Deck 8: Comparative Planetology II: the Origin of Our Solar System

Question 1

Table 8-1 of Universe, 11th ed (in the text). lists three general properties of the solar system. These deal with the size and composition of terrestrial planets versus jovian planets, directions and orientations of planetary orbits, and sizes of terrestrial planetary orbits versus jovian planetary orbits. Which planets do not fit into this general scheme?

A)None of these is correct.
B)only Earth
C)Earth and Venus
D)Pluto

Answer 1

A

Question 2

The most abundant elements in the universe, as revealed by spectroscopic analysis, in order of decreasing abundance (number of atoms) are:

A)nitrogen, oxygen, carbon, and helium.
B)hydrogen, helium, oxygen, and carbon.
C)helium, carbon, oxygen, and hydrogen.
D)hydrogen, helium, oxygen, and nitrogen.

Answer 2

B

Question 3

The fractional abundance of hydrogen by mass in the solar system is about:

A)99.9%.
B)98%.
C)only 20%.
D)71%.

Answer 3

D

Question 4

Which of these chemical elements is relatively rare in the universe?

A)carbon
B)oxygen
C)nitrogen
D)gold

Question 5

How has the present mix of chemical elements in the universe been produced?

A)All the known elements have been formed by the radioactive breakup of the heavy elements formed in the initial Big Bang.
B)All of the known elements were formed in the Big Bang.
C)H and He were formed in the Big Bang, while the heavier elements have been slowly forming by collisions in cold interstellar gas clouds.
D)H and some He were formed in the Big Bang, while the heavier elements have been slowly formed in the centers of stars over the life of the universe.

Question 6

Carbon atoms make up much of the structure of living organisms, including humans. Where were these carbon atoms formed?

A)in the Big Bang
B)within the Sun
C)within earlier generations of stars
D)within supernova explosions

Question 7

Just after the original Big Bang the abundance of elements heavier than helium was:

A)about the same as it is now.
B)much greater than it is now.
C)much smaller than it is now.
D)about the same as the abundance of helium at that time.

Question 8

Figure 8-4 of Universe, 11th ed. shows the abundance of the lighter elements in our region of the galaxy. What does this suggest about the abundance of water, H₂O?

A)Both H and O are relatively abundant, so H₂O should be relatively abundant.
B)H is relatively abundant, but O is not, so H₂O should not be abundant.
C)O is relatively abundant, but H is not, so H₂O should not be abundant.
D)Neither H nor O is relatively abundant, so H₂O should not be abundant.

Question 9

Our solar system seems to have formed about how long ago?

A)50,000 years
B)5 million years
C)5 billion years
D)13.5 billion years

Question 10

Suppose the ratio of radiogenic ⁴⁰K to nonradiogenic ³⁹K was 1:10 at the time a rock was formed, and that at that time also the ratio between radiogenic ⁴⁰Ar to ³⁹K was 1:20. Now, when the rock is analyzed, it is found that the ratios are ⁴⁰K/³⁹K = 1:20 and ⁴⁰Ar/³⁹K = 1:10. How old is the rock (in billions of years)?

A)0.13
B)1.3
C)13
D)26

Question 11

Suppose the ratio of radiogenic ²³⁸U to nonradiogenic ²⁰⁴Pb was 2:100 at the time a rock was formed, and also that at that time, the ratio of radiogenic ²⁰⁶Pb to ²⁰⁴Pb was 1:100. Now, when the rock is analyzed, it is found that the ratios are ²³⁸U/²⁰⁴Pb = 1:100 and ²⁰⁶Pb/²⁰⁴Pb = 2:100. How old is the rock (in billions of years)?

A)2.25
B)4.5
C)9
D)13.5

Question 12

Suppose the ratio of radiogenic ²³⁸U to nonradiogenic ²⁰⁴Pb was 4:100 at the time a rock was formed, and also that at that time, the ratio of radiogenic ²⁰⁶Pb to ²⁰⁴Pb was 1:100. Now, when the rock is analyzed, it is found that the ratios are ²³⁸U/²⁰⁴Pb = 1:100 and ²⁰⁶Pb/²⁰⁴Pb = 4:100. How old is the rock (in billions of years)?

A)2.25
B)4.5 b
C)9
D)13.5

Question 13

When dealing with radioactive decay of materials, we often read about the age of a particular rock. What is meant by the age of a rock?

A)It is the age of the atoms within the rock.
B)It is the time since the rock was formed and the elements within the rock were isolated with definite abundance ratios.
C)It is the age of the planet or moon on which the rock is found.
D)It is actually a misnomer, since only radiogenic elements can be dated. A rock can be dated only if it is a pure radiogenic element.

