21st Century Astronomy The Solar System Fifth Edition By Kay -Palen -Test Bank

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21st Century Astronomy The Solar System Fifth Edition By Kay -Palen -Test Bank

Chapter 1: Thinking Like an Astronomer

Learning Objectives

1.1 Earth Occupies a Small Place in the Universe

Define the bold-faced vocabulary terms within the chapter.

Multiple Choice: 1, 9, 14, 21, 29, 31, 36, 37, 40, 42, 43, 44

Short Answer: 11, 17, 18

List our cosmic address.

Multiple Choice: 22

Short Answer: 5

Differentiate the various components of our cosmic address.

Multiple Choice: 2, 6, 23

Short Answer: 1, 3

Relate the different sizes of, or the different distances between, the components of our cosmic address.

Multiple Choice: 10, 11, 15, 24, 25

Short Answer: 16

Relate astronomical distances with light-travel time.

Multiple Choice: 4, 7, 16, 17, 18, 19, 20, 26, 27, 28

Short Answer: 2, 4, 6, 10

Illustrate the size or history of the universe with scaled models.

Multiple Choice: 3, 5, 8, 12, 13

Short Answer: 7, 8, 9

1.2 Science Is a Way of Viewing the Universe

Compare the everyday and scientific meanings of theory.

Multiple Choice: 33, 35, 39

Short Answer: 23

Compare an idea with a hypothesis.

Multiple Choice: 32, 34

Short Answer: 12

Describe the steps of the scientific method.

Multiple Choice: 38, 41

Short Answer: 14, 20

Assess whether a given idea or explanation is scientific.

Multiple Choice: 45, 46

Short Answer: 13

Establish why all scientific knowledge is provisional.

Multiple Choice: 30

Short Answer: 15, 19, 21, 22

1.3 Astronomers Use Mathematics to Find Patterns

Identify patterns in nature.

Multiple Choice: 47, 48, 51

Short Answer: 24, 25, 26

Summarize the evidence for the statement “We are actually made of recycled stardust.”

Multiple Choice: 50, 52, 54

Short Answer: 27, 29, 30

Identify fields of science that relate to the study of origins.

Multiple Choice: 53

Short Answer: 28

Working It Out 1.1

Write numbers in both scientific and standard notation.

Multiple Choice: 49, 55, 57, 58, 68

Describe characteristics of real-world objects in terms of ratios.

Multiple Choice: 56, 59, 60

Determine the mathematical behavior of proportional systems.

Multiple Choice: 61, 62, 63, 64

Working It Out 1.2

Identify the x and y axes on a graph.

Define slope on a graph.

Read data from linear and logarithmic graphs.

Multiple Choice: 65, 66, 69, 70

Distinguish between linear and exponential curves on a graph.

Multiple Choice: 67

MULTIPLE CHOICE

  1. The word astronomy means
    1. “patterns among the stars.”
    2. “to study the stars.”
    3. “discovering the universe.”
    4. “the movement of the stars.”
    5. “personality traits set by the stars.”

ANS: A         DIF: Easy              REF: Section 1.1

MSC: Remembering

OBJ: Define the bold-faced vocabulary terms within the chapter.

  1. The number of planets in our Solar System is

ANS: B         DIF: Easy              REF: Section 1.1

MSC: Remembering

OBJ: Differentiate the various components of our cosmic address.

  1. According to the figure below, Earth is located approximately
    1. at the center of the Milky Way.
    2. near the center of the Milky Way.
    3. about halfway out from the center of the Milky Way.
    4. at the farthest outskirts of the Milky Way.
    5. outside the Milky Way, which is why we can see it as a band across the night sky.

ANS: C         DIF: Easy              REF: Section 1.1

MSC: Understanding

OBJ: Illustrate the size or history of the universe with scaled models.

  1. The average distance between Earth and the Sun is 1.5 × 1011 m, and light from the Sun takes approximately _________ to reach Earth.
    1. 8 seconds
    2. 8 minutes
    3. 8 hours
    4. 8 days
    5. 8 years

ANS: B         DIF: Easy              REF: Section 1.1

MSC: Applying

OBJ: Relate astronomical distances with light-travel time.

  1. Our universe is approximately 13.7 _________ years old.
    1. thousand
    2. million
    3. billion
    4. trillion

ANS: C         DIF: Easy              REF: Section 1.1

MSC: Remembering

OBJ: Illustrate the size or history of the universe with scaled models.

  1. Milky Way is the name of
    1. our solar system.
    2. the galaxy in which we live.
    3. the local group of galaxies we are in.
    4. the supercluster of galaxies we are in.

ANS: B         DIF: Easy              REF: Section 1.1

MSC: Understanding

OBJ: Differentiate the various components of our cosmic address.

  1. One of the nearest stars is Alpha Centauri, whose distance is 4.4 light-years. The time it takes light to travel from Alpha Centauri to us is
    1. 25 seconds.
    2. 3 minutes.
    3. 4 years.
    4. 600 years.

ANS: C         DIF: Easy              REF: Section 1.1

MSC: Applying

OBJ: Relate astronomical distances with light-travel time.

  1. The time it takes light to cross Neptune’s orbit is closest to which of the following?
    1. a second
    2. a quick meal
    3. a night’s sleep
    4. the time between presidential elections

ANS: C         DIF: Easy              REF: Section 1.1

MSC: Remembering

OBJ: Illustrate the size or history of the universe with scaled models.

  1. A light-hour is a measure of

ANS: B         DIF: Easy              REF: Section 1.1

MSC: Remembering

OBJ: Define the bold-faced vocabulary terms within the chapter.

  1. If one thinks about the distance between Earth and the Moon, 384,400 km, approximately how much of that distance would Saturn and its rings take up?
    1. much more than this distance
    2. less than half this distance
    3. more than half this distance
    4. exactly equal to this distance

ANS: B         DIF: Medium        REF: Section 1.1

MSC: Remembering

OBJ: Relate the different sizes of, or the different distances between, the components of our cosmic address.

  1. The diameter of the Moon is
    1. larger than the distance across the continental United States.
    2. roughly equal to the longest distance across Texas.
    3. more than half the distance across the continental United States.
    4. less than half the distance across the continental United States.

ANS: C         DIF: Medium        REF: Section 1.1

MSC: Remembering

OBJ: Relate the different sizes of, or the different distances between, the components of our cosmic address.

  1. The early universe was composed mainly of which two elements?
    1. hydrogen and helium
    2. carbon and oxygen
    3. hydrogen and oxygen
    4. carbon and iron
    5. nitrogen and oxygen

ANS: A         DIF: Easy              REF: Section 1.1

MSC: Remembering

OBJ: Illustrate the size or history of the universe with scaled models.

  1. What is the approximate number of stars in the Milky Way?
    1. 10 million
    2. 300 million
    3. 10 billion
    4. 300 billion
    5. 1 trillion

ANS: D         DIF: Medium        REF: Section 1.1

MSC: Remembering

OBJ: Illustrate the size or history of the universe with scaled models.

  1. The Local Group is the environment around
    1. the Earth-Moon system.
    2. the Sun that contains about a dozen stars.
    3. the Sun that contains over a million stars.
    4. the Milky Way that contains a few dozen galaxies.
    5. the Milky Way that contains a few thousand galaxies.

ANS: D         DIF: Medium        REF: Section 1.1

MSC: Remembering

OBJ: Define the bold-faced vocabulary terms within the chapter.

  1. The majority of the mass in our universe is made up of
    1. dark matter.

ANS: E         DIF: Medium        REF: Section 1.1

MSC: Remembering

OBJ: Relate the different sizes of, or the different distances between, the components of our cosmic address.

  1. The speed of light is approximately
    1. 3,000 km/s.
    2. 30,000 km/s.
    3. 300,000 km/s.
    4. 3 million km/s.
    5. 3 billion km/s.

ANS: C         DIF: Easy              REF: Section 1.1

MSC: Remembering

OBJ: Relate astronomical distances with light-travel time.

  1. If an event were to take place on the Sun, how long would it take for the light it generates to reach us?
    1. 8 minutes
    2. 11 hours
    3. 1 second
    4. 1 day
    5. It would reach us instantaneously.

ANS: A         DIF: Easy              REF: Section 1.1

MSC: Applying

OBJ: Relate astronomical distances with light-travel time.

  1. One of the nearest stars is Alpha Centauri, whose distance is 4.2 × 1016 How long does it take light to travel from Alpha Centauri to us?
    1. 25 seconds
    2. 3 minutes
    3. 4 years
    4. 560 years
    5. 6,200 years

ANS: C         DIF: Medium        REF: Section 1.1

MSC: Applying

OBJ: Relate astronomical distances with light-travel time.

  1. The distance to the nearest large spiral galaxy, the Andromeda Galaxy, is 2.4 × 1022 How long does it take light to travel from Andromeda to us?
    1. 4 years
    2. 360 years
    3. 2 thousand years
    4. 5 million years
    5. 5 billion years

ANS: D         DIF: Medium        REF: Section 1.1

MSC: Applying

OBJ: Relate astronomical distances with light-travel time.

  1. The distance to the center of the Laniakea cluster of galaxies is 5 × 1023 How long does it take light to travel from these galaxies to us?
    1. 7,000 years
    2. 54,000 years
    3. 120,000 years
    4. 12 million years
    5. 54 million years

ANS: E         DIF: Medium        REF: Section 1.1

MSC: Applying

OBJ: Relate astronomical distances with light-travel time.

  1. A light-year is a unit commonly used in astronomy as a measure of

ANS: D         DIF: Medium        REF: Section 1.1

MSC: Remembering

OBJ: Define the bold-faced vocabulary terms within the chapter.

  1. According to the figure below, if you were to specify your address in the universe, listing your membership from the smallest to largest physical structures, it would be
    1. Earth, Local Group, Solar System, Andromeda, the universe.
    2. Earth, Solar System, Local Group, Milky Way, the universe.
    3. Earth, Solar System, Milky Way, Local Group, Laniakea Supercluster, the universe.
    4. Earth, Solar System, Milky Way, Laniakea Supercluster, the universe.
    5. Earth, Laniakea Supercluster, Milky Way, Solar System, the universe.

ANS: C         DIF: Difficult       REF: Section 1.1

MSC: Understanding

OBJ: List our cosmic address.

  1. Which of the following is false?
    1. The Local Group is a member of the Laniakea Supercluster, which contains thousands of galaxies.
    2. The Local Group contains two large spiral galaxies and a few dozen dwarf galaxies.
    3. Our Solar System has eight classical planets.
    4. The Milky Way Galaxy contains approximately 100 million stars.
    5. The Laniakea Supercluster is one of many superclusters in the universe.

ANS: D         DIF: Difficult       REF: Section 1.1

MSC: Understanding

OBJ: Differentiate the various components of our cosmic address.

  1. If the diameter of the Milky Way is approximately 100,000 light-years, then our galaxy is _________ times larger than our Solar System. For reference, Pluto’s orbit has an approximate diameter of 80 astronomical units (AU).
    1. 100
    2. 1,000
    3. 10,000
    4. 106
    5. 108

ANS: E         DIF: Difficult       REF: Section 1.1

MSC: Applying

OBJ: Relate the different sizes of, or the different distances between, the components of our cosmic address.

  1. The majority of the energy in our universe is
    1. radiated by stars from the nuclear fusion going on in their cores.
    2. the kinetic energy found in the collisions of galaxies.
    3. the gravitational potential energy of superclusters.
    4. emitted in radioactive decays of unstable elements.
    5. made up of dark energy that permeates space.

ANS: E         DIF: Difficult       REF: Section 1.1

MSC: Remembering

OBJ: Relate the different sizes of, or the different distances between, the components of our cosmic address.

  1. After the Sun, the next nearest star to us is approximately _________ away.
    1. 8 light-seconds
    2. 80 light-minutes
    3. 40 light-hours
    4. 4 light-years
    5. 200 light-years

ANS: D         DIF: Medium        REF: Section 1.1

MSC: Remembering

OBJ: Relate astronomical distances with light-travel time.

  1. The figure below measures distances in the amount of time it takes light to travel. If the circumference of Earth is a snap of your fingers (1/7 second), the diameter of the Solar System is approximately equal to
    1. the length of a quick lunch.
    2. the time to turn a page in a book.
    3. the length of the work day.
    4. the time you spent in high school.
    5. a human lifetime.

ANS: C         DIF: Difficult       REF: Section 1.1

MSC: Applying

OBJ: Relate astronomical distances with light-travel time.

  1. If you compared the diameter of Earth, which is 13,000 km, to 1 second, then what unit of time would be equivalent to the size of the Milky Way, whose diameter is 1021 m, and what significant milestone would this time correspond to in our evolution?
    1. 2 million years, the length of time humans have existed on Earth
    2. 30,000 years, the length of time humans have lived in North America
    3. 400 years, the length of time humans have been exploring the skies with telescopes
    4. 4 billion years, the age of the Solar System
    5. 14 billion years, the age of the universe

ANS: A         DIF: Difficult       REF: Section 1.1

MSC: Applying

OBJ: Relate astronomical distances with light-travel time.

  1. _________ is the idea that the simplest explanation for a phenomenon is usually the correct one.
    1. Newton’s hypothesis
    2. Occam’s razor
    3. Aristotle’s test
    4. Einstein’s excuse
    5. The Copernican principle

ANS: B         DIF: Easy              REF: Section 1.2

MSC: Remembering

OBJ: Define the bold-faced vocabulary terms within the chapter.

  1. A scientific theory can be shown to be wrong if
    1. cultural beliefs evolve to contradict it.
    2. scientists gather new data that contradict its predictions.
    3. it cannot explain all phenomena.
    4. it was first proposed as a conjecture.
    5. a majority of people do not accept it.

ANS: B         DIF: Easy              REF: Section 1.2

MSC: Understanding

OBJ: Establish why all scientific knowledge is provisional.

  1. Albert Einstein is best known for his revolutionary theory of
    1. quantum mechanics.

ANS: A         DIF: Easy              REF: Section 1.2

MSC: Remembering

OBJ: Define the bold-faced vocabulary terms within the chapter.

  1. In science an idea that cannot be tested is
    1. a hypothesis.
    2. not a scientific idea.
    3. a theory.
    4. a principle.

ANS: B         DIF: Easy              REF: Section 1.2

MSC: Remembering

OBJ: Compare an idea with a hypothesis.

  1. A theory is
    1. tied to known physical laws.
    2. able to make testable predictions.
    3. a hypothesis that has withstood many attempts to falsify it.
    4. all of the above

ANS: D         DIF: Easy              REF: Section 1.2

MSC: Remembering

OBJ: Compare the everyday and scientific meanings of theory.

  1. A hypothesis is an idea that is
    1. falsifiable with current technology only.
    2. potentially falsifiable with future technology.
    3. not falsifiable.
    4. both a and b

ANS: D         DIF: Easy              REF: Section 1.2

MSC: Understanding

OBJ: Compare an idea with a hypothesis.

  1. A hypothesis may become a theory
    1. after many repeated attempts to falsify it fail.
    2. if a majority of scientists agree on its propositions.
    3. after it has been logically proved.
    4. if it makes at least one verifiable prediction.

ANS: A         DIF: Easy              REF: Section 1.2

MSC: Remembering

OBJ: Compare the everyday and scientific meanings of theory.

  1. A theoretical model is
    1. a made-up explanation.
    2. a detailed description in terms of known physical laws or theories.
    3. a testable assumption.
    4. a scientific law.

ANS: B         DIF: Easy              REF: Section 1.2

MSC: Remembering

OBJ: Define the bold-faced vocabulary terms within the chapter.

  1. A scientific principle is
    1. a scientific law.
    2. a detailed description in terms of known physical laws or theories.
    3. a general idea or sense about the universe.
    4. a testable statement.

ANS: B         DIF: Easy              REF: Section 1.2

MSC: Remembering

OBJ: Define the bold-faced vocabulary terms within the chapter.

  1. In the scientific method, if an observation does not support the hypothesis, what possible actions should happen next?
    1. Make additional predictions.
    2. Make more observations.
    3. Choose a new hypothesis or revise the current one.
    4. Both b and c

ANS: D         DIF: Medium        REF: Section 1.2

MSC: Remembering

OBJ: Describe the steps of the scientific method.

  1. Which of the following is false?
    1. A scientific theory is an undisputed fact.
    2. If continual testing of a hypothesis shows it to be valid, it may become an accepted theory.
    3. A hypothesis must always have one or more testable predictions.
    4. A scientific theory may eventually be proven wrong when scientists acquire new data.
    5. Scientific observations are used to test a hypothesis.

ANS: A         DIF: Medium        REF: Section 1.2

MSC: Analyzing

OBJ: Compare the everyday and scientific meanings of theory.

  1. The scientific method is a process by which scientists
    1. prove theories to be known facts.
    2. gain confidence in theories by failing to prove them wrong.
    3. show all theories to be wrong.
    4. test the ideas of Aristotle.
    5. survey what the majority of people think about a theory.

