leading to Io’s volcanoes and ice geology on other moons
What have we learned?
- What is special about Titan and other major moons of the solar system? - Titan is only moon with thick atmosphere - Many other major moons show signs of geological activity
- Why are small icy moons more geologically active than small rocky planets? - Ice melts and deforms at lower temperatures enabling tidal heating to drive activity
11.3 Jovian Planet Rings
Our goals for learning:
- What are Saturn’s rings like?
- How do other jovian ring systems compare
to Saturn’s?
- Why do the jovian planets have rings?
What are Saturn’s rings like?
