TEST BANK 21ST CENTURY
ASTRONOMY THE SOLAR SYSTEM 5TH EDITION BY KAY
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Chapter 11: Planetary Moons and
Rings
Learning
Objectives
11.1 Many Solar System Planets Have Moons
Predict why most moons in the solar system are found around
the giant planets.
Multiple Choice: 1, 2, 4, 10
Short Answer: 1
Compare and contrast the origin of moons with regular and
irregular orbits.
Multiple Choice: 3, 5, 6, 7, 8, 9
Short Answer: 2, 3, 4, 5, 7
11.2 Some Moons Have Geological Activity
and Water
Compare and contrast volcanism and cryovolcanism.
Multiple Choice: 20, 24
Short Answer: 11, 13
Relate the presence or absence of surface features to deduce
the history of a moon’s geological activity.
Multiple Choice: 12, 13, 14, 15, 19, 23, 29, 30, 31
Short Answer: 15, 16
Summarize the observations or characteristics that
differentiate between moons with current geological activity, possible
activity, past activity, and no activity.
Multiple Choice: 16, 17, 22, 25, 28, 32, 33
Short Answer: 8, 9
Explain how moons can be geologically active today whereas
comparably sized planets are geologically dead.
Multiple Choice: 11, 21
Short Answer: 10
Summarize the evidence for liquid oceans on giant planet
moons.
Multiple Choice: 18, 26, 27
Short Answer: 12
11.3 Rings Surround the Giant Planets
Explain how rings are observed around planets.
Multiple Choice: 37, 38, 39, 43, 44, 47, 48, 51
Short Answer: 17
Discuss the two proposed origins for rings around giant
planets.
Multiple Choice: 34, 35, 36, 41, 52, 56
Short Answer: 18, 22
Illustrate how moons provide orbital stability to ring
material.
Multiple Choice: 42, 57
Short Answer: 19, 21
Describe the typical composition of rings.
Multiple Choice: 40, 45, 46, 49, 50, 53, 54, 55
Short Answer: 20
11.4 Ring Systems Have a Complex Structure
Relate a ring’s appearance to its composition and density.
Multiple Choice: 59, 60, 61, 62, 63, 64, 65, 66, 68
Short Answer: 23, 24
Summarize the substructure of planetary rings.
Multiple Choice: 67
Short Answer: 25, 27, 28
Predict why some giant planets have bright rings and others
only have diffuse rings.
Multiple Choice: 58
Short Answer: 26
Estimate the likelihood of life on moons of the giant
planets.
Short Answer: 29, 30
Working It Out 11.1
Use a moon’s orbit to calculate the mass of its parent
planet.
Short Answer: 6
Working It Out 11.2
Compare the tidal forces experienced by two different moons.
Short Answer: 14
MULTIPLE CHOICE
1.
Who first discovered
moons around a planet in our Solar System other than Earth?
a.
Newton
b.
Kepler
c.
Galileo
d.
Huygens
e.
Einstein
2.
How many moons are
known in the Solar System?
a.
Less than 50
b.
At least 150
c.
Around 10
d.
Many thousands
3.
How do regular moons
rotate in comparison to their planets?
a.
in the same direction
b.
in the opposite
direction
c.
sometimes in the same
direction and sometimes in the opposite direction
d.
Unlike their planets,
moons don’t rotate at all.
4.
The only planet(s)
without a moon is (are)
a.
Mercury.
b.
Venus.
c.
Mars.
d.
Mercury and Venus.
e.
Mercury, Venus, and
Mars.
5.
Which of the following
is not a characteristic of regular moons?
a.
They revolve around
their planets in the same direction as the planets rotate.
b.
They have orbits that
lie nearly in the planets’ equatorial plane.
c.
They are usually
tidally locked to their parent planets.
d.
They are much smaller
than all of the known planets.
e.
They formed in an
accretion disk around their parent planet.
6.
Most large regular
moons probably formed
a.
when passing asteroids
were captured by the gravitational field of their planet.
b.
at the same time as
their planets and grew by accretion.
c.
after a collision
between a planet and a large asteroid fractured off a piece of the planet.
d.
after the period of
heavy bombardment in the early Solar System.
e.
after a planet got
kicked out of its orbit and was gravitationally captured by another planet.
7.
Which property of a
moon might lead you to believe it was a captured asteroid?
a.
It is tidally locked.
b.
Its orbital axis is
tilted by 5 degrees compared to the planet’s rotational axis.
c.
It rotates in the
opposite direction than its planet rotates.
d.
Its surface is very
smooth and lacks craters.
e.
It is roughly the size
of Earth’s moon.
8.
Assume that we discover
a new moon of Jupiter. It orbits Jupiter at a large distance and in the
opposite direction that Jupiter rotates. It is much smaller than most of
Jupiter’s other moons and has a density close to that of Earth rocks.
