Transcript
Astronomy: A Beginner's Guide to the Universe, 7e (Chaisson/McMillan)
Chapter 6 The Terrestrial Planets: A Study in Contrasts
1) Venus' rotation period is longer than its period of revolution around the Sun.
Answer: TRUE
Diff: 1
Section Ref.: 6.1
2) Mercury, Venus, and Earth have similar densities.
Answer: TRUE
Diff: 2
Section Ref.: 6.1
3) The density of Mars is very similar to that of the other terrestrial planets.
Answer: FALSE
Diff: 2
Section Ref.: 6.1
4) Venus can appear as a crescent through the telescope.
Answer: TRUE
Diff: 1
Section Ref.: 6.2
5) Mercury's rotation and revolution are an example of a 3:2 resonance.
Answer: TRUE
Diff: 2
Section Ref.: 6.2
6) Although it has no liquid water, Mercury has a tidal bulge.
Answer: TRUE
Diff: 2
Section Ref.: 6.2
7) Compared to Earth, Venus spins very rapidly on its axis.
Answer: FALSE
Diff: 1
Section Ref.: 6.2, 6.1
8) Atmospheric pressure on Mars is roughly half that of Earth's at sea level.
Answer: FALSE
Diff: 2
Section Ref.: 6.1
9) Venus' surface temperature cools off at night, much like Mercury's does.
Answer: FALSE
Diff: 2
Section Ref.: 6.3
10) Mercury has the widest variation in surface temperatures between night and day of any planet in the solar system.
Answer: TRUE
Diff: 1
Section Ref.: 6.3
11) The scarps on Mercury are extremely similar to the cratered lunar highlands in appearance.
Answer: FALSE
Diff: 2
Section Ref.: 6.4
12) We now know of polar caps on Mercury, the Moon, Earth, and Mars.
Answer: TRUE
Diff: 2
Section Ref.: 6.4
13) The surface temperature of Venus is 730K, even hotter than Mercury.
Answer: TRUE
Diff: 2
Section Ref.: 6.1
14) No evidence of impact craters has been found on Venus.
Answer: FALSE
Diff: 2
Section Ref.: 6.5
15) The surface of Mars is surprisingly smooth and featureless.
Answer: FALSE
Diff: 1
Section Ref.: 6.6
16) Mars has larger volcanoes than Earth's Hawaii.
Answer: TRUE
Diff: 1
Section Ref.: 6.6
17) The polar caps and dust storms of Mars can be seen with Earth-based telescopes.
Answer: TRUE
Diff: 2
Section Ref.: 6.6
18) The Moon's far side is more ancient and heavily cratered; on Mars, the same is true of its southern hemisphere.
Answer: TRUE
Diff: 2
Section Ref.: 6.6
19) Mars appears red in color because of refraction of light by its atmosphere, much like the color of the totally eclipsed Moon.
Answer: FALSE
Diff: 2
Section Ref.: 6.6
20) There is new evidence that water has flowed as mud on Mars in recent times.
Answer: TRUE
Diff: 2
Section Ref.: 6.6
21) Because of its axial tilt and more elliptical orbit, Mars' polar caps change size even more than the Earth's do.
Answer: TRUE
Diff: 2
Section Ref.: 6.6
22) The seasonal polar caps on Mars, which grow and shrink over the year, are primarily carbon dioxide.
Answer: TRUE
Diff: 1
Section Ref.: 6.6
23) Winds on Mars give rise to planet-wide dust storms.
Answer: TRUE
Diff: 2
Section Ref.: 6.6, 6.8
24) The low surface gravity helps Martian volcanoes grow to great heights.
Answer: TRUE
Diff: 1
Section Ref.: 6.6
25) The giant Borealis basin around the Martian north pole may have formed due to an impact with an asteroid twice the size of Ceres.
Answer: TRUE
Diff: 2
Section Ref.: 6.6
26) The Phoenix lander on Mars failed to confirm the presence of water ice under the surface.
Answer: FALSE
Diff: 1
Section Ref.: 6.6
27) Mercury has an unusually small core.
Answer: FALSE
Diff: 2
Section Ref.: 6.7
28) Mars has a weak magnetic field.
Answer: TRUE
Diff: 2
Section Ref.: 6.7
29) The Mars Rover found undisputed microfossils, proving life once existed on Mars.
