The Essential Cosmic Perspective, 8e (Bennett et al.)
Chapter 6 Formation of the Solar System
6.1 Multiple Choice Questions
1) How does the Sun’s mass compare with that of the planets?
A) It is about a hundred times more massive than Earth.
B) It is about a thousand times more massive than Earth.
C) It is about a hundred times more massive than all the planets combined.
D) It is about a thousand times more massive than all the planets combined.
E) It is about as massive as all the planets combined.
2) Where does nuclear fusion occur in the Sun?
A) on the surface
B) anywhere below the surface
C) in its core
D) just above the visible surface
E) all of the above
3) Which planet has the highest average surface temperature, and why?
A) Mercury, because it is closest to the Sun
B) Earth, because of its greenhouse effect
C) Venus, because of its dense carbon dioxide atmosphere
D) Mars, because of its red color
E) Jupiter, because it is so big
4) Which object, other than Earth, has visible water on its surface?
A) Mercury
B) Venus
C) Mars
D) the Moon
E) none of the above
5) Which of the following observations indicates that Mars had a warmer, thicker atmosphere in
the past?
A) Mars lacks atmospheric ozone.
B) There is a very deep and long canyon that extends across Mars.
C) There are dried-up riverbeds on Mars.
D) Mars has polar caps made of “dry ice.”
E) Mars has two small moons.
6) Which planet has a ring system?
A) Jupiter
B) Saturn
C) Uranus
D) Neptune
E) all of the above
7) Which planet could an astronaut visit without the need for a spacesuit (and survive)?
A) Mercury
B) Venus
C) the Moon
D) Mars
E) None; an astronaut would need a spacesuit to survive a visit to any other planet in the solar
system.
8) Which planet has the most extreme temperature difference between day and night?
A) Mercury
B) Venus
C) Earth
D) Mars
E) Jupiter
9) Which is the densest planet in the solar system?
A) Mercury
B) Venus
C) Earth
D) Mars
E) Jupiter
10) The planet with a density most similar to Earth is
A) Mercury.
B) Venus.
C) Jupiter.
D) Mars.
E) Uranus.
11) Which of the following is not a characteristic of the inner planets?
A) They are smaller than the outer planets.
B) They have solid, rocky surfaces.
C) Their orbits are relatively closely spaced.
D) They have substantial atmospheres.
E) They have relatively high densities.
12) Which of the following is not a characteristic of the outer planets?
A) They have relatively high densities.
B) They have thick atmospheres.
C) They are primarily made of hydrogen, helium, and hydrogen compounds.
D) Their orbits are separated by relatively large distances.
E) They have rings.
13) On average, a cupful of which planet would weigh the least?
A) Jupiter
B) Saturn
C) Uranus
D) Neptune
E) Mars
14) Which of the following is the only characteristic Pluto shares with the outer planets?
A) It is smaller than Earth.
B) It is made mostly of ices and rock.
C) Its rotation period is more than one Earth day.
D) It has multiple moons.
E) It doesn’t have a ring system.
15) Where are most of the known asteroids found?
A) between the orbits of Mars and Jupiter
B) in the Kuiper belt
C) in the Oort cloud
D) between the orbits of the jovian planets
E) between the orbits of the terrestrial planets
16) Which of the following is furthest from the Sun?
A) Pluto
B) Eris
C) an asteroid in the asteroid belt
D) a comet in the Kuiper belt
E) a comet in the Oort cloud
17) In what part of the solar system is Pluto found?
A) the asteroid belt
B) the Kuiper belt
C) the Oort cloud
D) the terrestrial planet region
18) What can we conclude from the fact that Neptune’s large moon Triton orbits in a direction
opposite to the direction in which Neptune rotates?
A) Triton must be made mostly of ice.
B) Triton must have formed as the result of a giant impact.
C) Triton must have been captured by Neptune.
D) Triton must have formed in place around Neptune.
E) Triton must be more dense than Neptune.
19) Why did the solar nebula heat up as it collapsed?
A) Nuclear fusion occurring in the core of the protosun produced energy that heated the nebula.