ANS: B         DIF: Medium        REF: Section 1.2

MSC: Applying

OBJ: Define the bold-faced vocabulary terms within the chapter.

  1. A _________ becomes a _________ when repeated testing of its predictions does not disprove it.
    1. hypothesis; scientific method
    2. theory; scientific revolution
    3. phenomenon; theory
    4. hypothesis; theory
    5. law; theory

ANS: D         DIF: Medium        REF: Section 1.2

MSC: Applying

OBJ: Describe the steps of the scientific method.

  1. The cosmological principle states that
    1. the universe is expanding in all directions at the same rate.
    2. a unique center of the universe exists.
    3. the universe looks the same everywhere and in all directions as long as you look on large enough spatial scales.
    4. physical laws change from place to place in the universe.
    5. the universe is in a “steady state.”

ANS: C         DIF: Medium        REF: Section 1.2

MSC: Remembering

OBJ: Define the bold-faced vocabulary terms within the chapter.

  1. Because of _____________, we can conclude that gravity works the same way on Earth as it does on Mars.
    1. Newton’s theory of relativity
    2. Einstein’s special theory of relativity
    3. Sagan’s planetary principle
    4. the cosmological principle
    5. the hypothetical statute

ANS: D         DIF: Medium        REF: Section 1.2

MSC: Applying

OBJ: Define the bold-faced vocabulary terms within the chapter.

  1. If you have a stuffy nose, a fever, chills, and body aches and a doctor treats you for the flu rather than four separate diseases that account for each of your symptoms, this is an application of
    1. Newton’s hypothesis
    2. Occam’s razor
    3. Aristotle’s test
    4. Einstein’s relativity
    5. Copernican principle

ANS: B         DIF: Difficult       REF: Section 1.2

MSC: Applying

OBJ: Define the bold-faced vocabulary terms within the chapter.

  1. One of the central assumptions in astronomy is that the physical laws of nature
    1. change when objects move at high speed.
    2. change throughout the age of the universe.
    3. depend on the mass of the objects involved.
    4. are the same everywhere in the universe.

ANS: D         DIF: Medium        REF: Section 1.2

MSC: Remembering

OBJ: Assess whether a given idea or explanation is scientific.

  1. The statement “our universe is but one of a multitude of isolated universes” is best characterized as a
    1. speculative but unscientific idea because it is not testable and therefore not falsifiable.
    2. scientific fact.
    3. physical law.
    4. hypothesis that is currently being tested.

ANS: A         DIF: Difficult       REF: Section 1.2

MSC: Applying

OBJ: Assess whether a given idea or explanation is scientific.

  1. The language of science is
    1. Greek
    2. mathematics
    3. calculus
    4. Java
    5. Latin

ANS: B         DIF: Easy              REF: Section 1.3

MSC: Remembering

OBJ: Identify patterns in nature.

  1. When you see a pattern in nature, it is usually evidence of
    1. a theory being displayed.
    2. quantum mechanics in action.
    3. a breakdown of random clustering.
    4. an underlying physical law.
    5. A decrease in entropy.

ANS: D         DIF: Easy              REF: Section 1.3

MSC: Understanding

OBJ: Identify patterns in nature.

  1. Scientific notation is used in astronomy primarily because it allows us to
    1. write very large and very small numbers in a convenient way.
    2. talk about science in an easy way.
    3. change easy calculations into hard calculations.
    4. change hard calculations into easy calculations.
    5. explain science to engineers.

ANS: A         DIF: Easy              REF: Working It Out 1.1

MSC: Remembering

OBJ: Write numbers in both scientific and standard notation.

  1. Which is an important element in the composition of your body that was produced by nuclear fusion inside a star or an explosion of a star?
    1. iron
    2. calcium
    3. oxygen
    4. carbon
    5. all of the above

ANS: E         DIF: Easy              REF: Section 1.3

MSC: Remembering

OBJ: Summarize the evidence for the statement “We are actually made of recycled stardust.”

  1. The figure below shows the night sky as it appears for an observer in the United States at the same time of the night but at four different seasons of the year. Which conclusion below is not reasonable based on these observations?
    1. Constellations do not change their location relative to one another, but which constellations appear in the night sky does change from season to season.
    2. There are some constellations such as Ursa Minor, Ursa Major, Cassiopeia, and Cephus that are always seen in the night sky.
    3. Some constellations such as Capricornus and Sagittarius are only visible during summer and fall.
    4. A good time to harvest crops would be when the constellation Pegasus is directly overhead.
    5. A good time to plant crops would be when the constellation Sagittarius is directly overhead.

ANS: E         DIF: Medium        REF: Section 1.3

MSC: Applying

OBJ: Identify patterns in nature.

  1. Which presently observed element or isotope was not produced in appreciable amounts in the very early universe shortly after the Big Bang?
    1. hydrogen
    2. helium-4
    3. deuterium
    4. carbon
    5. helium-3

ANS: D         DIF: Medium        REF: Section 1.3

MSC: Applying

OBJ: Summarize the evidence for the statement “We are actually made of recycled stardust.”

  1. The study of whether or not life exists elsewhere in the Solar System and beyond is called

ANS: D         DIF: Medium        REF: Section 1.3

MSC: Remembering

OBJ: Identify fields of science that relate to the study of origins.

  1. The most massive elements such as those that make up terrestrial planets like Earth were formed
    1. in the early universe.
    2. inside stars and supernovae.
    3. through meteor collisions.
    4. in the core of Earth.
    5. during the formation of the Solar System.

ANS: B         DIF: Medium        REF: Section 1.3

MSC: Remembering

OBJ: Summarize the evidence for the statement “We are actually made of recycled stardust.”

  1. The number 123,000 written in scientific notation is
    1. 23 × 106
    2. 23 × 105
    3. 23 × 103
    4. 23 × 10–6
    5. 23 × 103

ANS: B         DIF: Easy              REF: Working It Out 1.1

MSC: Applying

OBJ: Write numbers in both scientific and standard notation.

  1. If the radius of circle B is twice the radius of circle A, and the area of a circle is proportional to the radius squared (A ∝ r2), then the ratio of the area of circle B to that of circle A is
    1. 5.
    2. 25.
    3. 414.

ANS: A         DIF: Easy              REF: Working It Out 1.1

MSC: Applying

OBJ: Describe characteristics of real-world objects in terms of ratios.

  1. (6 × 105) × (3 × 10–2) =
    1. 8 × 103
    2. 8 × 104
    3. 8 × 106
    4. 8 × 108
    5. 8 × 10-3

ANS: B         DIF: Medium        REF: Working It Out 1.1

MSC: Applying

OBJ: Write numbers in both scientific and standard notation.

  1. (1.2 × 109 ) ÷ (4 × 10–3) =
    1. 3 × 106
    2. 3 × 105
    3. 3 × 1010
    4. 3 × 1011
    5. 3 × 1012

ANS: D         DIF: Medium        REF: Working It Out 1.1

MSC: Applying

OBJ: Write numbers in both scientific and standard notation.

  1. If the radius of circle B is 5 times the radius of circle A, then the ratio of the area of circle B to that of circle A is
    1. 2.
    2. 04.
    3. 025.

ANS: A         DIF: Medium        REF: Working It Out 1.1

MSC: Applying

OBJ: Describe characteristics of real-world objects in terms of ratios.

  1. If the radius of sphere B is 5 times the radius of sphere A, then the ratio of the volume of sphere B to the volume of sphere A is
    1. 008.
    2. 2.

ANS: E         DIF: Medium        REF: Working It Out 1.1

MSC: Applying

OBJ: Describe characteristics of real-world objects in terms of ratios.

  1. The area of a circle is related to its diameter by the formula . Using algebra to solve for D, we find that
    1. .
    2. .
    3. .
    4. .
    5. .

ANS: D         DIF: Medium        REF: Working It Out 1.1

MSC: Applying

OBJ: Determine the mathematical behavior of proportional systems.

  1. The volume of a sphere is related to its radius by the formula . Using algebra to solve for R, we get
    1. .
    2. .
    3. .
    4. .
    5. .

ANS: B         DIF: Difficult       REF: Working It Out 1.1

MSC: Applying

OBJ: Determine the mathematical behavior of proportional systems.

  1. If the speed of light is 3 × 105 km/s and 1 km =62 mile, what is the speed of light in miles per hour (mph)?
    1. 670 million mph
    2. 670 thousand mph
    3. 186 mph
    4. 186 thousand mph
    5. 2 billion mph

ANS: A         DIF: Difficult       REF: Working It Out 1.1

MSC: Applying

OBJ: Determine the mathematical behavior of proportional systems.

  1. The orbital period of Mercury is 88 days. What is its orbital period in units of seconds?
    1. 76000 seconds
    2. 6 million seconds
    3. 6 billion seconds
    4. 760 billion seconds
    5. 76 million seconds

ANS: B         DIF: Difficult       REF: Working It Out 1.1

MSC: Applying

OBJ: Determine the mathematical behavior of proportional systems.

  1. At a time step of 10 shown in the figure below, how many viruses are there?
    1. 500
    2. 1000
    3. 1500
    4. 2000

ANS: B         DIF: Easy              REF: Working It Out 1.2

MSC: Understanding

OBJ: Read data from linear and logarithmic graphs.

  1. Approximately how many viruses are at time step 5 in the figure below?
    1. 10
    2. 30
    3. 50
    4. 90
    5. 100

ANS: C         DIF: Difficult       REF: Working It Out 1.2

MSC: Understanding

OBJ: Read data from linear and logarithmic graphs.

  1. Which graph (a), (b), or (c) in the figures below is a plot of an exponential behavior?
    1. figure (a)
    2. figure (b)
    3. figure (c)
    4. both a and c
    5. both b and c

ANS: E         DIF: Medium        REF: Working It Out 1.2

MSC: Understanding

OBJ: Distinguish between linear and exponential curves on a graph.

  1. The number 1.5 x 104 is:
    1. 00015
    2. 0015
    3. 1500
    4. 15000
    5. 150000

ANS:D          DIF: Easy              REF: Working It Out 1.1

MSC: Understanding

OBJ: Write numbers in both scientific and standard notation.

  1. What are the units of the vertical axis?
    1. km
    2. hour
    3. km/hour
    4. hour/km

ANS: B         DIF: Easy              REF: Working It Out 1.2

MSC: Understanding

OBJ: Identify the x and y axes on a graph.

  1. What is the slope of line?
    1. 1 km/hour
    2. 1 hour/km
    3. 10 km/hour
    4. 10 hour/km

ANS: D         DIF: Easy              REF: Working It Out 1.2

MSC: Understanding

OBJ: Define slope on a graph.

SHORT ANSWER

  1. What is the only thing that makes the Sun an exceptional star?

ANS: The fact that it is our star!  DIF: Easy   REF: Section 1.1  MSC: Remembering

OBJ: Differentiate the various components of our cosmic address.

  1. Why might the universe be described as a sort of “time machine”?

ANS: The finite speed of light means that objects observed at larger distances are observed as they existed further in the past.

DIF: Easy  REF: Section 1.1  MSC: Remembering

OBJ: Relate astronomical distances with light-travel time.

  1. What is the Local Group?

ANS: The group of a dozen or so galaxies including the Milky Way that are within a few million light-years of each other.

DIF: Easy  REF: Section 1.1  MSC: Remembering

OBJ: Differentiate the various components of our cosmic address.

  1. Describe how talking about time can give us a feeling for distance.

ANS: If speed is constant, a difference in time is directly related to a difference in distance. A time difference is easier to conceptualize.

DIF: Medium  REF: Section 1.1   MSC: Understanding

OBJ: Relate astronomical distances with light-travel time.

  1. Suppose you were writing to a pen pal in another universe. What address would you put on the envelope that included all the major structures in which we reside? (Hint: Your cosmic address should begin with “Earth” and end with “the universe.”)

ANS: The address would be Earth, Solar System, Milky Way, Local Group, Laniakea Supercluster, the universe.   DIF: Medium  REF: Section 1.1   MSC: Remembering

OBJ: List our cosmic address.

  1. What would you say to someone who said, “It would take light-years to get to the Andromeda Galaxy”?

ANS: You would have to tell them that light-years is a unit of distance not time.

DIF: Medium  REF: Section 1.1  MSC: Applying

OBJ: Relate astronomical distances with light-travel time.

  1. If you compare the diameter of Earth to 1 minute of time, then what interval of time would represent the diameter of the Solar System? Assume the diameter of the Solar System is approximately 80 AU.

ANS: The diameter of Earth is 2 × 6,378 km = 1.3 × 107 m, and 80 AU = 80 × 1.5 × 1011 m = 1.2 × 1013 m. Thus, the diameter of the Solar System would be represented by 1.2 × 1013 m × (1 minute)/(1.3 × 107 m) = 9.4 × 105 minutes = 1.8 years.

DIF: Difficult  REF: Section 1.1  MSC: Analyzing

OBJ: Illustrate the size or history of the universe with scaled models.

  1. Using the method of comparing times to get a handle on the large distances in astronomy, compare the size of Earth to the size of the visible universe. Start by making the size of Earth comparable to a snap of your fingers, which lasts about 1/7 second. Show your computation.

ANS: If the size of Earth is like a snap of your fingers (1/7 second), the size of the visible universe would be 13.7 billion years ≈ 3 × 4.5 billion years = 3 times the age of the Solar System.

DIF: Medium  REF: Section 1.1  MSC: Analyzing

OBJ: Illustrate the size or history of the universe with scaled models.

  1. Using the method of comparing distances to time intervals to get a handle on the large distances in astronomy, compare the diameter of our Solar System, which is 6 × 1012, to the diameter of the galaxy, which is 1.2 × 1021, by calculating the time it would take for light to travel these diameters. For reference, the speed of light is 3 × 108 m/s.

ANS: The time it takes light to travel across the diameter of the Solar System is t 5 d/v 5 6 3 1012 m/ (3 3 108 m/s) 5 20,000 s 3 (1 h/3600 s) 5 5.5 h. The time it takes light to travel across the diameter of the galaxy is t 5 1.2 3 1021 m/(3 3 108 m/s) 5 4 3 1012 s 3 (1 h/3600 s) 3 (1 day/24 h) 3 (1 y/365 day) 5 130,000 y.   DIF: Difficult  REF: Section 1.1  MSC: Analyzing

OBJ: Illustrate the size or history of the universe with scaled models.

  1. What implication does the finite speed of light have on what we observe in the universe?

ANS: It means we see objects as they were when the light left them. Looking further away from Earth is also looking further back in time.

DIF: Difficult  REF: Section 1.1  MSC: Applying

OBJ: Relate astronomical distances with light-travel time.

  1. Describe the two main aspects of the cosmological principle.

ANS: (1) What we see around us is representative of what the universe is like in general, and (2) the physical laws valid on Earth are valid everywhere.   DIF: Easy  REF: Section 1.2   MSC: Remembering

OBJ: Define the bold-faced vocabulary terms within the chapter.

  1. What makes an idea a hypothesis?

ANS: A hypothesis must be a falsifiable idea.   DIF: Easy  REF: Section 1.2   MSC: Remembering

OBJ: Compare an idea with a hypothesis.

  1. Why is the statement “The Big Bang was caused by a collision between other universes” not scientific?

ANS: The statement is not scientific because it is not testable.

DIF: Easy  REF: Section 1.2   MSC: Applying

OBJ: Assess whether a given idea or explanation is scientific.

  1. An observation does not support your hypothesis. What do you do next?

ANS: Make more observations, revise the hypothesis, or choose a new hypothesis.

DIF: Easy  REF: Section 1.2   MSC: Understanding

OBJ: Describe the steps of the scientific method.

  1. Before 2014 the supercluster we resided in was called the Virgo Supercluster. Based on a new way of classifying superclusters we are now a member of the Laniakea Supercluster. What is this change an example of?

ANS: The provisional nature of scientific knowledge.   DIF: Easy  REF: Section 1.2   MSC: Understanding

OBJ: Establish why all scientific knowledge is provisional.

  1. What accounts for 95 percent of the mass of the universe?

ANS: Dark matter and dark energy, the latter having an equivalent mass are related by E = mc2.

DIF: Easy  REF: Section 1.1   MSC: Remembering

OBJ: Relate the different sizes of, or the different distances between, the components of our cosmic address.

  1. What is a theoretical model?

ANS: A theoretical model is a detailed description of the properties of a particular system in terms of known physical laws or theories, which can be used to make predictions.

DIF: Easy  REF: Section 1.2   MSC: Remembering

OBJ: Define the bold-faced vocabulary terms within the chapter.

  1. In pre-Renaissance times, it was believed that celestial objects were made of a different substance than Earth and obeyed different rules. Which modern scientific principle is a better description of the universe?

ANS: The cosmological principle.

DIF: Medium  REF: Section 1.2  MSC: Applying

OBJ: Define the bold-faced vocabulary terms within the chapter.

