Jovian Planet Systems

7/19/2011

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?

7/19/2011

Are jovian planets all alike?

7/19/2011

Jovian Planet Composition

• Jupiter and Saturn
• Mostly H and He gas
• ​
• Uranus and Neptune
• Mostly hydrogen compounds: water (H₂O), methane (CH₄), ammonia (NH₃)
• Some H, He, and rock

7/19/2011

Density Differences

• Uranus and Neptune are denser than Saturn because they have less H/He, proportionately.

7/19/2011

Density Differences

• But that explanation doesn’t work for Jupiter….

7/19/2011

Sizes of Jovian Planets

• Adding mass to a jovian planet compresses the underlying gas layers.

7/19/2011

Sizes of Jovian Planets

• 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.

7/19/2011

Rotation and Shape

• Jovian planets are not quite spherical because of their rapid rotation.

7/19/2011

What are jovian planets like on the inside?

7/19/2011

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. WHY?

7/19/2011

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.

7/19/2011

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.

7/19/2011

Comparing Jovian Interiors

• Models suggest cores of jovian planets have similar composition.
• Lower pressures inside Uranus and Neptune mean no metallic hydrogen.

​

7/19/2011

Jupiter’s Internal Heat

• Jupiter radiates twice as much energy as it receives from the Sun.

​

• Energy probably comes from slow contraction of interior (releasing potential energy).

7/19/2011

Internal Heat of Other Planets

• Saturn also radiates twice as much energy as it receives from the Sun.
• Energy probably comes from differentiation (helium rain).
• Neptune emits nearly twice as much energy as it receives, but the source of that energy remains mysterious.

7/19/2011

What is the weather like on jovian planets?

7/19/2011

Jupiter’s Atmosphere

• Hydrogen compounds in Jupiter form clouds.

​

• Different cloud layers correspond to freezing points of different hydrogen compounds.

7/19/2011

Jovian Planet Atmospheres

• Other jovian planets have cloud layers similar to Jupiter’s.

​

• Different compounds make clouds of different colors.

7/19/2011

Jupiter’s Colors

• Ammonium sulfide clouds (NH₄SH) reflect red/brown.
• Ammonia, the highest, coldest layer, reflects white.

7/19/2011

Saturn’s Colors

• Saturn’s layers are similar, but deeper in and farther from the Sun (more subdued).

7/19/2011

Methane on Uranus and Neptune

• Methane gas of Neptune and Uranus absorbs red light but transmits blue light.
• Blue light reflects off methane clouds, making those planes look blue.

7/19/2011

Jupiter’s Bands

7/19/2011

Jupiter’s Great Red Spot

• Is a storm twice as wide as Earth
• Has existed for at least three centuries

7/19/2011

Weather on Jovian Planets

• All the jovian planets have strong winds and storms.

7/19/2011

Do jovian planets have magnetospheres like Earth’s?

7/19/2011

Jupiter’s Magnetosphere

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

7/19/2011

Other Magnetospheres

• All jovian planets have substantial magnetospheres, but Jupiter’s is the largest by far.

7/19/2011

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) Its core creates a magnetic field, but it is very weak.

7/19/2011

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) Its core creates a magnetic field, but it is very weak.

7/19/2011

What have we learned?

• Are jovian planets all alike?
• Jupiter and Saturn are mostly H and He gas.
• Uranus and Neptune 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.

​

7/19/2011

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 the largest by far.

7/19/2011

A Wealth of Worlds: Satellites of Ice and Rock

Our goals for learning:

• What kinds of moons orbit the 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?

7/19/2011

What kinds of moons orbit the jovian planets?

7/19/2011

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

7/19/2011

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

7/19/2011

Small Moons

• These are far more numerous than the medium and large moons.
• They do not have enough gravity to be spherical: Most are “potato-shaped.”

7/19/2011

Small Moons

• They are captured asteroids or comets, so their orbits do not follow usual patterns.

​

7/19/2011

Why are Jupiter’s Galilean moons so geologically active?

7/19/2011

Io’s Volcanic Activity

• Io is the most volcanically active body in the solar system, but why?