B) As the cloud shrank, its gravitational potential energy was converted to thermal energy.
C) Radiation from other nearby stars that had formed earlier heated the nebula.
D) The shock wave from a nearby supernova heated the gas.
E) As the cloud shrank, its kinetic energy was converted to gravitational potential energy.
20) Why did the solar nebula flatten into a disk?
A) The interstellar cloud from which the solar nebula formed was originally somewhat flat.
B) The force of gravity pulled the material downward into a flat disk.
C) As the nebula cooled, the gas and dust settled onto a disk.
D) It flattened as a natural consequence of collisions between particles in the nebula, changing
random motions into more orderly ones.
21) According to our theory of solar system formation, why do all the planets orbit the Sun in the
same direction and in nearly the same plane?
A) The original solar nebula happened to be disk-shaped.
B) Any planets that once orbited in the opposite direction or a different plane were ejected from
the solar system.
C) The laws of conservation of energy and conservation of angular momentum ensure that any
rotating, collapsing cloud will end up as a spinning disk.
D) The Sun formed first, and as it grew in size it spread into a disk, rather like the way a ball of
dough can be flattened into a pizza by spinning it.
E) We would expect that a very small fraction of all planetary systems would have planets
orbiting in such a pattern, so ours turned out that way due to random chance.
22) Which of the following lists the composition of the solar nebula from highest to lowest
percentage of mass?
A) light gases (H, He), hydrogen compounds (H2O, CH4, NH3), rocks, metals
B) hydrogen compounds (H2O, CH4, NH3), light gases (H, He), rocks, metals
C) light gases (H, He), hydrogen compounds (H2O, CH4, NH3), metals, rocks
D) hydrogen compounds (H2O, CH4, NH3), light gases (H, He), metals, rocks
E) hydrogen compounds (H2O, CH4, NH3), rocks, metals, light gases (H, He)
23) What percentage of the solar nebula’s mass consisted of hydrogen and helium gases?
A) 0.5 percent
B) 5 percent
C) 50 percent
D) 98 percent
E) 100 percent
24) What percentage of the mass of the solar nebula consisted of elements other than hydrogen
and helium?
A) 0 percent
B) 0.1 percent
C) 2 percent
D) 20 percent
E) 80 percent
25) If the freezing point of all ices was at a much lower temperature, what change would that
imply for the formation of our solar system?
A) The gas giants could have formed closer to the sun.
B) There would be no change in where gas giants could form, because the freezing point of ices
did not affect the formation of gas giants.
C) The gas giants would have to form at a larger distance from the sun.
D) The gas giants could not have formed at all.
26) What kind of material in the solar nebula could condense at temperatures as high as 1,500 K,
such as existed in the inner region of the nebula?
A) rocks
B) metals
C) silicon-based minerals
D) hydrogen compounds
E) molecules such as methane and ammonia
27) What is the origin of the large moons orbiting in the equatorial planes of the jovian planets?
A) They are captured asteroids.
B) They are captured comets.
C) They are captured planets.
D) They were formed by condensation and accretion in a disk of gas around the planet.
E) They were formed by giant impacts.
28) Observations of young stars (as well as theory) tell us that when the Sun was young, the solar
wind
A) was weaker than it is today.
B) was stronger than it is today.
C) was about the same strength as it is today.
D) was nonexistent.
E) had a different composition than it does today.
29) Which of the following are relatively unchanged fragments from the early period of planet
building in the solar system?
A) asteroids
B) Kuiper belt comets
C) Oort cloud comets
D) all of the above
30) According to our theory of solar system formation, why do we find some exceptions to the
general rules and patterns of the planets?
A) Our theory is not quite correct because it cannot explain these exceptions.
B) Most of the exceptions are the result of giant impacts or close gravitational encounters.
C) The exceptions probably represent objects that formed recently, rather than early in the
history of the solar system.
D) The exceptions probably represent objects that were captured by our solar system from
interstellar space.
E) The exceptions are probably the result of the Sun passing very close to another star billions of
years ago.
31) Based on our current theory of Earth’s formation, the water we drink likely comes from
A) ice that condensed in the solar nebula in the region where Earth formed.
