Chapter 8 Notes: Olivia Ward

Jovian Planet Systems

8.1 A Different Kind of Planet
What are jovian planets made of?

• Jovian Planet Composition
  
  • Jupiter and Saturn
    
    • Mostly H and He gas (He found in the Sun).
  • Uranus and Neptune
    
    • Mostly hydrogen compounds: H2O, CH4 (methane), NH3 (ammonia)
    • Some H, He, and rock
• Jovian Planet Formation
  
  • Beyond the frost line, planetesimals could accumulate ice.
  • Hydrogen compounds are more abundant.
  • Jovian cores are very similar to the mass of 10 Earths.
• Differences in Jovian Planet Formation
  • Timing: The planet that forms the earliest captures the most H and He. Capture ceases after the first solar wind blows the leftover gas away.
  • Location: The planet that forms in a denser part of the nebula forms its core first.
• Density Differences
  
  • Uranus and Neptune are denser than Saturn because they have less H and He, proportionally.
  • This explanation doesn't apply to Jupiter.
• Sizes of Jovian Planets
  
  • Adding mass to a jovian planet compresses the underlying gas layers.
  • Greater compression: Jupiter is not much larger than Saturn even though it's 3 times as massive.
  • Jovian planets with even more mass can be smaller than Jupiter.

What are some jovian planets like on the inside?

•  Everything is theoretical due to high pressures (not able to observe cores).
• Interiors of Jovian Planets
  
  • No solid surface
  • Layers under high pressure and temperatures
  • Cores (~ 10 Earth masses) made of hydrogen compounds, metals, and rock
  • The layers are different for the different planets.
• Inside Jupiter
  
  • Higher pressures of Jupiter causes the phase of hydrogen to change with depth.
  • Hydrogen acts like a metal at great depths because its electrons move freely.
  • The core is thought to be made of rock, metals, and hydrogen compounds.
  • The core is about the size of Earth, but 10 times as massive.
• Comparing Jovian Interiors
  
  • Jupiter's strong magnetic field gives it an enormous magnetosphere.
  
  

What is the weather like on jovian planets?

• 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.
• Jupiter's Colors
  
  • Ammonium sulfide clouds (NH4SH) reflect red/brown.
  • Ammonia, the highest, coldest layer reflects white.
• Saturn's Colors
  
  • Saturn's layers are similar but deeper in and farther away from the Sun (less colors).
• Methane on Uranus and Neptune
  • Methane gas on Neptune and Uranus absorb red light, seen as blue.
  • Blue light reflects off methane clouds, making the planets look blue.
• Jupiter's Great Red Spot
  
  • A storm twice as wide as Earth
  • Has existed for at least 3 centuries
• Weather on Jovian Planets
  
  • All jovian planets have strong winds and storms.

8.2 A Wealth of Worlds: Satellites of Ice and Rock
What kinds of moons orbit the jovian planets?

• Jupiter's 4 moons: Io, Europa, Ganymede, Callisto
  
  • Sizes of Moons
    
    • Small sized moons (< 300 km)
      • No geological activity
    • Medium sized moons (300 - 1500 km)
      
      • Geological activity in the past
    • Medium and large moons (> 1500 km)
      
      • Ongoing geological activity
      • Enough self-gravity to be spherical
      • Have substantial amounts of ice
      • Formed in orbit around jovian planets
      • Circular orbits in same direction as planet rotation
• Small moons
  
  • Far more numerous than the medium and large moons (the smaller the objects, the more).
  • Not enough gravity to be spherical (potato shaped)

Why are Jupiter's Galilean moons geologically active?

• Io's Volcanic Activity
  
  • Io is the most volcanically active body in the solar system (predicted by Stanton Peale) (sublimation = solid to gas)
  • Io's Volcanoes
    
    • Volcanic eruptions continue to change the surface.
  • Tidal Heating
    
    • Io is squished and stretched as it orbits Jupiter.
    • Io is hot.
• Orbital Resonances
  
  • Every seven days, Io, Europa, and Ganymede line up.
    
    • Io: 4 orbits
    • Europa: 2 orbits
    • Ganymede: 1 orbit
• Europa's Oceans: Water World?
  
  • Ice is less dense than liquid water.
  • Tidal stresses crack Europa's surace ice.
  • Europa's interior also warmed by tidal heating (liquid water or warm, convecting ice)
• Ganymede
  
  • Largest moon in the solar system
  • Clear evidence of geological activity
  • Tidal heating plus heat from radioactive decay
• Callisto
  • "Classic" crater ice ball
  • No tidal heating, no orbital resonances
  • It has magnetic field.

What geological activity do we see on Titan and other moons?

• Titan's Atmosphere
  
  • Titan is the only moon in the solar system with a thick atmosphere (blue).
  • Consists mostly of nitrogen with some argon, methane, and ethane.
• 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.
• Titan's "Lakes"
  
  • Radar imaging of Titan's surface has revealed dark, smooth regions that may be lakes of liquid methane.
• Medium Moons of Saturn
  
  • Almost all show evidence of past volcanism / tectonics.
• Ongoing Activity on Enceladus
  
  • Fountains of ice particles and water vapor from the surface of Enceladus indicate that geological activity is ongoing.
• Medium Moons of Uranus
  
  • Varying amounts of geological activity occur.
  • Moon Miranda has tectonic features.
• Neptune's Moon Triton
  
  • Similar to Pluto, but larger.
  • Evidence of past geological activity.

Why are jovian moons more geologically active than small rocky planets?

• Rocky Planets vs. Icy Moons
  
  • Rocky Planets
    
    • Rock melts at higher temperatures
    • Only large rocky planets have enough heat for activity.
  • Icy Moons
    
    • Ice melts at lower temperatures.
    • Tidal heating can melt internal ice, driving activity.

8.3  Jovian Planet Rings
What are Saturn's rings like?

• Rings are debris.
  
  • They are made up of numerous, tiny individual particles.
• They orbit over Saturn's equator.
  
• They are very thin.
  
• Gap Moons
  
  • Some small moons create gaps within rings.

Why do the jovian planets have rings?

• Jovian Ring Systems
  • All 4 jovian planets have rings.
  • They form from dust created in impacts on moons orbiting those planets.
• How do we know?
  
  • Rings aren't leftover from planet formation because the particles are too small to have survived.
  • They must be continuously replaced.
  • Source: impacts with jovian moons.
• Ring Formation
  
  • Jovian planets all have rings because they possess many small moons.
  • Impacts on these moons are random.
  • Saturn's rings have been an "accident."