The Essential Cosmic Perspective, 8e (Bennett et al.)
Chapter 8 Jovian Planet Systems
8.1 Multiple Choice Questions
1) If Jupiter were scaled to the size of a basketball, Earth would be the closest to the size of
A) a pinhead.
B) a marble.
C) a baseball.
D) a grapefruit.
E) a basketball.
2) Approximately how many times greater is the atmospheric pressure in Jupiter’s core than on
Earth’s surface?
A) 10 thousand
B) 100 thousand
C) 1 million
D) 10 million
E) 100 million
3) What is the most likely method in which Jupiter generates its internal heat?
A) radioactive decay
B) internal friction due to its high rotation rate
C) chemical processes
D) nuclear fusion in the core
E) by contracting, changing gravitational potential energy into thermal energy
4) How do the size and mass of Jupiter’s core compare to the size and mass of Earth?
A) Jupiter’s core is the same size and mass.
B) Jupiter’s core is about 10 times larger both in size and mass.
C) Jupiter’s core is about 10 times larger in size and has the same mass.
D) Jupiter’s core is about the same size but is 10 times more massive.
E) Jupiter doesn’t have a core—it is made entirely from hydrogen and helium.
5) Why is Jupiter denser than Saturn?
A) It is made of a different composition than Saturn, including a higher proportion of hydrogen
compounds and rocks.
B) The extra mass of Jupiter compresses its interior to a greater extent than that of Saturn.
C) Its core is much larger than Saturn’s.
D) It has a greater proportion of helium to hydrogen compared to Saturn.
E) Scientists do not know why this is so.
6) Why is Neptune denser than Saturn?
A) It has a different composition than Saturn, including a higher proportion of hydrogen
compounds and rocks.
B) It has a greater proportion of hydrogen than Saturn.
C) The extra mass of Neptune compresses its interior to a greater extent than that of Saturn.
D) Its hydrogen is molecular, whereas Saturn’s hydrogen is atomic.
E) It is not denser than Saturn.
7) Why is Saturn almost as big as Jupiter, despite its smaller mass?
A) Jupiter’s greater mass compresses it more and increases its density.
B) Saturn’s rings make the planet look bigger.
C) Saturn is further from the Sun, thus cooler, and therefore less compact.
D) Saturn has a larger proportion of hydrogen and helium than Jupiter, and is therefore less
dense.
E) Jupiter’s strong magnetic field constrains its size.
8) How do the jovian planet interiors differ from one another?
A) All have cores of about the same mass, but differ in the amount of surrounding hydrogen and
helium.
B) The core mass decreases with the mass of the planet.
C) The composition changes from mostly ammonia in Jupiter and Saturn to mostly methane in
Uranus and Neptune.
D) The composition changes from mostly hydrogen in Jupiter and Saturn to mostly helium in
Uranus and Neptune.
E) All have about the same amount of hydrogen and helium but the proportion of rocks is greater
in those planets closer to the Sun.
9) Why do the jovian planet interiors differ from one another?
A) The more distant planets formed in a cooler region of the solar nebula and therefore contain a
greater proportion of ices than the closer jovian planets.
B) They differ due to giant impacts at the late stages of planet formation.
C) Accretion took longer further from the Sun, so the more distant planets formed their cores
later and captured less gas from the solar nebula than the closer jovian planets.
D) The more distant planets had longer to form than the closer planets, since the solar nebula
lasted longer at greater distances from the Sun.
10) Why does Jupiter have several distinct cloud layers?
A) Different layers represent clouds made of gases that condense at different temperatures.
B) Different layers represent the various regions where the temperature is cool enough for liquid
water to condense.
C) Different gases are present at different altitudes in Jupiter’s atmosphere.
D) Winds prevent clouds from forming at some altitudes, so we see clouds only at the other
altitudes.
E) Clouds form randomly, so on average there are always several layers.
11) Why are there no visible impact craters on the surface of Io?
A) It is too small to have been bombarded by planetesimals in the early solar system.
B) Its close proximity to Jupiter protects it from impacts.
C) They have been covered up by Io’s active surface geology.
D) Any craters that existed have been eroded through the strong winds on Io’s surface.