B) chemical reactions that occurred in Earth’s crust after Earth formed.
C) chemical reactions that occurred in Earth’s core after Earth formed.
D) material left behind during the giant impact that formed the Moon.
E) water bearing planetesimals that impacted Earth.
32) The heavy bombardment phase of the solar system lasted
A) a few million years.
B) tens of millions of years.
C) a few hundred million years.
D) about a billion years.
E) to the present time.
33) Which of the apparent exceptions to the solar nebular theory cannot be explained by a giant
impact event?
A) the formation of the Moon
B) the large metallic core of Mercury
C) the backward rotation of Venus
D) the extreme axis tilt of Uranus
E) the orbit of Triton in the opposite direction to Neptune’s rotation
34) Which of the following does the solar nebular theory not predict?
A) planets orbit the Sun in nearly circular orbits in a flattened disk
B) the compositional differences between the terrestrial and jovian planets
C) the equal number of terrestrial and jovian planets
D) the presence of asteroids and comets
E) planets orbit the Sun in the same direction
35) The age of the solar system can be established by radiometric dating of
A) the oldest rocks on Earth.
B) the oldest rocks on the Moon.
C) the oldest meteorites.
D) the atmosphere of Mars.
E) It hasn’t been done yet, but the age of the solar system could be obtained from a sample of Io’s
surface.
36) What do meteorites reveal about the solar system?
A) They reveal that meteorites are about the same age as most Earth rocks.
B) Nothing, because they come from other star systems.
C) They reveal that the solar system once contained 10 planets.
D) They reveal that the age of the solar system is approximately 4.6 billion years.
E) They reveal that the early solar system consisted mostly of hydrogen and helium gas.
37) Suppose you find a rock that contains some potassium-40 (half-life of 1.25 billion years).
You measure the amount and determine that there are 5 grams of potassium-40 in the rock. By
measuring the amount of its decay product (argon-40) present in the rock, you realize that there
must have been 40 grams of potassium-40 when the rock solidified. How old is the rock?
A) 1.25 billion years
B) 2.5 billion years
C) 3.75 billion years
D) 5 billion years
E) none of the above
38) Every 4.5 billion years, half of the atoms in a sample of uranium-238 will undergo
radioactive decay and become atoms of lead-206. Suppose you lived in another planetary system
around a faraway star and found a meteorite that was originally made of uranium-238, but is now
one-quarter uranium-238 and three-quarters lead-206. What would be your best estimate of that
planetary system’s age?
A) 9 billion years
B) 4.5 billion years
C) 2.25 billion years
D) 13.5 billion years
39) Why can we assume that a rock sample containing argon-40 had none of this isotope when
the rock initially formed?
A) Argon-40 has a very short half-life so it is unlikely to be in an original rock sample.
B) Argon-40 is a gas that does not combine with other elements, so it would not be present in a
rock when it formed.
C) Argon-40 can only be made in supernova explosions.
D) Argon-40 has a higher condensation temperature than most rocks.
40) Why do Earth rocks have much younger ages than most meteorites?
A) Earth formed billions of years after most meteorites formed.
B) Most Earth rocks have been melted and reformed since Earth formed from the solar nebula.
C) Meteorites formed before the solar nebula began to condense.
D) Most meteorites come from other planetary systems that formed before our solar system.
6.2 True/False Questions
1) Oceans cover more of Earth’s surface than land.
2) All four of the giant outer planets—Jupiter, Saturn, Uranus, and Neptune—have rings.
3) The jovian planets have no solid surface.
4) Pluto is part of the Oort Cloud.
5) All planets orbit the Sun in the same direction (counterclockwise as viewed from above
Earth’s North Pole).
6) All the planets in the solar system have at least one moon.
7) The more massive planets in the solar system tend to be less dense than the lower mass
planets.
8) All the planets in the solar system rotate (spin) in the same direction as they orbit the Sun.
9) Within the frost line, planetesimals were composed entirely of rock, and outside the frost line,
planetesimals were composed entirely of ice.
10) Impacts were extremely common in the young solar system but are less common today.