Answer: FALSE
Diff: 2
Section Ref.: 6.7
30) Venus and Mercury both have magnetic fields similar to Earth's.
Answer: FALSE
Diff: 2
Section Ref.: 6.7
31) Mercury's magnetic field is generated by the same dynamo effect as Earth's.
Answer: FALSE
Diff: 3
Section Ref.: 6.7
32) Carbon dioxide is the predominant atmospheric gas on Venus.
Answer: TRUE
Diff: 1
Section Ref.: 6.3, 6.8
33) Running water continues to be the major erosive factor of Mars today.
Answer: FALSE
Diff: 2
Section Ref.: 6.6
34) Running water played a major role in shaping Mars in ancient times.
Answer: TRUE
Diff: 2
Section Ref.: 6.6
35) Which of these gets so bright as to be seen in daylight at times?
A) Mercury
B) Venus
C) Mars
D) Jupiter
E) Saturn
Answer: B
Diff: 1
Section Ref.: 6.1
36) Which three worlds have almost identical densities?
A) Mercury, Venus, and Earth
B) Mercury, Mars, and our Moon
C) Deimos, Phobos, and our Moon
D) Earth, Moon, and Mars
E) Mercury, Earth, and Mars
Answer: A
Diff: 2
Section Ref.: 6.1
37) Which planet shows the widest range of surface temperatures between day and night?
A) Mercury
B) Venus
C) Earth
D) Mars
E) Uranus
Answer: A
Diff: 1
Section Ref.: 6.2
38) How does Mercury's rotation relate to the Sun?
A) It always keeps one face tidally locked toward the Sun, as our Moon does with us.
B) Its year is much shorter, only 88 days, than its slow rotation of 243 days on its axis.
C) Its rotation rate is 2/3 as long as its year, due to tidal resonances.
D) Its day is the same length as its year.
E) It does not spin at all, being tidal stopped by the solar tides.
Answer: C
Diff: 2
Section Ref.: 6.2
39) Venus' rotation on its axis
A) is the fastest of the terrestrial planets.
B) is clockwise, unlike most other solar system objects.
C) shows it is tidally locked in its orbit around the Sun.
D) is highly tilted to its orbital plane, causing large seasonal changes.
E) prevents us from seeing all of its surface features.
Answer: B
Diff: 2
Section Ref.: 6.2
40) Mercury presents the same side to the Sun
A) every other orbit.
B) all the time, just like our Moon.
C) every 12 hours.
D) every third orbit.
E) twice every orbit.
Answer: A
Diff: 3
Section Ref.: 6.2
41) The atmospheric pressure on Venus
A) shows an extreme change with the seasons.
B) is much lower than on Earth.
C) is about the same as on Mercury.
D) is much higher than on Earth.
E) causes variations in surface temperature.
Answer: D
Diff: 1
Section Ref.: 6.3
42) What is the main constituent of the atmosphere of Venus?
A) oxygen
B) nitrogen
C) hydrogen
D) carbon dioxide
E) sulfuric acid
Answer: D
Diff: 1
Section Ref.: 6.3
43) The main constituent of the Martian atmosphere is
A) hydrogen.
B) helium.
C) methane.
D) carbon dioxide.
E) nitrogen.
Answer: D
Diff: 1
Section Ref.: 6.3
44) Why are Mars' seasons more extreme than those of the earth?
A) Mars' seas dried up long ago.
B) Mars' axial tilt is slightly more than our 23.5 degrees.
C) Mars' orbit is more eccentric than our almost circular one.
D) Mars' weather is affected by evaporation from the polar ice in its summer.
E) All of these contribute to the huge seasonal changes that Mars experiences.
Answer: E
Diff: 3
Section Ref.: 6.2, 6.6
45) Which body has the densest atmosphere?
A) Mercury
B) Venus
C) Earth
D) Mars
E) our Moon
Answer: B
Diff: 2
Section Ref.: 6.3
46) One of the effects of Mercury's very slow spin is
A) extreme variations in its surface temperature.
B) an intensely powerful magnetic field.
C) tectonic activity.
D) wind patterns that are slow, but global in size.
E) large variations in the size of its polar cap.
Answer: A
Diff: 3
Section Ref.: 6.3
47) Mercury's surface most resembles which of these?
