Astronomy 241: Foundations of Astrophysics I

13. Giant Planets

“Gas Giants” “Water Worlds”

Two Types of Jovian Planets

Internal Structure: Heat Sources

J. & S. put out lots of heat — not due to radioactivity since H and He isotopes are stable.

— Jupiter: left-over heat.

— Saturn: + He settling.

U. puts out very little heat —— bottled up in interior?

N. puts out more heat —— deeper convection.

Internal Structure: Magnetic Fields

J. & S. have strong fields which are well-aligned with rotation.

U. & N. have weaker fields which are highly mis-aligned.

— convection in metallic H! — local dynamo in “ocean”?

Internal Structure: Magnetic Fields

12 hours on Jupiter

Outward Appearance

Outward Appearance: Cloud Colors

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Dis

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low

clo

ud t

ops NH3

NH4SH

H2O

Outward Appearance: Belts

Convection and rapid rotation organize atmospheric motion.

Belts: sinking gas exposes red NH4SH clouds; circulates faster.

Zones: rising gas forms white

NH3 clouds; circulates slower.

Jupiter Unpeeled

Outward Appearance: Circulation Patterns

Approaching Jupiter

Outward Appearance: Great Red Spot

Outward AppearanceOutward Appearance: Great Red Spot

Jupiter's Great Red Spot Region

H

Outward Appearance: Saturn

Saturn … Four Years On

Bands like Jupiter’s, but less dramatic since atmosphere is deeper due to weaker gravity.

Outward Appearance: Uranus & Neptune

Their atmospheres are deep, methane-rich, and very cold.

• Cloud layers are too deep to be easily seen.

• Methane (CH4) absorbs red light, transmits blue.

— blue planets with subtle cloud features.

Outward Appearance: Uranus & Neptune

Great Dark Spot