Jessie Horn: Chapter 8 Notes

Chapter 8: Jovian Planet Systems
Jovian Planet Composition

• Jupiter and Saturn: Composed of mostly H and He gas
• Uranus and Neptune: Composed of mostly hydrogen compounds, water, methane, ammonia, some H, He, and rock.

Jovian Planet Formation

• Beyond the frost line, planetesimals could accumulate ICE. 
• Hydrogen compounds are more abundant than rock/metal so jovian planets got bigger and acquired H/He atmospheres. 
• The jovian cores are very similar (approximately the mass of 10 Earths)
• The jovian planets differ in the amount of H/He gas accumulated.

Differences in Jovian Planet Formation

• TIMING: The planet that forms earliest captures the most hydrogen and helium gas. 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/He, proportionately. 
• But that explanation doesn't work for Jupiter.

Sizes of Jovian Planets

• Adding mass to a jovian planet compresses the underlying gas layers.
• Greater compression is why Jupiter is not much larger than Saturn even though it is three times more massive.
• Jovian planets with even more mass can be smaller than Jupiter.

Interiors of Jovian Planets

• No solid surface
• Layers under high pressure and temperatures
• Cores made of hydrogen compounds, metals, and rock
• The layers are different for the different planets

Inside Jupiter

• High pressure inside of Jupiter causes the phase of hydrogen to change with depth
• Hydrogen acts lie a metal at great depths because its electrons move freely
• The core is though to be made of rock, metals, and hydrogen compounds
• The core is about the same size as Earth but 10 times as massive

Jupiter's Magnetosphere 

• Jupiter's strong magnetic field gives it an enormous magnetosphere
• Gases escaping Io feed the donut-shaped Io torus

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 reflect red/brown
• Ammonia, the highest, coldest layer, reflects white

Saturn's Colors

• Saturn's layers are similar but are deeper in and farther from the Sun-more subdued 

Methane on Uranus and Neptune

• Methane gas on Neptune and Uranus absorb red light but transmits blue light
• Blue light reflects off methane clouds, making those 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 the jovian planets have strong winds and storms 

Sizes of Moons

• Small moons (<300 km): no geological activity
• Medium-sized moons (300-1500 km): geological activity in past
• Large moons (>1500 km): Ongoing geological activity 

Medium and Large Moons

• 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
• Not enough gravity to be spherical: "potato-shaped" 

Io's Volcanic Activity

• Io is the most volcanically active body in the solar system
• Volcanic eruptions continue to change Io's surface

Tidal Heating: Io is squished and stretched as it orbits Jupiter.

Orbital Resonances: The tugs add up over time, making all three orbits elliptical. Every 7 days, these three moons line up.

Tidal stresses crack Euroa's surface ice: Tidal flexing closes crack, grinds up ice. Tidal flexing opens crack, leaving two ridges.

Europa's interior also warmed by tidal heating. 

Ganymede

• Larges moon in the solar system
• Clear evidence of geological activity 

Callisto

• "Classic" cratered iceball
• No tidal heating, no orbital resonances

Titan's Atmosphere

• Titan is the only moon in the solar system that has a thick atmosphere (needs a strong gravity field)
• It 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 and/or 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 large tectonic features and few craters 

Neptune's Moon Triton

• Similar to Pluto, but larger
• Evidence for past geological activity 

Rocky Planets vs. Icy Moons

• Rock melts at higher temps
• Only large rocky planets have enough heat for activity
• Ice melts at lower temps
• Tidal heating can melt internal ice, driving activity

Jovian Ring Systems

• All four jovian planets have ring systems
• Otheres have ring particles that are smaller and darker than Saturn's

Ring Formation

• Jovian planets all have rings because they possess many small moons close-in
• Impacts on these moons are random
• Saturn's incredible rings may be an "accident" of our time

Saturn's Rings are made up of countless individual ice particles. They are extremely thin with many gaps

Jovian planets have rings because ring systems of other jovian planets are much fainter with smaller, darker, less numerous particles. Ring particles are probably debris from moons.