A) the Earth's deserts
B) the lunar far side
C) the lunar mare
D) Venus' polar regions
E) Mars' deserts
Answer: B
Diff: 2
Section Ref.: 6.4
48) The scarps on Mercury were probably caused by
A) tectonic activity.
B) meteorite bombardment.
C) a tidal bulge.
D) volcanism.
E) the crust cooling and shrinking.
Answer: E
Diff: 2
Section Ref.: 6.4
49) What did radar astronomers find in the polar regions of Mercury?
A) rift valleys
B) large mare basins, such as near our Moon's south pole
C) temperatures cold enough to allow thin sheets of water ice
D) polar caps of dry ice that vary seasonally, much like Mars
E) auroral displays much like Earth's
Answer: C
Diff: 2
Section Ref.: 6.3
50) Our most detailed maps of Venus come from
A) the Magellan space probe.
B) the Hubble Space Telescope.
C) direct observation from Earth-based optical telescopes.
D) manned landings.
E) Earth-based radio telescopes.
Answer: A
Diff: 1
Section Ref.: 6.5
51) The surface of Venus can be observed with
A) the Mt. Wilson 100" telescope.
B) radar observations.
C) most amateur telescopes.
D) the Hubble Space Telescope.
E) All of these have provided detailed observations about the surface of our sister planet.
Answer: B
Diff: 2
Section Ref.: 6.5
52) What percentage of the surface of Venus could be characterized as continental-sized highlands?
A) less than 10%
B) about 30%, like the Earth
C) 45%
D) 75%
E) 100%
Answer: A
Diff: 2
Section Ref.: 6.5
53) Which statement is true of Venus' surface?
A) There are two continent sized uplands.
B) It has remained unchanged for billions of years.
C) Atmospheric pressure is very low.
D) There is an extensive hydrosphere.
E) There are no shield volcanoes.
Answer: B
Diff: 2
Section Ref.: 6.5
54) Like Olympus Mons, volcanoes on Venus
A) form where continental plates collide.
B) are much larger than typical volcanoes on Earth.
C) have been extinct for billions of years.
D) only form at the equator.
E) are shield volcanoes.
Answer: E
Diff: 3
Section Ref.: 6.5
55) Valles Marineris is the most striking example of a(n)
A) impact crater.
B) shield volcano.
C) oceanic trench.
D) rift valley.
E) scarp.
Answer: D
Diff: 1
Section Ref.: 6.6
56) The deepest depression found on the surface of Mars is the
A) Mariana Trench.
B) Caloris basin.
C) Valles Marineris rift.
D) Hellas Basin.
E) Mare Crisium.
Answer: D
Diff: 1
Section Ref.: 6.6
57) We have not yet found meteoroids and meteorites derived from
A) Venus.
B) the Moon.
C) Mars.
D) asteroids.
E) comets.
Answer: A
Diff: 2
Section Ref.: 6.6
58) The name of the NASA mission(s) that landed on Mars in 1976 was
A) Voyager.
B) Magellan.
C) Viking I and II.
D) Venera 14.
E) Galileo.
Answer: C
Diff: 2
Section Ref.: 6.6
59) Which of the following characterizes a shield volcano?
A) It sits above a hot spot in the planet's mantle.
B) It is formed by moving tectonic plates.
C) It can erupt only briefly before being dragged off the hot spot.
D) It cannot get as high as Mt. Everest before the thin crust starts slumping.
E) It cannot grow very large, for it has a very short span of eruption.
Answer: A
Diff: 2
Section Ref.: 6.5, 6.6
60) What is true of Mars?
A) Its magnetic field is stronger than Earth's
B) Its atmosphere is mostly water vapor.
C) Iron oxide on the surface is responsible for its reddish color.
D) A pool of water was discovered by the Mars Rover.
E) Definite microfossils have been found.
Answer: C
Diff: 3
Section Ref.: 6.6
61) That the Tharsis region on Mars has so few craters
A) proves tectonic activity is taking place.
B) is due to the very low elevation of the region.
C) suggests it is the youngest region on the planet.
D) suggests it is at the center of a particularly strong magnetic field.
E) is due to annual flooding and water erosion.
Answer: C
Diff: 3
Section Ref.: 6.6
62) The largest difference between Mars' northern and southern hemispheres is that
A) the southern appears older, with more impact craters.
B) the northern has all the outflows and must have been much hotter.