  1. Why does a theory that continues to be supported by the results of experimental tests need further tests?

ANS: There may be observational tests or measurements that might be performed with greater precision for which the predictions of the theory might fail.   DIF: Medium  REF: Section 1.2   MSC: Remembering

OBJ: Establish why all scientific knowledge is provisional.

  1. Describe the main steps involved in the scientific method.

ANS: First you make a hypothesis and then you make a prediction based on your hypothesis. Finally, you test your prediction through experimentation to prove or disprove your original hypothesis. You revise your hypothesis, if necessary, when the experiments disagree with your hypothesis.

DIF: Medium  REF: Section 1.2   MSC: Understanding

OBJ: Describe the steps of the scientific method.

  1. What two pre-Renaissance beliefs are contradicted by the cosmological principle?

ANS: (1) Earth is at the center of our universe, and (2) celestial objects are made of a different substance than Earth and obey different rules.

DIF: Medium  REF: Section 1.2   MSC: Remembering

OBJ: Establish why all scientific knowledge is provisional.

  1. Describe two ways in which Einstein’s new theories changed commonly accepted scientific views of his time.

ANS: Mass and energy are manifestations of the same phenomenon. Thus, you can convert one into the other. Time and space are not separable but are intimately related to one another. Thus, Newton’s law of gravity is only a special case of a more general law Einstein called general relativity. However, Newton’s law of gravity is much easier for most calculations in our day-to-day lives.

DIF: Medium  REF: Section 1.2   MSC: Understanding

OBJ: Establish why all scientific knowledge is provisional.

  1. How would you respond to someone who stated that “Evolution is not proven; it is just a theory”?

ANS: You would need to explain that in science, a theory is not something that is proven; rather it our best explanation based on available data. Thus, calling something a theory does not diminish its importance.   DIF: Difficult  REF: Section 1.2  MSC: Applying

OBJ: Compare the everyday and scientific meanings of theory.

  1. There are many different areas of science, but a common factor in each is the evaluation and analysis of patterns. What patterns does astronomy deal with? (Describe it in general and give at least one concrete example.)

ANS: Astronomy deals with patterns related to celestial objects. One example is that patterns in the sky mark the changing of seasons, the coming of rains, the movement of herds, and the planting and harvesting of crops. An additional example is that the Sun rises and sets at a specific time because Earth orbits the Sun.   DIF: Easy  REF: Section 1.3   MSC: Understanding

OBJ: Identify patterns in nature.

  1. An observed pattern in nature is usually a sign of some underlying physical reason. Give an example of this in astronomy, citing the pattern and the reason behind it.

ANS: The Sun rises and sets each day. This pattern is due to Earth’s daily rotation on its axis. The stars visible in the sky at a given time of day change throughout the year, but the pattern repeats every year. This is due to Earth’s orbital motion around the Sun in 1 year.   DIF: Easy  REF: Section 1.3  MSC: Applying

OBJ: Identify patterns in nature.

  1. It is often said that “mathematics is the language of science.” Explain why this is true.

ANS: Math is a formal system used when describing and analyzing patterns, and explaining the reasons for patterns is the heart of science. Thus, math is the language of science.

DIF: Easy  REF: Section 1.3   MSC: Understanding

OBJ: Identify patterns in nature.

  1. If the elements that make up Earth and our bodies were not present in the early universe, where did they come from?

ANS: They were formed by nuclear fusion inside stars.   DIF: Easy  REF: Section 1.3  MSC: Applying

OBJ: Summarize the evidence for the statement “We are actually made of recycled stardust.”

  1. What is the field of science that relates to the study of origin of life?

ANS: Astrobiology.  DIF: Easy  REF: Section 1.3

MSC: Remembering

OBJ: Identify fields of science that relate to the study of origins.

  1. Describe briefly why the phrase “we are stardust” is literally true.

ANS: Massive stars make heavy elements during their lifetime. When they eventually explode in a supernova, some of these heavy elements, as well as additional ones that are created in the explosion itself, are ejected into space, where they eventually cool and condense to form new solar systems and everything in them, including us.

DIF: Medium  REF: Section 1.3

MSC: Understanding

OBJ: Summarize the evidence for the statement “We are actually made of recycled stardust.”

  1. Life as we know it requires the heavy elements made in stars. Could life as we know it have existed when the first stars in the universe formed?

ANS: The heavy elements that make up our bodies were not yet formed, so life as we know it would have been impossible.

DIF: Difficult  REF: Section 1.3

MSC: Understanding

OBJ: Summarize the evidence for the statement “We are actually made of recycled stardust.”

 

Chapter 12: Dwarf Planets and Small Solar System Bodies

Learning Objectives

12.1 Dwarf Planets May Outnumber Planets

Distinguish the characteristics of a dwarf planet from a planet.

Multiple Choice: 1, 2, 3, 4, 6, 7, 8, 9

Short Answer: 1, 3, 4

Establish why Pluto was once considered a planet, but now is classified as a dwarf planet.

Multiple Choice: 5, 11

Short Answer: 2

12.2 Asteroids Are Pieces of the Past

Identify the different locations of asteroids in the solar system.

Multiple Choice: 12, 15, 17, 20

Differentiate an asteroid from a dwarf planet.

Multiple Choice: 10, 13, 14, 18, 19, 29

Short Answer: 5, 11

Summarize the differences between C-, S-, and M-type asteroids.

Multiple Choice: 21, 23, 24, 25

Short Answer: 8

Describe how tidal effects from Jupiter keep main-belt asteroids from forming a planet and cause the Kirkwood gaps.

Multiple Choice: 16

Short Answer: 6

Summarize what we have learned about asteroids from satellite visits and landings.

Multiple Choice: 22, 26, 27, 28

Short Answer: 7, 10

12.3 Comets Are Clumps of Ice

Describe the two homes of comets.

Multiple Choice: 30, 35

Distinguish between the orbital characteristics of long- and short-period comets.

Multiple Choice: 31, 34, 36, 37, 38, 39, 46, 47

Short Answer: 12

Describe the four parts of an active comet.

Multiple Choice: 33, 40, 41, 45

Short Answer: 18, 19, 21

Illustrate the changes in a comet’s appearance over the course of its orbit.

Multiple Choice: 42, 43

Short Answer: 13, 14, 15, 16, 17, 20

Summarize what we have learned about comets from satellite visits and landings

Multiple Choice: 32, 44

12.4 Meteorites Are Remnants of the Early Solar System

Differentiate between meteors, meteorites, and meteoroids.

Multiple Choice: 56, 57

Short Answer: 22

Differentiate between the different compositions and origins of meteorites.

Multiple Choice: 48, 49, 59, 61, 63, 64, 65, 66

Short Answer: 23

Summarize the origins of meteoroids that Earth encounters.

Multiple Choice: 58

Illustrate the origin of meteor showers.

Multiple Choice: 51, 52, 53, 54, 55

Short Answer: 26

Explain how asteroids and meteorites provide critical clues to the origin and history of our Solar System

Multiple Choice: 50, 60, 62, 67

Short Answer: 24, 25

12.5 Collisions Still Happen Today

Summarize why it is important to search for and characterize all near-Earth objects.

Multiple Choice: 68, 70

Short Answer: 27, 28, 29

Working It Out 12.1

Calculate perihelion and aphelion distances of an orbit based on an object’s orbital eccentricity.

Short Answer: 9

Working It Out 12.2

Calculate the energy of an impact.

Multiple Choice: 69

Short Answer: 30

MULTIPLE CHOICE

  1. Which of the following types of solar system debris were not discovered until the age of telescopes?
    1. comets
    2. meteoroids
    3. zodiacal dust
    4. asteroids
    5. all of the above

ANS: D         DIF: Medium        REF: Section 12.1

MSC: Remembering

OBJ: Distinguish the characteristics of a dwarf planet from a planet.

  1. What group of solar system objects does Pluto belong to?
    1. the Trojan asteroids
    2. the dwarf planets
    3. the giant objects
    4. the terrestrial planets

ANS: B         DIF: Easy              REF: Section 12.1

MSC: Remembering

OBJ: Distinguish the characteristics of a dwarf planet from a planet.

  1. Pluto is composed primarily of
    1. a rocky core surrounded by ice.
    2. metallic hydrogen.

ANS: C         DIF: Easy              REF: Section 12.1

MSC: Remembering

OBJ: Distinguish the characteristics of a dwarf planet from a planet.

  1. Pluto has an atmosphere that comes and goes over an orbital period, because
    1. the atmosphere escapes into space because of the low escape velocity from Pluto.
    2. the atmosphere is pulled away from the planet by interaction with its moon Charon.
    3. the atmosphere “freezes out” when Pluto is at its farthest from the Sun.
    4. chemical reactions between Pluto’s atmosphere and gas expelled by its many volcanoes generates carbon dioxide, which is too heavy to stay aloft in the atmosphere.

ANS: C         DIF: Medium        REF: Section 12.1

MSC: Understanding

OBJ: Distinguish the characteristics of a dwarf planet from a planet.

  1. Pluto is classified as a dwarf planet because
    1. it has not cleared out other bodies from its orbit.
    2. it is more than 1,000 times smaller than Earth’s moon.
    3. it has no moons of its own.
    4. it has a unique chemical composition that is very different from other planets.
    5. it orbits just outside the Solar System.

ANS: A         DIF: Easy              REF: Section 12.1

MSC: Applying

OBJ: Establish why Pluto was once considered a planet but now is classified as a dwarf planet.

  1. Which of following is false?
    1. Pluto has five moons.
    2. Pluto has a mass that is 10 times less than Earth’s mass.
    3. Pluto’s orbit sometimes brings it closer to the Sun than Neptune.
    4. Pluto was discovered by Clyde Tombaugh in 1930.
    5. Pluto has a thin atmosphere.

ANS: B         DIF: Medium        REF: Section 12.1

MSC: Remembering

OBJ: Distinguish the characteristics of a dwarf planet from a planet.

  1. Pluto has a density that is roughly equal to two times that of
    1. a feather.
    2. a rock.

ANS: B         DIF: Easy              REF: Section 12.1

MSC: Remembering

OBJ: Distinguish the characteristics of a dwarf planet from a planet.

  1. Currently the surface of the dwarf planet Eris is covered with _________, which makes it have the highest albedo of any object in the Solar System.
    1. methane ice
    2. water ice
    3. nitrogen ice
    4. sulfur dioxide ice
    5. carbon dioxide ice

ANS: A         DIF: Medium        REF: Section 12.1

MSC: Remembering

OBJ: Distinguish the characteristics of a dwarf planet from a planet.

  1. Eris, Ceres, and Haumea are examples of
    1. dwarf planets.
    2. meteor showers.

ANS: B         DIF: Easy              REF: Section 12.1

MSC: Remembering

OBJ: Distinguish the characteristics of a dwarf planet from a planet.

  1. The dwarf planet Eris has a moon called Dysnomia, which is much smaller in mass than Eris. If Dysnomia has an orbital period of 16 days and orbits Eris at a distance of 40,000 km, then what is the mass of Eris?
    1. 2 × 1013 kg
    2. 2 × 1022 kg
    3. 2 × 1028 kg
    4. 2 × 1032 kg
    5. 2 × 1035 kg

ANS: B         DIF: Difficult       REF: Section 12.2

MSC: Applying

OBJ: Differentiate an asteroid from a dwarf planet.

  1. How does the mass of Pluto compare to that of Earth?
    1. It is around 100 times smaller.
    2. It is around 1000 times smaller.
    3. It is around 450 times smaller.
    4. It is around 10 times smaller.

ANS: C         DIF: Medium        REF: Section 12.1

MSC: Remembering

OBJ: Establish why Pluto was once considered a planet but now is classified as a dwarf planet.

  1. Where are asteroids found?
    1. between Mars and Jupiter
    2. inside Earth’s orbit, halfway to the Sun
    3. in the farthest reaches of the Solar System, beyond Pluto
    4. throughout the Solar System

ANS: D         DIF: Easy              REF: Section 12.2

MSC: Remembering

OBJ: Identify the different locations of asteroids in the solar system.

  1. When combined, asteroids have a mass equivalent to
    1. about 1/10th the mass of Earth’s Moon.
    2. about equal to the mass of Earth’s Moon.
    3. about 1/2 the mass of Earth’s Moon.
    4. about 1/25th the mass of Earth’s Moon.

ANS: D         DIF: Easy              REF: Section 12.2

MSC: Remembering

OBJ: Differentiate an asteroid from a dwarf planet.

  1. Meteorites are
    1. remnants of a single object near Pluto that never coalesced to form a planet.
    2. fragments of planetesimals between Mars and Jupiter.
    3. comets that formed close enough to the Sun to have lost all their volatiles.
    4. objects ejected from Saturn’s rings.

ANS: B         DIF: Medium        REF: Section 12.2

MSC: Remembering

OBJ: Differentiate an asteroid from a dwarf planet.

  1. Why do some short period comets have orbits within the orbit of Jupiter?
    1. They were created from the asteroid belt between Mars and Jupiter.
    2. They actually orbit Jupiter rather than the Sun.
    3. As they traveled to the inner Solar System from the Kuiper Belt, they suffered a gravitational encounter with Jupiter, which trapped them.
    4. As they traveled to the inner Solar System from the Kuiper Belt, they collided with one another and no longer had enough speed to reach the Kuiper Belt again.

ANS: C         DIF: Difficult       REF: Section 12.2

MSC: Remembering

OBJ: Identify the different locations of asteroids in the solar system.

  1. The Kirkwood gaps are regularly spaced gaps in the asteroid distribution. What causes the gaps to appear?
    1. The pressure of the solar wind is especially strong at these locations, evacuating asteroids out of them.
    2. They are regions where gravitational pull from Mars is overcome by gravitational pull from Jupiter.
    3. They are regions where an object and Jupiter would regularly line up during their orbits, causing the object to repeatedly be tugged by Jupiter’s gravity until it leaves that orbit.
    4. They are regions between Jupiter and Saturn where the combined effect of both planets’ gravity prevents objects from orbiting there.

ANS: C         DIF: Medium        REF: Section 12.2

MSC: Applying

OBJ: Describe how tidal effects from Jupiter keep main-belt asteroids from forming a planet and cause the Kirkwood gaps.

  1. Most asteroids are located between the orbits of
    1. Earth and Mars.
    2. Mars and Jupiter.
    3. Jupiter and Saturn.
    4. Neptune and Pluto.
    5. the Kuiper Belt and the Oort Cloud.

ANS: B         DIF: Easy              REF: Section 12.2

MSC: Remembering

OBJ: Identify the different locations of asteroids in the solar system.

  1. Most asteroids are
    1. very large (>100 km).
    2. large (30−100 km).
    3. medium (10−30 km).
    4. small (1−10 km).
    5. very small (<1 km).

ANS: E         DIF: Difficult       REF: Section 12.2

MSC: Remembering

OBJ: Differentiate an asteroid from a dwarf planet.

  1. The mass of all the known asteroids combined is approximately equal to
    1. half the mass of Earth.
    2. three times the mass of Earth.
    3. twice the mass of Mars.
    4. the mass of Mars.
    5. less than one-third the mass of the Moon.

ANS: E         DIF: Easy              REF: Section 12.2

MSC: Remembering

OBJ: Differentiate an asteroid from a dwarf planet.

  1. Which group of asteroids regularly crosses Earth’s orbit and thus might possibly collide with our planet?
    1. the Amors
    2. the Atens
    3. the Kuiper Belt objects
    4. the Trojans
    5. all of the above

ANS: B         DIF: Medium        REF: Section 12.2

MSC: Remembering

OBJ: Identify the different locations of asteroids in the solar system.

  1. Asteroids are primarily composed of
    1. hydrogen and helium.
    2. ice and dust.

ANS: C         DIF: Easy              REF: Section 12.2

MSC: Remembering

OBJ: Summarize the differences between C-, S-, and M-type asteroids.

  1. Most asteroids are closest in shape to
    1. a potato.
    2. a banana.
    3. a hot dog.
    4. a stick.
    5. a baseball.

ANS: A         DIF: Easy              REF: Section 12.2

MSC: Remembering

OBJ: Summarize what we have learned about asteroids from satellite visits and landings.

  1. The darkest asteroids are
    1. M-type.
    2. S-type.
    3. C-type.
    4. A-type.
    5. Q-type.

ANS: C         DIF: Difficult       REF: Section 12.2

MSC: Remembering

OBJ: Summarize the differences between C-, S-, and M-type asteroids.

  1. Iron meteorites are fragments of which type of asteroid?
    1. A-type
    2. C-type
    3. M-type
    4. Q-type
    5. S-type

ANS: C         DIF: Medium        REF: Section 12.2

MSC: Applying

OBJ: Summarize the differences between C-, S-, and M-type asteroids.

  1. Carbonaceous chondrite meteorites are fragments of which type of asteroid?
    1. A-type
    2. C-type
    3. M-type
    4. Q-type
    5. S-type

ANS: B         DIF: Medium        REF: Section 12.2

MSC: Applying

OBJ: Summarize the differences between C-, S-, and M-type asteroids.

