chapter 8a jovian planet systems. 8.1 a different kind of planet our goals for learning what are...

Chapter 8aJovian Planet Systems

8.1 A Different Kind of Planet

Our Goals for Learning

• What are jovian planets made of?

• What are jovian planets like on the inside?

• What is the weather like on jovian planets?

Jovian Planets - A Different Kind of Planet

• Bigger & more massive• Lower density, different composition• Rings• Numerous moons

What are jovian planets made of?

• Jupiter & Saturn: almost all H & He, very little metal & rock (less dense)

• Uranus & Neptune: <50% H & He, the rest hydrogen compounds (water, methane, ammonia), with some metal & rock (more dense)

Why are they different?

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.

Jovian planet formation

• The jovian cores are very similar:

~10x Earth masses

• The jovian differences are in the amount of H/He gas accumulated.

Why did that amount differ?

Differences in Jovian planet formation

• TIMING: the planet that forms earliest captures the most hydrogen & helium gas. Capture ceases after the first solar wind blew the leftover gas away.

• LOCATION: the planet that forms in a denser part of the nebula forms its core first.

Density Differences

0

0.5

1

1.5

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Jupit

er

Saturn

Uranus

Nep

tune

Den

sity

(g/

cc)

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

Density Differences

0

0.5

1

1.5

2

Jupit

er

Saturn

Uranus

Nep

tune

Den

sity

(g/

cc)

But that explanation doesn’t work for Jupiter….

• Jupiter and Saturn are nearly the same size• But Jupiter is 3x more massive than Saturn

What are jovian planets like on the inside?

• 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?

Layers Differ in PhaseNotes: [Density of liquid water is ~

1g/cm3.]

Metallic hydrogen conducts electricity; it is not solid.

Core is hydrogen compounds, metals, rocks. Highly compressed! 10 x the mass of Earth inside a volume the size of Eath.

Jupiter

Less mass less gravity less compression.

Boundaries of the layers are deeper in less massive jovian planets.

The physical states of the cores of the less massive jovians are less extreme (could be liquid).

Why different?

Magnetic Fields• Jupiter has a powerful magnetic field

generated by its rotating, convecting layer of metallic hydrogen.

What is the weather like on jovian planets?

Colorful surface features reveal:– Clouds of different compositions– Wind speeds– Storms, some long-lived

Planet colors

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

Jupiter’s colors

Planet colors

Saturn’s layers are the same, but deeper in and farther from the Sun --- more subdued.

Saturn’s Colors

Uranus and Neptune’s upper layers are colder still, allowing methane to condense.

Methane gas absorbs red light and trasmits blue light reflected by clouds

Jupiter winds and storms• Earth’s rotation makes storms ‘spin’.

• Jupiter’s fast rotation stretches storms in to bands that surround the planet.

• High east/west winds (up to 400 km/hr)

The Great Red Spot

• twice as wide as the Earth

• Has existed for at least 3 centuries

Storms on the other jovian planets

• Saturn: fast winds

• Neptune: can see storms, but not as long lived.

• Uranus: dull when Voyager 2 flew by, but HST captured major storms.– Extreme tilt means that Uranus’ southern

hemisphere may just now be getting sunshine for the first time in decades.

What have we learned?

• What are jovian planets made of?

• Jupiter and Saturn are made almost entirely of hydrogen and helium, while Uranus and Neptune are made mostly of hydrogen compounds mixed with metal and rock. These differences arose because all four planets started from ice-rich planetesimals of about the same size, but captured different amounts of hydrogen and helium gas from the solar nebula.

What have we learned?• What are jovian planets like on

the inside?

• The jovian planets have layered interiors with very high internal temperatures and pressures. All have a core about 10 times as massive as Earth, consisting of hydrogen compounds, metals, and rock. They differ mainly in their surrounding layers of hydrogen and helium.

What have we learned?• What is the weather like on

jovian planets?

• The jovian planets all have multiple cloud layers that help determine the colors of the planets, fast winds, and large storms. Some storms, such as the Great Red Spot, can apparently rage for centuries or longer.