C) the northern is higher overall, despite some high volcanoes in the south.
D) the southern has a polar cap, but none ever forms in the north.
E) the southern is much darker, with large mare-like basaltic lava flows.
Answer: A
Diff: 3
Section Ref.: 6.6
63) The presence of a Mercurian magnetic field surprised the planetary scientists on the Mariner 10 team because
A) Mercury is low in iron.
B) Mercury spins too rapidly to produce a stable dynamo.
C) it's still too hot for its core to have differentiated.
D) the dynamo theory predicted that Mercury was spinning too slowly for one.
E) Mercury lacks an iron core.
Answer: D
Diff: 2
Section Ref.: 6.7
64) Much of the water on Mars
A) is thought to be in a layer of permafrost just below the surface.
B) lies in shallow pools near the poles.
C) is locked in the seasonal ice cap.
D) is found in deep pools near the equator.
E) is in the form of clouds.
Answer: A
Diff: 2
Section Ref.: 6.9
65) Of all the planets known in antiquity, ________ is the hardest to observe visually.
Answer: Mercury
Diff: 1
Section Ref.: 6.1
66) Compared to the orbits of Venus and Earth, the orbits of both Mercury and Mars have much ________ eccentricity.
Answer: higher
Diff: 2
Section Ref.: 6.1
67) The only two planets which can transit the Sun are ________.
Answer: Mercury and Venus
Diff: 2
Section Ref.: 6.1
68) The Sun's tidal pull has slowed Mercury's rotation down to a period ________ that of its year.
Answer: 2/3
Diff: 2
Section Ref.: 6.2
69) The direction of the rotation of Venus is exceptional because it is in a ________ direction.
Answer: retrograde or clockwise
Diff: 1
Section Ref.: 6.2
70) The planet which shows us the widest range of surface temperatures between day and night is ________.
Answer: Mercury
Diff: 1
Section Ref.: 6.2
71) Of all the planets, the axial tilt and rotation period of ________ is most like our own.
Answer: Mars
Diff: 1
Section Ref.: 6.2
72) While featureless in visible light, we can see some detail in Venus' clouds using ________.
Answer: ultraviolet light
Diff: 3
Section Ref.: 6.2
73) Because of their low surface gravities, the Moon and Mercury lack ________.
Answer: atmosphere
Diff: 1
Section Ref.: 6.3
74) The clouds on Venus are made primarily of ________.
Answer: sulfuric acid.
Diff: 1
Section Ref.: 6.3
75) ________ are great wrinkle marks on Mercury's crust, due to its core contracting.
Answer: Scarps
Diff: 2
Section Ref.: 6.4
76) The surface of Mercury looks very similar to ________.
Answer: the lunar far side
Diff: 2
Section Ref.: 6.4
77) The most effective wavelengths to see through the clouds of Venus to the surface are ________.
Answer: radio or radar
Diff: 2
Section Ref.: 6.5
78) Smooth rolling plains, modest highlands and lowlands, and no water describes the surface of ________.
Answer: Venus
Diff: 2
Section Ref.: 6.5
79) Unlike our Moon and Mars, all the impact craters found on Venus are ________ in size.
Answer: large
Diff: 1
Section Ref.: 6.5
80) In age, the surface of Venus is much ________ than even the lunar mare.
Answer: younger
Diff: 2
Section Ref.: 6.5
81) As with the lunar mare and Earth's ocean basins, the chief rock in the low plains of Venus is ________.
Answer: basalt
Diff: 1
Section Ref.: 6.5
82) Mars appears red due to ________ on its surface.
Answer: rust, or iron oxide
Diff: 1
Section Ref.: 6.6
83) Of all the planets, only ________ has surface features easily seen from Earth with ground-based telescopes.
Answer: Mars
Diff: 1
Section Ref.: 6.6, Disc. 6.1
84) The largest volcano in the solar system, ________, is found on Mars.
Answer: Olympus Mons
Diff: 1
Section Ref.: 6.6
85) Directly opposite the Tharsis uplift and volcanoes on Mars lies the deep ________, perhaps suggesting impact cause and volcanic effect.
Answer: Hellas basin
Diff: 3
Section Ref.: 6.6
86) Mercury's core is unusually ________, which may help explain its magnetic field.
Answer: large
Diff: 1
Section Ref.: 6.7
87) The planet ________ has the least variation in temperatures on the surface between day and night.