​

7/19/2011

Io’s Volcanoes

• Volcanic eruptions continue to change Io’s surface.

7/19/2011

Tidal Heating

Io is squished and stretched as it orbits Jupiter.

But why is its orbit so elliptical?

7/19/2011

Orbital Resonances

The tugs add up over time, making all three orbits elliptical.

Every 7 days, these three moons line up.

7/19/2011

Europa’s Ocean: Waterworld?

7/19/2011

Tidal stresses crack Europa’s surface ice.

7/19/2011

Europa’s interior also warmed by tidal heating.

7/19/2011

Ganymede

• Largest moon in the solar system
• Clear evidence of geological activity
• Tidal heating plus heat from radio-active decay?

7/19/2011

Callisto

• “Classic” cratered iceball
• No tidal heating, no orbital resonances
• But it has a magnetic field!?

7/19/2011

Thought Question

How does Io get heated by Jupiter?

​

• a) auroras
• b) infrared light
• c) tidal resonance
• d) volcanoes

7/19/2011

Thought Question

How does Io get heated by Jupiter?

​

• a) auroras
• b) infrared light
• c) tidal resonance
• d) volcanoes

7/19/2011

What is remarkable about Titan and other major moons of the outer solar system?

7/19/2011

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.

7/19/2011

Titan’s Surface

• Huygens probe provided first look at Titan’s surface in early 2005.
• It found liquid methane and “rocks” made of ice.

​

7/19/2011

Medium Moons of Saturn

• Almost all of them show evidence of past volcanism and/or tectonics.

7/19/2011

Medium Moons of Saturn

• Ice fountains of Enceladus suggest it may have a subsurface ocean.

7/19/2011

Medium Moons of Uranus

• They have varying amounts of geological activity.

​

• Miranda has large tectonic features and few craters (possibly indicating an episode of tidal heating in past).

7/19/2011

Neptune’s Moon Triton

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

​

7/19/2011

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

7/19/2011

Rocky Planets versus 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.

7/19/2011

What have we learned?

• What kinds of moons orbit the jovian planets?
• Moons come in many sizes.
• The level of geological activity depends on a moon’s size.
• Why are Jupiter’s Galilean moons so geologically active?
• Tidal heating drives geological activity, leading to Io’s volcanoes and ice geology on other moons.

​

7/19/2011

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.

​

7/19/2011

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?

7/19/2011

What are Saturn’s rings like?

7/19/2011

What are Saturn’s rings like?

• They are made up of numerous, tiny individual particles.
• They orbit around Saturn’s equator.
• They are very thin.

7/19/2011

Earth-Based View of Saturn

7/19/2011

Spacecraft View of Ring Gaps

7/19/2011

Artist’s Conception of Rings Close-Up

7/19/2011

Gap Moons

• Some small moons create gaps within rings.

7/19/2011

Shepherd Moons

• A pair of small moons can force particles into a narrow ring.

7/19/2011

Resonance Gaps

• Orbital resonance with a larger moon can also produce a gap.

7/19/2011

How do other jovian ring systems compare to Saturn’s?

7/19/2011

Jovian Ring Systems

• All four jovian planets have ring systems.
• Others have smaller, darker ring particles than Saturn.

7/19/2011

Why do the jovian planets have rings?

7/19/2011

Why do the jovian planets have rings?

• They formed from dust created in impacts on moons orbiting those planets.

How do we know?

7/19/2011

How do we know?

• Rings aren’t leftover from planet formation because the particles are too small to have survived for so long.
• There must be a continuous replacement of tiny particles.
• The most likely source is impacts with jovian moons.

7/19/2011

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.

7/19/2011

What have we learned?

• What are Saturn’s rings like?
• They are made up of countless individual ice particles.
• They are extremely thin with many gaps.
• How do other jovian ring systems compare to Saturn’s?
• The other jovian planets have much fainter ring systems with smaller, darker, less numerous particles.
• Why do the jovian planets have rings?
• Ring particles are probably debris from moons.

​

7/19/2011