11) Most of Earth’s water likely resulted from impacts with icy planetesimals that originated in
the outer regions of the solar system.
12) The Moon probably formed at the same time that Earth formed, rather like the formation of a
double planet.
13) Based on our theory of how our own solar system formed, we would expect that other solar
systems would be quite common.
14) Jupiter and the other gas giants formed close to the sun and migrated outward.
15) A key clue to how the solar system formed is the observation that all the planets orbit close
to the same plane.
16) Outside the frost line, planetesimals could form into larger objects due to the presence of
both rock and ice.
17) With the exception of Venus, planetary surface temperatures decrease at greater distances
from the sun.
18) Within 4 AU of the Sun, all planets have solid surfaces.
6.3 Process of Science Questions
1) The Solar Nebula as a Scientific Theory: You are describing the solar nebula theory to a
friend. You point out that it provides an explanation for the regular motion in our solar system,
the division of the planets into terrestrial and jovian types, and an explanation for the origin and
nature of comets and asteroids. Your friend agrees that this is all very nice, but that it seems that
the solar nebula theory fails the basic criteria for a scientific theory, to make predictions about
the natural world that can be observationally tested. In her opinion, all the solar nebula theory
does is explain known facts, albeit in a compelling and economical way. How would you answer
your friend and make the case that the solar nebula theory is indeed a scientific theory that has
passed many observational tests? Can you think of any predictions that the solar nebula theory
has made that were confirmed only within the last decade or so?
2) Exceptions to a Scientific Theory: The solar nebula theory gives compelling explanations for
the many regularities of our solar system. Nevertheless, the theory also claims to be perfectly
consistent with the many exceptions to its basic predictions. This seems like a glaring
contradiction in which the solar nebula theory would be consistent with any observed fact and
hence not a scientific theory at all (why not?). Provide a deeper resolution to this apparent
paradox by explaining how some of the basic exceptions in our own solar system are
incorporated into the solar nebula theory. Is it really true that the theory would be consistent with
any observed facts?
3) More pattern finding: Examine table 6.1 from the textbook on page 150. Identify and describe
one pattern in the data. Give specific information to support the pattern you describe.
6.4 Short Answer Questions
1) In the 1800s, many people assumed that Venus would have tropical temperatures, but instead
it is very hot. Explain why tropical temperatures would have made sense given what was known
in the 1800s, and why Venus instead turns out to be very hot.
2) Briefly summarize the differences between terrestrial and jovian planets.
3) Describe the ways in which Pluto is different from the terrestrial and jovian planets in the
solar system.
4) Briefly summarize the observed patterns of motion in our solar system that are consistent with
the nebular theory.
5) List at least three of the notable exceptions to the general patterns of the solar system.
6) Suppose the entire solar nebula had cooled to a very low temperature before the solar wind
cleared it away. Do you think Earth would be the same? Why or why not?
7) Explain why the early Earth did not form with water, and how it gained it later in its
formation.
8) Briefly describe the modern theory of how our Moon formed.
9) Suppose you discovered a meteorite that contains small amounts of potassium-40, which has a
half-life of 1.25 billion years, and its decay product argon-40. You determine that 1/16 of the
original potassium-40 remains; the other 15/16 has decayed into argon-40. How old is the
meteorite? Based on your answer, where is this meteorite probably from?
10) Explain how the age of a rock can be determined by radiometric dating.
11) If we were to re-run the formation of the solar system, what would likely be the same and
what would likely be different?
12) How would the solar system be different today if the entire planet forming disk had been
warmer than 300K? Why?
13) Briefly describe the two main lines of evidence for the modern theory of the moon’s
formation, wherein the Earth was hit by an approximately Mars-sized object.
6.5 Mastering Astronomy Reading Quiz
1) Which of the following lists the planets of our solar system in the correct order from closest to
farthest from the Sun?
A) Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
B) Mercury, Earth, Venus, Mars, Jupiter, Saturn, Neptune, Uranus
C) Mercury, Venus, Mars, Earth, Saturn, Jupiter, Neptune, Uranus
D) Earth, Mars, Mercury, Venus, Jupiter, Saturn, Uranus, Neptune