ASTR 263 Chapter 11

Saturn's rings look bright because __________.

light from the Sun reflects off the material in the rings

Saturn's rings are composed of __________.

lots of individual particles of ice and rock

Saturn's many moons affect its rings through

orbital resonances.

Using the data in the table Satellites of the Solar System in the textbook, identify the orbital resonance relationship between Titan and Hyperion.

4:3

What causes synchronous rotation?

A massive planet exerts a tidal force on a moon that causes the moon to align itself such that its tidal bulges always point toward and away from the planet.

Why are Saturn's rings so thin?

Any particle in the ring with an orbital tilt would collide with other ring particles, flattening its orbit.

Which of the following is not a piece of evidence supporting the idea that Europa may have a subsurface ocean?

Astronomers have detected small lakes of liquid water on Europa's surface.

Why do we think that ring particles must be replenished over time? Where we think ring particles come from? Choose the correct statement.

Because collisions are constantly occurring within the ring systems, ring particles are continually being ground down to dust. Dust cannot survive long in ring systems because sunlight pressure makes the particles slowly fall onto the planet. So we think that ring systems cannot survive very long and thus that ring particles must be replenished, probably by impacts on small embedded moons and ring particles by micrometeorites and the occasional larger impacts.

Which medium-size moon is in a 2:1 resonance with Enceladus?

Dione

How might its capture be relevant to its geological activity?

Even though Triton is much smaller than our Moon, Triton' surface shows evidence of relatively recent geological activity. This can be because of the tidal heating that occurred when the moon was captured.

Why is Io more volcanically active than our moon?

Io has a different internal heat source.

All the following statements are true. Which one is most important in explaining the tremendous tidal heating that occurs on Io?

Io orbits Jupiter on an elliptical orbit as a result of orbital resonances with other satellites.

Io's elliptical orbit is necessary to its tidal heating. This elliptical orbit, in turn, is a result of the orbital resonance among Io, Europa, and Ganymede. This orbital resonance causes Io to have a more elliptical orbit than it would otherwise, because __________.

Io, Europa and Ganymede periodically return to the same orbital positions, creating the same gravitational tugs

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

Its density would increase, but its diameter would barely change.

Which of the following best explains why many jovian moons have been more geologically active than the Moon or Mercury?

Jovian moons are made mostly of ice that can melt or deform at lower temperatures than can the rock and metal that make up the Moon and Mercury.

Which of the following most likely explains why Jupiter's interior releases so much heat?

Jupiter is contracting gradually.

Which of the following statements correctly describes the motion of the particles in Saturn's rings?

Particles in the inner rings orbit Saturn at a faster speed than particles in the outer rings.

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

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.

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

Saturn, where it generates heat as it falls downward.

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

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

Which of the following best explains why we see horizontal "stripes" in photographs of Jupiter and Saturn?

The light stripes are regions of high clouds, and the dark stripes are regions where we can see down to deeper, darker clouds.

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

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

Jupiter likely formed first since it is the largest jovian planet and closest to the Sun.

True

Which statement about Saturn's rings is not true?

The rings must look much the same today as they did shortly after Saturn formed.

Why does Jupiter have three distinct layers of clouds?

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

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

They actually contain relatively little material in a gaseous state.

Which of the following best describes the nature of planetary rings?

They are composed of countless individual particles.

What is the relevance of tidal heating to the possibility of life on jovian moons?

Tidal heating can lead to subsurface zones of liquid water.

Which moon shows evidence of rainfall and erosion by some liquid substance?

Titan

Why do astronomers believe that Triton is a captured moon?

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

Which jovian planet should have the most extreme seasonal changes?

Uranus

The two jovian planets that contain the highest proportions of hydrogen compounds are ___________.

Uranus and Neptune

We now know of many Jupiter-size planets around other stars. Suppose that future observations show that one of these planets has two orbiting moons. What additional information, if any, would we need to decide whether these moons experience tidal heating?

We need to know their orbital periods.

What is the Cassini division of Saturn's rings?

a large gap, visible from Earth

We cannot see tidal forces or tidal heating; rather, we predict that they must occur based on the orbital characteristics of the moons. What observational evidence confirms that tidal heating is important on Io?

active volcanoes on Io

Saturn's rings

are continually supplied with new particles by impacts with small moons.

In light of what we know about geological activity on the terrestrial worlds, why might it seem surprising to find geological activity on jovian moons?

because they are relatively small in size

Which of the following gases is not a significant ingredient of the jovian planet atmospheres?

carbon dioxide

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?

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

Orbital resonance also gives Europa an elliptical orbit, so it experiences tidal heating, too. However, Europa experiences less tidal heating than Io, because Europa __________ than Io.

is farther from Jupiter

Io experiences tidal heating primarily because __________.

its elliptical orbit causes the tidal force to vary as Io orbits Jupiter.

Which of the following is most unlikely to be found on Titan?

lakes of liquid water in the warmer equatorial regions

Which of the following is not due to tidal forces?

the backward orbit of Triton (a moon of Neptune)