Therefore, this moon is most likely
a.
a regular moon that
formed with Jupiter in the early Solar System.
b.
an irregular moon that
is most likely a captured asteroid.
c.
an irregular moon that
is most likely a captured comet.
d.
an irregular moon that
is most likely a protoplanet that collided with Jupiter in the early Solar
System and then was caught in orbit by Jupiter’s gravity.
e.
More information is
needed before any conclusion can be made.
9.
If a moon has a
retrograde orbit, then it
a.
orbits in the opposite
direction than its planet rotates.
b.
orbits in the opposite direction
than its planet revolves around the Sun.
c.
orbits in a clockwise
direction as viewed from the planet’s north pole.
d.
both a and c
e.
all of the above
10.
Why do the giant
planets have the largest share of moons in the solar system?
a.
There was more rocky
material present at their orbital positions, so they collected more moons
b.
Being the most massive
planets in the solar system, they were able to gather more material to form
moons than the terrestrial planets
c.
The temperature of the
solar nebula at other locations in the solar system was too high for moons to
form around the terrestrial planets
d.
Since they rotate
faster than the terrestrial planets, the giant planets were able to ‘spin off’
clumps of material which formed moons
11.
Why are some moons such
as Io and Enceladus geologically active even though they are small in size
compared to the planets?
a.
Unlike some planets,
these moons have additional supplies of radioactive elements providing the
necessary heating to drive geological activity
b.
The interiors of these
moons contain a larger supply of heavy elements such as iron than found in
terrestrial planets, which contributes to greater heating and high geological
activity
c.
Tidal forces from the
Sun are especially large for these moons, leading to greater interior heating
and more geological activity
d.
The interiors of these
moons are heated by the rapidly changing direction and strength of tidal forces
from Jupiter, resulting in geological activity
12.
Which of the following
can be used as an indicator of the age of a moon’s surface?
a.
color of the surface
b.
crater density
c.
volcanic activity
d.
radioactive dating
e.
all of the above
13.
Based on the image
below, this moon
a.
is geologically active.
b.
is possibly
geologically active.
c.
was geologically active
in the past but is no longer active.
d.
is geologically dead.
14.
Based on the image
below, this moon
a.
is geologically active.
b.
is possibly
geologically active.
c.
was geologically active
in the past but is not longer active.
d.
is geologically dead.
e.
More information is
needed before any conclusion can be made.
15.
Based on the image
below, this moon
a.
is geologically active.
b.
is possibly
geologically active.
c.
was geologically active
in the past but is no longer active.
d.
is geologically dead.
e.
More information is
needed before any conclusion can be made.
16.
Which object has been
turned inside out numerous times, leading to a situation where lighter elements
have escaped, sulfur compounds compose the crust, and primarily heavier
elements make up its core?
a.
Mercury
b.
Titan
c.
Callisto
d.
Pluto
e.
Io
17.
How does the geological
activity on Io compare to the activity on other moons?
a.
It is almost completely
inactive.
b.
It occurs at widely
spaced intervals but is highly active when it does occur.
c.
It is very active on a
regular basis.
d.
It used to be inactive
but has slowly increased activity over the past few million years.
18.
What sort of liquids do
astronomers believe exist on Saturn’s moon, Titan?
a.
Lakes of liquid
nitrogen, N2
b.
Lakes of normal water,
H2O
c.
Lakes of ammonia and
hydrogen sulfide
d.
Lakes of methane,
ethane, and other hydrocarbons
19.
What does a darkened
surface indicate on a rocky moon compared to one with a lighter surface?
a.
It indicates the
presence of cooling lava from volcanic eruptions.
b.
It indicates that the
surface of the darkened moon is younger than the lighter moon.
c.
It indicates that the surface
of the darkened moon is younger than the lighter moon.
d.
It indicates an
elevated level of organic compounds on the surface.
20.
What makes extremophile
organisms different from other life forms?
a.
They can live in
extreme conditions, such as very low or high temperature environments,
oxygen-poor environments, or environments with extremely low light levels.
b.
They live only in
environments with extremely high temperatures, such as near volcanic vents.
c.
They live in
environments lacking in organic compounds.
d.
They live in
environments where little to no water is found, such as deserts.
21.
Io has the most
volcanic activity in the Solar System because
a.
it is continually being
bombarded with material in Saturn’s E ring.
b.
it is one of the
largest moons and its interior is heated by radioactive decays.
c.
of gravitational
friction caused by the moon Enceladus.
d.
its interior is tidally
heated as it orbits around Jupiter.
e.
the ice on the surface
creates a large pressure on the water below.
22.
Which of the following
moons is not geologically active?
a.
Callisto
b.
Triton
c.
