AST 111 Lecture 20 Jovian Worlds I. Jovian Worlds = 50 Earths.

AST 111 Lecture 20

Jovian Worlds I

Jovian Worlds

= 50 Earths

Jovian Worlds

= 1400 Earths!

Jovian Worlds

Jovian worlds are not known to have solid surfaces!*

*Possibly have solid cores.

Jovian Rotation and Shape

• They rotate rapidly– 10 hr day on Jupiter and

Saturn– 16-17 hr day on Uranus

and Neptune

• Bulges out equatorial regions

• Due to formation

Mass vs. Size

Jupiter has three times the mass ofSaturn, but it is only 20% larger.

Why not 3 times as large?

Adding more and more gas…

• Jovian worlds much like a stack of pillows

• As more gas gets added, the gas below compresses

• Keep adding gas, planet does not get larger– Gets more dense

Adding more and more gas…

Jupiter 3x more massive than Saturn, only slightly larger!

Jovian Worlds

• Hydrogen, helium, and hydrogen compounds

• Formed beyond frost line in solar nebula

• So why are they so different?

What are they made of?

• Jupiter and Saturn:– Mostly H and He– Few percent H

compounds– Little rock and metal

• Uranus and Neptune:– Less than half H and He– Primarily H compounds– Little rock and metal

Why different amounts of stuff?

• All Jovian worlds:

– Grew from ice-rich planetesimals • These were all 10x Earth’s mass

– Had enough gravity to hang onto H and He

Why different amounts of stuff?

• The “ice seeds” of the Jovian worlds:

– Packed closer together closer to the Sun

– More spread out farther from the Sun

Why different amounts of stuff?

• Icy planet seeds same mass, but:

• Farther out, took longer to form

• Had less time to acquire H and He before Sun turned on

• What does this say about Jovian planet size farther out?

Jovian Planet Size

Structure of Jovian Planets

• Determined by:– Computer models– Lab experiments– Spacecraft

• Galileo spacecraft studied Jupiter– Models show some Jovian structures to be similar

Specific Example: Jupiter

• Galileo dove into Jupiter’s atmosphere– Survived to 200km (0.3%

Jupiter’s radius)

• 1.0 g / cm3 is the density of water

• Pressure causes phase changes

Structure of Jovian Planets

• Saturn: less gravity, H changes phase deeper

• Uranus and Neptune: not enough gravity to have liquid or metallic H

Jovian Atmospheres

• On Earth, only water condenses to form clouds

• On Jovian worlds, several gases can condense to form clouds

• Hydrogen compounds responsible for colorful appearances – Ammonia: Whitish-yellow– Ammonium Hydrosulfide: Orange– Water: White– Methane: Blue, must be COLD!

Jovian Atmospheres

• “Atmospheres” means “cloud layer and above”– It’s what we see

• About 100-200 miles deep

• Different gases condense at different altitudes.

Jovian Atmospheres

• Saturn and Jupiter have same 3-layer cloud structure

• Saturn:– Lower temperature– Cloud layers deeper in

atmosphere– More “subdued” surface

Jovian Atmospheres

• Uranus and Neptune:

– COLD!

– If there are NH3, NH4SH and H20 clouds:• Buried deep within planet

– Methane condenses in their upper atmospheres• Slush of methane snow

Colors of Jovian Atmospheres

• Jupiter and Saturn

– Water and ammonia reflect white light

– Ammonium hydrosulfide reflects brown and red light

• Uranus and Neptune

– Methane gas absorbs red light

– Methane clouds reflect blue light

Methane

Wind and Storms on Jupiter

• Solar heat causes air on equator to warm, rise, move to poles– Earth has this too

• Creates “circulation cells”

• Split by Coriolis force– Stronger for faster

rotation

Why stripes of color?

• Consider the circulation cells– Rising on one edge– Falling on the other

• Rising edge brings ammonia (white) to where it can condense– Then falls as ammonia snow

• Falling edge is depleted of ammonia– We see the brownish NH4SH

Why the stripes of color?

Wind and Storms on the Others

• Bands are present on Saturn and Neptune– Slower rotation and

smaller size, fewer bands

• Also have large storms– Great Red Spot on

Jupiter– Great Dark Spot on

Neptune