Question 14

The ages of meteorites have been found through radioactive dating. One major difficulty with this technique is that:

A)the original abundances of the elements are not precisely known.
B)relatively large samples (approximately 10 cm in diameter) are needed for testing.
C)the half-lives of the elements are not precisely known.
D)the age of the meteorites is greater than the half-life of any of the radioactive elements.

Question 15

The oldest rocks, as measured by radioactive age dating, have been found:

A)on Earth.
B)in the lunar highlands.
C)in the maria of the lunar lowlands.
D)in meteorites.

Question 16

The oldest rocks yet found by radioactive age dating, in order of decreasing age, are:

A)Earth rocks, lunar rocks, and meteorites.
B)meteorites, lunar rocks, and Earth rocks.
C)lunar rocks, Earth rocks, and meteorites.
D)lunar rocks, meteorites, and Earth rocks.

Question 17

The half-life of radiogenic ¹⁴C is 5730 years. How long must you wait until 90% of the original sample remains?

A)less than 5730 years
B)5730 years
C)9 × 5730 = 51,570 years
D)more than 51,570 years

Question 18

It is found by the radioactive age-dating technique that only one-quarter of the original sample of a radiogenic element remains, so the time is calculated to be two half-lives. What does this time represent?

A)the age of the universe
B)the age of the solar system
C)the time since the formation of the elements
D)the time since the rock was formed

Question 19

In order to employ the radioactive age-dating technique on a sample of rock, it is necessary to know all of these except one. Which is the exception?

A)the amount of the radioactive element in the rock
B)the amount in the rock of the stable element into which the radioactive element decays
C)the amount in the rock of some nonradiogenic element for reference
D)the mass of the rock when it was formed

Question 20

Radioactive decay in an atom occurs because:

A)the atom has more protons than electrons.
B)the atom has more protons than neutrons.
C)the nucleus contains a mix of neutrons and protons, which is not stable.
D)the nucleus, originally stable, has been made unstable by exposure to the nuclear reactions in a nearby star.

Question 21

How did the temperature of the solar nebula develop?

A)The nebula formed from cold gas and dust, and it remained cold until sufficient oxygen had accumulated so that combustion was possible.
B)The nebula formed from cold gas and dust, and it remained cold until nuclear reactions developed.
C)The gas and dust remained cold as they collapsed to form a much denser nebula. Here friction developed between the particles, and this gradually raised the temperature.
D)As the nebula collapsed, gravitational potential energy was converted into kinetic energy, and the temperature rose.

Question 22

Which of these statements is an example of Kelvin-Helmholtz contraction?

A)a contraction of the planet Mercury as it cooled, with consequent buckling of the surface
B)a contraction of a dense cloud of gas slowly gets hotter due to the release of gravitational energy
C)the condensation of ices (e.g., ammonia) onto dust particles in the early solar nebula
D)a contraction of a thin cloud of gas, in which the temperature remains constant due to the escape of infrared radiation

Question 23

The most likely mechanism for the solar system's formation appears to be:

A)a capture theory in which the planets were formed elsewhere and were captured by the gravitational pull of the Sun as they drifted through space.
B)the idea that the planets were formed deep in the interior of the Sun and were later flung out by the Sun's angular momentum.
C)that the solar system was once a galaxy, from which the Sun and planets are the remnants.
D)that a cloud of gas and dust condensed to form the Sun, while planets formed later by condensation and accretion within the nebular disk.

Question 24

To be accepted as a reasonable picture of the formation of the solar system, the nebular hypothesis must explain all of the these statements except one. Which is the exception?

A)All the planets orbit the Sun in the same direction.
B)All the planetary orbits lie close to the ecliptic.
C)The magnetic fields vary greatly in magnitude and direction.
D)The vast bulk of the solar system's mass lies in the center.

Question 25

In a rotating physical system (e.g., a star formation region or a skater), what happens to the rotation rate (or angular speed) when the mass of the system condenses toward the center of rotation?

A)It varies periodically.
B)It decreases.
C)Since rotation depends only on the initial rotation speed, it remains the same.
D)It increases.

Question 26

As the early Sun got smaller in a Kelvin-Helmholtz contraction, its interior became hotter and gained thermal energy. What was the source of this energy?

A)the tidal pull of a passing star
B)gravitational potential energy released by inward-falling material
C)nuclear energy from the interior
D)energy released by radioactive decay

Question 27

The protosun became a full-fledged star when:

A)thermonuclear fusion reactions began at its center.
B)the temperature began to rise at its center.
C)it became hot enough to emit light and heat.
D)planetary formation was complete.

Question 28

An early theory of solar system formation was the tidal hypothesis-the idea that a star passed close enough to the Sun to draw out a long filament of material that then condensed to form the planets and other solar system bodies. Why was this theory discredited?

