The Outer Planets

Ch 11.2 (p390-396)

Vocabulary

• Galilean moons (393) – The four largest moons of Jupiter – Io, Europa, Ganymede, and Callisto – which were first discovered by Galileo Galilei in 1610

The Gas Giants• The outer planets are called the gas giants

because they are primarily made of hydrogen and helium.

• They have strong gravitational forces due to their large masses.– The strong gravity creates tremendous

atmospheric pressure that changes gases to liquids.

– Most these planets have thick gas and liquid interiors covering a small, solid core

Jupiter• Largest planet

– 11 times the diameter of Earth– Twice the mass of all the other planets combined– Rotates faster than any other planet– Like all outer planets, it has a ring system

Jupiter’s Atmosphere

• 90% hydrogen, 10% helium• 1000km deep• Dense, colorful clouds• Because Jupiter rotates so quickly, the clouds

stretch into bands• The Great Red Spot is a storm of swirling gases

Jupiter’s Structure

• 80% hydrogen, 20% helium• Thick solid core• 1000km past the outer edge of

the cloud layer, the pressure is so great hydrogen gas changes to liquid

• Scientists do not know what the core is made of– They suspect it is rock and iron

The Moons of Jupiter

• Jupiter has at least 63 moons

• The 4 largest were discovered by Galileo in 1610– We call these Galilean Moons

• Io, Europa, Ganymede, and Callisto

• All made of rock and ice

• Collisions between Jupiter’s moons and meteorites likely resulted in Jupiter’s rings

Saturn

• 6th planet• Has horizontal bands of

clouds• 90% hydrogen, 10%

helium• Least dense planet

– Its density is less than that of water

Saturn’s Structure

• Similar to Jupiter– An outer gas layer, a thick layer

of liquid hydrogen, and a solid core

• Ring system is the largest and most complex– 7 bands of rings, each containing

thousands of narrower ringlets– Main ring system is over

70,000km wide and less than 30m thick

Saturn’s Moons

• At least 60 moons

• 5 largest – Titan, Rhea, Bdione, Iapetus, and Tethys

• Most of Saturn’s moons are chucks of ice less than 10km in diameter

• Titan is larger than Mercury– It is the only moon in the solar system with a

dense atmosphere– In 2005 the Huygen probe landed on Titan

Uranus

• 7th planet• Narrow, dark rings• Deep atmosphere composed mostly of hydrogen

and helium and some methane– The methane gas gives it a bluish color

• Beneath the atmosphere is a thick, slushy layer of water ammonia, and other materials

• Below that is a solid, rocky core

Uranus’s Axis and Moons• Uranus has a tilted axis of rotation

– Maybe caused by a collision with an Earth-sized object

• At least 27 moons– Largest are Titania and Oberon (smaller than our

moon)• Titania has an icy cracked surface that might once have

been covered by an ocean

Neptune

• Discovered in 1846• Atmosphere is like Uranus

– Hydrogen, helium, and some methane

• Interior is also like Uranus– Partially frozen water and ammonia with a rock and iron core

• 13 moons and a faint ring system– Triton is the largest. It has a surface of frozen nitrogen and

geysers that erupt nitrogen gas

• Swirling storm s and high winds sometimes exceeding 1000km/h