E) Io’s thick atmosphere obscures the view of the craters.
12) What is the primary reason an icy moon is likely to be more geologically active than a rocky
moon of the same size?
A) Ice has a lower melting point than rock.
B) Ice is less rigid than rock.
C) Ice contains more radioactive elements than rock.
D) Ice is affected by tidal forces to a greater extent than rock.
E) Ice is less dense than rock.
13) What mechanism is most responsible for generating the internal heat of Io that drives its
volcanic activity?
A) accretion
B) radioactive decay
C) differentiation
D) tidal heating
E) bombardment
14) Which of the following is not due to tidal forces?
A) the synchronous rotation of the Moon around Earth
B) the volcanos on Io
C) the synchronous rotation of the Galilean moons
D) the grooved terrain of Enceladus
E) the retrograde orbit of Triton
15) What is the most abundant gas in Titan’s atmosphere?
A) methane
B) nitrogen
C) hydrogen compounds
D) oxygen
E) argon
16) Which of the following statements about Titan is not true?
A) It may have oceans of liquid methane.
B) Its atmosphere is mostly nitrogen.
C) Its temperature is too cold for liquid water to exist.
D) Its surface is hidden from view by its thick atmosphere.
E) It is the coldest moon in the solar system.
17) Which moon did the Huygens spacecraft land on?
A) Ganymede
B) Callisto
C) Europa
D) Titan
E) Triton
18) What did the photographs from the Huygens probe reveal as it landed on Titan?
A) dry, featureless plains
B) a water world of frozen ice sheets
C) a pockmarked surface covered with volcanos
D) river valleys and an ancient shoreline
E) nothing; there was zero visibility due to the methane smog
19) What is the average thickness of Saturn’s rings?
A) a few million kilometers
B) a few tens of thousands of kilometers
C) a few hundred kilometers
D) a few kilometers
E) a few tens of meters
20) Which of the following best describes the composition of the particles forming Saturn’s
rings?
A) water ice
B) metallic grains
C) methane ice
D) volcanic rock
E) hydrogen and helium
21) Why are Saturn’s rings so thin?
A) Saturn’s gravity prevents particles from migrating upwards out of the rings.
B) The “gap” moons shepherd the particles and maintain its thin profile.
C) Any particle in the ring with an orbital tilt would collide with other ring particles, flattening
its orbit.
D) Solar radiation pressure keeps particles pressed into the rings.
E) The current thinness is a short-lived phenomenon that is special to this time.
22) Planetary rings
A) orbit in the equatorial plane of their planet.
B) are composed of a large number of individual particles that orbit their planet in accord with
Kepler’s laws.
C) exist around all of the jovian planets.
D) all of the above
23) What is the Cassini division in Saturn’s rings?
A) a dark ring, visible from Earth, composed of dark, dusty particles
B) a large gap, visible from Earth, produced by an orbital resonance with the moon Mimas
C) the imaginary circle marking the halfway point of Saturn’s rings
D) the widest ring of Saturn, located between two large ring gaps
E) the most opaque ring of Saturn, made of highly reflective ice particles
24) Which of the jovian planets have rings?
A) Jupiter
B) Saturn
C) Uranus
D) Neptune
E) all of the above
25)
What would be the approximate radius of a hydrogen/helium planet with a mass one-tenth that of
Jupiter?
A) about 0.7 times the radius of Jupiter
B) about 0.5 times the radius of Jupiter
C) about 1 time the radius of Jupiter
D) about 0.9 times the radius of Jupiter
26)
If a planet is found with a radius 5% greater than Jupiter, which is the best first estimate of that
planet’s mass?
A) about 0.3 times Jupiter’s mass
B) about 1 times Jupiter’s mass
C) about 3 times Jupiter’s mass
D) about 10 times Jupiter’s mass
27)
The Galileo spacecraft dropped a probe into Jupiter’s atmosphere that survived 200 km, or 0.3%
of Jupiter’s radius. Which is the deepest layer that this probe was able to directly sample?
A) gaseous hydrogen layer
B) liquid hydrogen layer
C) metallic hydrogen layer
D) rocky core
28) Where is Jupiter’s strong magnetic field generated?
