Chapter 4

Why did the solar nebula heat up as it collapsed?

As the cloud shrank, its gravitational potential energy was converted to kinetic energy and then into thermal energy.

According to our theory of solar system formation, why do we find some exceptions to the general rules and patterns of the planets?

Most of the exceptions are the result of giant impacts or close gravitational encounters.

How does the Sun's mass compare with that of the planets?

It is about a thousand times more massive than all the planets combined.

Which of the following statements was true beyond the frost line (but not interior to it)? It was cold enough for hydrogen compounds to condense into ices. This was the only region that flattened into a disk. It was so warm that only metal and rock could condense from the gas. No object as small as a terrestrial planet could form.

It was cold enough for hydrogen compounds to condense into ices.

What's unusual about our Moon?

It's surprisingly large relative to the planet it orbits.

Now consider the second major feature (two types of planets). Which of the following statements are true for the terrestrial and jovian planets in our solar system? Jovian planets are larger in size than terrestrial planets. Jovian planets are made most of metal, rock, and helium. Jovian planets orbit farther from the Sun than terrestrial planets. Jovian planets have more moons than terrestrial planets. Jovian planets are larger in mass than terrestrial planets.

Jovian planets are larger in size than terrestrial planets. Jovian planets orbit farther from the Sun than terrestrial planets. Jovian planets have more moons than terrestrial planets. Jovian planets are larger in mass than terrestrial planets.

The jovian planets in our solar system are _________.

Jupiter, Saturn, Uranus, and Neptune

Which of the following lists the planets of our solar system in the correct order from closest to farthest from the Sun?

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune

Why are terrestrial planets more dense than the jovian planets?

Only dense materials could condense in the inner solar nebula.

Based on what the nebular theory tells us about the formation of our own solar system, what does the theory predict for the possibility of other planetary systems? Planetary systems should be common. Planetary systems should be very rare. Most stars should have one or two planets, but not more. Other planetary systems should be identical to our own.

Planetary systems should be common.

About 2% of our solar nebula consisted of elements heavier than hydrogen and helium. However, the very first generation of stars in the universe probably consisted only of hydrogen and helium. Which of the following statements is most likely to have been true about these first-generation stars?

Planets were likely very rare or non-existent around these first-generation stars

Which of the following is not a characteristic of the outer planets?

They have relatively high densities.

Which of the following is not a characteristic of the inner planets?

They have substantial atmospheres.

What do meteorites reveal about the solar system?

They reveal that the age of the solar system is approximately 4.6 billion years.

What is the origin of the large moons orbiting in the equatorial planes of the jovian planets?

They were formed by condensation and accretion in a disk of gas around the planet.

The terrestrial planets are made almost entirely of elements heavier than hydrogen and helium. According to modern science, where did these elements come from?

They were produced by stars that lived and died before our solar system was born.

A key clue to how the solar system formed is the observation that all the planets orbit close to the same plane.

True

Based on our theory of how our own solar system formed, we would expect that other solar systems would be quite common.

True

Most of Earth's water likely resulted from impacts with icy planetesimals that originated in the outer regions of the solar system.

True

Outside the frost line, planetesimals could form into larger objects due to the presence of both rock and ice.

True

The more massive planets in the solar system tend to be less dense than the lower mass planets.

True

All the following statements are true. Which of them are considered to be "exceptions" to the general trends described by the first three major features of the solar system?

Uranus rotates with an axis tilt that lies nearly in the ecliptic plane. Our Moon has a diameter more than 1/4 the diameter of Earth. Venus rotates in a direction opposite to the rotation of the other terrestrial planets.

Which of the following observations of an extrasolar planet system would be inconsistent with the nebular theory of planet formation?

a system in which all the planets orbit in completely different planes

Which of the following is thought to explain many of the "exceptions to the rules" of our solar system? the frost line giant impacts the solar nebula conservation of angular momentum the heavy bombardment

giant impacts

Today, scientists have a theory (the nebular theory) that explains all the major characteristics of the solar system. In science, we expect a theory like this not only to explain the observed characteristics of our solar system but also to predict __________.

general characteristics of other solar systems

What is Jupiter's main ingredient?

hydrogen and helium

According to our present theory of solar system formation, which of the following lists the major ingredients of the solar nebula in order from the most abundant to the least abundant?

hydrogen and helium gas; hydrogen compounds; rock; metal

The composition of the solar nebula was 98%

hydrogen and helium.

