Chapter 12

Conceptual Quiz
Part A
How does the largest asteroid, Ceres, compare in size to the planets?
Hint A.1
Study Section 12.1
ANSWER:

It is smaller than the terrestrial planets but larger than Pluto. It is about the size of a terrestrial planet. It is no larger than a typical mountain on one of the terrestrial planets. It is about half the diameter of Pluto, the smallest planet.
Part B
If we could put all the asteroids together, their total mass would be ______.
Hint B.1
Study Section 12.1
ANSWER:

about the mass of Mercury much less than the mass of any terrestrial planet. greater than the mass of Earth but less than the mass of Jupiter about the mass of Earth
Part C
Why isn't there a planet where the asteroid belt is located?
Hint C.1
Study Section 12.1
ANSWER:

The temperature in this portion of the solar nebula was just right to prevent rock from sticking together. There was too much rocky material to form a terrestrial planet, but not enough gaseous material to form a jovian planet. Gravitational tugs from Jupiter prevented material from collecting together to form a planet. There was not enough material in this part of the solar nebula to form a planet.
Part D
Gaps in the asteroid belt (often called Kirkwood gaps) are caused by ______.
Hint D.1
Study Section 12.1
ANSWER:

tidal forces from the Sun. orbital resonances with Jupiter. the competing gravitational tugs of Mars and Jupiter. tidal forces from Jupiter.
Part E
How can we determine the reflectivity of an asteroid?
Hint E.1
Study Section 12.1
ANSWER:

By measuring its mass and radius. By taking a photograph of it. By comparing its brightness in visible light to its brightness in infrared light. By where it is located in the asteroid belt.
Part F
Suppose you find a meteorite made almost entirely of metal. According to current theory, which of the following statements must be true?
Hint F.1
Study Section 12.1
ANSWER:

Your meteorite is a fragment of an object from the Kuiper belt. Radiometric dating will show the age of your meteorite to be 4.6 billion years. Your meteorite was blasted off the surface of Mars by an impact. Your meteorite is a fragment from the core of a large asteroid that had undergone differentiation and then was shattered by a collision.
Part G
Which of the following objects are probably NOT located in the same region of the solar system in which they originally formed?
Hint G.1
Study Section 12.2
ANSWER:

asteroids of the asteroid belt Kuiper belt comets Pluto Oort cloud comets
Part H
Suppose there were no solar wind. How would the appearance of a comet in our inner solar system be different?
Hint H.1
Study Section 12.2
ANSWER:

It would have only one tail instead of two. It would not have a nucleus. It would not have a coma. It would be much brighter in appearance.
Part I
Suppose we discover a new comet on an orbit that brings it closer to the Sun than Mercury every 125 years. What can we conclude?
Hint I.1
Study Section 12.2
ANSWER:

It has been on its current orbit for only a very short time compared to the age of our solar system. It has a coma and tail during most of each orbit. It came from the Oort cloud. It came from the Kuiper belt.
Part J
Why won't Pluto collide with Neptune?
Hint J.1
Study Section 12.3
ANSWER:

Pluto orbits the Sun exactly 3 times for every 2 Neptune orbits, which ensures the two planets never come close together. Pluto's orbit never comes anywhere close to Neptune's orbit. Pluto is always much farther from the Sun than Neptune. Actually, a collision of the two is inevitable within the next billion years.
Part K
What is Charon thought to have in common with our own Moon?
Hint K.1
Study Section 12.3
ANSWER:

The same average density. They have the same basic composition. Both probably formed as a result of giant impacts. They have the same approximate mass.
Part L
Which of the following is NOT a piece of evidence supporting the idea that Pluto is a large comet of the Kuiper belt?
Hint L.1
Study Section 12.3
ANSWER:

Pluto's orbit is very similar to the orbits of other known Kuiper belt comets. Pluto's composition appears to match that of other known Kuiper belt comets. Pluto is not even the largest object orbiting in the region of the Kuiper belt. Triton, which must once have orbited the Sun before being captured by Neptune, is larger than Pluto. Pluto grows a coma and a long tail when it is at the point in its orbit closest to the Sun.
Part M
The discovery of "Planet X"...
Hint M.1
Study Section 12.3
ANSWER:

was surprising, due to its "backwards" orbit around the Sun. was not surprising, because the existence of a very massive Planet X had been predicted nearly a century ago. was surprising, since we thought we knew about all large objects in the solar system. was not surprising, because other Kuiper belt objects approaching the size of Pluto had already been discovered.
Part N
When we see a meteor shower, it means that:
Hint N.1
Study Section 12.2
ANSWER:

Earth is crossing the orbit of a comet. You should duck and run for cover to avoid being blasted on the head by a rock from space. An Earth-approaching asteroid has recently come very close to our planet. The solar wind is unusually strong.
Part O
When you see the bright flash of a meteor, what are you actually seeing?
Hint O.1
Study Section 12.2
ANSWER:

Emission of visible light from a particle that has not yet entered Earth's atmosphere. The flash that occurs when a speeding rock from space hits the ground. A star that has suddenly shot across the sky. The glow from a pea-size particle and the surrounding air as the particle burns up in our atmosphere.
Part P
Fossil evidence suggests a mass extinction occurring 65 million years ago. Which of the following is NOT a piece of evidence supporting the idea that an impact caused this mass extinction?
Hint P.1
Study Section 12.4
ANSWER:

Unusually large abundances of iridium and other rare metals in a layer of clay that dates to 65 million years ago. An impact crater along the coast of Mexico that dates to 65 million years ago. Grains of quartz that must have formed under very high pressure are found in a layer of clay that dates to 65 million years ago Fossilized dinosaur bones that contain fragments of rock that must have been shot out by the impact.
Part Q
How often should we expect impacts of 10-km objects --- large enough to produce mass extinction --- to hit the Earth?
Hint Q.1
Study Section 12.4
ANSWER:

on average, about once every few centuries once in Earth's history on average, about once every 100,000 years on average, about once every hundred million years
Part R
On average, how often should an asteroid or comet strike Earth with as much energy as that of a hydrogen bomb (like the Tunguska impact)?
Hint R.1
Study Section 12.4
ANSWER:

Once every million years. Once every few centuries.