Ch. 29.3 The Outer Planets

Consist of the gas giant planets Jupiter, Saturn, Uranus, and Neptune.

Pluto is recently demoted, and is no longer considered a planet(It’s a dwarf planet).

The gas giants are more massive, but much less dense than the inner planets.

Thick hydrogen / helium atmospheres, with probable dense cores.

Since they are similar to Jupiter, they are also known as Jovian planets.

The Gas Giants

Jupiter 5th planet from the sun. The largest; over twice the mass of all

other planets combined. Orbit period is 12 years. Fastest rotation; once every 9 hours

and 50 minutes. Many moons (63 at last count) and at

least 4 rings. High internal temp. due to intense

pressure (30,000 C).

Resulting metallic hydrogen creates enormous magnetic field.

Composed of 92% hydrogen and helium (similar to the sun; a failed star?).

No solid surface. Alternating swirling (due to rapid

rotation) colorful bands suggest ammonia, methane, and water vapor.

Great Red Spot is giant rotating storm several hundred years old.

Jupiter

The Great Red Spot

Saturn

6th planet; 2nd largest in the solar system.

Avg. temp. -176 C. Many moons (61 at last count) and a

large, complex ring system. Rapid rotation, once every 10 hours

and 30 minutes. Bands of colored clouds.

Least dense planet (lower density than water).

Orbit period 29.5 years.

Saturn

Uranus

7th planet from the sun; 3rd largest. Discovered in 1781 (1st planet

discovered since ancient times). Almost 3 billion km from the sun. At least 22 moons and 11 small rings. Horizontal rotation, once every 17

hrs. Orbit period 84 years.

Greenish atmosphere color from methane, with atmosphere mostly hydrogen and helium.

Surface temp. -214 C. Interior may be water and methane

slush. Temp. increases with depth, up to

7000 C in a rock / metal core.

Uranus

Neptune

8th planet; 4th largest, but very similar to Uranus in size and mass.

Orbit period 164 years. Rotates once every 16 hours. 11 moons, 4 rings.

Existence predicted before it was discovered, after astronomers noticed variations in Uranus’ expected orbit.

Position was determined mathematically, then it was discovered there in the mid-1800’s.

4.5 billion km from the sun. Blue-green color, with white clouds of

frozen methane in the upper part of the hydrogen/helium atmosphere.

Strong winds, over 1000 km/hr. An Earth-sized storm, the Great Dark

Spot. Surface temp. -225 C.

Neptune and its large moon Triton