CHAPTER 8 Review & Discussion:

2. Mercury and the Earth each have massive iron cores, which push their mean densities up to around 6 grams/cm^3. On the other hand, the Moon has little iron, and therefore it does not have a significant iron core. Hence the mean density of the Moon is only about 3 grams/cm^3.

3. The escape velocity is very low on Mercury and the Moon because they have relatively low masses. Therefore most of the gas that would have formed their atmospheres escaped into space long ago.

5. Mercury has a 3:2 spin-orbit resonance. This means that Mercury experiences exactly 3 sidereal days for every 2 sidereal years. This also imples that the length of the solar day on Mercury is equal to 2 sideral years. Mercury can't settle into a 1:1 spin-orbit resonance because it is in an elliptical orbit, unlike the Moon.

9. We think that the lunar highlands are older than the maria because (1) the surface is more heavily cratered and (2) radioactive dating indicates a much higher age.

CHAPTER 9 Review & Discussion:

1. Venus is very bright because it is the closest planet to Earch and it has a very high albedo.

2. Venus is always in the same region of the sky as the Sun because it is an inferior planet, meaning that it is closer to the Sun than the Earth is.

4. Radio observations showed that the surface of the planet is very hot, much hotter than expected based upon the observations of the cloud-tops visible from Earth.

5. The ultaviolet images revealed fast-moving upper layers of clouds. These clouds had velocities of up to 400 km/hr.

7. The atmosphere of Venus is 96.5 percent carbon dioxide, and 3.5 percent nitrogen, plus other trace gasses. The clouds are made of sulfuric acid.

8. The runaway greenhouse effect occurs when the temperature of a planet is too high for oceans to form and absorb most of the carbon dioxide and water vapor. The failure to remove these greenhouse gasses leads to further heating of the atmosphere, in a runaway process. The water vapor became so hot that is rose high in the atmosphere, until it was broken up by ultraviolet radiation from the Sun. After that, the hydrogen gas escaped into space and the oxygen reacted to form more carbon dioxide and sulphur dioxide.

14. We think that Venus does not have a magnetic field because of the very slow rotation of the planet. This is despite the fact that the planet probably has a molten core.

CHAPTER 10 Review & Discussion:

1. The best time to observe Mars from Earth is during favorable opposition, when the distance between the two planets is at a minimum.

4. Mars is red due to the presence of iron oxide (rust) on its surface.

8. The evidence that water once flowed on Mars consists of dry runoff channels, riverbeds, and outflow channels.

9. There probably is some liquid water on Mars today, as we see in the seasonal outflows that are observed near the equator. There is also likely to be vast quantities of water locked in the permafrost layer beneath the ground at higher latitudes.

13. The presence of iron on the surface of Mars suggests that Mars never melted as extensively as the Earth did, and therefore it did not undergo complete differentiation.

CHAPTER 11 Review & Discussion:

2. Differential rotation is the failure of an object to rotate as a single solid body. We can observe differential rotation on Jupiter by following the motions of the cloud bands.

4. The Great Red Spot is a storm that has been visible from Earth for over 300 years. The source of its energy is probably the oppositely-directed flows to the north and south of the spot.

5. The colors indicate clouds with various compositions. The different clouds lie at different altitudes in the atmosphere. The highest clouds are white and composed of ammonia ice. The yellows, reds, and browns are found in lower cloud layers which contain ammonium hydrosulfide ice.

6. Jupiter retained most of its original atmosphere because it has a very high mass, and because the temperature was not as high as that of the terrestrial planets during their formation.

11. Io's volcanic activity is due to the tidal force of Jupiter. The planet cannot achieve a synchronous orbit due to the pull of the moon Europa.

CHAPTER 12 Review & Discussion:

2. Saturn's rings are tilted with respect to the ecliptic. Therefore from Earth we sometimes see the upper surface of the rings, and sometimes the lower surface. We also sometimes see the rings nearly edge-on, in which case they almost disappear. The next time they will be seen edge-on is in the year 2025.

3. Saturn is less massive than Jupiter, and therefore its upper layer of ammonia ice clouds is thicker, which hides the more colorful clouds layers below.

4. Saturn has a cloud layer 2.5 times thicker than Jupiter due to its lower gravity.

7. The Roche limit is the closest that a moon can approach a planet within breaking apart due to the tidal force of the planet. Planetary rings are all within the Roche limit, and therefore the ring material cannot coalesce into a moon.

CHAPTER 13 Review & Discussion:

1. Astronomers suspected an eighth planet beyond Uranus because Uranus seemed to be under the influence of another body. This caused its orbit to be slightly non-elliptical.

2. The rotation axis of Uranus is tilted by 98 degrees from the north celestial pole. This tilt may be due to a violent collision in the distant past.

3. Methane is primarily responsible for the blue-green coloration of Uranus and Neptune. These planets have much more methane in their atmospheres than is present in the atmospheres of Jupiter and Saturn.

6. The magnetic fields of Uranus and Neptune are tilted and offset relative to the rotation axis. They are much stronger than Earth's magnetic field.

8. Miranda displays a wide range of surface terrains that seems surprising for its small size. Miranda has probably experienced one or more catastrophic events.