A) rocky core
B) metallic hydrogen layer
C) liquid hydrogen layer
D) gaseous hydrogen layer
E) cloud tops
29) Why do Uranus and Neptune appear blue?
A) Oceans that are visible through their atmospheres are blue.
B) The nitrogen gas in their atmospheres absorbs all colors except blue.
C) The methane gas in their atmospheres absorbs all colors except blue.
D) Small dust grains preferentially scatter blue light.
30) What kind of observations can astronomers use to study Io’s volcanoes?
A) visible-light images to study the distribution of sulfur compounds on its surface
B) visible-light images to study plumes using reflected sunlight
C) infrared images to study warm plumes on Io’s night-side
D) spectroscopy to determine the composition of the plumes
E) all of the above
31) The large Jovian satellites have sizes comparable to Mercury. Why do they have an icy
composition compared to Mercury’s rocky composition?
A) They are captured comets.
B) They formed from hydrogen compounds expelled by the Jovian planets.
C) They experienced many more cometary impacts during the Late Heavy Bombardment.
D) They formed beyond the frost line, where ices were more abundant than metals and rock.
8.2 True/False Questions
1) If Jupiter were 10 times more massive, it would actually have a smaller radius.
2) Hydrogen exists as a gas, liquid, and solid within Jupiter.
3) If Jupiter were 10 times more massive, it would generate nuclear fusion in its core and be a
star instead of a planet.
4) Jupiter’s Great Red Spot is a low-pressure storm, like a hurricane on Earth.
5) Only one of the moons of the jovian planets has an atmosphere thicker than Earth’s
atmosphere.
6) The water-ice particles forming Saturn’s rings are frozen together into a thin sheet that rotates
around Saturn like a solid body.
7) The mass of Saturn can be determined by applying Kepler’s 3rd Law to the motion of a single
ice particle in its rings.
8) It is impossible to land a spacecraft on any moons of the Jovian planets because they are
mostly gaseous.
9) The Huygens landing showed that the surface of Titan is made of mostly rock.
10) Titan’s surface may contain lakes of liquid methane.
11) Jupiter is the only Jovian planet with large storms.
12) Ganymede is larger than Mercury, but it is not classified as a planet because it orbits Jupiter
as opposed to the sun.
13) If the Jovian planets had solid surfaces, their large storms would likely dissipate faster.
8.3 Process of Science Questions
1) Unification in Science: One of the true pleasures of science is to discover that two rather
different phenomena are really manifestations of the same set of physical principles. To this end,
explain how the volcanoes on Io, the subsurface ocean on Europa, and the gaps in Saturn’s rings
reflect the operation of the same physical principle.
2) Io’s Volcanoes Predicted: The intense volcanic activity on Io came as somewhat of a surprise
to many when it was discovered by the Voyager mission in 1979. Nevertheless, argue that all of
the elements were in place to make a prediction of intense volcanic activity on Io before the
Voyager mission. Search the web for the history of Io’s volcanism to see if such a prediction was
actually made.
3) Probing the Interior of Jupiter: Astronomers claim to have a reasonable model for interior
structure of Jupiter. What is the observational basis for this model? Does it make any predictions
that have been put to observational tests? How is the interior structure of the Earth known
(review Chapter 7 if necessary)? Do you think the interior structure of Jupiter is more or less
well-tested than that of the interior structure of the Earth? Explain.
4) Observing Galilean moons: The Galileo spacecraft launched to Jupiter carried a small
telescope (about 25 cm in diameter) for collecting visible light images. Explain why this
telescope collects images with much better spatial resolution than even the largest Earth-bound
telescopes (for example, the 10 meter Keck telescopes).
8.4 Short Answer Questions
1) Why does it make sense that the jovian planets farther from the Sun have less mass?
2) The satellite Amalthea orbits Jupiter at just about the same distance in kilometers at which
Mimas orbits Saturn. Yet Mimas takes almost twice as long to orbit. What can you deduce from
this difference qualitatively? Since Jupiter and Saturn are not very different in radius, what else
can you conclude?
3) Suppose the jovian planet atmospheres were composed 100 percent of hydrogen and helium
rather than 98 percent of hydrogen and helium. How would the atmospheres be different in terms
of color and weather?