Europa
d.
Enceladus
e.
Io
23.
The varied colors found
on Io’s surface are due to the presence of various molecules containing
a.
sulfur.
b.
silicon.
c.
iron.
d.
mercury.
e.
magnesium.
24.
Cryovolcanism occurs
when
a.
molten lava freezes
when it reaches the surface because of extremely low temperatures.
b.
volcanoes erupt
underwater.
c.
an icy moon has
volcanoes emitting molten lava from deep underground.
d.
low-temperature liquids
explode through the surface because of increasing pressure underground.
e.
a comet hits an object
and causes volcanic eruptions.
.
25.
Based on the image
below, this moon
a.
is geologically active.
b.
is possibly
geologically active.
c.
was geologically active
in the past but is no longer active.
d.
is geologically dead.
26.
Which of the following
moons is thought to have a vast ocean of water beneath its frozen surface?
a.
Triton
b.
Europa
c.
Ganymede
d.
Io
e.
Callisto
27.
What leads astronomers
to believe that some large moons associated with the giant planets have
compositions that are roughly half water?
a.
Spectroscopic analysis
indicates the presence of large bodies of water.
b.
They have average
densities midway between water and rock.
c.
Space probes have
drilled into the surfaces of many of the moons and detected water.
d.
Rocks and other
features that form only in the presence of water have been observed.
e.
Astronomers have
observed the gravitational effects of tides on those moons.
28.
Titan is a
high-priority candidate for the search for life outside Earth primarily because
it has
a.
liquid water.
b.
a dense atmosphere like
Earth’s.
c.
warm temperatures.
d.
active volcanoes.
e.
organic material.
29.
Titan’s thick
atmosphere is believed to have been created when ultraviolet photons broke
apart methane molecules, ultimately creating the observed smoglike conditions.
However, this process would likely remove all of the atmospheric methane in
roughly 10 million years, yet we still see its presence today. What is the most
likely cause?
a.
Cometary impacts
periodically bring new methane to Titan.
b.
Ethane rains down out
of the atmosphere, combines with surface rocks, and creates new methane.
c.
Infrared photons give
atmospheric molecules enough energy to recombine into methane.
d.
Volcanoes on Titan
periodically release new methane into the atmosphere.
e.
Bacteria on Titan
constantly replenish the methane in the atmosphere.
30.
From where does Titan’s
thick, nitrogen-rich atmosphere likely arise?
a.
photodissociation of
methane and ammonia in its atmosphere
b.
emitted by frequent
volcanic eruptions
c.
deposited by ongoing
cometary impacts over the age of the Solar System
d.
photosynthesis of algae
in oceans that lie beneath its icy surface
e.
released from
underground reservoirs from early impacts.
31.
On which of Saturn’s
moons did the Cassini-Huygens Probe land in 2004?
a.
Callisto
b.
Io
c.
Europa
d.
Enceladus
e.
Titan
32.
Which of the following
moons do scientists believe most closely represents the primordial Earth,
although at a much lower temperature?
a.
Titan
b.
Europa
c.
Callisto
d.
Io
e.
Ganymede
33.
Which of the following
moons is geologically dead?
a.
Callisto
b.
Io
c.
Europa
d.
Enceladus
e.
Titan
34.
How do particles from
the moon Enceladus wind up in Saturn’s E ring?
a.
Volcanoes erupt and
expel silicates into space.
b.
Water geysers erupt
from the surface and expel them into space.
c.
Cosmic rays bombard the
surface rock on Enceladus and expel them into space.
d.
A collision with a
co-orbiting moon knocked rocky debris into orbit around Saturn.
e.
Strong winds from
Saturn blow material off of Enceladus’s surface.
35.
Which moon gives rise
to the particles that make up Saturn’s E ring?
a.
Titan
b.
Triton
c.
Callisto
d.
Enceladus
e.
Thethys
36.
What is the escape
velocity from Europa, whose radius is 1,600 km and mass is 5 × 1022
kg?
a.
27 km/s
b.
7.0 km/s
c.
2.0 km/s
d.
15 km/s
37.
Two years after first
being observed, astronomers reported that Saturn’s rings vanished. What
happened to them?
a.
The old ring system
dissipated, and since then a new one has formed.
b.
The orbital plane of
the rings was seen edge-on, and the rings were too thin to be visible.
c.
Most telescopes used
hundreds of years ago couldn’t adequately resolve the ring system.
d.
Astronomers were
looking at the wrong planet, leading to the chance discovery of Uranus.
e.
They were hidden behind
some of Saturn’s many moons.
38.
The density of
particles in a planet’s rings can be measured using
a.
infrared light.
b.
the Doppler shift.
c.
shadows cast by nearby
moons.
d.
light from background
stars.
e.
their proper motions.
39.
