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The Essential Cosmic Perspective

Jeffrey Bennett, Megan Donahue, Nicholas Schneider

Chapter 9

Asteroids, Comets, and Dwarf Planets: Their Nature, Orbits, and Impacts - all with Video Answers

Educators

Chapter Questions

00:40

Problem 1

Briefly define asteroid, comet, dwarf planet, meteor, and meteorite. How did the discovery of Eris force astronomers to reconsider the definition of planet?

Zachary Warner
Zachary Warner
Numerade Educator
04:56

Problem 2

How large are asteroids? How does the total mass of all asteroids compare to the mass of a terrestrial world?

Rashmi Sinha
Rashmi Sinha
Numerade Educator
01:07

Problem 3

Distinguish between primitive meteorites and processed meteorites in terms of both composition and origin.

Rodger Claar
Rodger Claar
Numerade Educator
00:54

Problem 4

What do meteorites and spacecraft observations tell us about the geology of asteroids?

William Dunkerton
William Dunkerton
Numerade Educator
01:22

Problem 5

Where is the asteroid belt located, and why? Explain how orbital resonances with Jupiter affect the asteroid belt.

Banhishikha Sinha
Banhishikha Sinha
Numerade Educator
00:26

Problem 6

What produces the coma and tails of a comet? What is the mucleus? Why do the tails point away from the Sun?

Zachary Warner
Zachary Warner
Numerade Educator
02:07

Problem 7

How are meteor showers linked to comets, and why do they recur at about the same time each year?

Shital Rijal
Shital Rijal
Numerade Educator
00:38

Problem 8

Describe the Kuiper belt and Oort cloud in terms of their locations and the orbits of comets within them. How did comets come to exist in these two regions?

Zachary Warner
Zachary Warner
Numerade Educator
00:46

Problem 9

Briefly describe Pluto and Charon. Why won't Pluto collide with Neptune? How do we think Charon formed?

Zachary Warner
Zachary Warner
Numerade Educator
01:31

Problem 10

Briefly describe the evidence suggesting that an impact caused the mass extinction that killed off the dinosaurs. How might the impact have led to the mass extinction?

Zachary Warner
Zachary Warner
Numerade Educator
01:23

Problem 11

How often should we expect impacts of various sizes on Earth? How serious a threat do we face from these impacts?

Michael Sorola
Michael Sorola
Numerade Educator
01:10

Problem 12

Briefly summarize the role of the jovian planets in shaping the orbits of small bodies in the solar system and in influencing life on Earth.

Jheremiah Simon
Jheremiah Simon
Numerade Educator
00:39

Problem 13

Suppose someone claimed to make the discoveries described below. (These are not real discoveries.) Decide whether each discovery should be considered reasonable or surprising. More than one right answer may be possible, so explain your answer clearly.
A small asteroid that orbits within the asteroid belt has an active volcano.

Liuxi Sun
Liuxi Sun
Numerade Educator
00:29

Problem 14

Suppose someone claimed to make the discoveries described below. (These are not real discoveries.) Decide whether each discovery should be considered reasonable or surprising. More than one right answer may be possible, so explain your answer clearly.
Scientists discover a meteorite that, based on radiometric dating is 7.9 billion years old.

Zachary Warner
Zachary Warner
Numerade Educator
01:30

Problem 15

Suppose someone claimed to make the discoveries described below. (These are not real discoveries.) Decide whether each discovery should be considered reasonable or surprising. More than one right answer may be possible, so explain your answer clearly.
An object that resembles a comet in size and composition is discovered orbiting in the inner solar system.

Matthew Miranda
Matthew Miranda
Numerade Educator
00:48

Problem 16

Suppose someone claimed to make the discoveries described below. (These are not real discoveries.) Decide whether each discovery should be considered reasonable or surprising. More than one right answer may be possible, so explain your answer clearly.
Studies of a large object in the Kuiper belt reveal that it is made almost entirely of rocky (as opposed to icy) material.

Shoukat Ali
Shoukat Ali
Other Schools
01:30

Problem 17

Suppose someone claimed to make the discoveries described below. (These are not real discoveries.) Decide whether each discovery should be considered reasonable or surprising. More than one right answer may be possible, so explain your answer clearly.
Astronomers discover a previously unknown comet that will be brightly visible in our night sky about 2 years from now.

Matthew Miranda
Matthew Miranda
Numerade Educator
02:17

Problem 18

Suppose someone claimed to make the discoveries described below. (These are not real discoveries.) Decide whether each discovery should be considered reasonable or surprising. More than one right answer may be possible, so explain your answer clearly.
A mission to Eris finds that it has lakes of liquid water on its surface.