Answer: Venus
Diff: 2
Section Ref.: 6.8
88) Carbon dioxide dominates the atmospheres of Venus and Mars, but on Earth most of it lies underground as ________.
Answer: carbonate (or limestone) rocks
Diff: 2
Section Ref.: 6.8
89) The ALH84001,meteorite, discovered in Antarctica, came from ________, and suggests it may once have had life.
Answer: Mars
Diff: 2
Section Ref.: 6.8
90) The greatest rift valley system yet found is ________ on Mars.
Answer: Valles Marineris
Diff: 2
Section Ref.: 6.7
91) While ________ gas is the main atmospheric component of both Mars and Venus, its density means it plays a far larger role in heating Venus.
Answer: carbon dioxide
Diff: 1
Section Ref.: 6.8
92) The great barometric changes accompany the sublimation of carbon dioxide in the Martian spring and summer, creating planet-wide ________.
Answer: dust storms
Diff: 2
Section Ref.: 6.8
93) What is the primary effect the carbon dioxide in Venus' atmosphere has on the planet?
Answer: The high concentration of carbon dioxide has caused a runaway greenhouse effect that results in very high surface temperatures.
Diff: 2
Section Ref.: 6.8
94) Why is Venus' rotation unusual?
Answer: Venus is the only terrestrial planet to rotate retrograde (or backwards or clockwise) on its axis.
Diff: 1
Section Ref.: 6.2
95) What is unusual about the rotational (spin) and orbital periods of Venus?
Answer: Venus' day is actually longer than its year. It takes longer to spin once on its axis than to complete one orbit around the Sun.
Diff: 3
Section Ref.: 6.2, Appendix 3
96) If Mars' atmosphere is mostly carbon dioxide, why isn't it as hot as Venus?
Answer: Although it has a carbon dioxide atmosphere, Mars' atmosphere is very thin, much less dense than Venus' or even Earth's.
Diff: 1
Section Ref.: 6.3
97) How does the rotation of Venus' clouds compare to the rotation of its surface?
Answer: The clouds rotate much faster than the surface.
Diff: 3
Section Ref.: 6.3
98) Describe the relation between Mercury's spin and orbit.
Answer: One rotation of Mercury on its axis (its day) is exactly 2/3 of its orbital period (its year).
Diff: 2
Section Ref.: 6.2
99) Why is the atmospheric pressure at the surface of Venus so much higher than Earth's?
Answer: The atmosphere is much more massive than Earth's and extends to a much greater height above the surface.
Diff: 1
Section Ref.: 6.3
100) Why do our best radar maps of Venus come from the Magellan space probe?
Answer: Magellan went into orbit around Venus and used radar to penetrate the clouds and map the surface. Visual wavelength telescopes cannot see through the clouds.
Diff: 2
Section Ref.: 6.5
101) Why were the Russian Venera spacecraft so important to our understanding of Venus?
Answer: They were the first spacecraft to soft land on the planet and send images of the surface back to Earth.
Diff: 3
Section Ref.: 6.5
102) What are coronae?
Answer: large, circular volcanic upwellings on the surface of Venus
Diff: 3
Section Ref.: 6.5
103) Describe the primary difference between the northern and southern hemispheres on Mars.
Answer: The northern hemisphere is primarily plains (lowlands) with few craters and extensive lava flows. The southern hemisphere is heavily cratered highlands.
Diff: 2
Section Ref.: 6.6
104) Where is most of the water on Mars believed to be?
Answer: In the polar caps and a layer of permafrost just below the surface.
Diff: 2
Section Ref.: 6.6
105) How is the Mars Rover mission different from the Global Surveyor mapping mission?
Answer: The Mars Rover mission landed two probes, Spirit and Opportunity, on the surface. They traveled over the surface collecting and analyzing samples. Global Surveyor was an orbiting spacecraft.
Diff: 2
Section Ref.: 6.6, 6.7
106) Other than its atmosphere, name two properties of Venus that are unique among the terrestrial planets.
Answer: Venus rotates clockwise and has not been shown to have a magnetic field.
Diff: 2
Section Ref.: 6.2, 6.7
107) In what way is Mercury's core unusual?
Answer: Mercury has the largest core relative to the size of the planet.