How do astronomers take
such detailed, close-up pictures of ring systems?
a.
They send satellites to
the outer planets to take pictures for us.
b.
They take them using
backyard telescopes, just like Galileo did.
c.
They take them using
the largest optical telescopes on Earth.
d.
They have astronauts in
space take pictures of them.
e.
They wait until the
planet is closest to Earth and use the Hubble Space Telescope.
40.
What did Galileo deduce
from his observations of Saturn’s rings?
a.
The rings are very
thin.
b.
The rings are made of
reflective water ice.
c.
The rings vary in size
and shape.
d.
There are objects
orbiting very close to Saturn.
41.
Which giant planets
have rings?
a.
All of them
b.
Only Jupiter and Saturn
c.
Only Saturn
d.
None of them
42.
What influence do pairs
of shepherd moons have on the giant planets’ rings?
a.
They keep the rings
systems completely stable forever.
b.
They only allow the
rocky ring systems to remain stable while destabilizing the icy ring systems.
c.
They cause the rings to
eventually fall into Saturn by gravitational tugs on the ring particles.
d.
They keep rings between
the pair narrow by gravitational tugs on the ring particles.
43.
Which of the giant
planets does not have rings?
a.
Jupiter
b.
Saturn
c.
Uranus
d.
Neptune
e.
None: all of the giant
planets have rings.
44.
Which of the following planets
has the most complex and conspicuous ring system?
a.
Mars
b.
Jupiter
c.
Saturn
d.
Uranus
e.
Neptune
45.
Astronomers originally
planned to have the Pioneer 11 space probe pass through the Cassini Gap
in Saturn’s rings. Would this mission have been successful?
a.
Yes, but they decided
that it was more important to observe Saturn’s moons.
b.
Yes, but they decided
to land on the rings instead.
c.
No, because the Cassini
Gap turns out to be too narrow.
d.
No, because the Cassini
Gap is not completely empty.
e.
No, because the same gravitational
influences that create the Cassini Gap would have destroyed the probe.
46.
Of what are Saturn’s
brightest rings primarily made?
a.
a thin, solid surface
of rock and ice
b.
an orbiting cloud of
high-density gas
c.
hundreds to thousands
of smaller ringlets
d.
a very diffuse
collection of dust
e.
house-sized rocks
47.
Saturn’s rings
disappear from sight every
a.
40 years.
b.
25 years.
c.
15 years.
d.
8 years.
e.
6 months.
48.
How does the thickness
of Saturn’s bright ring system compare to its diameter?
a.
It’s about 10 times
thinner.
b.
It’s about 1,000 times
thinner.
c.
It’s about 10,000 times
thinner.
d.
It’s about 100,000
times thinner.
e.
It’s about 10 million
times thinner.
49.
Saturn’s G ring, as
shown in the image below, is known as
a.
a ringlet.
b.
an arclet.
c.
a diffuse ring.
d.
a spoke.
e.
a crepe ring.
50.
If a planetary ring had
an inner diameter of 100,000 km, an outer diameter of 120,000 km, a thickness
of 10 m, and a density of 100 kg/m3, what would be the total mass of
material in this ring?
a.
6 × 1020
kg
b.
5 × 1023
kg
c.
4 × 1015
kg
d.
2 × 1021
kg
e.
3 × 1018
kg.
51.
If you wanted to search
for faint rings around a giant planet by sending a spacecraft on a flyby, it
would be best to make your observations
a.
as the spacecraft
approached the planet.
b.
after the spacecraft
passed the planet.
c.
while orbiting the
planet.
d.
during the closest
flyby.
e.
while orbiting one of
its moons.
52.
Which of the following
is not a way to renew particles in a ring system?
a.
shredding an object
that came within a planet’s Roche limit
b.
a collision between
moons or other objects near the ring system
c.
eruptions on a nearby
moon, sending particles into space
d.
a planet’s gravity
drawing particles from the nearby interstellar medium
e.
impacts on a nearby
moon, sending particles into space
53.
Of what are Saturn’s
rings primarily made?
a.
water ice
b.
methane
c.
nitrogen
d.
dark organic material
e.
dark silicate material
54.
The mass of all of
Saturn’s bright rings is comparable to the mass of
a.
a small comet.
b.
a small icy moon.
c.
Earth’s Moon.
d.
Mars.
e.
Venus.
55.
Ring particles range in
size from tiny grains to
a.
house-sized boulders.
b.
basketball-sized boulders.
c.
city-sized chunks.
d.
tennis ball-sized
rocks.
e.
fingernail-sized
pebbles.
56.
Ring material
a.
is made primarily of
fine dust.
b.
has always orbited the
giant planets.
c.
reflects more than 75
percent of the light that falls on it.
d.
must constantly be
renewed.
e.
is made primarily of
kilometer-sized rocks.