Rodger Claar
Rodger Claar
Numerade Educator
00:29

Problem 19

Suppose someone claimed to make the discoveries described below. (These are not real discoveries.) Decide whether each discovery should be considered reasonable or surprising. More than one right answer may be possible, so explain your answer clearly.
Geologists discover a crater from a 5 -kilometer object that impacted Earth more than 100 million years ago.

Zachary Warner
Zachary Warner
Numerade Educator
00:49

Problem 20

Suppose someone claimed to make the discoveries described below. (These are not real discoveries.) Decide whether each discovery should be considered reasonable or surprising. More than one right answer may be possible, so explain your answer clearly.
Archaeologists learn that the fall of ancient Rome was caused in large part by an asteroid impact in Asia.

Zachary Warner
Zachary Warner
Numerade Educator
00:48

Problem 21

Suppose someone claimed to make the discoveries described below. (These are not real discoveries.) Decide whether each discovery should be considered reasonable or surprising. More than one right answer may be possible, so explain your answer clearly.
In another solar system, astronomers discover an object the size of Earth orbiting its star at the distance of the Kuiper belt.

Shoukat Ali
Shoukat Ali
Other Schools
04:48

Problem 22

Suppose someone claimed to make the discoveries described below. (These are not real discoveries.) Decide whether each discovery should be considered reasonable or surprising. More than one right answer may be possible, so explain your answer clearly.
Astronomers discover an asteroid with an orbit suggesting that it will impact Earth in the year 2064.

Jason Taylor-Pestell
Jason Taylor-Pestell
Numerade Educator
00:45

Problem 23

Choose the best answer to each of the following. Explain your reasoning with one or more complete sentences.
The asteroid belt lies between the orbits of (a) Earth and Mars. (b) Mars and Jupiter. (c) Jupiter and Saturn.

Zachary Warner
Zachary Warner
Numerade Educator
02:32

Problem 24

Choose the best answer to each of the following. Explain your reasoning with one or more complete sentences.
Jupiter nudges the asteroids through the influence of (a) tidal forces. (b) orbital resonances. (c) magnetic fields.

Sarah Mccrumb
Sarah Mccrumb
Numerade Educator
00:55

Problem 25

Choose the best answer to each of the following. Explain your reasoning with one or more complete sentences.
Can an asteroid be pure metal? (a) No; all asteroids contain rock. (b) Yes; it must have formed where only metal could condense in the solar nebula. (c) Yes; it must be from the core of a shattered asteroid.

Liuxi Sun
Liuxi Sun
Numerade Educator
00:55

Problem 26

Choose the best answer to each of the following. Explain your reasoning with one or more complete sentences.
Did a large terrestrial planet ever form in the region of the asteroid belt? (a) No, because there was never enough mass there. (b) No, because Jupiter prevented one from accreting. (c) Yes, but it was shattered by a giant impact.

Liuxi Sun
Liuxi Sun
Numerade Educator
02:00

Problem 27

Choose the best answer to each of the following. Explain your reasoning with one or more complete sentences.
What does Pluto most resemble? (a) a terrestrial planet (b) a jovian planet (c) a comet.

Matthew Miranda
Matthew Miranda
Numerade Educator
00:52

Problem 28

Choose the best answer to each of the following. Explain your reasoning with one or more complete sentences.
How big an object causes a typical "shooting star"? (a) a grain of sand or a small pebble (b) a boulder (c) an object the size of a car.

Matthew Miranda
Matthew Miranda
Numerade Educator
06:59

Problem 29

Choose the best answer to each of the following. Explain your reasoning with one or more complete sentences.
Which have the most elliptical and tilted orbits? (a) asteroids (b) Kuiper belt comets (c) Oort cloud comets

Zachary Warner
Zachary Warner
Numerade Educator
06:59

Problem 30

Choose the best answer to each of the following. Explain your reasoning with one or more complete sentences.
Which are thought to have formed farthest from the Sun?
(a) asteroids (b) Kuiper belt comets (c) Oort cloud comets

Zachary Warner
Zachary Warner
Numerade Educator
11:16

Problem 31

Choose the best answer to each of the following. Explain your reasoning with one or more complete sentences.
About how often does a 1 -kilometer object strike Earth?
(a) every year (b) every million years (c) every billion years

DM
Debra Mangion
Numerade Educator
01:05

Problem 32

Choose the best answer to each of the following. Explain your reasoning with one or more complete sentences.
What would happen if a 1-kilometer object struck Earth? (a) It would break up in the atmosphere without causing widespread damage. (b) It would cause widespread devastation and climate change. (c) It would cause a mass extinction.