  1. Until spacecraft flew by asteroids, scientists did not have a good idea of what they looked like. Which of the following missions was the first to fly by an asteroid?
    1. NEAR Shoemaker
    2. Rosetta
    3. Galileo
    4. Dawn
    5. Stardust

ANS: C         DIF: Medium        REF: Section 12.2

MSC: Remembering

OBJ: Summarize what we have learned about asteroids from satellite visits and landings.

  1. The most straightforward way to determine the mass of an asteroid is if it has
    1. a rocky composition.
    2. a moon.
    3. an orbit that lies between Earth and Mars.
    4. carbonaceous chondrites.
    5. a magnetic field.

ANS: B         DIF: Easy              REF: Section 12.2

MSC: Applying

OBJ: Summarize what we have learned about asteroids from satellite visits and landings.

  1. In November 2005, the Japanese spacecraft Hayabusa brought back a sample from which type of object for the first time?
    1. comet
    2. asteroid
    3. moon
    4. terrestrial planet
    5. gas giant planet

ANS: B         DIF: Medium        REF: Section 12.2

MSC: Remembering

OBJ: Summarize what we have learned about asteroids from satellite visits and landings.

  1. Remnants of volcanic activity on the asteroid Vesta indicate that members of the asteroid belt
    1. were once part of a single protoplanet that was shattered by collisions.
    2. have all undergone significant chemical evolution since formation.
    3. occasionally grow large enough to become differentiated and geologically active.
    4. were once a part of a young Mars.
    5. used to be volcanic moons orbiting other planets.

ANS: C         DIF: Medium        REF: Section 12.2

MSC: Understanding

OBJ: Differentiate an asteroid from a dwarf planet.

  1. What is the relative importance of collisions between comets compared to collisions between meteoroids and asteroids?
    1. They are not very important.
    2. They are very important.
    3. They are somewhat important, especially for short-period comets.
    4. They are only important for long-period comets.

ANS: A         DIF: Medium        REF: Section 12.3

MSC: Applying

OBJ: Describe the two homes of comets.

  1. Which type of comet is the most common?
    1. short-period comets
    2. long-period comets
    3. There are approximately equal numbers of both.
    4. Astronomers have no way of knowing this.

ANS: B         DIF: Easy              REF: Section 12.3

MSC: Remembering

OBJ: Distinguish between the orbital characteristics of long- and short-period comets.

  1. How do astronomers identify the parent comet of a meteor observed in Earth’s atmosphere?
    1. They use the brightness of the meteor.
    2. They accurately measure the time of the night when the meteor is seen.
    3. They measure how long a streak the meteor generates in the atmosphere.
    4. They use the speed and direction of a cometary meteor’s flight to identify its parent comet.

ANS: D         DIF: Difficult       REF: Section 12.3

MSC: Applying

OBJ: Summarize what we have learned about comets from satellite visits and landings.

  1. Identify the object shown in the figure below.
    1. an active comet
    2. a meteor shower
    3. a meteorite
    4. an asteroid
    5. zodiacal dust

ANS: A         DIF: Easy              REF: Section 12.3

MSC: Remembering

OBJ: Describe the four parts of an active comet.

  1. A comet having an orbit of 50 years would likely have come from the
    1. Atens family.
    2. Oort Cloud.
    3. Trojan family.
    4. zodiacal zone.
    5. Kuiper Belt.

ANS: E         DIF: Medium        REF: Section 12.3

MSC: Applying

OBJ: Distinguish between the orbital characteristics of long- and short-period comets.

  1. Most comets originate
    1. near Earth and Venus, in the early Solar System.
    2. far from the planets, many thousands of astronomical units (AU) from the Sun.
    3. from the region between the orbits of Jupiter and Neptune.
    4. between the Sun and Mercury.
    5. between the orbits of Mars and Jupiter.

ANS: B         DIF: Easy              REF: Section 12.3

MSC: Applying

OBJ: Describe the two homes of comets.

  1. The one orbital characteristic that both short- and long-period comets share is
    1. mostly prograde orbits.
    2. orbits with completely random tilts.
    3. mostly retrograde orbits.
    4. orbital periods longer than any planet.
    5. highly eccentric orbits.

ANS: E         DIF: Medium        REF: Section 12.3

MSC: Applying

OBJ: Distinguish between the orbital characteristics of long- and short-period comets.

  1. Approximately how often does a spectacularly active, visible comet appear?
    1. once a year
    2. once every 5 years
    3. once every 10 years
    4. once every 50 years
    5. once every 1,000 years

ANS: C         DIF: Medium        REF: Section 12.3

MSC: Remembering

OBJ: Distinguish between the orbital characteristics of long- and short-period comets.

  1. Comet Halley is unique because
    1. it was the first comet whose return was predicted.
    2. it is a member of the Jovian family but has a retrograde orbit.
    3. its period is less than a human lifetime.
    4. it was successfully visited by a spacecraft.
    5. it was the brightest comet ever observed by humans.

ANS: A         DIF: Medium        REF: Section 12.3

MSC: Applying

OBJ: Distinguish between the orbital characteristics of long and- short-period comets.

  1. With a semimajor axis of 18 AU, Comet Halley has a period of
    1. 7 years.
    2. 16 years.
    3. 32 years.
    4. 67 years.
    5. 76 years.

ANS: E         DIF: Easy              REF: Section 12.3

MSC: Remembering

OBJ: Distinguish between the orbital characteristics of long- and short-period comets.

  1. The nucleus of the typical comet is approximately _________ in size.
    1. 10 km
    2. 1,000 km
    3. 100 m
    4. 10 m
    5. 1 cm

ANS: A         DIF: Medium        REF: Section 12.3

MSC: Remembering

OBJ: Describe the four parts of an active comet.

  1. The nuclei of a comet is mostly
    1. solid ice.
    2. solid rock.
    3. liquid water.
    4. a porous mix of ice and dust.
    5. frozen carbon dioxide.

ANS: D         DIF: Medium        REF: Section 12.3

MSC: Applying

OBJ: Describe the four parts of an active comet.

  1. When a comet comes close to the Sun, its volatile ice sublimates and transforms directly from the solid to _________ phase.
    1. liquid
    2. crystalline
    3. energized
    4. gas
    5. ionized

ANS: D         DIF: Medium        REF: Section 12.3

MSC: Remembering

OBJ: Illustrate the changes in a comet’s appearance over the course of its orbit.

  1. Why does the dust tail separate from the ion tail?
    1. The dust has no charge, so it is not affected by the solar wind.
    2. Dust cannot sublimate as ice can, so it cannot form a tail as easily.
    3. The dust tail forms on the leading side of the nucleus, whereas the gas tail forms on the opposite side.
    4. Dust particles are more massive than ions, so their accelerations are less.
    5. The dust tail has the opposite charge as the ion tail.

ANS: D         DIF: Difficult       REF: Section 12.3

MSC: Understanding

OBJ: Illustrate the changes in a comet’s appearance over the course of its orbit.

  1. Which of the following comets has not been visited by spacecraft?
    1. Halley
    2. Wild 2
    3. Tempel 1
    4. Hartley 2
    5. Shoemaker-Levy 9

ANS: E         DIF: Easy              REF: Section 12.3

MSC: Remembering

OBJ: Summarize what we have learned about comets from satellite visits and landings.

  1. Comet nuclei, absent their tails, are very dark because
    1. they are made of water ice.
    2. they have iron and nickel mixed with ice.
    3. they have organic molecules mixed with ice.
    4. they are covered in rock.
    5. they are too cold to emit any light.

ANS: C         DIF: Easy              REF: Section 12.3

MSC: Remembering

OBJ: Describe the four parts of an active comet.

  1. Suppose we discover a comet whose orbit was very highly eccentric, retrograde, had a very large tilt with respect to the ecliptic plane, and a period of 2,000 years. Where is the most likely place of origin for this comet?
    1. the Kuiper Belt
    2. the Oort Cloud
    3. the asteroid belt
    4. the Jovian family
    5. outside the Solar System

ANS: B         DIF: Medium        REF: Section 12.3

MSC: Applying

OBJ: Distinguish between the orbital characteristics of long- and short-period comets.

  1. Which of the following does not describe comets in the Oort Cloud?
    1. long period
    2. pristine condition
    3. cold temperatures
    4. randomly directed orbits
    5. flattened distribution in space

ANS: E         DIF: Easy              REF: Section 12.3

MSC: Understanding

OBJ: Distinguish between the orbital characteristics of long- and short-period comets.

  1. What is the main source of meteors?
    1. short-period comets
    2. long-period comets
    3. asteroids
    4. terrestrial planets

ANS: C         DIF: Medium        REF: Section 12.4

MSC: Applying

OBJ: Differentiate between the different compositions and origins of meteorites.

  1. Which type of meteorite is most commonly found on Earth?
    1. metallic
    2. stony
    3. glassy
    4. They are all equally common.

ANS: B         DIF: Easy              REF: Section 12.4

MSC: Remembering

OBJ: Differentiate between the different compositions and origins of meteorites.

  1. What implication does the composition of cometary nuclei have for the creation of life?
    1. They hold water, which is needed by all life.
    2. They hold organic compounds, evidence that the ingredients necessary for the creation of life were present in the early solar nebula.
    3. Bacteria have been found in cometary nuclei, proving that life on Earth came from comets.
    4. They hold oxygen, which is needed for all life.

ANS: B         DIF: Difficult       REF: Section 12.4

MSC: Applying

OBJ: Explain how asteroids and meteorites provide critical clues to the origin and history of our Solar System.

  1. The minimum size of a meteoroid that is capable of surviving its passage through Earth’s atmosphere and hitting the ground is about as big as
    1. a car.
    2. a house.
    3. a basketball.
    4. a grain of sand.
    5. your fist.

ANS: E         DIF: Medium        REF: Section 12.4

MSC: Remembering

OBJ: Illustrate the origin of meteor showers.

  1. The Perseid meteor shower will occur
    1. every month.
    2. every year.
    3. every 4 years.
    4. every 76 years.
    5. every 132 years.

ANS: B         DIF: Easy              REF: Section 12.4

MSC: Remembering

OBJ: Illustrate the origin of meteor showers.

  1. The meteoroids in the Leonids meteor shower, which occurs every November, come from
    1. dust in the star-forming Leo nebula.
    2. dust melted off Comet Tempel-Tuttle.
    3. debris from the collision of Comet Shoemaker-Levy 9.
    4. zodiacal dust.
    5. dust blown off of Earth’s surface.

ANS: B         DIF: Medium        REF: Section 12.4

MSC: Applying

OBJ: Illustrate the origin of meteor showers.

  1. The Lyrid meteor shower occurs every year on approximately April 21 because
    1. the Lyrae constellation is directly overhead at midnight.
    2. Earth passes through a cloud of debris left behind by Comet Thatcher.
    3. Earth passes through a cloud of debris left over from the Solar System’s formation.
    4. Earth undergoes a periodic volcanic eruption every April.
    5. the Sun is located in the Lyrae constellation at noon.

ANS: B         DIF: Medium        REF: Section 12.4

MSC: Remembering

OBJ: Illustrate the origin of meteor showers.

  1. A large meteor shower will often occur once a year because
    1. Earth typically has one large volcanic eruption every year.
    2. Earth’s orbit passes through the Apollo asteroid belt.
    3. the Sun goes through a yearly solar cycle.
    4. Jupiter routinely disturbs the orbits of asteroids in the Jovian belt.
    5. Earth passes through the debris left behind by a specific comet.

ANS: E         DIF: Easy              REF: Section 12.4

MSC: Understanding

OBJ: Illustrate the origin of meteor showers.

  1. Identify the phenomenon shown in the figure below.
    1. an active comet
    2. a meteor shower
    3. a meteorite
    4. an asteroid
    5. zodiacal dust

ANS: B         DIF: Easy              REF: Section 12.4

MSC: Applying

OBJ: Differentiate between meteors, meteorites, and meteoroids.

  1. Meteor showers appear as if they are coming from one particular place in the sky because
    1. that is the direction in which the comet is coming toward us.
    2. that is the direction in which the comet is moving away from us.
    3. that is the direction toward which Earth is traveling.
    4. that is the direction Earth just passed.
    5. that is the location in the sky from which the meteors originate.

ANS: C         DIF: Medium        REF: Section 12.4

MSC: Understanding

OBJ: Differentiate between meteors, meteorites, and meteoroids.

  1. Antarctica is the best hunting ground for meteorites for all of the following reasons except
    1. the ground is covered with ice.
    2. more meteorites fall there than on other locations on Earth.
    3. few native rocks are found on the glaciers.
    4. meteorites are protected from weathering and contamination there.
    5. by searching at different depths in the ice you can determine the history of impacts over time.

ANS: B         DIF: Medium        REF: Section 12.4

MSC: Understanding

OBJ: Summarize the origins of meteoroids that Earth encounters.

  1. Identify the object shown in the figure below.
    1. a meteor
    2. a chondrite meteorite
    3. an achondrite meteorite
    4. an iron meteorite
    5. an asteroid

ANS: B         DIF: Easy              REF: Section 12.4

MSC: Applying

OBJ: Differentiate between the different compositions and origins of meteorites.

  1. Meteorites contain clues to all of the following except
    1. the age of the Solar System.
    2. the temperature in the early solar nebula.
    3. changes in the rate of cratering in the early Solar System.
    4. the composition of the primitive Solar System.
    5. the physical processes that controlled the formation of the Solar System.

ANS: C         DIF: Difficult       REF: Section 12.4

MSC: Understanding

OBJ: Explain how asteroids and meteorites provide critical clues to the origin and history of our Solar System.

  1. The most common type of meteorites are
    1. stony meteorites.
    2. iron meteorites.
    3. achondrite meteorites.
    4. stony-iron meteorites.
    5. carbonaceous chondrite meteorites.

ANS: A         DIF: Easy              REF: Section 12.4

MSC: Remembering

OBJ: Differentiate between the different compositions and origins of meteorites.

  1. Which group of meteorites represents the conditions in the earliest stages of the formation of the Solar System?
    1. chondrites
    2. achondrites
    3. icy meteorites
    4. iron meteorites
    5. stony-iron meteorites

ANS: A         DIF: Medium        REF: Section 12.4

MSC: Remembering

OBJ: Explain how asteroids and meteorites provide critical clues to the origin and history of our Solar System.

  1. Although most meteorites have ages around 4.5 billion years, a small subset has ages around 1.3 billion years. What caused the substantial difference in age between these two populations of meteorites?
    1. These meteorites just happened to form later than most meteorites.
    2. Not all meteorites hit Earth in the early Solar System. We should expect to find younger meteorites as more meteors pass through the atmosphere.
    3. The younger meteorites were created when a protoplanet collided with Earth, creating the Moon. The leftover fragments became meteorites.
    4. These meteorites were thrown into space after an impact with Mars and afterward some happened to collide with Earth.
    5. The younger ones are the result of comets repeatedly passing close to the Sun, melting their surfaces and making them appear younger.

ANS: D         DIF: Medium        REF: Section 12.4

MSC: Understanding

OBJ: Differentiate between the different compositions and origins of meteorites.

  1. Identify the object shown in the image below.
    1. an active comet
    2. a meteor shower
    3. a meteorite
    4. an asteroid
    5. zodiacal dust

ANS: E         DIF: Medium        REF: Section 12.4

MSC: Understanding

OBJ: Differentiate between the different compositions and origins of meteorites.

  1. Which of the following likely helps replenish the zodiacal dust in the vicinity of Earth the most?
    1. comets
    2. asteroids
    3. the Moon
    4. volcanoes on Earth
    5. tornados on Earth

ANS: A         DIF: Medium        REF: Section 12.4

MSC: Applying

OBJ: Differentiate between the different compositions and origins of meteorites.

  1. All of the zodiacal dust in the Solar System combined is roughly equal in mass to
    1. a meteoroid.
    2. a comet.
    3. the Moon.
    4. a terrestrial planet.

ANS: B         DIF: Easy              REF: Section 12.4

MSC: Remembering

OBJ: Differentiate between the different compositions and origins of meteorites.

  1. In the early universe, when the Solar System had yet to be cleared of the debris out of which it formed, which type of object would have been most likely to deposit water onto Earth’s surface?
    1. comets
    2. asteroids
    3. a Mars-sized protoplanet
    4. Both comets and asteroids appear to be sources.
    5. None, because water is not a major component of any of the objects above.

ANS: D         DIF: Easy              REF: Section 12.4

MSC: Understanding

OBJ: Explain how asteroids and meteorites provide critical clues to the origin and history of our Solar System.

  1. In 1994, dozens of fragments of Comet Shoemaker-Levy 9 collided with
    1. the Moon.

ANS: A         DIF: Easy              REF: Section 12.5

MSC: Remembering

OBJ: Summarize why it is important to search for and characterize all near-Earth objects.