57.
All of the following
ring structures are known to be created by shepherd moons except
a.
braided rings.
b.
spokes.
c.
scalloped edges.
d.
ring gaps.
e.
knots and kinks.
58.
Why are some of
Saturn’s rings diffuse?
a.
Unlike other things,
the particles in diffuse rings collide infrequently, allowing them to maintain
highly elliptical and/or inclined orbits and spread out
b.
The particles in
diffuse rings are especially small compared to other rings, causing them to
look less well defined
c.
The diffuse rings are
made of tiny particles of methane, while the particles in other rings are made
primarily of water ice
d.
The diffuse rings are
comprised of charged particles, which spread out due to the magnetic forces
from Saturn’s magnetic field
59.
Jupiter’s rings are
made of material from
a.
its innermost moons.
b.
its upper atmosphere.
c.
its outermost moons.
d.
only Io.
e.
only its retrograde
moons.
60.
How do Uranus’s rings
differ from the ring systems of the other giant planets?
a.
Uranus has only one
ring made up of fine dust.
b.
Uranus has the most
spectacular ring system with many bright, wide rings.
c.
Uranus has 13 rings
that are narrow and widely spaced.
d.
Uranus has rings that
are clumped into several arclike segments.
e.
Uranus has rings that
are solid enough to land on.
61.
If the Moon had active
volcanoes,
a.
the Moon would have a
thick hydrogen atmosphere.
b.
Earth might have a
ring.
c.
the Moon’s surface
would have more craters than it currently does.
d.
life could not exist on
Earth.
e.
the Moon would have
different phases than we see today.
62.
What observational
setup is required to observe backlit rings?
a.
The light source doing
the backlighting has to have wavelengths much longer than the size of the ring
particles.
b.
The light source doing
the backlighting has to have wavelengths comparable to the size of the ring
particles.
c.
The light source doing
the backlighting has to have wavelengths much shorter than the size of the ring
particles.
d.
The light source doing
the backlighting must be a blackbody source peaking in the visible part of the
spectrum.
63.
Which of the following
is false?
a.
The sizes of planetary
ring material ranges from tiny grains to house-sized boulders.
b.
Some rings around giant
planets are made from particles that are ejected by its moons.
c.
Planetary rings can be
made when a moon is torn apart by tidal forces.
d.
The material in
planetary rings orbit the planet while obeying Kepler’s third law.
e.
Planetary rings around
the giant planets usually remain for tens of billions of years.
64.
What is the most likely
reason that a planet’s rings would reflect more than 50 percent of the sunlight
they receive?
a.
They are made of ice.
b.
They are made of
silicate rock.
c.
They are made of
liquid.
d.
They are made of iron.
e.
They are very old.
65.
Saturn’s rings are much
brighter than the rings of the other giant planets because
a.
Saturn is closer to the
Sun and receives a higher flux of sunlight.
b.
the material in
Saturn’s rings is made mostly of ice rather than rock.
c.
Saturn’s rings have
over 100 times more material in them.
d.
Saturn’s rings are
tilted by a larger angle relative to our line of sight.
e.
the material in
Saturn’s rings is much hotter than material in other ring systems.
66.
Particles that make up
the rings of Uranus and Neptune are composed of
a.
rocky material from
tidally disrupted moons.
b.
organic material that
has darkened because of bombardment by high-energy, charged particles.
c.
icy material from
tidally disrupted comets.
d.
magma from volcanic
eruptions on the surfaces of their moons.
e.
all of the above
67.
Rings that look like
they are intertwined (but are not) are caused by
a.
new laws of physics.
b.
ring material on highly
elliptical orbits.
c.
the gravitational
influence of small moons.
d.
electromagnetic
interaction of the rings with Saturn’s magnetic field.
e.
meteoroid impacts.
68.
Rings of giant planets
are very thin compared to their diameters mainly because
a.
of collisions between
ring particles.
b.
moons that tidally
disrupt have small diameters.
c.
energy is conserved
when a moon tidally disrupts.
d.
the planets have large
tidal forces.
e.
shepherd moons force
them to be extremely thin.
69.
Extremophiles on Earth
have been found
a.
in the scalding waters
of Yellowstone’s hot springs.
b.
in the bone-dry
oxidizing environment of Chile’s Atacama Desert.
c.
in the Dead Sea.
d.
in the deep subsurface
ice of the Antarctic ice sheet.
e.
all of the above
70.
Through what process do
some living organisms find energy to survive deep under the ocean?
a.
electrolysis
b.
photosynthesis
c.
plasmosynthesis
d.
chemosynthesis
e.
magnetosynthesis
71.
SHORT ANSWER
1.
What are the two basic
materials of which the moons in the solar system are composed? For each type of
material, name an example of a moon whose surface is composed primarily of that
material.