Which of the following types of material can condense into what we call ice at low temperatures?

hydrogen compounds

In essence, the nebular theory holds that _________.

our solar system formed from the collapse of an interstellar cloud of gas and dust

Now consider why the observed patterns of motion lead to the conclusion that the planets were not born in separate, random events. The reason for this conclusion is that, if the planets had been born in separate, random events, we would expect that __________.

planetary orbits would have many different orientations and directions, rather than all being in the same direction and in the same plane

In the context of studying major bodies of our solar system, what category of object does our Moon best fit?

terrestrial world

The solar system contains vast numbers of small bodies, which we call asteroids when they are rocky and comets when they are icy. These small bodies are concentrated in the region(s) of the solar system that we call

the asteroid belt the Kuiper belt the Oort cloud

Which of the following does the solar nebular theory not predict?

the equal number of terrestrial and jovian planets

What substances existed as solid flakes within the innermost regions (within about the inner 0.3 AUAU) of the solar system before planets began to form?

none

According to our theory of solar system formation, which law best explains why the solar nebula spun faster as it shrank in size?

the law of conservation of angular momentum

About how old is the solar system?

4.5 billion years

What percentage of the mass of the solar nebula consisted of elements other than hydrogen and helium?

2 percent

When did the objects that we now see as asteroids and comets form in the solar system? After solid particles condensed from the gas but before the planets finished forming.Before the cloud flattened into a disk. After the planets finished forming. After the cloud flattened into a disk but before solid particles condensed from the gas.

After solid particles condensed from the gas but before the planets finished forming.

Suppose you view the solar system from high above Earth's North Pole. Which of the following statements about planetary orbits will be true?

All the planets orbit counterclockwise around the Sun.

Consider the first major feature (orderly motions). Which of the following correctly describe patterns of motion in our solar system? Select all that apply. All the planets orbit the Sun in nearly the same plane. Major moons generally have polar orbits, meaning orbits that take them over the north and south poles of the planet they orbit. The outer planets are so large that they nearly collide with each other on each orbit. Inner planets orbit the Sun in the opposite direction from the outer planets. The Sun and most of the planets rotate in the same direction that the planets orbit. Planets have nearly circular orbits.

All the planets orbit the Sun in nearly the same plane. The Sun and most of the planets rotate in the same direction that the planets orbit. Planets have nearly circular orbits.

All the planets in the solar system have at least one moon.

False

All the planets in the solar system rotate (spin) in the same direction as they orbit the Sun.

False

Why did the solar nebula flatten into a disk?

It flattened as a natural consequence of collisions between particles in the nebula, changing random motions into more orderly ones.

According to our theory of solar system formation, what three major changes occurred in the solar nebula as it shrank in size?

It got hotter, its rate of rotation increased, and it flattened into a disk.

What do we mean by the frost line when we discuss the formation of planets in the solar nebula?

It is a circle at a particular distance from the Sun, beyond which the temperature was low enough for ices to condense

In light of what you've learned about the formation of our own solar system, decide whether the discovery should be considered reasonable or surprising.

Reasonable. This is very close to the layout of our solar system

In light of what you've learned about the formation of our own solar system, decide whether the discovery should be considered reasonable or surprising.

Surprising. According to our current theories, objects that form beyond the jovian planets should include a great deal of ice.

In light of what you've learned about the formation of our own solar system, decide whether the discovery should be considered reasonable or surprising.

Surprising. In the process of nebular capture the formation of large number moons at a jovian planet is more likely that at a terrestrial planet.

For the purposes of seeking a theory to explain the formation of the solar system, we identify four major features of our solar system. Which of the following represent these four major features?

Swarms of asteroids and comets populate the solar system. Planets fall into two major categories (terrestrial and jovian). Large bodies in the solar system have orderly motions. Several exceptions to the general trends stand out.

Which of the following is not a major difference between the terrestrial and jovian planets in our solar system?

Terrestrial planets contain large quantities of ice, and jovian planets do not.

What is the giant impact hypothesis for the origin of the Moon?

The Moon formed from material blasted out of the Earth's mantle and crust by the impact of a Mars-size object.

Which of the following is not evidence supporting the idea that our Moon formed as a result of a giant impact?

The Pacific Ocean appears to be a large crater-probably the one made by the giant impact.

According to our present theory of solar system formation, which of the following statements about the growth of terrestrial and jovian planets is not true?

The jovian planets began from planetesimals made only of ice, while the terrestrial planets began from planetesimals made only of rock and metal.

According to our theory of solar system formation, why do all the planets orbit the Sun in the same direction and in nearly the same plane?

The laws of conservation of energy and conservation of angular momentum ensure that any rotating, collapsing cloud will end up as a spinning disk.

Consider only the first major feature, which concerns observed patterns of motion in the solar system. Scientifically, which of the following possible conclusions is justified from the patterns of motion alone?

The planets were not each born in a separate, random event.