  1. Consider a meteoroid with a diameter of 10 cm and a mass of 2 kg that hits Earth head-on while traveling at a speed of 25,000 m/s. How many times larger or smaller is the meteoroid’s kinetic energy compared to that of a typical train whose mass is 2 × 106 kg and speed is 25 m/s?
    1. The meteoroid’s kinetic energy is equal to that of the train.
    2. The meteoroid’s kinetic energy is 1,000 times less than that of the train.
    3. The meteoroid’s kinetic energy is 1,000 times greater than that of the train.
    4. The meteoroid’s kinetic energy is 106 times greater than that of the train.
    5. The meteoroid’s kinetic energy is 109 times greater than that of the train.

ANS: A         DIF: Difficult       REF: Working it Out 12.2

MSC: Applying

OBJ: Calculate the energy of an impact.

  1. A recent estimate finds that approximately 800 meteorites with mass greater than 0.1 kg strike the surface of Earth each day. If a house covers an area of roughly 100 m2, then what is the probability that your house will be struck by a meteorite in your 100-year lifetime? Note that the radius of Earth is 6,400 km.
    1. 1 in 1 × 104
    2. 1 in 2 × 105
    3. 1 in 4 × 106
    4. 1 in 6 × 107
    5. 1 in 8 × 108

ANS: B         DIF: Difficult       REF: Section 12.5

MSC: Applying

OBJ: Summarize why it is important to search for and characterize all near-Earth objects.

SHORT ANSWER

  1. List the names of the known dwarf planets and their approximate location in the Solar System.

ANS: As of printing, there are five dwarf planets: (1) Pluto—Kuiper Belt; (2) Eris—Kuiper Belt; (3) Haumea—Kuiper Belt; (4) Makemake—Kuiper Belt; (5) Ceres—asteroid belt.

DIF: Medium  REF: Section 12.1

MSC: Remembering

OBJ: Distinguish the characteristics of a dwarf planet from a planet.

  1. Give the two main differences between the orbital properties of the dwarf planet Pluto and those of planets in our Solar System.

ANS: (1) Pluto’s orbital plane is tilted significantly relative to the ecliptic, unlike the planets, and (2) it has not cleared its orbit of smaller bodies because of its small mass, but shares them with many other objects. This is not the case for planets.

DIF: Medium  REF: Section 12.1

MSC: Remembering

OBJ: Establish why Pluto was once considered a planet but now is classified as a dwarf planet.

  1. The dwarf planet Eris is covered in methane ice, whereas the surface of Saturn’s moon Enceladus is covered in water ice. Why does methane exist in ice form on Eris but not Enceladus?

ANS: Eris is located much farther from the Sun that Enceladus (the closest it reaches the Sun is around 39 AU, whereas Enceladus is at the same distance as Saturn from the Sun, 10 AU). This means Eris is much colder than Enceladus; cold enough for methane to solidify into ice.

DIF: Difficult  REF: Section 12.1  MSC: Applying

OBJ: Distinguish the characteristics of a dwarf planet from a planet.

  1. An astronomer observes a dwarf planet that has a small diameter but is rather bright, so she concludes that it must have a high albedo. Why?

ANS: The brightness of a reflecting object depends on the flux of light emitted by its surface. This in turn depends on its emitting surface area and albedo (the fraction of light reflected). The emitting surface area depends on the diameter of the object. A small diameter implies a small emitting area, so the only way to reach the observed brightness is for the albedo to be very high.

DIF: Difficult  REF: Section 12.1   MSC: Remembering

OBJ: Distinguish the characteristics of a dwarf planet from a planet.

  1. Name three properties of the dwarf planets Pluto and Eris that are similar.

ANS: They have relatively similar masses and densities, and are made primarily of rock and ice. They are similar in size, and both have moons. They also have large distances from the Sun and elliptical orbits.

DIF: Easy  REF: Section 12.2  MSC: Applying

OBJ: Differentiate an asteroid from a dwarf planet.

  1. Suppose a collision between two large asteroids creates a handful of smaller asteroid fragments, some of which orbit at 2.7 AU from the Sun and some which orbit at 2.5 AU from the Sun. Based on the asteroid distribution plot shown in Figure 12.5, which of the two smaller asteroid groups will have a stable orbit around the Sun, and why?

ANS: The asteroids at 2.5 AU fall into a 3:1 resonance with Jupiter, that is, a Kirkwood gap. This means that Jupiter will gravitationally tug on them in the same place on their orbit each time they go around the Sun. This will cause them to fall out of the orbit at 2.5 AU.

DIF: Difficult  REF: Section 12.2  MSC: Applying

OBJ: Describe how tidal effects from Jupiter keep main-belt asteroids from forming a planet and cause the Kirkwood gaps.

  1. Give examples of a C-type asteroid and an S-type asteroid that have been observed by spacecraft. What did we learn about each type?

ANS: An example of a C-type asteroid would be Mathilde. It is nonreflective (because of its composition of carbon compounds), has a low density (indicating that it is porous), and has many craters (therefore dating back to the early Solar System). Some examples of an S-type asteroid are Gaspra (which is made up of different types of rock, is cratered, and is irregularly shaped), Ida (which is composed of relatively solid rock, shows evidence of past landslides and therefore the presence of soil, and—based on the number of craters it has—suggests an age of around 1 billion years old), and Eros (which is composed of solid rock, has a cratered surface, and has similar composition to primitive meteorites).

DIF: Medium  REF: Section 12.2   MSC: Understanding

OBJ: Summarize what we have learned about asteroids from satellite visits and landings.

  1. What does the existence of M-type asteroids tell us about their origin?

ANS: They were once the metallic cores of larger, differentiated objects.

DIF: Easy  REF: Section 12.2   MSC: Remembering

OBJ: Summarize the differences between C-, S-, and M-type asteroids.

  1. Comets have highly eccentric orbits, with eccentricities of 0.95 to 0.99 being common. Suppose a certain comet has an eccentricity of 0.99. If the semimajor axis of its orbit is 2,500 AU, what will be its distance at perihelion and at aphelion? Is this most likely a Kuiper Belt object or an Oort Cloud comet? (Note: For an ellipse, a(1 + e) is the distance from one focus to the farther edge of the long axis and a(1e) is the distance from the same focus to the closer edge of the long axis.)

ANS: Aphelion is the point of maximum distance from the Sun, which equals a(1 + e) = 2,500 AU (1 + 0.99) = 4,975 AU. Perihelion is the point of closest approach, which equals a(1 − e) = 2,500 AU (1 − 0.99) = 25 AU. This comet would probably be from the Oort Cloud because the aphelion distance is too large for the Kuiper Belt.

DIF: Difficult  REF: Working it Out 12.1   MSC: Applying

OBJ: Calculate perihelion and aphelion distances of an orbit based on an object’s orbital eccentricity.

  1. Why are asteroids considered to be excellent sources for studying conditions in the early Solar System, whereas planets themselves are not?

ANS: Asteroids are planetesimals that never accreted onto planets during planet formation, so they have not been subject to any of the weathering or processing that planets have undergone. As such, they maintain the chemical and physical signatures of conditions in the early Solar System and are invaluable for study.

DIF: Medium  REF: Section 12.2

MSC: Understanding

OBJ: Summarize what we have learned about asteroids from satellite visits and landings.

  1. Describe the relationship between planets, dwarf planets, planetesimals, asteroids, and meteorites.

ANS: Planetesimals are large aggregates of rock and ice that are held together by their gravity and reach sizes of 1 km or more. They are the chunks from which planets form. If planetesimals aggregate into a large enough body to be self-gravitating and spherical, but not able to clear the orbit of other debris, they are called dwarf planets. Asteroids are smaller than planetesimals; they are irregular chunks of rock and ice that have not aggregated to form a planetesimal, or are chunks of rock and ice knocked off planetesimals during collisions. Meteorites are smaller still, and are mostly chunks of rock knocked off asteroids during collisions which have fallen to Earth.

DIF: Medium  REF: Section 12.2   MSC: Understanding

OBJ: Differentiate an asteroid from a dwarf planet.

  1. Consider three comets that have orbital periods of 10, 100, and 1,000 years. Where would each of these comets likely originate, in the Oort Cloud or the Kuiper Belt? If you wanted to study material that was the best example of pristine Solar System material, which would you study?

ANS: For all objects, including comets, that orbit the Sun, Kepler’s law (P2 = A3) applies; thus, the longer the period, the farther from the Sun the object orbits. The comet with a period of 1,000 years would be the one that is farthest from the Sun during most of its orbit and might contain more pristine Solar System material. The 10- and 100-year comets are short-period comets and probably come from the Kuiper Belt, which extends out to 50 AU. The 1,000-year comet is a long-period comet and probably came from the Oort Cloud.

DIF: Medium  REF: Section 12.3   MSC: Applying

OBJ: Distinguish between the orbital characteristics of long- and short-period comets.

  1. Why do long-period comets usually put on a much more visually spectacular display than short-period comets?

ANS: Long-period comets have not passed perihelion as often as short-period comets, so their volatile ices remain close to the surface. Short-period comets have burned off much of their volatile ices on previous passages, leaving a nucleus coated in a (relatively) thick layer of dust and organic material.

DIF: Easy  REF: Section 12.3   MSC: Understanding

OBJ: Illustrate the changes in a comet’s appearance over the course of its orbit.

  1. In its 1986 trip around the Sun, it was estimated that Comet Halley lost approximately 100 billion kg of material. The total mass of the nucleus was estimated to be 3 × 1014 Assuming the mass loss rate is constant with each passage, and assuming the nucleus remains intact until there is nothing left, how many more times will we see Comet Halley? Explain why your answer is an upper limit.

ANS: The number of trips equals the total mass of the comet divided by the mass lost each trip. # trips = 3 × 1014 kg/1011 kg/trip = 3,000 trips. This is an upper limit because as more of the nucleus is eaten away, the surface area/volume ratio will (eventually) change significantly, which can alter the amount of material lost with each trip. Also, it is unlikely that a porous object will remain intact until the last of its material is gone. The comet will probably break apart before it completely loses all its material.

DIF: Difficult  REF: Section 12.3   MSC: Applying

OBJ: Illustrate the changes in a comet’s appearance over the course of its orbit.

  1. Do icy cometary nuclei melt and move from solid to liquid phase as they are warmed by the radiation from the Sun?

ANS: No, they sublimate. Their ices change from solids directly into gases without ever going through the liquid stage because the material is under very low pressure.

DIF: Medium  REF: Section 12.3   MSC: Understanding

OBJ: Illustrate the changes in a comet’s appearance over the course of its orbit.

  1. Assume the larger circle shown in the figure below is the Sun, and the smaller circle is the head of a comet. If the comet is moving away from the Sun, draw and label the two tails onto the comet.

ANS: Both tails should be pointing away from the Sun, with the dust tail slightly curved and the ion tail moving directly away from the Sun.

DIF: Medium  REF: Section 12.3

MSC: Understanding

OBJ: Illustrate the changes in a comet’s appearance over the course of its orbit.

  1. How is it possible for the tail of a comet to actually move ahead of the comet itself?

ANS: The tail is blown outward by the solar wind, which points radially away from the Sun in all directions. As the comet passes perihelion and begins to move back toward the outer Solar System, its tails are blown ahead of the nucleus itself.

DIF: Medium  REF: Section 12.3

MSC: Understanding

OBJ: Illustrate the changes in a comet’s appearance over the course of its orbit.

  1. Looking at the image below, identify the two tails.

ANS: The top tail is pointing directly away from the sun and therefore is the ion tail. The curved tail on the bottom is the dust tail, made of particles heavier than the ions which are pushed less effectively by the solar wind.

DIF: Easy  REF: Section 12.3  MSC: Applying

OBJ: Describe the four parts of an active comet.

  1. If you can model the mass in Comet Halley as a sphere 5 km in radius, what is its density if it has a mass of 1014 kg? How does that density compare to that of water (1,000 kg/m3)?

ANS: The volume of a sphere 5 km in radius is 4/3π × (5 × 103 m)3 = 5.236 × 1011 m3. So the density of Comet Halley is 1014 kg/(5.235 × 1011 m3) = 191 kg/m3, which is far less than that of water.

DIF: Difficult  REF: Section 12.3   MSC: Applying

OBJ: Describe the four parts of an active comet.

  1. Let’s say that you discovered a comet in the outer Solar System that had an average albedo of 0.6. If its surface was composed of a mixture of organic substances, which had an albedo of 0, and ice, which had an albedo of 1.0, then what percent of its surface is covered by organic substances?

ANS: Let X be the fraction of the surface that is covered by organic substances. The average albedo would be equal to [X · 0 + (1 − X ) · 1] = (1 − X ). If (1 − X ) = 0.6, then X = 0.4, and 40 percent of the surface is covered by organic substances.

DIF: Difficult  REF: Section 12.3

MSC: Applying

OBJ: Illustrate the changes in a comet’s appearance over the course of its orbit.

  1. Why does a comet usually have two tails, one that is straight and one that is curved? What materials compose each tail, and why do they have different shapes?

ANS: The straight tail is made of ionized gas and is called the ion tail. It points directly away from the Sun because the charged particles in the tail interact with the particles in the solar wind. The curved tail is the dust tail, and it is not as straight as the dust tail because dust particles are more massive than the particles in the ion tail. Thus, the dust tail is less affected by the solar wind.

DIF: Medium  REF: Section 12.3

MSC: Understanding

OBJ: Describe the four parts of an active comet.

  1. Give the definitions of meteoroid, meteor, and meteorite, and clearly explain how they differ.

ANS: Meteoroids are rocks too small to be asteroids in orbit around the Sun. Meteors are the bright streaks in the sky made when a meteoroid enters the atmosphere. Meteorites are the rocks that survive meteoroids’ passage through Earth’s atmosphere and land on the ground.

DIF: Medium  REF: Section 12.4

MSC: Remembering

OBJ: Differentiate between meteors, meteorites, and meteoroids.

  1. You find a blackened rock lying on top of the snow. You find that it is fairly dense and suspect it might be a meteorite. You take it to a lab, and they cut it open to reveal many small spherical, glassy particles set into the surrounding rock. Is this a meteorite? Why, or why not?

ANS: Yes, it is likely that you have found a stony meteorite with chondrules. Meteorites are typically denser than earth rocks and have a blackened appearance after falling through Earth’s atmosphere. The small spherical, glassy particles are the chondrules that often range in size from sand grains to marbles.

DIF: Medium  REF: Section 12.4   MSC: Applying

OBJ: Differentiate between the different compositions and origins of meteorites.

  1. How might impacts have helped increase Earth’s water supply in the early history of the Solar System?

ANS: Icy planetesimals formed near the orbits of the giant planets. As the giant planets formed and grew, they produced strong gravitational interactions with nearby planetesimals. These interactions caused some icy planetesimals to be thrown outward to form the Kuiper Belt and Oort Cloud; others were thrown inward toward the Sun. It is likely that some of the objects thrown in toward the Sun hit Earth. Because most of the mass in comet nuclei is water ice, the impact and temperature of Earth would have melted the ice, thus giving new water to Earth’s surface.

DIF: Medium  REF: Section 12.4

MSC: Understanding

OBJ: Explain how asteroids and meteorites provide critical clues to the origin and history of our Solar System.

  1. What is the best way to look for comet and asteroid dust in the solar system?

ANS: These dust particles are called zodiacal dust and orbit along the plane of the ecliptic, where all asteroids and short period comets are located. To see the dust, look toward the horizon shortly after the sky has gone completely dark. The reflected sunlight off the zodiacal dust (called zodiacal light) can be seen as a faint vertical column of light rising from the western horizon and oriented with the ecliptic.

DIF: Medium  REF: Section 12.4   MSC: Applying

OBJ: Explain how asteroids and meteorites provide critical clues to the origin and history of our Solar System.

  1. What is the origin of meteor showers, and why are they sometimes more intense than at other times?

ANS: Meteor showers are produced when Earth passes through the dust from short-period comets. The paths of these comets intersect the orbit of Earth. The meteor dust is heated to incandescence as it passes through Earth’s atmosphere and can be seen as a brief streak of light as it burns up. When Earth passes especially close to the tail of a short-period comet, the meteor showers are especially intense, reaching hundreds of thousands of meteors per hour.

DIF: Medium  REF: Section 12.4   MSC: Applying

OBJ: Illustrate the origin of meteor showers.

  1. What kind of comet was Shoemaker-Levy 9, and why?

ANS: It originated in the Kuiper Belt, which makes it a short-period comet.

DIF: Difficult  REF: Section 12.5   MSC: Applying

OBJ: Summarize why it is important to search for and characterize all near-Earth objects.

  1. Describe two modern-day (within the past 150 years) events when comets or asteroids collided with a planet. Cite the planet, and describe the major consequences of the collision.