ANS: Rocky material and ices. Some examples of moons with
rocky surfaces are Io, Ganymede, and Callisto. Some examples of icy moons are
Europa and Enceladus.
DIF: Medium REF: Section 11.1 MSC: Remembering
OBJ: Predict why most moons in the solar system are found
around the giant planets.
2.
Explain how a planet
obtains a regular moon orbiting it.
ANS: Regular moons are usually formed from an accretion disk
surrounding the parent planet as the parent planet itself is forming.
DIF: Easy REF: Section 11.1 MSC: Remembering
OBJ: Compare and contrast the origin of moons with regular
and irregular orbits.
3.
What are the orbital
characteristics of a regular moon?
ANS: Regular moons orbit in the same direction as their
parent planet rotates. Regular moons also orbit in the equatorial plane of
their parent planet. Many orbital moons are tidally.
DIF: Easy REF: Section 11.1 MSC: Remembering
OBJ: Compare and contrast the origin of moons with regular
and irregular orbits.
4.
What are three
characteristics of the orbits of irregular moons, and how are irregular moons
formed?
ANS: Irregular moons are probably captured asteroids. Three
characteristics of irregular moons are (1) retrograde orbits, (2) large
distances from their planet, and (3) chaotic orbits or orbital axes that are
misaligned with the planet’s rotational axis.
DIF: Medium REF: Section 11.1 MSC: Remembering
OBJ: Compare and contrast the origin of moons with regular
and irregular orbits.
5.
Name two properties of
moons that are in tidally locked orbits.
ANS: (1) They always keep the same side facing the planet,
and (2) the side facing the planet is subject to collision with any nearby
debris surrounding the planet, so it is much more heavily cratered than the far
side.
DIF: Medium REF: Section 11.1 MSC: Understanding
OBJ: Compare and contrast the origin of moons with regular
and irregular orbits.
6.
The semimajor axis of
Iapetus’ orbit around Saturn is approximately 3.56 × 106
km, and its orbital period is approximately 79 days. Use these data and
Newton’s version of Kepler’s third law to calculate the mass of Saturn.
ANS: The Newtonian version of Kepler’s third law is Msaturn
= 4Ï€2/G × (A3/P2),
where A is the semimajor axis in kilometers, P is the orbital
period in seconds, and G = 6.67 × 10-20
km3/kg s2. Plugging in these numbers, Msaturn
= (4Ï€2/6.67 × 10-20)
× [(3.56 × 106)3/(79*24*3600)2] = 5.7 × 1026
kg.
DIF: Difficult REF: Working it Out 11.1
MSC: Understanding
OBJ: Use a moon’s orbit to calculate the mass of its parent
planet.
7.
What’s the most likely
way a dwarf planet such as Pluto was able to acquire four moons comparable in
size to itself?
ANS: Pluto and its small moons formed in a similar way to how
Earth’s Moon formed, that is, from a giant collision between early Pluto and a
planetesimal, which fragmented into the objects we see today.
DIF: Easy REF: Section 11.1 MSC:
Understanding
OBJ: Compare and contrast the origin of moons with regular
and irregular orbits.
8.
The color of a moon’s
surface contains clues as to its age. What is the typical relationship between
surface color and surface age, and why does this relationship exist?
ANS: Darker surfaces are typically older, and brighter
surfaces are typically younger. This is because water ice is a common surface
material among the moons of the outer solar system. Water ice reflects the
majority of light that hits its surface making it very bright. Over time,
meteorite dust darkens a moon’s surface. So, a bright surface means that some
activity has recently refreshed the surface with new water ice.
DIF: Medium REF: Section 11.2 MSC: Applying
OBJ: Summarize the observations or characteristics that
differentiate between moons with current geological activity, possible
activity, past activity, and no activity.
9.
Name three
characteristics of a geologically active moon.
ANS: A geologically active moon would have a (1) relatively
bright surface that is (2) free of many impact craters and is likely to have
(3) volcanic activity.
DIF: Easy REF: Section 11.2 MSC: Applying
OBJ: Summarize the observations or
characteristics that differentiate between moons with current geological
activity, possible activity, past activity, and no activity.
10.
Why is Io, a moon that
is smaller and farther from the Sun than our own Moon, still geologically
active?
ANS: Tidal stresses from Jupiter continually cause Io’s
interior to flex, keeping it heated and preventing it from cooling completely.
DIF: Easy REF: Section 11.2 MSC: Understanding
OBJ: Explain how moons can be
geologically active today while comparably-sized planets are geologically dead.
11.
What material has been
seen erupting from the surface of the icy moon Enceladus, and why?
ANS: Geysers of water erupt from the surface of Enceladus
because tidal stresses from Saturn heat up the interior and melt water below
its icy surface.