Danielle Ashley
Danielle Ashley
Numerade Educator
00:40

Problem 33

The Pluto Debate. Research the decision to demote Pluto to dwarf planet. In your opinion, is this a good example of the scientific process? Does it exhibit the hallmarks of science described in Chapter $3 ?$ Compare your conclusions to opinions you find about the debate, and describe how you think astronomers should handle this or similar debates in the future.

Zachary Warner
Zachary Warner
Numerade Educator
02:18

Problem 34

Life or Death Astronomy. In most cases, the study of the solar system has little direct effect on our lives. But the discovery of an asteroid or comet on a collision course with Earth is another matter. How should the standards for verifiable observations described in Chapter 3 apply in this case? Is the potential danger so great that any astronomer with any evidence of an impending impact should spread the word as soon as possible? Or is the potential for panic so great that even higher standards of verification ought to be applied? What kind of review process, if any, would you set in place? Who should be informed of an impact threat, and when?

William Dunkerton
William Dunkerton
Numerade Educator
03:15

Problem 35

Assessing Impact Danger. Roles: Scribe (collects data and takes
notes on the group's activities), Proposer (proposes hypotheses and explanations of the data), Skeptic (points out weaknesses in the hypotheses and explanations), Moderator (leads group discussion and makes sure everyone contributes). Activity:
Assess the risks we face on Earth from meteorite and comet impacts as follows.
a. Consider the question of the odds that human civilization will be destroyed by an impact during your lifetime. Determine the kinds of information you would need, develop a method for making the estimate, and write down your method.
b. Analyze Figure 9.27 and determine whether it contains any of the necessary information.
c. Apply your group's method to estimate the probability that civilization will be destroyed by an impact during your lifetime, which you can assume to be 100 years for the purpose of this exercise
d. Estimate the probability that an impact will cause "widespread devastation" somewhere on Earth during your lifetime.
e. Finding near-Earth asteroids early greatly increases our chances of deflecting them. Given the probabilities from parts cand d and considering the damage these events would cause, decide as a group how much money per year should be spent on finding near-Earth asteroids and explain your reasoning.

Lourence Gonhovi
Lourence Gonhovi
Numerade Educator
00:45

Problem 36

The Role of Jupiter. Suppose that Jupiter had never existed. Describe at least three ways in which our solar system would be different, and clearly explain why.

Jheremiah Simon
Jheremiah Simon
Numerade Educator
04:03

Problem 37

Life Story of an Iron Atom. Imagine that you are an iron atom in a processed meteorite made mostly of iron. Tell the story of how you got to Earth, beginning from the time you were part of the gas in the solar nebula 4.6 billion years ago. Include as much detail as possible. Your story should be scientifically accurate but also creative and interesting.

Ibrahim Abdullahi
Ibrahim Abdullahi
Numerade Educator
01:41

Problem 38

Asteroids vs. Comets. Contrast the compositions and locations of comets and asteroids, and explain in your own words why they have turned out differently.

Rodger Claar
Rodger Claar
Numerade Educator
00:26

Problem 39

Comet Tails. Describe in your own words why comets have tails. Why do most comets have two distinct visible tails, and why do the tails go in different directions? Why is the third, invisible tail of small pebbles of interest to us on Earth?

Zachary Warner
Zachary Warner
Numerade Educator
00:38

Problem 40

Oort Cloud vs. Kuiper Belt. Explain in your own words how and why there are two different reservoirs of comets. Be sure to discuss where the two groups of comets formed and what kinds of orbits they travel on.

Zachary Warner
Zachary Warner
Numerade Educator
01:17

Problem 41

Project: Dirty Snowballs. If there is snow where you live or study. make a dirty snowball. (The ice chunks that form behind tires work well.) How much dirt does it take to darken snow? Find out by allowing your dirty snowball to melt in a container and measuring the approximate proportions of water and dirt afterward.

Rupsa Sarkar
Rupsa Sarkar
Numerade Educator
04:56

Problem 42

Be sure to show all calculations clearly and state your final answers in complete sentences.
Adding Up Asteroids. It's estimated that there are a million asteroids 1 kilometer across or larger. If a million asteroids kilometer across were all combined into one object, how big would it be? How many I-kilometer asteroids would it take to make an object as large as Earth? (Hint: You can assume they're spherical. The expression for the volume of a sphere is $\frac{4}{3} \pi r^{3}$ where $r$ is the radius.).