ANS: Shoemaker-Levy 9 crashed into Jupiter’s atmosphere in 1994. Fireballs were seen in the Jovian atmosphere as a result. An asteroid exploded in Earth’s atmosphere above Tunguska, Siberia, in 1908. Trees were burned or flattened over an area equal to 2,150 km2. In 2013, an asteroid exploded in the atmosphere over Russia’s Ural mountains, injuring hundreds and damaging thousands of buildings in the area.

DIF: Easy  REF: Section 12.5   MSC: Remembering

OBJ: Summarize why it is important to search for and characterize all near-Earth objects.

  1. Describe two challenges faced by astronomers in identifying potential collisions between Earth and Earth-crossing asteroids and meteorites.

ANS: (1) There are numerous such objects (many thousands or millions), so tracking them all is an enormously difficult task. (2) They often have low albedos, which make them very dim, and they follow orbits that can make them nearly impossible to see until they are close to impact.

DIF: Medium  REF: Section 12.5   MSC: Applying

OBJ: Summarize why it is important to search for and characterize all near-Earth objects.

  1. Consider a small comet nucleus whose diameter is 1 km and mass is 5 × 1011 It hits Earth head-on, traveling at a speed of 1,000 m/s. How many times larger or smaller is the comet’s kinetic energy compared to that of a typical train pulling 20 boxcars whose total mass is 2 × 106 kg and speed is 25 m/s?

ANS: Kinetic energy is equal to 1/2mv2. Therefore, the ratio of the kinetic energy of the comet to that of the train equals (Mcomet/Mtrain) × (vcomet/vtrain)2 = (5 × 1011/2 × 106) × (1,000/25)2 = 4 × 108.

DIF: Difficult  REF: Working it Out 12.2

MSC: Applying

OBJ: Calculate the energy of an impact.

 

Chapter 24: Life

Learning Objectives

Define the boldfaced vocabulary terms within the chapter.

24.1 Life Evolves on Earth

Describe life.

Multiple Choice: 7, 8

Compare and contrast the major theories presented in this text of how life originated on Earth.

Multiple Choice: 1, 9, 16, 17

Short Answer: 3

Explain why the earliest forms of life on Earth must have been extremophiles.

Multiple Choice: 2, 10, 11, 12, 20, 23

Short Answer: 5

Establish why mutation and heredity lead to evolution.

Multiple Choice: 6, 14, 15, 24

Short Answer: 4

Illustrate the process of natural selection.

Multiple Choice: 13, 30

Summarize the evolution of life from its first origins on Earth until today.

Multiple Choice: 3, 4, 5, 18, 19, 21, 22, 25, 26, 27, 28, 29

Short Answer: 1, 2, 6, 7

24.2 Life Has Evolved through Physical and Chemical Processes

Explain why carbon is favored as the, but is not the only, chemical basis of life.

Multiple Choice: 34, 35, 36, 37, 38, 39

Short Answer: 9, 10

Explain the evidence that the human body is specifically made of star dust.

Multiple Choice: 33, 40, 41

Short Answer: 11, 12

24.3 Where Do Astronomers Look for Life?

Assess whether we expect to find life outside of Earth.

Multiple Choice: 48

Short Answer: 25

Describe the conditions scientists believe are necessary for the evolution of life.

Multiple Choice: 44, 55, 60

Short Answer: 15, 19, 20, 21, 24

Describe the methods currently being used to search for life in the Solar System.

Short Answer: 17, 18

Compare and contrast the Solar System locations where scientists hope to find evidence for life.

Multiple Choice: 45, 47, 50, 51, 53, 56, 61

Short Answer: 16, 22

Illustrate how the habitable zone changes for stars of different masses.

Multiple Choice: 49, 52, 54, 57, 58, 59

Short Answer: 23

Describe a galactic habitable zone.

Multiple Choice: 46

Summarize the current state of our attempts to find life beyond Earth.

Multiple Choice: 66

24.4 Scientists are Searching for Signs of Intelligent Life

Describe the methods currently being used to search for intelligent extraterrestrial life.

Multiple Choice: 62, 63, 64, 67, 68

Short Answer: 26, 29

Assess why it is unlikely that we will communicate with extraterrestrial beings.

Multiple Choice: 65, 69, 70

Short Answer: 27, 28, 30

Working It Out 24.1

Calculate population changes using exponential growth.

Multiple Choice: 31, 32

Short Answer: 8

Working It Out 24.2

Use the Drake Equation to assess the probable number of intelligent civilizations in the Milky Way capable of communicating with us.

Multiple Choice: 42, 43

Short Answer: 13, 14

MULTIPLE CHOICE

  1. In 1952, chemists Harold Urey and Stanley Miller mixed ammonia, methane, and hydrogen in a closed container, zapped it with electrical sparks, and found that
    1. they could induce cold fusion to occur,
    2. they could not induce any amino acids to form.
    3. single-celled microorganisms had been spontaneously created.
    4. they had created many amino acids.
    5. they had created life in a test tube.

ANS: D   DIF: Easy        REF: 24.1

MSC: Understanding

OBJ: Compare and contrast the major theories presented in this text of how life originated on Earth.

  1. In which of the following locations has life not been found on Earth?
  2. near deep-oceans hydrothermal vents
  3. in extremely dry deserts
  4. in Arctic ice
  5. in hot sulfur springs
  6. None of the above. Life has been found in all of these locations.

ANS: E   DIF: Easy        REF: 24.1

MSC: Remembering

OBJ: Explain why the earliest forms of life on Earth must have been extremophiles.

  1. How did the presence of cyanobacteria on Earth in the past allow eventually the appearance of advanced life forms like humans?
  2. It represented the first form of life.
  3. It initiated the oxygenation of the atmosphere.
  4. It fertilized the soil to let plants grow.
  5. It increased the carbon dioxide in the atmosphere, causing the greenhouse effect.
  6. It was the first life-form based on DNA.

ANS: B   DIF: Easy        REF: 24.1

MSC: Analyzing

OBJ: Summarize the evolution of life from its first origins on Earth until today.

  1. Complex microorganisms that have complex DNA enclosed in a cell nucleus are called

ANS: D   DIF: Easy        REF: 24.1

MSC: Remembering

OBJ: Summarize the evolution of life from its first origins on Earth until today.

  1. Why was the comet or asteroid impact 65 million years ago (ironically) an event that benefited the evolution of humans?
  2. It deposited a significant amount of nitrogen into the Earth’s atmosphere.
  3. It led to an increase in global UV radiation, which killed off most of the forests and jungles.
  4. Mammals got an evolutionary boost.
  5. Plant life began to decline.
  6. It brought human DNA to Earth.

ANS: C   DIF: Easy        REF: 24.1

MSC: Understanding

OBJ: Summarize the evolution of life from its first origins on Earth until today.

  1. The ability for one generation to pass on its characteristics to future generations is known as
    1. natural selection.
    2. self-replication.

ANS: C   DIF: Easy        REF: 24.1

MSC: Remembering

OBJ: Establish why mutation and heredity lead to evolution.

  1. Which of the following is not a property of life known on Earth?
  2. It has evolved.
  3. It is self-sufficient, since it has its own internal source of energy
  4. It is capable of reproduction.
  5. It involves carbon-based chemistry.
  6. It uses water as a biological solvent.

ANS: B   DIF: Easy        REF: 24.1

MSC: Remembering

OBJ: Describe life.

  1. What makes molecules organic?
  2. They can reproduce.
  3. They are very complex.
  4. They are unique to Earth.
  5. They need oxygen to form.
  6. They contain carbon.

ANS: E   DIF: Easy        REF: 24.1

MSC: Understanding

OBJ: Describe life.

  1. The earliest life-forms on Earth likely appeared
  2. within a billion years after the formation of the Solar System.
  3. 65 billion years after the formation of the Solar System.
  4. 6 billion years ago.
  5. 250 million years ago.
  6. 20 million years ago.

ANS: A   DIF: Easy        REF: 24.1

MSC: Remembering

OBJ: Compare and contrast the major theories presented in this text of how life originated on Earth.

  1. The current oxygen level in the Earth’s atmosphere was reached about
  2. 6 billion years ago.
  3. 2 billion years ago.
  4. 20 million years ago.
  5. 250 million years ago.
  6. 540 million years ago.

ANS: D   DIF: Easy        REF: 24.1

MSC: Remembering

OBJ: Explain why the earliest forms of life on Earth must have been extremophiles.

  1. The “waste” product in the process of photosynthesis is
  2. carbon dioxide.
  3. amino acids.

ANS: C   DIF: Easy        REF: 24.1

MSC: Remembering

OBJ: Explain why the earliest forms of life on Earth must have been extremophiles.

  1. Which of the following is not an example of extremophiles?
  2. organisms that thrive at high temperatures
  3. organisms that thrive without light
  4. organisms that photosynthesize
  5. organisms that thrive in highly acidic environments
  6. organisms that thrive in environments with high radiation levels

ANS: C   DIF: Easy        REF: 24.1

MSC: Applying

OBJ: Explain why the earliest forms of life on Earth must have been extremophiles.

  1. Natural selection essentially implies the ability to
  2. pass on a genetic code to the next generation.
  3. avoid the interaction with the environment.
  4. self-replicate.
  5. adapt and survive.
  6. reject genetic mutations.

ANS: D   DIF: Medium  REF: 24.1

MSC: Understanding

OBJ: Illustrate the process of natural selection.

  1. Heredity essentially implies the ability to
  2. pass on a genetic code to the next generation.
  3. avoid the interaction with the environment.
  4. self-replicate.
  5. adapt and survive.
  6. reject genetic mutations.

ANS: A   DIF: Medium  REF: 24.1

MSC: Understanding

OBJ: Establish why mutation and heredity lead to evolution.

  1. Choose the incorrect statement about mutations:
  2. Mutations always lead to improvements in an organism’s ability to survive and reproduce.
  3. According to the theory of evolution, chemical reactions resulting in the mutation of a molecule are a natural and inevitable occurrence.
  4. Mutations can be incorporated into a species’ genetic code.
  5. Mutations cause the diversification of species
  6. Mutations are influenced by the interaction of organisms with their environment.

ANS: A   DIF: Medium  REF: 24.1

MSC: Applying

OBJ: Establish why mutation and heredity lead to evolution.

  1. What was the goal of the Urey-Miller experiment schematized in the figure below?
  2. to create a microorganism
  3. to simulate the formation of Earth
  4. to simulate the Big Bang
  5. to simulate the early universe
  6. to simulate the formation of the building blocks of life

ANS: E   DIF: Medium  REF: 24.1

MSC: Understanding

OBJ: Compare and contrast the major theories presented in this text of how life originated on Earth.

  1. What was the reason for adding hydrogen sulfide to the “primitive atmosphere” simulated in the Urey-Miller experiment?
  2. to mimic the alteration of the primitive atmospheric composition due to volcanic outgassing
  3. to sterilize all potential bacterial or microbial life forms in the active volume of the experiment
  4. no reason; it was a purely accidental insertion of this toxic gas in the reaction chamber
  5. to speed up the chemical reactions with a catalyst. to test the survival chance of extremophiles forming in the experimental chamber

ANS: A   DIF: Medium  REF: 24.1

MSC: Understanding

OBJ: Compare and contrast the major theories presented in this text of how life originated on Earth.

  1. Imagine that you built a time machine and successfully traveled 2 billion years back in time. What would happen?
  2. You would see dinosaurs roaming Earth.
  3. You would see forests and insects everywhere on Earth.
  4. You probably would be killed by the ongoing heavy bombardment of Earth.
  5. You would probably die due to the severe scarcity of oxygen.
  6. You would be floating in space because, Earth hadn’t formed yet.

ANS: D   DIF: Medium  REF: 24.1

MSC: Evaluating

OBJ: Summarize the evolution of life from its first origins on Earth until today.

  1. If we compressed the whole history of the Earth in a single day, at what time would the first plants on land appear?
  2. 5:00 A.M.
  3. 9:10 A.M.
  4. 12:00 noon
  5. 9:30 P.M.
  6. 5:20 P.M.

ANS: D   DIF: Medium  REF: 24.1

MSC: Applying

OBJ: Summarize the evolution of life from its first origins on Earth until today.

  1. The image below shows an Australian shoreline. Which of the following forms of early life on Earth does it depict?
  2. stromatolites
  3. fish colonies
  4. eukaryotes
  5. meteorites
  6. fungi

ANS: A   DIF: Medium  REF: 24.1

MSC: Remembering

OBJ: Explain why the earliest forms of life on Earth must have been extremophiles.

  1. What is the major difference between prokaryotes and eukaryotes?
  2. Eukaryotes have DNA, and prokaryotes have RNA.
  3. Eukaryotes have a nuclear membrane surrounding their DNA, and prokaryotes do not.
  4. Eukaryotes are plants, and prokaryotes are animals.
  5. Eukaryotes appeared on Earth before prokaryotes.
  6. Eukaryotes are single-celled, and prokaryotes are multicellular.

ANS: B   DIF: Medium  REF: 24.1

MSC: Remembering

OBJ: Summarize the evolution of life from its first origins on Earth until today.

  1. If we model the history of the Earth as a single day, at what time would the dinosaurs be wiped out by a large asteroid or comet?
  2. 05:20 m.
  3. 10:45 m.
  4. 07:21 m.
  5. 11:16 m.
  6. 07:21 m.

ANS: D   DIF: Medium  REF: 24.1

MSC: Applying

OBJ: Summarize the evolution of life from its first origins on Earth until today.

  1. Choose the incorrect answer about the stromatolites:
  2. They are some of the oldest evidence of life-forms on Earth.
  3. They date back about 3.5 billion years.
  4. They are prokaryotes.
  5. They are produced by cyanobacteria.
  6. There are no known living examples in existence nowadays.

ANS: E   DIF: Medium  REF: 24.1

MSC: Remembering

OBJ: Explain why the earliest forms of life on Earth must have been extremophiles.

  1. Which of the following events is the oldest in the history of life evolution on Earth?
  2. the Cambrian explosion
  3. the appearance of first plants on land
  4. the demise of dinosaurs
  5. the branching of primates away from other mammals
  6. the first human civilizations

ANS: A   DIF: Medium  REF: 24.1

MSC: Remembering

OBJ: Establish why mutation and heredity lead to evolution.

  1. The evolution of terrestrial life involves all but which of the following?
  2. mechanisms of change
  3. mutation
  4. heredity
  5. natural selection
  6. silicon-based chemistry

ANS: E   DIF: Medium  REF: 24.1

MSC: Understanding

OBJ: Summarize the evolution of life from its first origins on Earth until today.

  1. Which of the sketches shown in the figure below could describe the evolutionary phylogenetic tree on Earth? In each diagram, time increases upward, and each branch represents a different species.
  2. A
  3. B
  4. C
  5. D
  6. E

ANS: A   DIF: Medium  REF: 24.1

MSC: Applying

OBJ: Summarize the evolution of life from its first origins on Earth until today.

  1. Animals are most closely related to which of the following branches?
  2. bacteria
  3. archaea
  4. flagellates
  5. fungi
  6. cyanobacteria

ANS: D   DIF: Medium  REF: 24.1

MSC: Applying

OBJ: Summarize the evolution of life from its first origins on Earth until today.

  1. Which of the following occurred approximately 500 million years ago?
  2. the extinction of the dinosaurs
  3. the Cambrian explosion
  4. the formation of the Moon
  5. the rise of mammals
  6. the birth of the first humans

ANS: B   DIF: Difficult REF: 24.1

MSC: Remembering

OBJ: Summarize the evolution of life from its first origins on Earth until today.

  1. If we modeled the history of the Earth as a single day, at what time would the first humans branch out from chimpanzees?
  2. 11:58 P.M.
  3. 10:10 P.M.
  4. 11:35 P.M.
  5. 09:00 P.M.
  6. 06:00 P.M.

ANS: A   DIF: Medium  REF: 24.1

MSC: Applying

OBJ: Summarize the evolution of life from its first origins on Earth until today.

  1. Which of the following properties would be the unique marker of life?
  2. structure
  3. self-replication
  4. utilizing energy from environment
  5. reacting to stimuli within environment
  6. evolutionary adaptation

ANS: E   DIF: Difficult REF: 24.1

MSC: Applying

OBJ: Illustrate the process of natural selection.

  1. Exponential growth generally describes a population
    1. that has a constant rate of growth.
    2. that doubles in size in an infinitesimally small fraction of a second.
    3. that has virtually an infinite space available for growth.
    4. that is not undergoing natural selection.
    5. of Si-based molecular structures.

ANS: A  DIF: Difficult  REF: Working It Out 24.1

MSC: Applying

OBJ: Calculate population changes using exponential growth.

  1. In the context of self-replication of molecules, if each of them is successfully copying itself every 2 minutes, how long does it take to have a population growth factor of the order of a billion?
  2. 1 hour
  3. 2 hours
  4. 10 minutes
  5. 2 minutes
  6. 2 billion minutes

ANS: A  DIF: Medium  REF: Working It Out 24.1

MSC: Applying

OBJ: Calculate population changes using exponential growth.