A)A star this close to the Sun would form a binary star system rather than the single star we actually have.
B)Such a long filament would be thickest near the Sun and would form the largest planets there.
C)Stars move so slowly that any star this close to the Sun four and a half billion years ago would still be in the solar vicinity.
D)Tidal forces strong enough to pull a filament out of the Sun would also be strong enough to cause it to disperse before it could condense into planets.

Question 29

The planetary system was probably formed from three different categories of material with different condensation temperatures (the temperature at which the material melts): gases, ices, and rocks. Which is the correct order of these materials, in increasing condensation temperature?

A)rocks, gases, and ices
B)rocks, ices, and gases
C)gases, rocks, and ices
D)gases, ices, and rocks

Question 30

Which of the these types of material has the highest condensation temperature in the planetary system?

A)hydrogen
B)rocks and dust grains
C)nitrogen gas
D)gases such as methane, ammonia, and water vapor

Question 31

The most common ices in the early solar nebula were:

A)hydrogen and helium.
B)water ice and carbon dioxide.
C)hydrogen, methane, and ammonia.
D)water ice, methane, and ammonia.

Question 32

Which substances form ice in the outer solar system?

A)carbon dioxide and iron oxides
B)hydrogen and helium
C)water, carbon dioxide, and minerals rich in iron, silicon, magnesium, and sulfur
D)water, ammonia, and methane

Question 33

Various ices condense at temperatures less than 300 K. What is the smallest distance from the Sun in the early solar nebula at which these ices would have condensed to form solid particles? (See Figure 8-10 of Universe, 11th ed.)
​
​

A)2 au
B)5 au
C)1 au
D)1.5 au

Question 34

In the early solar nebula, iron sulfide condensed into solid form at a temperature of about 750 K. What is the smallest distance from the Sun at which this would have happened? (See Figure 8-10 of Universe, 11th ed.)
​
​

A)0.5 au
B)1.6 au
C)0.2 au
D)0.9 au

Question 35

What is the process of chemical differentiation?

A) the separation of different chemical compounds into different regions of the solar nebula; e.g., rocky grains in the inner nebula, icy grains in the outer nebula
B) the sinking of heavy material to the center of a planet or other object and the rising of lighter material toward the surface
C) the condensation of different chemical compounds at different temperatures and therefore at different times-iron first, rock next, and ices last
D) a separation of different chemical compounds into different types of grains in any given part of the solar nebula; e.g., grains of ice, rock, and iron

Question 36

The reason most of the terrestrial planets have dense, iron cores is because:

A)iron solidifies at the highest temperatures, so the iron core condensed first from the solar nebula. The rocky material then condensed directly onto the iron core as the nebula cooled.
B)terrestrial planets were initially molten or partially molten, and the iron sank to the center.
C)iron is magnetic, so there was a rapid accretion of iron dust grains into a core, followed by a slow accretion of rocky grains.
D)iron solidifies at the highest temperatures, so the iron core condensed first from the solar nebula. Rocky planetesimals then formed as the nebula cooled further, and gradually impacted onto the iron core.

Question 37

According to modern theories, one significant difference between the formation of the terrestrial and jovian planets is that:

A)both formed by accretion of planetesimals, but the jovian planets became massive enough to attract gas onto them directly from the solar nebula.
B)both formed by accretion of rocky and icy planetesimals, but the terrestrial planets were close enough to the Sun that almost all of the ice escaped back to space after the planets formed.
C)the terrestrial planets formed close to the Sun where there was lots of rock but no ice, whereas the jovian planets formed far from the Sun, where there was lots of hydrogen and ice but no rocky material.
D)the terrestrial planets formed by accretion of planetesimals, whereas the jovian planets formed from streamers of hot gas that shot out of the protostar.

Question 38

How are many of the satellites of the jovian planets thought to have formed?

A)They are small planets in their own right but were captured by the jovian planets early in the solar system's history.
B)They are fragments of one large satellite orbiting around each of the planets.
C)They are from a disk of material around the planet, similar to the way the planets formed around the Sun.
D)They are from material thrown off the planet when one or more large planetesimals or small planets collided with it.

Question 39

The environment where the jovian planets initially formed contained all these ingredients except one. Which was the exception?

A)rocks
B)metals
C)ices (water, methane, and ammonia)
D)liquids (water and ammonia)

Question 40

How do we explain the relatively low mass of Mars, which is much smaller than Earth or Venus?

A)Mars was fully formed in the outer regions of the solar system and migrated inward to its present orbit well after most planetesimals had disappeared. Thus, it did not grow further.
B)Mars was flung out of the still-molten Earth.
C)The early migration of Jupiter to the present location of Mars's orbit cleared away the planetesimals, which might have enlarged Mars after it formed somewhat later.
D)At some time early in the solar system, Mars and Jupiter exchanged orbits-after Jupiter had already swept up all the planet-building materials from Mars's present orbit.

Question 41

The Grand Tack model helps to explain all of these except one. Which is the exception?