Rashmi Sinha
Rashmi Sinha
Numerade Educator
03:01

Problem 43

Be sure to show all calculations clearly and state your final answers in complete sentences.
Impact Energies. A relatively small impact crater 20 kilometers in diameter could be made by a comet 2 kilometers in diameter traveling at 30 kilometers per second $(30,000 \mathrm{m} / \mathrm{s})$
a. Assume that the comet has a total mass of $4.2 \times 10^{12}$ kilograms. What is its total kinetic energy? (Hint: The kinetic energy is equal to $\frac{1}{2} m v^{2}$, where $m$ is the comet's mass and $v$ is its speed. If you use mass in kilograms and velocity in $\mathrm{m} / \mathrm{s}$, the answer for kinetic energy will have units of joules.
b. Convert your answer from part a to an equivalent in megatons of TNT, the unit used for nuclear bombs. Comment on the degree of devastation such a comet could cause if it struck a populated region on Earth. (Hint: One megaton of TNT releases $4.2 \times 10^{15}$ joules of energy.

Dharmendra Jain
Dharmendra Jain
Numerade Educator
03:15

Problem 44

Be sure to show all calculations clearly and state your final answers in complete sentences.
The "Near Miss" of Toutatis. The 5-kilometer asteroid Toutatis passed a mere 1.5 million kilometers from Earth in 2004 Suppose Toutatis were destined to pass somewhere within 1.5 million kilometers of Earth. Calculate the probability that this "somewhere" would have meant that it slammed into Earth. Based on your result, do you think it is fair to call the 2004 passage a "near miss"? Explain. (Hint: You can calculate the probability by considering an imaginary dartboard of radius 1.5 million kilometers in which the bull's-eye has Earth's radius, 6378 kilometers.).

Lourence Gonhovi
Lourence Gonhovi
Numerade Educator
04:56

Problem 45

Be sure to show all calculations clearly and state your final answers in complete sentences.
Room to Roam. It's estimated that there are a trillion comets in the Oort cloud, which extends out to about 50,000 AU. What is the total volume of the Oort cloud, in cubic AU? How much space does each comet have in cubic AU, on average? Take the cube root of the average volume per comet to find the comets' typical spacing in AU. (Hints: For the purpose of this calculation, you can assume the Oort cloud fills the whole sphere out to 50,000 AU. The volume of a sphere is given by $\frac{4}{3} \pi r^{3}$, where $r$ is the radius.

Rashmi Sinha
Rashmi Sinha
Numerade Educator
04:56

Problem 46

Be sure to show all calculations clearly and state your final answers in complete sentences.
Comet Dust Accumulation. A few hundred tons of comet dust are added to Earth daily from the millions of meteors that enter our atmosphere. Estimate the time it would take for Earth to get $0.1 \%$ heavier at this rate. Is this mass accumulation significant for Earth as a planet? Explain.

Rashmi Sinha
Rashmi Sinha
Numerade Educator
01:09

Problem 47

Rise of the Mammals. Suppose the impact 65 million years ago had not occurred. How do you think our planet would be different? For example, do you think that mammals still would eventually have come to dominate Earth? Would we be here? Defend your opinions.

William Dunkerton
William Dunkerton
Numerade Educator
00:40

Problem 48

How Should Kids Count Planets? The demotion of Pluto from planet to dwarf planet affected many teachers because they had to change from talking about nine planets to eight, and even a decade after the demotion many teachers still haven't fully accepted it. Should they? How would you recommend that school teachers deal with the new definitions? Be sure to consider both alternative definitions and the fact that it remains possible that the International Astronomical Union may change the definitions again in the future.

Zachary Warner
Zachary Warner
Numerade Educator
01:41

Problem 49

Asteroid and Comet Missions. Learn about a current or planned space mission to study asteroids or comets. What are its scientific goals? Write a one- to two-page summary of your findings.

Rodger Claar
Rodger Claar
Numerade Educator
02:18

Problem 50

Impact Hazards. Many groups are searching for near-Earth asteroids that might impact our planet. They use something called the Torino Scale to evaluate the possible danger posed by an asteroid based on how well we know its orbit. What is this scale? What object has reached the highest level on this scale? What were the estimated chances of impact, and when?

William Dunkerton
William Dunkerton
Numerade Educator
07:21

Problem 51

Beneficial Asteroids. Learn about one of several efforts under way to mine asteroids for human benefit. How far along are the efforts? Discuss the issues that will determine if they succeed.

LA
Lazarus Arnau
Numerade Educator