Diff: 2
Section Ref.: 6.7
108) If its density suggests its core is similar to ours, why does Venus lack a magnetic field?
Answer: Venus' rotation is too slow to drive the dynamo effect that creates the magnetic field Earth has.
Diff: 3
Section Ref.: 6.7
109) What is the significance of large percentage of oxygen in Earth's atmosphere?
Answer: According to the way we believe the atmosphere evolved, the oxygen is an indication that life is present.
Diff: 2
Section Ref.: 6.8
110) Will Mars ever appear to the unaided eye as large as the Moon at closest approach? Explain.
Answer: No. Mars is small, and even at closest approach it is so distant from Earth that it takes large telescopes with the best conditions to resolve surface features as small as 100 km across. With the unaided eye, Mars appears as a small point of reddish light shining more brightly than the stars.
Diff: 2
Section Ref.: 6.1, 6.6
111) While surface conditions differ greatly, name three ways that Venus and Earth are indeed "sister planets."
Answer: No other two planets in the solar system are so similar in size, mass, density, and surface gravity.
Diff: 2
Section Ref.: 6.1
112) When are Mercury and Venus easiest to observe from Earth? Why? How much of then can we see at that time?
Answer: At greatest elongations, they rise farthest east and west of the Sun, and can be best seen in evening and morning twilight. But they will appear only half lit.
Diff: 2
Section Ref.: 6.1
113) How and why would the noon Sun appear different to an observer on Mercury compared to one on Earth?
Answer: Mercury's rotation axis is almost perpendicular to its orbit. This means the angle of the Sun with the southern (or northern) horizon never changes. On Mercury, an observer at the equator would always see the noon Sun overhead, an observer at the pole would always see it on the horizon. On Earth, the altitude of the Sun changes over the year because of the 23.5 degree axial tilt.
Diff: 3
Section Ref.: 6.2
114) Which terrestrial planets lack seasons? Why?
Answer: Mercury and Venus are both so close to the Sun that it probably tidally locked their equators toward it. Without an axial tilt the angle of the Sun's rays never changes so there are no seasons.
Diff: 3
Section Ref.: 6.2
115) On rare occasions, Mercury and Venus can transit the Sun, crossing directly between us and our Sun. If you were watching the event closely, such as on June 5, 2012, you might note a "tear-drop" effect as Venus came on and left the solar disk, very different from the disk of Mercury. Explain.
Answer: Mercury is airless, but the dense Venusian atmosphere can refract sunlight, creating the bending of light noted in the "tear-drop."
Diff: 3
Section Ref.: 6.3
116) If Venus' clouds block much of the sunlight before it reaches the surface, why is the planet so hot?
Answer: The carbon dioxide in the dense atmosphere creates a greenhouse effect. Some sunlight (and its energy) still reaches the surface and is reradiated as heat. Heat (or infrared radiation) is trapped beneath the atmosphere, causing an increase in the temperature at the surface.
Diff: 3
Section Ref.: 6.8
117) Contrast the compositions and heights of the clouds of Earth and Venus.
Answer: Our clouds of water droplets occur in our troposphere, within about 12 km of the surface. On Venus, the much thicker upper-level cloud deck of sulfuric acid droplets lies about 50-70 km above its surface.
Diff: 3
Section Ref.: 5.3, 6.3
118) Why do we know much more about the surface of Mars than that of Venus?
Answer: Venus has a thick cloud cover that prevents us from seeing the surface with visible light. Radar can map the surface, but its longer wavelength means the resolution is worse. Mars' atmosphere is thin enough that we can see surface detail from Earth. Also, we have landed several spacecraft on Mars, some of which have traveled over the surface. The few spacecraft that made successful soft landings on Venus were very short lived.
Diff: 3
Section Ref.: 6.3, 6.6
119) Mars and Mercury are similar in size, and Mercury is even denser. Why then is it Mars that has more atmosphere?
Answer: Its location is too close to the Sun; Mercury's gases boil away in the solar wind. Colder Mars has enough gravity to hang on to more, even though its water is no longer liquid today.
Diff: 2
Section Ref.: 6.4
120) How are surfaces of Mercury and the Moon similar? Different? Why?
Answer: Both are airless worlds with many ancient impact craters. On our Moon, the tides of Earth drew out the mare on the Earth side, while Mercury's lava flows were much less extensive than the mare. But as its core cooled and shrank, Mercury's crust developed huge scarps, great wrinkles that run for hundreds of miles.