DIF: Medium REF: Section 11.2
MSC: Understanding
OBJ: Compare and contrast volcanism
and cryovolcanism.
12.
Europa is a very interesting
moon that scientists are considering visiting with a spacecraft in order to
search for signs of life. What is it about this moon that makes it so
interesting, and what surface features give us clues about its interior?
ANS: Europa has an icy surface riddled with cracks. It
appears that liquid or slush rises up from the cracks and solidifies. Jupiter’s
tidal force may keep Europa’s interior liquid, and deep oceans filled with
water may exist under its icy surface, which might contain extreme forms of
life.
DIF: Medium REF: Section 11.2
MSC: Understanding
OBJ: Summarize the evidence for
liquid oceans on giant planet moons.
13.
If ultraviolet photons
destroy methane, why do scientists think Titan has so much of it in its
atmosphere?
ANS: Internal heating drives cryovolcanism on Titan,
constantly releasing methane into Titan’s atmosphere.
DIF: Medium REF: Section 11.2 MSC: Applying
OBJ: Compare and contrast volcanism
and cryovolcanism.
14.
Compare the tidal force
exerted by Saturn on Titan to the tidal force exerted by Saturn on Rhea.
ANS: The tidal force exerted by Saturn on a moon of mass Mmoon,
radius Rmoon, and distance from Saturn dmoon
is Ftidal = 2GMsaturnMmoonRmoon/d3moon.
The ratio of tidal forces on Titan compared to that on Rhea can be obtained noting
that 2GMsaturn drops out of the ratio of tidal forces so that
Ftidal(Titan)/Ftidal(Rhea) = (RTitan/d3Titan)/
(RRhea/d3Rhea) = [2576/(1.22 × 106)3]/[763/(527,108)3]
= 0.27. So the tidal force on Rhea is stronger than that on
Titan.
DIF: Difficult REF: Working it Out 11.2
MSC: Applying
OBJ: Compare the tidal forces
experienced by two different moons.
15.
Ganymede is one of the
largest moons in the Solar System. It shows some terrain that is ancient and
heavily cratered, younger terrain with fewer craters, but no terrain that is
free of craters. Why would Ganymede’s geological activity stop?
ANS: Ganymede’s geological activity probably stopped because
its interior solidified after differentiation stopped releasing energy.
DIF: Medium REF: Section 11.2 MSC: Applying
OBJ: Relate the presence or absence
of surface features to deduce the history of a moon’s geological activity.
16.
What can we conclude
from a random distribution of volcanoes on a moon, and why?
ANS: We can conclude there is little or no plate tectonic
activity on the moon. The movement of plates causes friction and resistance at
plate tectonic boundaries, which in turn causes heating and volcanic activity
at the edges of the plates. This leads to spatially correlated groups of
volcanoes.
DIF: Difficult REF: Section 11.2 MSC: Applying
OBJ: Relate the presence or absence
of surface features to deduce the history of a moon’s geological activity.
17.
Explain how Uranus’s
rings were first discovered.
ANS: Uranus’s rings were first discovered through stellar occultation,
which consists of observing how starlight is dimmed as a ring passes in front
of a background star.
DIF: Easy REF: Section 11.3 MSC: Applying
OBJ: Explain how rings are observed
around planets.
18.
What are the two known
sources of ring material around the giant planets?
ANS: (1) Tidal stresses on objects such as moons, asteroids,
and comets when they come close to the Roche lobe of a giant planet, and (2)
volcanic eruptions on moons, which fling material at speeds exceeding the
escape velocity of the moons and into ringlike orbits surrounding a giant
planet.
DIF: Medium REF: Section 11.3 MSC: Applying
OBJ: Discuss the two proposed
origins for rings around giant planets.
19.
Describe some of the
effects that moons can have on nearby ring systems.
ANS: Shepherd moons can create gaps, sharp edges, knots,
twists, and ropelike features in the rings. Moons are also responsible for
changing the density of rings, creating arclets and ring arcs, and creating
gaps, via orbital resonances.
DIF: Medium REF: Section 11.3 MSC: Applying
OBJ: Illustrate how moons provide
orbital stability to ring material.
20.
Explain why it was
difficult for the Voyager space probe to detect Jupiter’s ring system as
it was approaching the planet but easy to detect the rings once the probe
passed behind Jupiter.
ANS: Jupiter’s ring system is composed mostly of tiny dust
grains. Particles this small tend to scatter light in the direction in which
the light was originally traveling. As the space probe approached Jupiter, the
Sun and the probe were on the same side of the ring system, so all of the light
scattered off the ring was directed away from the probe. As the probe passed
behind Jupiter, the Sun was now on the opposite side of the ring system from
the probe, and all of the light scattered off the ring was directed toward the
probe.