  1. Which one of the following is not an element commonly found in living organisms?
  2. helium
  3. hydrogen
  4. oxygen
  5. phosphorus
  6. nitrogen

ANS: A   DIF: Easy        REF: 24.2

MSC: Remembering

OBJ: Explain the evidence that the human body is specifically made of star dust.

  1. Which of the following elements are not found in DNA molecules?
  2. carbon
  3. nitrogen
  4. hydrogen
  5. helium
  6. oxygen

ANS: D   DIF: Easy        REF: 24.2

MSC: Remembering

OBJ: Explain why carbon is favored as the, but is not the only, chemical basis of life.

  1. The atomic elements that make the structure of DNA are
  2. carbon, hydrogen, oxygen, nitrogen, and phosphorus.
  3. carbon, hydrogen, oxygen, nitrogen, and sulfur.
  4. sodium, chlorine, calcium, copper, zinc, and potassium.
  5. zinc, iodine, iron, calcium, and carbon.
  6. hydrogen, helium, carbon, nitrogen, and oxygen.

ANS: A   DIF: Medium  REF: 24.2

MSC: Remembering

OBJ: Explain why carbon is favored as, but is not the only, chemical basis of life.

  1. The atomic elements that make the structure of the amino acids are
  2. carbon, hydrogen, oxygen, nitrogen, and phosphorus.
  3. carbon, hydrogen, oxygen, nitrogen, and sulfur.
  4. sodium, chlorine, calcium, copper, zinc, and potassium.
  5. zinc, iodine, iron, calcium, and carbon.
  6. hydrogen, helium, carbon, nitrogen, and oxygen.

ANS: B   DIF: Medium  REF: 24.2

MSC: Remembering

OBJ: Explain why carbon is favored as, but is not the only, chemical basis of life.

  1. The most abundant elements manufactured by stars through nuclear reactions are
  2. iron, silicon, carbon, and sulfur.
  3. helium, carbon, nitrogen, and oxygen.
  4. zinc, iodine, iron, calcium, and carbon.
  5. carbon, hydrogen, oxygen, and phosphorus.
  6. carbon, iron, lithium, and argon.

ANS: B   DIF: Medium  REF: 24.2

MSC: Remembering

OBJ: Explain why carbon is favored as, but is not the only, chemical basis of life.

  1. Choose the incorrect statement about amino acids.
  2. They form proteins.
  3. They contain no more than five elements.
  4. Life forms on Earth use 20 specific amino acids.
  5. There are tens of types of amino acids that involve silicon-based chemistry.
  6. Amino acids have been synthesized from mixtures of water, methane, ammonia, and hydrogen. energized by electric sparks

ANS: D   DIF: Medium  REF: 24.2

MSC: Remembering

OBJ: Explain why carbon is favored as the, but is not the only, chemical basis of life.

  1. A second best atomic candidate conducive to complex molecules, possibly enabling biological life forms, is

ANS: D   DIF: Medium  REF: 24.2

MSC: Understanding

OBJ: Explain why carbon is favored as the, but is not the only, chemical basis of life.

  1. Which of the following sequences correctly ranks the numbers of atoms in the human body from highest to lowest?
  2. CONS
  3. CONP
  4. HOCN
  5. HOCP
  6. OHCN

ANS: C   DIF: Medium  REF: 24.2

MSC: Remembering

OBJ: Explain the evidence that the human body is specifically made of star dust.

  1. Carbon forms the backbone of our complex DNA structure primarily because
  2. it is the most abundant element in the universe after hydrogen and helium.
  3. it reacts easily with oxygen.
  4. it remains solid even at high temperatures.
  5. a carbon atom can bond with up to four other atoms at a time.
  6. it can form multiple types of crystal structures.

ANS: D   DIF: Difficult REF: 24.2

MSC: Understanding

OBJ: Explain the evidence that the human body is specifically made of star dust.

  1. The Drake equation estimates the number of
  2. exoplanets in the Milky Way
  3. exoplanets in their respective habitable zones
  4. extraterrestrial life forms within the Milky Way, capable of communication
  5. advanced civilizations that would self-destruct
  6. planets with a high Earth index of similarity (EIS)

ANS: C  DIF: Easy  REF: Working It Out 24.2

MSC: Understanding

OBJ: Use the Drake Equation to assess the probable number of intelligent civilizations in the Milky Way capable of communicating with us.

  1. A value of N =1 for the Drake equation signifies that
  2. one out of every 10 solar systems in our galaxy harbors intelligent life.
  3. one out of every 10 solar systems in our galaxy harbors life of some kind.
  4. one out of every 10 galaxies in our universe harbors intelligent life.
  5. one out of every 10 galaxies in our universe harbors life of some kind.
  6. approximately one intelligent civilization in the universe is created every 10 billion years.

ANS: C  DIF: Medium  REF: Working It Out 24.2

MSC: Applying

OBJ: Use the Drake Equation to assess the probable number of intelligent civilizations in the Milky Way capable of communicating with us.

  1. The field of astrobiology uses our knowledge of ___________ to study life in the universe.
  2. biology
  3. chemistry
  4. physics
  5. astronomy
  6. all of the above

ANS: E   DIF: Easy        REF: 24.3

MSC: Understanding

OBJ: Describe the conditions scientists believe are necessary for the evolution of life.

  1. Which of the following Solar System objects is not a good candidate for future searches for life?
  2. Mars, because it once had liquid water on the surface
  3. Jupiter’s moon Europa, because it appears to have liquid water under its frozen surface
  4. Saturn’s moon Titan, because it has an atmosphere containing many organic molecules
  5. Venus, because it can host extremophiles
  6. Saturn’s moon Enceladus, because its cryovolcanoes indicate that it has liquid water under the surface

ANS: D   DIF: Easy        REF: 24.3

MSC: Evaluating

OBJ: Compare and contrast the solar-system locations where scientists hope to find evidence for life.

  1. If we wanted to look for other civilizations within the Milky Way, where should we look?
  2. near high-mass stars, because they live longer
  3. near low-mass stars, because their habitable zones are farther from their stars
  4. near the galactic center, because the higher temperature makes life more likely
  5. far from the galactic center, because planets are less exposed to harmful gamma rays and X-rays coming from the galactic center
  6. in the halo of the Milky Way, because stars in the halo have more heavy elements than stars in the disk

ANS: D   DIF: Easy        REF: 24.3

MSC: Applying

OBJ: Describe a galactic habitable zone.

  1. Which of the following bodies in the Solar System lacks an atmosphere?
  2. Venus
  3. Mars
  4. Titan
  5. Europa
  6. Earth

ANS: D   DIF: Easy        REF: 24.3

MSC: Remembering

OBJ: Compare and contrast the solar-system locations where scientists hope to find evidence for life.

  1. If future exploration of the moons of Jupiter and Saturn discover primitive life forms, it would imply a __________ probability of finding an advanced civilization somewhere else in the Milky Way because ____________________________________.
  2. higher; it shows that life can exist in environments that are very different from those found on Earth
  3. higher; it would show that life can survive travel through space after leaving the Earth
  4. much lower; primitive life forms have nothing to do with the existence of advanced civilizations
  5. decreased; it would show that primitive life forms outside the Earth cannot evolve into more complex species
  6. decreased; it would show that primitive life forms are far more common than advanced ones

ANS: A   DIF: Medium  REF: 24.3

MSC: Understanding

OBJ: Assess whether we expect to find life outside of Earth.

  1. Based on what we know about the evolution of life on Earth, which of the planets shown in the figure below would be most likely to host an advanced civilization?
  2. Planet A
  3. Planet B
  4. Planet C
  5. Planet D
  6. Planet E

ANS: C   DIF: Medium  REF: 24.3

MSC: Applying

OBJ: Illustrate how the habitable zone changes for stars of different masses.

  1. Which of the following bodies of the Solar System shows the poorest evidence of water?
  2. Mercury
  3. Europa
  4. Enceladus
  5. Titan
  6. Mars

ANS: A   DIF: Medium  REF: 24.3

MSC: Evaluating

OBJ: Compare and contrast the Solar System locations where scientists hope to find evidence for life.

  1. Which of the following bodies of the Solar System has not yet been landed upon by spacecraft?
  2. Europa
  3. Titan
  4. Moon
  5. Mars
  6. Venus

ANS: A   DIF: Medium  REF: 24.3

MSC: Remembering

OBJ: Compare and contrast the Solar System locations where scientists hope to find evidence for life.

  1. Which of the following is not an essential property that would lead to a high Earth Similarity Index?
  2. distance from its star
  3. size
  4. density
  5. greenhouse effect
  6. age of central star

ANS: E   DIF: Medium  REF: 24.3

MSC: Understanding

OBJ: Illustrate how the habitable zone changes for stars of different masses.

  1. The Solar System body to which humans have dedicated the largest number of landing missions so far is

ANS: D   DIF: Medium  REF: 24.3

MSC: Remembering

OBJ: Compare and contrast the Solar System locations where scientists hope to find evidence for life.

  1. What does “habitable zone around a star” mean in the current framework of the search for exoplanets?
  2. the region around the star where the inhabitants of nearby planetary systems can safely visit
  3. the region around the star where planetary temperatures would not be too hot or too cold and liquid water could exist
  4. the region around the star where planets have icy moons
  5. the region around the star where planets can form an atmosphere
  6. the region around the star where intelligent civilization are not exposed to harmful doses of radiation

ANS: B   DIF: Medium  REF: 24.3

MSC: Understanding

OBJ: Illustrate how the habitable zone changes for stars of different masses.

  1. The ability of a celestial body to retain an atmosphere would depend mainly on which of the following properties?
  2. mass and size
  3. age and composition
  4. presence of life forms on it
  5. tilt of the axis of rotation
  6. period of rotation

ANS: A   DIF: Medium  REF: 24.3

MSC: Understanding

OBJ: Describe the conditions scientists believe are necessary for the evolution of life.

  1. Planets that are close to their stars may lack the day-night cycle due to
  2. having a large fraction of the sky covered by the stellar disk.
  3. being tidally locked.
  4. having short orbital periods.
  5. lacking an atmosphere.
  6. lacking moons.

ANS: B   DIF: Medium  REF: 24.3

MSC: Analyzing

OBJ: Compare and contrast the Solar System locations where scientists hope to find evidence for life.

  1. Scientists define the habitable zone in our Solar System as being (roughly) bracketed by the orbits of
  2. Mercury and Mars.
  3. Mercury and the main asteroid belt.
  4. Venus and Mars.
  5. Earth and Saturn.
  6. Earth and comets in the trans-Neptunian region.

ANS: C   DIF: Medium  REF: 24.3

MSC: Remembering

OBJ: Illustrate how the habitable zone changes for stars of different masses.

  1. The habitable zone for a 2M star is _____________ and covers a ______ distance range compared with the habitable zone for a 1M
  2. closer inward; narrower
  3. further outward; narrower
  4. further outward; wider
  5. closer inward; the same
  6. further outward; the same

ANS: C   DIF: Medium  REF: 24.3

MSC: Applying

OBJ: Illustrate how the habitable zone changes for stars of different masses.

  1. Why are the high-mass stars less likely to have planets with advanced/intelligent life forms?
  2. High-mass stars are short-lived; hence evolution has less time to happen.
  3. High-mass stars are too big, and their habitable zone is very narrow.
  4. High-mass stars are too hot, and their habitable zone is too far from them.
  5. High-mass stars are too blue, and intelligent life forms can see only white light.
  6. High-mass stars don’t form planets around them.

ANS: A   DIF: Difficult REF: 24.3

MSC: Analyzing

OBJ: Illustrate how the habitable zone changes for stars of different masses.

  1. Based on what you know of the Earth’s evolutionary timeline, what percent of Earthlike planets in a star cluster with an age of 2 billion years likely hosts intelligent life?
  2. 0
  3. 10 percent
  4. 30 percent
  5. 50 percent
  6. 100 percent

ANS: A   DIF: Difficult REF: 24.3

MSC: Applying

OBJ: Describe the conditions scientists believe are necessary for the evolution of life.

  1. What would be the main factors determining whether water can exist in a liquid state on the surface of a planet?
  2. the presence of photosynthetic and highly intelligent life forms
  3. the age and mass of the central star
  4. the atmospheric pressure and temperature on the planetary surface
  5. the color and temperature of the central star
  6. the existence of carbon-based biology

ANS: C   DIF: Difficult REF: 24.3

MSC: Applying

OBJ: Compare and contrast the Solar System locations where scientists hope to find evidence for life.

  1. The main goal of the Allen Telescope Array is to search for
  2. silicon-based life forms in other planetary systems,
  3. electromagnetic signals from civilizations inhabiting habitable planets,
  4. exoplanets in other galaxies,
  5. dark energy,
  6. artificial satellites drifting out of control around Earth,

ANS: B   DIF: Easy        REF: 24.4

MSC: Remembering

OBJ: Describe the methods currently being used to search for intelligent extraterrestrial life.

  1. We search for intelligent life in the universe most effectively by
  2. sending out spacecraft with messages on them.
  3. using radio telescopes to search for radio signals.
  4. monitoring ultraviolet radiation emitted by stars.
  5. sending spacecraft to explore other worlds.
  6. all of the above

ANS: B   DIF: Easy        REF: 24.4

MSC: Understanding

OBJ: Describe the methods currently being used to search for intelligent extraterrestrial life.

  1. SETI’s Allen Telescope Array is designed to search ___________ for signs of intelligent life.
  2. more than a thousand stars
  3. more than a million stars
  4. more than a billion stars
  5. galaxies in the Local Group
  6. the 100 closest spiral galaxies

ANS: B   DIF: Easy        REF: 24.4

MSC: Remembering

OBJ: Describe the methods currently being used to search for intelligent extraterrestrial life.

  1. What is the main impediment for interstellar travel?
  2. the high cost of technology enabling travel at the speed of light
  3. the fear of encountering hostile life-forms
  4. the well-kept secrecy about warp drive
  5. the instability of wormholes
  6. the current lack of know-how regarding how to travel at speeds approaching the speed of light

ANS: E   DIF: Easy        REF: 24.4

MSC: Evaluating

OBJ: Assess why it is unlikely that we will communicate with extraterrestrial beings.

  1. Nowadays, the number of confirmed exoplanets is approaching
  2. a dozen.
  3. 106.
  4. 2,000.
  5. 104.

ANS: C   DIF: Medium  REF: 24.3

MSC: Remembering

OBJ: Summarize the current state of our attempts to find life beyond Earth.

  1. When the Pioneer and Voyager spacecraft were launched into space in the 1970s, they were outfitted with messages describing where they came from. Why is it fairly unlikely that an alien civilization will use them to find us?
  2. The extremely large distances between stars means it will take a very long time before spacecraft reach another planetary system.
  3. They will probably rust and fall apart as they get older.
  4. They will burn up as the Sun’s gravity pulls them in.
  5. They will likely run into Kuiper Belt objects before they leave the Solar System.
  6. They are moving so fast through space that they would be very difficult to catch.

ANS: A   DIF: Medium  REF: 24.4

MSC: Applying

OBJ: Describe the methods currently being used to search for intelligent extraterrestrial life.

  1. In 1974, astronomers sent a message toward globular cluster M13. If life exists there, and it returns our signal, we won’t receive it for at least another 50,000 years. Why?
  2. It will take that long for the space probe carrying our signal to reach the life forms there.
  3. Based on the age of the stars in M13, we anticipate it would take that long for a civilization to evolve enough to interpret and respond to our signal.
  4. M13 is far enough away that even light takes a very long time to reach it.
  5. It will take that long before our Solar System and M13 are properly aligned again.
  6. The universe will have expanded substantially after M13 receives our message; therefore, it will take much longer for their response to make it back to Earth.

ANS: C   DIF: Medium  REF: 24.4

MSC: Applying

OBJ: Describe the methods currently being used to search for intelligent extraterrestrial life.

  1. People argue against the possibility of time travel by saying, “If humans will eventually be able to travel back in time, then where are all the tourists from the future?” This idea is similar to the ___________, only applied to time travel instead of alien space travel.
  2. Drake equation
  3. cosmological principle
  4. Fermi paradox
  5. Urey-Miller experiment
  6. evolutionary tree of life

ANS: C   DIF: Difficult REF: 24.4

MSC: Analyzing

OBJ: Assess why it is unlikely that we will communicate with extraterrestrial beings.

  1. If the most pessimistic assumptions in the Drake equation were true, we would
  2. have to wait for millions of years to get a message back from the nearest intelligent life.
  3. have to wait approximately 40 years to get a message back from the nearest intelligent life.
  4. be the only intelligent life in the universe.
  5. need to concentrate on the Andromeda Galaxy when searching for intelligent life.
  6. need to concentrate on the most distant galaxies to find signs of intelligent life.

ANS: A   DIF: Difficult REF: 24.4

MSC: Applying

OBJ: Assess why it is unlikely that we will communicate with extraterrestrial beings.