Which one of the following is not one of the four major features of the solar system? Several exceptions to the general trends stand out. Swarms of asteroids and comets populate the solar system. Large bodies in the solar system have orderly motions. Planets fall into two major categories (terrestrial and jovian). The solar system contains eight planets plus dwarf planets (such as Ceres, Pluto, and Eris).

The solar system contains eight planets plus dwarf planets (such as Ceres, Pluto, and Eris).

Suppose you start with 1 kilogram of a radioactive substance that has a half-life of 10 years. Which of the following statements will be true after 20 years pass?

You'll have 0.25 kilogram of the radioactive substance remaining.

Which of the following are relatively unchanged fragments from the early period of planet building in the solar system?

all of the above

Where would you expect terrestrial planets to form in the solar nebula?

anywhere between the innermost regions (within about the inner 0.3 AUAU) and the frost line

According to our present theory of solar system formation, why were solid planetesimals able to grow larger in the outer solar system than in the inner solar system?

because only metal and rock could condense in the inner solar system, while ice also condensed in the outer solar system

Suppose the solar nebula had been too warm for ices to condense anywhere. If a planet had still formed at Jupiter's location, it most likely would have turned out pretty much the same as the real Jupiter. been similar in composition to Earth, with a much smaller mass than the real Jupiter. been smaller in mass than the real Jupiter, but still made mostly of H/He.

been similar in composition to Earth, with a much smaller mass than the real Jupiter.

Which of the following did not occur during the collapse of the solar nebula?

concentrating denser materials nearer the Sun

Planetary orbits in our solar system are:

fairly circular and in the same plane.

The inner planets are small and rocky and the outer planets are mostly large and gaseous because the spin of the disk caused the denser rock and metals to remain towards the center of the solar system, while the lighter material were flung farther from the Sun. the Sun's gravity caused the denser rock and metals to settle towards the center of the solar system while the lighter materials remained farther from the Sun.hydrogen is more abundant than rocks and metals so that beyond the frost line hydrogen froze to form the jovian planets. hydrogen compounds are more abundant than rocks and metals so that beyond the frost line the gravity of large ice planetesimals could capture the abundant light gases.

hydrogen compounds are more abundant than rocks and metals so that beyond the frost line the gravity of large ice planetesimals could capture the abundant light gases.

As the solar nebula collapsed under its own gravity, it heated up and spun up. it cooled down and spun down. it cooled down and spun up. it heated up and spun down.

it heated up and spun up.

According to our theory of solar system formation, what are asteroids and comets?

leftover planetesimals that never accreted into planets

The temperature of the protoplanetary disk allowed rocks and metals to freeze both in the inner region and outer region, and hydrogen compounds to freeze only in the outer region. hydrogen compounds, rocks, and metals to freeze in the inner region only. rocks and metals to freeze both in the inner region and outer region, and hydrogen compounds and H/He gases to freeze only in the outer region. rocks and metals to freeze in the inner region only, and hydrogen compounds to freeze in the outer region only.

rocks and metals to freeze both in the inner region and outer region, and hydrogen compounds to freeze only in the outer regio

The jovian planets are thought to have formed as gravity drew hydrogen and helium gas around planetesimals made of __________.

rocks, metals, and ices

What substances were found in the innermost regions (within about the inner 0.3 AUAU) of the solar system before planets began to form?

rocks, metals, hydrogen compounds, hydrogen, and helium, all in gaseous form

The age of the solar system can be established by radiometric dating of

the oldest meteorites.

The planets in our solar system are thought to have come from a cloud of gas in the Orion nebula. clumps of rocky material that exist between stars. the Sun (they were flung out from the spinning Sun) .the same cloud of gas and dust in which the Sun formed.

the same cloud of gas and dust in which the Sun formed.

As the solar nebula collapsed, it became a disk because the Sun's gravity pulled the nebula material into the ecliptic plane. collisions between particles made the particles go in more-or-less the same direction. the initial cloud was disk shaped. the self-gravity of the nebula pulled the material into the ecliptic plane.

the self-gravity of the nebula pulled the material into the ecliptic plane.

If the solar nebula initially had no angular momentum, there would not be any planets orbiting the Sun. the planets would orbit closer to the Sun. the planets would orbit farther away from the Sun.

there would not be any planets orbiting the Sun.

Observations of young stars (as well as theory) tell us that when the Sun was young, the solar wind

was stronger than it is today.

Suppose the solar nebula had cooled much more before the solar wind cleared away the remaining gas. In that case, the terrestrial planets likely would have ended up the same as they are now.being made entirely of H/He gas. with a higher abundance of hydrogen compounds and larger size. with a higher abundance of metals and larger size.

with a higher abundance of hydrogen compounds and larger size.