Diff: 3
Section Ref.: 6.7
121) On our Moon, Mercury, Earth, and Mars, there are a variety of meteor craters in terms of size. Yet all those found on Venus are over 5 kilometers across. Explain.
Answer: The atmosphere of Venus is much thicker, so that only the largest asteroids (probably at least a kilometer across) can survive the fiery transit of this dense atmosphere and arrive intact at the surface to create such damage. Only the strong survive.
Diff: 3
Section Ref.: 6.5
122) Mars is often called a "midway world," similar in some respects to Earth, and in others to our Moon. Explain.
Answer: Like our Moon, much of Mars is ancient cratered terrain, and its density is closer to that of the Moon than Earth. But like us, Mars has seasonal variations, polar caps, clouds, an atmosphere, dust storms, and signs of past liquid water and erosion.
Diff: 3
Section Ref.: 6.6
123) Our Moon and Mars both show very different hemispheres. Compare them and explain why this occurred in each case.
Answer: The far side of our Moon and southern hemisphere of Mars are ancient and heavily cratered. The near side of the Moon has the striking mare, lava flows pulled out by our tides, while the northern hemisphere of Mars sits opposite the Hellas impact basin, and has great volcanoes on the Tharsis bulge and great plains, smoothed by either lava or water.
Diff: 3
Section Ref.: 6.7
124) Why was the discovery of a substantial magnetic field around Mercury a surprise? How was it detected?
Answer: In its close passes by Mercury, Mariner 10 found a field that is much stronger than Mercury's very slow rotation would have led us to expect with the dynamo theory.
Diff: 2
Section Ref.: 6.7
125) What, other than its existence, is unusual about the magnetic field of Mercury?
Answer: It is still being generated, through an unknown process, and is significantly offset from the planet's center.
Diff: 3
Section Ref.: 6.7
126) Relate Mercury's scarps to the differentiation process.
Answer: As Mercury was molten, the dense iron core formed from sinking iron and nickel. But smaller Mercury cooled off much faster than Earth, so its core cooled and started shrinking as it froze solid. This contraction caused the crust above to wrinkle and form the vast scarps that run across Mercury's crust.
Diff: 2
Section Ref.: 6.4
127) The vast flood deposits prove Mars once had much running water. What happened to it?
Answer: As Martian volcanism died down, the atmosphere became too thin for greenhouse gases to keep the water liquid. Most froze in the polar caps or as tundra underground, and some was also lost into space, like Venus lost its due to exposure to ultraviolet light.
Diff: 2
Section Ref.: 6.8
128) Contrast the atmosphere of Venus with its clouds.
Answer: The atmosphere is almost entirely carbon dioxide, but the clouds are made of droplets of sulfuric acid, the result of water and sulfur dioxide erupting from its volcanoes chemically combining over time.
Diff: 2
Section Ref.: 6.8
129) What is the most abundant gas in the atmospheres of Mars and Venus? Explain why it is not as abundant in Earth's atmosphere.
Answer: The carbon dioxide so abundant on our neighbors was first dissolved in the Earth's early water oceans, then deposited beneath them in carbonate rocks such as limestone. Also, photosynthesis took much of the remaining carbon dioxide and water and combined them to make carbohydrates and release oxygen into our unique atmosphere.
Diff: 3
Section Ref.: 6.8
130) Why isn't there water on Venus?
Answer: High temperatures and the runaway greenhouse effect drove water vapor high up in the atmosphere, where solar ultraviolet radiation split it into hydrogen and oxygen atoms. The light hydrogen boiled off into space, and the oxygen combined with crustal rocks.
Diff: 3
Section Ref.: 6.8
131) Water is one of the most common substances in the universe, and vital to us on Earth. What happened to it on Mars?
Answer: At first, while erupting volcanoes thickened it, Mars' atmosphere was dense enough to stay warm enough for liquid water to flow over much of Mars' ancient surface. But as the core of Mars cooled down, volcanism declined, and Mars' atmosphere lost much of its initial water to space, due to its less surface gravity then our own. Today there is still much water frozen in the polar caps and tundra, and on some occasions it melts fast enough to erupt as small mud flows imaged by the Mars Global Surveyor recently.
Diff: 3
Section Ref.: 6.8
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