SHORT ANSWER

  1. Briefly explain why astrobiology is a highly interdisciplinary field.

ANS: Astrobiology is only apparently (by name) an oversimplified combination of two disciplines: astronomy and biology. A few other sciences actually profoundly interconnect with the area of astrobiology: chemistry, geology, and, of course, physics. The search for life first involves understanding what life means from a biological standpoint, and how it arises, evolves, adapts, survives, and reproduces in changing environments. The study of complex molecular structures ties into chemistry, the search for habitable worlds brings in the science of astronomy, understanding how planets and moons evolve emerges into geology, etc., just to give a few examples.

DIF: Easy  REF: 24.1  MSC: Analyzing

OBJ: Summarize the evolution of life from its first origins on Earth until today.

  1. What is the origin of the atmospheric oxygen on planet Earth?

ANS: The origin of the atmospheric oxygen on Earth is related to photosynthetic organisms, starting with the ancient cyanobacteria. The current levels of oxygen were reached about 250 million years ago, following the Cambrian explosion, the appearance of first plants and large forests.

DIF: Easy  REF: 24.1  MSC: Analyzing

OBJ: Summarize the evolution of life from its first origins on Earth until today.

  1. Describe the experiment depicted in the figure shown below. What was the goal of the experiment? Was the experiment a success?

ANS: This image shows the Urey-Miller experiment performed in the early 1950s. The goal of the experiment was to simulate the conditions in the primitive atmosphere of a young Earth. The experiment successfully showed that the energy provided by sparks (simulating lightning) triggered a series of chemical reactions that permitted the formation of amino acids and components of nucleic acids, which are fundamental molecular blocks of biological life forms.

DIF: Medium  REF: 24.1  MSC: Applying

OBJ: Compare and contrast the major theories presented in this text of how life originated on Earth.

  1. What determines whether or not a specific mutation is passed on to future generations?

ANS: Mutations can be either good or bad for a species. When a mutation occurs and it increases the survival and reproduction chance (i.e., rate) of the organism then that advantageous mutation is more likely carried on to future generations.

DIF: Medium  REF: 24.1  MSC: Understanding

OBJ: Establish why mutation and heredity lead to evolution.

  1. Explain what is meant by organisms that are extremophiles.

ANS: Extremophiles are organisms (microbes, bacteria, etc.) that have been found to thrive (survive and reproduce) in environments that would pose a threat to the large majority of life forms; for example, scientists have discovered organisms that live in highly acidic or unusually high temperatures or in places completely hidden from sunlight, etc. Such cases are a direct indication that evolution can take unexpected turns in a struggle for survival in otherwise hostile environments.

DIF: Medium  REF: 24.1  MSC: Remembering

OBJ: Explain why the earliest forms of life on Earth must have been extremophiles.

  1. If the entire history of the Solar System were scaled to fit into one day, what time of day would microorganisms first form, oxygen start becoming a significant component of the atmosphere, and humans split off from their genetic ancestors?

ANS: The Earth is 4.6 billion years old. Microorganisms have existed for at least 3.5 billion years ago, so in our rescaled timeframe that event occurs at (4.6 − 3.5)/ 4.5 × 24 hr = 5.87 hr or 5:52 A.M. Oxygen began to fill the atmosphere about 2 billion years ago, so in our scaled day that would occur at (4.6 − 2)/4.6 × 24 hrs = 13.56 hr or 1:36 P.M. Humans evolved approximately 6 million years ago, so in our scaled day that would occur at (4.6 − 0.006)/4.6 × 24 hr = 23.97 hr or 11:58 P.M.

DIF: Difficult  REF: 24.1  MSC: Applying

OBJ: Summarize the evolution of life from its first origins on Earth until today.

  1. Discuss one possibility considered by scientists to explain the migration of life from sea to land during the epoch preceding the Cambrian era.

ANS:

  • The “Snowball Earth” scenario proposes that Earth underwent a phase of extremely cold temperatures a couple hundred million years prior to the Cambrian era. The extreme cold lead to a severe decline or even extinction of predatory animals, which allowed new species to adapt, survive, and reproduce.
  • With a significant increase in atmospheric oxygen, the production of ozone in the stratosphere was also favored. The ozone played a protective role against the harmful UV solar radiation, and organisms could migrate from sea to land.

DIF: Difficult  REF: 24.1  MSC: Understanding

OBJ: Summarize the evolution of life from its first origins on Earth until today.

  1. Explain why in a self-replicating system (e.g., bacterial populations) in which a member would copy itself every minute, even mutations that have only a slim rate of occurrence could still significantly improve the survival chance of the system.

ANS: If the doubling time by self-replication is one minute, it implies that in one hour alone the population would consist of Pf = Po × 260, which means a growth factor of the order of 1018. Even if mutations have slim chances of occurrence (fractions of a percent) and beneficial ones would even be many orders of magnitude more rare, the number of members in the system is so large that overall the changes can still be numerically significant and impactful towards the survival of the population. Over very many generations, the effects of even a small difference in selective advantage becomes important enough for a rare mutation to become the dominant type. Of course this happens faster when there is a large selective advantage.

DIF: Difficult  REF: Working It Out 24.1   MSC: Applying

OBJ: Calculate population changes using exponential growth.

  1. What would be the main advantages and disadvantages of silicon-based chemistry for alien life forms?

ANS: Silicon, just like carbon, could have four simultaneous bonds with other atoms, which means it could create large numbers of chemical combinations. Scientists indicate that Si-bonds can survive at temperature higher than those that would break the C-based ones. This could mean that potential biological structures employing Si-based chemistry might survive and thrive in more extreme temperature environments—for instance, on planets otherwise too close to their parent stars. Silicon, however, has a higher atomic mass and size, and it cannot produce the complexity specific to C-based molecular structures. This may suggest that Si-based life forms should be simpler than those based on C-structures.

DIF: Easy  REF: 24.2  MSC: Analyzing

OBJ: Explain why carbon is favored as the, but is not the only, chemical basis of life.

  1. If the DNA contains only five different atomic species, how do we explain the diversity of life forms on Earth?

ANS: The atoms are combined in billions of ways, which ensures the huge diversity of life forms on planet Earth.

DIF: Easy            REF: 24.2        MSC: Understanding

OBJ: Explain why carbon is favored as the, but is not the only, chemical basis of life.

  1. What are the four main elements that make up all living organisms on the Earth?

ANS:

CHON: carbon, hydrogen, oxygen, and nitrogen

DIF: Easy  REF: 24.2  MSC: Remembering

OBJ: Explain the evidence that the human body is specifically made of star dust.

  1. Explain why scientists think we are specifically made of star stuff, or, more poetically that humans are the “children of stars.”

ANS: Although this specific discussion was also presented in an earlier chapter, it is worth emphasizing that (1) carbon, oxygen, and nitrogen rank second, third, and fourth after hydrogen in terms of count of atoms in the human body, and the same three elements are also the most common products of stellar nucleosynthesis after helium, and (2) the backbone of our DNA and amino acids involve four of the five most abundant elements in the universe symbolized by C H O N. The small amounts of other (more massive) atomic species, like Fe or even heavier, participating in the biochemistry of the human body are also the product of stellar “alchemy,” being produced by core fusion (up to iron) or during supernovae, as shown in an earlier chapter.

DIF: Difficult  REF: 24.2  MSC: Understanding

OBJ: Explain the evidence that the human body is specifically made of star dust.

  1. Name three main dangers (one human and two astrophysical) that could threaten the continued existence of human life on Earth.

ANS: Some examples include the following:

  • The Sun’s evolving to become a red giant and burning away the Earth’s atmosphere.
  • A large asteroid or comet hitting the Earth, although some life, even if it were in primitive form, might survive even a large collision.
  • human overpopulation and overuse of natural resources
  • increasing carbon emission leading to global warming
  • wars

DIF: Easy  REF: Working It Out 24.2

MSC: Understanding

OBJ: Use the Drake Equation to assess the probable number of intelligent civilizations in the Milky Way capable of communicating with us.

  1. In Drake’s equation, what factors would be more robustly constrained by the study of reasonable large samples of exoplanets?

ANS: The increasing number of discovered planetary systems and exoplanets help scientists to better constrain and statistically refine factors like fp—the fraction of stars that form planetary systems; to a lesser extent ne—the number of planets and moons in each planetary system with an environment suitable for life—could be further evaluated, although the search for moons orbiting exoplanets is in its infancy.

DIF: Difficult  REF: Working It Out 24.2

MSC:  Analyzing

OBJ: Use the Drake Equation to assess the probable number of intelligent civilizations in the Milky Way capable of communicating with us.

  1. As our sun ages, it slowly gets brighter. For example, the Sun is about 30 percent brighter than it was in its infancy, 4.5 billion years ago, and it will become about 30 percent in the next 3 billion years or so. Explain how this would affect the definition of a habitable zone in our Solar System.

ANS: If the Sun gets brighter, the Earth intercepts more photons per unit time and it is warming up. The water evaporation rate would speed up. Therefore, the habitable zone, where stable liquid water would be possible, would move further out and would cover a wider radial domain.

DIF: Easy  REF: 24.3  MSC: Applying

OBJ: Describe the conditions scientists believe are necessary for the evolution of life.

  1. Why would scientists consider that microbes are unlikely to exist on the surface of Mars?

ANS: Mars has a very cold environment and a very thin atmosphere, which implies a very low surface pressure. The extreme cold is unfavorable to survival of life forms, but even more harmful is the almost direct exposure to harmful cosmic rays and high energy photons.

DIF: Easy  REF: 24.3  MSC: Evaluating

OBJ: Compare and contrast the solar-system locations where scientists hope to find evidence for life.

  1. How is the Planetary Habitability Index (PHI) different than the Earth Similarity Index (ESI)?

ANS: The PHI is a broader measure of habitability, departing from the constraints of the unique template Earth. It is a broader measure of habitability, accounting for:

  1. i) does the planet has a surface suitable for organisms to grow?
  2. ii) what is the source of energy?
  • iii) is there a solvent in a liquid state?
  1. iv) what type of chemistry is at play?

As of now, however, it is still poorly constrained because of insufficient measurements of exoplanets properties.

DIF: Easy  REF: 24.3  MSC: Understanding

OBJ: Describe the methods currently being used to search for life in the Solar System.

  1. Explain how the discovery of life on another body of our own Solar System would change our perspective on life elsewhere in the universe.

ANS: The discovery of even primitive life forms on another body of the Solar System would be beyond significant, because that would constitute direct evidence that life can arise independently twice within the same system. Such an event would imply that the odds of life arising elsewhere in the universe are much higher than currently estimated.

DIF: Easy  REF: 24.3  MSC: Evaluating

OBJ: Describe the methods currently being used to search for life in the Solar System.

  1. What stars, in terms of mass, are preferred by scientists in the search for highly evolved life-forms and why?

ANS: Based on our understanding of life on Earth, highly advanced life-forms are the outcome of very long periods of evolution, of the order of a few billion years. The higher the stellar mass, the shorter is its main sequence existence, and, in turn, the shorter is the timeframe and the lower the chance for intelligent life forms to emerge in the evolutionary sequence. Since even a 3 M star would have its lifespan of the order of a few hundred million years, scientists would rather prefer the 0.6−1.4 M range, where stars’ lifespans are of the order of billions of years. Note that the habitable zone of small (and thus very cool) stars is so close to the star that planets in the habitable zone are more likely to be tidally locked.

DIF: Medium  REF: 24.3  MSC: Understanding

OBJ: Describe the conditions scientists believe are necessary for the evolution of life.

  1. If you wanted to find intelligent life in the universe, what spectral types of stars would you prioritize for study and why?

ANS: The driving argument is that it took approximately 4.5 billion years for advanced/complex life to develop on Earth; therefore, one should search G- and K-type stars (and later types) because their main- sequence lifetimes are at least that long.

DIF: Medium  REF: 24.3  MSC: Applying

OBJ: Describe the conditions scientists believe are necessary for the evolution of life.

  1. Explain why the presence of oxygen in a planetary atmosphere is not a definitive marker for the presence of life on that body.

ANS: The atmospheric oxygen on our planet is linked to the photosynthetic organisms. The dissociation of water molecules, however, could also produce free oxygen that can accumulate in an atmospheric layer around a planet or moon.

DIF: Medium  REF: 24.3  MSC: Understanding

OBJ: Describe the conditions scientists believe are necessary for the evolution of life.

  1. What makes Titan an attractive target in the search for life-forms?

ANS: Titan has a thick atmosphere rich in organic compounds and has extended lakes of liquid methane on its surface. Scientists also suspect that an under- surface (liquid) water ocean also exists.

DIF: Medium  REF: 24.3  MSC: Applying

OBJ: Compare and contrast the solar-system locations where scientists hope to find evidence for life.

  1. Planet Kepler 438-b is currently ranked as number 1 on the scale of Earth Similarity Index (ESI =88). It orbits the central star at an average distance of 0.166 A.U Based on the figure below, what would be the temperature and spectral type of the central star?

ANS: The high ESI value clearly indicates that the planet is inside the habitable zone (green area) of its star. The average distance of 0.166 AU. would imply that the planet orbits a star with an estimated temperature of about 3500 K, likely of type K transitioning towards M.

DIF: Difficult  REF: 24.3  MSC: Applying

OBJ: Illustrate how the habitable zone changes for stars of different masses.

  1. What are the basic requirements for life, based on the Earth-bound template we have available?

ANS: Life forms can arise and develop if there is a source of energy available (e.g., starlight), complex chemistry is possible (e.g., C-based or Si-based) and there is a liquid solvent (e.g., water) favorable to chemical reactions.

DIF: Difficult  REF: 24.3  MSC: Applying

OBJ: Describe the conditions scientists believe are necessary for the evolution of life.

  1. What kinds of interesting objects potentially hosting life would be omitted if the search is exclusively focused on planets orbiting within the habitable zones of their stars?

ANS: Based on what we know from our own Solar System, there are moons orbiting Jupiter (e.g., Europa) and Saturn (e.g., Titan, Enceladus) whose environments could harbor primitive life forms. From the diversity of planetary systems discovered in the last decade or so, we know that there should be numerous planets that don’t orbit their parent stars anymore; they have been flung out from their original system. Such planets are very difficult to detect, however. There are also planets that orbit binary stellar systems in a complex “choreography” and the corresponding habitable zone would be much more difficult to define.

DIF: Difficult  REF: 24.3  MSC: Evaluating

OBJ: Assess whether we expect to find life outside of Earth.

  1. What is SETI, what is its main objective, and how does it plan to achieve it?

ANS: SETI stands for Search for Extraterrestrial Intelligence. Its main objective is to search for intelligent life in the universe using radio telescopes to detect non-natural emission from intelligent life at radio wavelengths.

DIF: Easy  REF: 24.4  MSC: Remembering

OBJ: Describe the methods currently being used to search for intelligent extraterrestrial life.

  1. Explain why the Pioneer plaques and the Voyager phonograph records are rather symbolic attempts at communication with extraterrestrial intelligent life forms?

ANS: Consider the fact that the nearest star is about 4.3 ly away. The interstellar cruising speed of Voyager is about 10.5 mi/s, which would require more than 76,000 years for a one-way trip. So, the fate of Pioneer and Voyager spacecrafts would be to drift through space for many, many years. . . Communication via electromagnetic radiation is by far the best we can hope for.

DIF: Easy  REF: 24.4  MSC: Understanding

OBJ: Assess why it is unlikely that we will communicate with extraterrestrial beings.

  1. How is Drake’s equation different from the typical equations we encounter in science textbooks?

ANS: Drake’s equation contains very uncertain variables. While it is a very useful way to break the complex problem of estimating the likelihood of extraterrestrial civilizations capable of communication, its seven factors follow a sequence of increased uncertainty being based on a great deal of assumptions.

DIF: Easy  REF: 24.4  MSC: Evaluating

OBJ: Assess why it is unlikely that we will communicate with extraterrestrial beings.

  1. Why are radio waves considered the optimum spectral domain to deliver and search for signals to/from extraterrestrial intelligent life forms?

ANS: As we learned in a previous chapter, radio waves easily penetrate the dust and gas of the interstellar medium and thus travel long distances without being absorbed.

DIF: Easy  REF: 24.4  MSC: Applying

OBJ: Describe the methods currently being used to search for intelligent extraterrestrial life.

  1. What is the so-called Fermi paradox?

ANS: The Fermi paradox essentially summarizes the apparent conundrum of scientists: if intelligent life in the universe is common, why is communication between worlds not happening . . . or at least why has it not been witnessed or confirmed yet? Humans have been broadcasting electromagnetic signals for about 80 years, which means that they have covered only about 80 light-years so far. Note that there are about 2,000 catalogued stars within a radius of 50 light-years around us. There is no scientific evidence that aliens have communicated with us via electromagnetic radiation or that they have physically visited our planet or neighborhood.

DIF: Medium  REF: 24.4  MSC: Understanding

OBJ: Assess why it is unlikely that we will communicate with extraterrestrial beings.

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