Chapter 11

Question 1

rings (planetary)

Answer 1

The collections of numerous small particles orbiting a planet within its Roche tidal zone.

Question 2

jovian nebulae

Answer 2

The clouds of gas that swirled around the jovian planets, from which the moons formed.

Question 3

Io torus

Answer 3

A donut-shaped charged-particle belt around Jupiter that approximately traces Io’s orbit.

Question 4

Galilean moons

Answer 4

The four moons of Jupiter that were discovered by Galileo: Io, Europa, Ganymede, and Callisto.

Question 5

moonlets

Answer 5

Very small moons that orbit within the ring systems of jovian planets.

Question 6

Cassini division

Answer 6

A large, dark gap in Saturn’s rings, visible through small telescopes on Earth.

Question 7

metallic hydrogen

Answer 7

Hydrogen that is so compressed that the hydrogen atoms all share electrons and thereby take on properties of metals, such as conducting electricity. It occurs only under very high-pressure conditions, such as those found deep within Jupiter.

Question 8

shepherd moons

Answer 8

Tiny moons within a planet’s ring system that help force particles into a narrow ring; a variation on gap moons.

Question 9

gap moons

Answer 9

Tiny moons located within a gap in a planet’s ring system. The gravity of a gap moon helps clear the gap.

Question 10

belts (on a jovian planet)

Answer 10

Dark bands of sinking air that encircle a jovian planet at a particular set of latitudes.

Question 11

tidal heating

Answer 11

A source of internal heating created by tidal friction. It is particularly important for satellites with eccentric orbits such as Io and Europa.

Question 12

orbital resonance

Answer 12

A situation in which one object’s orbital period is a simple ratio of another object’s period, such as 1/2, 1/4, or 5/3. In such cases, the two objects periodically line up with each other, and the extra gravitational attractions at these times can affect the objects’ orbits.

Question 13

Great Red Spot

Answer 13

A large, high-pressure storm on Jupiter.

Question 14

Roche tidal zone

Answer 14

The region within two to three planetary radii (of any planet) in which the tidal forces tugging an object apart become comparable to the gravitational forces holding it together; planetary rings are always found within the Roche tidal zone.

Question 15

The energy in the atmospheres of most of the jovian planets comes ___________,

Answer 15

both the Sun and their interiors, in roughly equal proportions

Question 16

Overall, Jupiter’s composition is most like that of ______.

Answer 16

the Sun (Both are made mostly of hydrogen and helium.)

Question 17

How do typical wind speeds in Jupiter’s atmosphere compare to typical wind speeds on Earth?

Answer 17

They are much faster than hurricane winds on Earth.

Question 18

What is the Great Red Spot?

Answer 18

a long-lived, high-pressure storm on Jupiter (It has been seen ever since telescopic observations of Jupiter began some 400 years ago.)

Question 19

What atmospheric constituent is responsible for the blue color of Uranus and Neptune?

Answer 19

methane (The low temperatures of these distant planets allow for the formation of methane clouds that contribute to the blue color.)

Question 20

How does the strength of Jupiter’s magnetic field compare to that of Earth’s magnetic field?

Answer 20

Jupiter’s magnetic field is about 20,000 times as strong as Earth’s.

Question 21

Which moon has a thick atmosphere made mostly of nitrogen?

Answer 21

Titan

Question 22

The Huygens probe took numerous pictures as it descended to Titan’s surface in 2005. What did the pictures show?

Answer 22

features or erosion, including what appeared to be dry river valleys and lakebeds (Titan is far too cold for liquid water, so these features probably were carved by liquid methane or ethane.)

Question 23

Suppose you could float in space just a few meters above Saturn’s rings. What would you see as you looked down on the rings?

Answer 23

countless icy particles, ranging in size from dust grains to large boulders

Question 24

Jupiter and the other jovian planets are sometimes called “gas giants.” In what sense is this term misleading?

Answer 24

They actually contain relatively little material in a gaseous state.

Question 25

According to our theory of solar system formation, why did Uranus and Neptune end up to be much less massive than Jupiter and Saturn?

Answer 25

Particles in the solar nebula were more spread out at greater distances, so that accretion took longer and there was less time to pull in gas before the solar wind cleared the nebula.

Question 26

What would happen to Jupiter if we could somehow double its mass?

Answer 26

Its density would increase but its diameter would barely change.

Question 27

Which planet may have helium rain in its interior, and what does this rain do?

Answer 27

Saturn, where it generates heat as it falls downward.

Question 28

Why does Jupiter have three distinct layers of clouds?

Answer 28

The three layers represent clouds made of gases that condense at different temperatures.

Question 29

Uranus and Neptune have methane clouds but Jupiter and Saturn do not. Which factor explains why?

Answer 29

Temperatures on Jupiter and Saturn are too high for methane to condense.

Question 30

Why is the radiation so intense in the region that traces Io’s orbit around Jupiter (the Io torus)?

Answer 30

The region is full of gases that become ionized after they are released from volcanoes on Io.

Question 31

Why do astronomers believe that Triton is a captured moon?

Answer 31

Triton orbits Neptune in a direction opposite that of Neptune’s rotation.