The Jovian Worlds

Admin nonsense:

HW#7 is posted, due Nov 11
No class next Thursday (Nov 6)

Quick Thumbnail Properties

Jupiter	Saturn	Uranus	Neptune

D=5.2 AU M=317 M_earth R=11.2 R_earth	D=9.5 AU M=90 M_earth R=9.4 R_earth	D=19.2 AU M=14 M_earth R=4.1 R_earth	D=30.1 AU M=17 M_earth R=3.9 R_earth

how would we measure mass?

knowing mass and size, we can calculate densities :

	density (gm/cm³)
Jupiter	1.33
Saturn	0.70
Uranus	1.32
Neptune	1.64
Earth	5.52

Jovian planets, showing relative sizes

Composition:

cores: rocky with lots of Hydrogen-rich material ("ices") mixed in.

atmospheres: mostly Hydrogen and Helium, with other H-rich compounds mixed in.

Rapidly rotating:

	Rotation Period (Hours)
Jupiter	9.8
Saturn	10.6
Uranus	17.3
Neptune	19.2

rapid rotation leads to a squashing of the Jovians, particularly Saturn

what do you expect for the winds? why?

Jovian Interiors

How do we figure out what's going on inside the planets? We only see the cloud tops.

Let's take a trip down into Jupiter:

Cloudtops	125K	1 bar	clouds
7000 km down (10%)	2000K	500,000 bars	liquid hydrogen
14,000 km down (20%)	5,000K	2 million bars	metallic hydrogen
60,000 km down (90%)	20,000K	100 million bars	rocky core

Jupiter's heat -- it gives off twice as much heat as it gets from the Sun! Where does this come from? Very, very slow gravitational contraction.

The other planets: can we use density to tell us about their interiors?

Imagine taking a ball of gas, and adding more and more gas.

At first, more stuff means bigger planet. Adding more and more, eventually gravity will take over and start squeezing the ball down in size. This means that very massive gas balls are denser than low mass gas balls.

Go back and look at densities of the gas giants. Does this picture fit the data? What does that tell us?

Comparing the Interiors:

Heat sources:

Jupiter: slow contraction
Saturn: "helium drip", helium condenses and moves inward, a form of differentiation.
Uranus: no helium rain, no leftover heat from accretion, no contraction: no internal heat.
Neptune: should be like Uranus, but has more internal heat. Why? contraction? greenhouse effect (from methane)?

Jovian Atmospheres

Again, start with Jupiter. Composition :

Mostly hydrogen and helium. These are colorless gasses.

Next most common elements are oxygen, carbon and nitrogen. They get bound up with hydrogen to form molecules:

methane (CH₄)

ammonia (NH₃)

water (H₂O)

acetylene (C₂H₂)

ethane (C₂H₆)

propane (C₃H₈)

Why don't the flammable molecules "explode" on Jupiter? What's missing? Why is it missing?

Weather:

Jupiter has strong convection in its atmosphere (why?), bringing warm air from the interior up to the cooler outer layers. When this happens, molecules can condense into clouds :

inner clouds: water vapor (H₂ O)

higher up: ammonium hydrosulfide (NH₄SH) -- reddish clouds

highest up: ammonia (NH₄ ) -- white clouds

Jupiter also has circulation cells, like the Earth. They are broken up by the Coriolis effect into belts and zones, with extremely strong wind shear. Why is this so much stronger on Jupiter than on the Earth?

Strong wind shear sets up cyclonic storms, like the Great Red Spot.

Jupiter in Action

More Jupiter in Action

Comparing Atmospheres

How are the Jovian atmospheres different?

What causes this difference?

Different compositions:

Saturn: colder than Jupiter, so clouds form deeper, harder to see

Fewer complex molecules in the atmospheres of outer planets

Uranus, Neptune: methane (CH4) rich

Different weather patterns:

what factors are related to weather?

does this make sense looking at the Jovian planets' "weather"?

Magnetic fields

Jupiter's liquid metallic hydrogen interior plus fast rotation gives it a whopping magnetic field.

The charged particles from the solar wind interact with this magnetic field, protecting Jupiter's atmosphere and giving rise to pretty impressive aurorae.

Saturn has a weaker magnetic field, Uranus and Neptune weaker still. Why?

Pictures of the Jovian aurorae, from the Hubble Space Telescope.