DIF: Medium REF: Section 11.3
MSC: Understanding
OBJ: Describe the typical
composition of rings.
21.
Why do we suspect that
the inner planets do not have rings?
ANS: They lack small moons to act as shepherds of the ring
material, which lends stability to a ring system and allows them to last over
long periods of time.
DIF: Difficult REF: Section 11.3 MSC: Applying
OBJ: Illustrate how moons provide
orbital stability to ring material.
22.
Do a planet’s rings
last forever? Why or why not?
ANS: Because ring particles collide over time, they lose
energy and angular momentum and eventually will fall into the planet. They do
not last forever, and must be replenished via some mechanism such as the
crushing of new icy or rocky material.
DIF: Medium REF: Section 11.3 MSC: Applying
OBJ: Discuss the two proposed
origins for rings around giant planets.
23.
Explain how pictures
such as the one below are taken. Where must the camera be in relation to the
planet and the Sun? Why do the rings appear so bright from this direction?
ANS: This picture was taken using the technique of
backlighting. The camera must be on the opposite side of the planet from the
Sun. Backlighting occurs when light falls on very small objects, such as the
particles in Saturn’s rings. Because very little of the light is scattered
backward or to the sides of the particles, they appear much brighter from this
angle, making it easier to see the small particles in the diffuse rings.
DIF: Difficult REF: Section 11.4
MSC: Understanding
OBJ: Relate a ring’s appearance to
its composition and density.
24.
Rank the four giant
planets’ ring systems from brightest to darkest.
ANS: Saturn’s rings are the brightest, followed by Jupiter’s
ring. Uranus’s and Neptune’s ring systems are the darkest (consider them tied).
DIF: Easy REF: Section 11.4 MSC:
Remembering
OBJ: Relate a ring’s appearance to
its composition and density.
25.
What do astronomers
believe causes the spokelike features associated with Saturn’s B ring?
ANS: Meteoroid impacts with larger ring particles send dust
above the ring plane. These particles become ionized, and Saturn’s magnetic
field causes them to drift outward.
DIF: Difficult REF: Section 11.4
MSC: Remembering
OBJ: Summarize the substructure of
planetary rings.
26.
Describe the main
difference(s) between a thin ring and a diffuse ring.
ANS: Particles in thin rings (such as Saturn’s A, B, or C
rings) are close together and collide frequently, forcing the particles into
distributions that are vertically very thin and orbits that are very regular.
Particles in diffuse rings (such as Saturn’s G ring) are far apart and collide
infrequently, allowing them to preserve a range of orbital shapes and
inclinations. This makes the diffuse rings fuzzier and thicker than thin rings.
DIF: Medium REF: Section 11.4
MSC: Understanding
OBJ: Predict why some giant planets
have bright rings and others only have diffuse rings.
27.
Describe the origin of
the Encke Gap.
ANS: The Encke Gap in Saturn’s A ring is caused by Pan, the
Saturnian moon orbiting within the gap. Gravitational tugs by Pan dislodge ring
particles from its vicinity, preventing rings from forming stable orbits there.
DIF: Medium REF: Section 11.4
MSC: Understanding
OBJ: Summarize the substructure of
planetary rings.
28.
Why does the Adams Ring
around Neptune clump into arcs rather than uniform rings?
ANS: It is believed that gravitational forces caused by
orbital resonances between ring particles and the Neptunian moon Galatea (just
inside the Adams Ring) result in particles that preferentially congregate into
arcs.
DIF: Medium REF: Section 11.4
MSC: Understanding
OBJ: Summarize the substructure of
planetary rings.
29.
Looking at the life
forms found to exist in extreme environments on Earth suggests that there are
probably three things needed for life. What are they?
ANS: The three things needed for life appear to be liquid
water, an energy source (sunlight, geothermal energy, or chemical energy) and
organic, compounds.
DIF: Difficult REF: Section 11.4
MSC: Understanding
OBJ: Estimate the likelihood of
life on moons of the giant planets.
30.
Describe how
astronomers believe conditions on the surface of Titan may reflect those on
Earth early in its history, when life first arose.
ANS: The presence of large quantities of nitrogen and
hydrocarbons such as methane in the atmosphere of Titan should allow for the
formation of molecules needed to form DNA and RNA, as well as amino acids. The
destruction of these compounds by solar radiation and recombination of their
components into gases produces complex organic molecules, which can rain out of
the atmosphere and form a “sludge” comparable to the organic molecules needed
for life to arise on Earth. The plausibility of this scenario was demonstrated
in the laboratory in the 1950s in the Urey-Miller experiment (see Chapter 24).
DIF: Difficult REF: Section 11.4
MSC: Understanding
OBJ: Estimate the likelihood of
life on moons of the giant planets.
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