A)Mars has a relatively small mass.
B)The asteroid belt contains a few icy objects as well as many rocky objects.
C)Neptune's current location would not allow it to grow rapidly enough to account for its large size.
D)The orbital motions of all the planets are in the same direction around the Sun.

Question 42

The asteroid belt is:

A)a spherical solar system halo of icy objects far beyond the orbit of Pluto.
B)a flat region just outside the orbit of Neptune in which icy and rocky objects circle the Sun.
C)the collection of both rocky and icy objects orbiting the Sun between the orbits of Mars and Jupiter.
D)the swarm of small satellites around Jupiter made from ice and dust.

Question 43

The Kuiper belt is:

A)a spherical solar system halo of icy objects far beyond the orbit of Pluto.
B)a flat region just outside the orbit of Neptune in which icy and rocky objects circle the Sun.
C)the collection of both rocky and icy objects orbiting the Sun between the orbits of Mars and Jupiter.
D)the swarm of small satellites around Jupiter made from ice and dust.

Question 44

The Oort cloud is:

A)a spherical solar system halo of icy objects far beyond the orbit of Pluto.
B)a flat region just outside the orbit of Neptune in which icy and rocky objects circle the Sun.
C)the collection of rocky objects orbiting the Sun between the orbits of Mars and Jupiter.
D)the swarm of small satellites around Jupiter.

Question 45

Of all the stars with metal abundances like the Sun surveyed so far by the radial velocity method, about how many have planets in orbit around them?

A)much less than 1%
B)10%-20%
C)50%-60%
D)virtually all of them

Question 46

Astrometry is the branch of astronomy dealing with the measurement of the:

A)ages of stars and galaxies.
B)accurate motions of stars with respect to the Sun.
C)precise positions of stars and galaxies.
D)precise surface temperatures of stars.

Question 47

Astrometry is the very precise measurement of:

A)a star's brightness (e.g., to measure light variations).
B)a star's blackbody curve (e.g., to measure the star's temperature).
C)a star's position in the sky (e.g., to measure its motion).
D)lines in a star's spectrum (e.g., to measure the Doppler shift).

Question 48

What is surprising about the planet orbiting the star 51 Pegasi?

A)It has a mass similar to that of Saturn, but its orbital radius is similar to that of Mars.
B)It has a mass almost as large as Jupiter, but its orbital radius is smaller than that of Mercury.
C)Its mass is similar to that of Mercury, but its orbital radius is similar to that of Jupiter.
D)Its mass and orbital radius are almost identical to that of Jupiter, indicating that 51 Pegasi may have a planetary system that is a twin of our own.

Question 49

Of the extrasolar planets that have been found, many have masses comparable to that of Jupiter but orbits smaller than Earth's. What is believed to be the most likely explanation for this surprising combination?

A)The protoplanetary disk was much denser than that of the Sun, and larger planets formed. Collisions between these planets then sent some of them into much smaller orbits.
B)Friction with the protoplanetary disk caused planets formed farther from the Sun to lose energy and migrate inward.
C)"Planets" are, in fact, low-mass objects that formed separately in the same manner as stars, and were later captured into the orbits in which we now see them.
D)The protoplanetary disk was much denser than that of the Sun, allowing large planets to form very close to the star.

Question 50

Some exoplanets appear to have very surprising characteristics, namely Jupiter-like masses but very small orbital radii. However, an uncertainty in observational precision may render this observation meaningless. What uncertainty is this?

A)The radial velocity method can only give a lower limit for a planet's mass, so exoplanets could be massive brown dwarf or low-mass stars.
B)The astrometric method can only give an upper limit for a planet's mass, so exoplanets could be terrestrial planets.
C)The astrometric method can only give a lower limit to the orbital radius, so exoplanets could be orbiting at the proper distance expected for a jovian planet.
D)The radial velocity method cannot distinguish between orbital variations due to a planet and stellar pulsations where the radial velocity variations are caused by the motion of the star's surface. Thus, there may be no planets at all.

Question 51

Suppose an exoplanet is in an orbital plane perpendicular to our line of sight. Which one of the following methods might be used to detect this planet?

A)astrometric measurement of the "wobble"
B)transits
C)the radial velocity method
D)ultraviolet excess

Question 52

Each of these is a technique used to discover exoplanets except one. What is the exception?

A)microlensing
B)transits
C)the radial velocity method
D)ultraviolet excess

Question 53

Interaction between newly formed planets and gas and dust left over in the stellar nebula may account for our observation of:

A)large planets in orbits near their stars, but not the large eccentricities of their orbits.
B)the large eccentricities of the orbits, but not the existence of large planets so close to their stars.
C)both the existence of large planets in near orbits and the large eccentricities of the orbits.
D)neither the existence of large planets in near orbits nor the large eccentricities of the orbits.