4) Describe the possible origins of Jupiter’s vibrant colors. Contrast these with the origins of the
colors of the other jovian planets.
5) Contrast Jupiter’s magnetosphere with that of Earth and of the other jovian planets.
6) Explain how the resonance among Io, Europa, and Ganymede makes their orbits slightly
elliptical.
12
7) What is “ice geology”? Give an example illustrating why it is important in the outer solar
system.
8) Describe some of the results from the Cassini/Huygens mission to Saturn and its moons.
9) Describe two leading scenarios for the origin of the planetary rings. What makes us think that
ring systems must be continually replenished?
10) What about Triton’s orbit makes it such an unusual satellite?
11) How would Jupiter be different if it rotated more slowly?
12) Explain why Titan is of great interest to astronomers.
13) Which of the following applies to Io?
A) the most volcanically active body in the solar system
B) thought to have a deep, subsurface ocean of liquid water
C) probably a captured Kuiper Belt object
D) the only moon of a jovian planet with an atmosphere thicker than Earth’s atmosphere
14) Which of the following applies to Europa?
A) the most volcanically active body in the solar system
B) thought to have a deep, subsurface ocean of liquid water
C) probably a captured Kuiper Belt object
D) the only moon of a jovian planet with an atmosphere thicker than Earth’s atmosphere
15) Which of the following applies to Triton?
A) the most volcanically active body in the solar system
B) thought to have a deep, subsurface ocean of liquid water
C) probably a captured Kuiper Belt object
D) the only moon of a jovian planet with an atmosphere thicker than Earth’s atmosphere
16) Which of the following applies to Titan?
A) the most volcanically active body in the solar system
B) thought to have a deep, subsurface ocean of liquid water
C) probably a captured Kuiper Belt object
D) the only moon of a jovian planet with an atmosphere thicker than Earth’s atmosphere
17) Which of the following applies to Ganymede?
A) the most volcanically active body in the solar system
B) thought to have a deep, subsurface ocean of liquid water
C) probably a captured Kuiper Belt object
D) the largest moon in the solar system
8.5 Mastering Astronomy Reading Quiz
1) Which of the following is not a general characteristic of the four jovian planets in our solar
system?
A) They are higher in average density than are the terrestrial planets.
B) They lack solid surfaces.
C) They are composed mainly of hydrogen, helium, and hydrogen compounds.
D) They are much more massive than any of the terrestrial planets.
2) Which of the following best describes the internal layering of Jupiter, from the center
outward?
A) core of rock, metal, and hydrogen compounds; thick layer of metallic hydrogen; layer of
liquid hydrogen; layer of gaseous hydrogen; cloud layer
B) core of rock and metal; mantle of lower density rock; upper layer of gaseous hydrogen; cloud
layer
C) solid rock core; layer of solid metallic hydrogen; layer of pure liquid hydrogen; cloud layer
D) liquid core of hydrogen compounds; liquid hydrogen layer; metallic hydrogen layer; gaseous
hydrogen layer; cloud layer
3) Which of the following statements comparing the jovian interiors is not thought to be true?
A) They all have the same exact set of internal layers, though these layers differ in size.
B) They all have cores of roughly the same mass.
C) They all have cores that contain at least some rock and metal.
D) Deep in their interiors, they all have pressures far higher than those found in the deepest
oceans on Earth.
4) Overall, Jupiter’s composition is most like that of ________.
A) the Sun
B) Earth
C) a comet
D) an asteroid
5) Jupiter’s colors come in part from its three layers of clouds. Which of the following is not the
primary constituent of one of Jupiter’s cloud layers?
A) clouds of sulfuric acid
B) clouds of water
C) clouds of ammonium hydrosulfide
D) clouds of ammonia
6) How do typical wind speeds in Jupiter’s atmosphere compare to typical wind speeds on Earth?
A) They are much faster than average wind speeds on Earth.
B) They are about the same as average wind speeds on Earth.
C) They are slightly slower than average wind speeds on Earth.
7) What is the Great Red Spot?
A) a long-lived, high-pressure storm on Jupiter
B) a hurricane that comes and goes on Jupiter
C) a place where reddish particles from Io impact Jupiter’s surface
D) a region on Jupiter where the temperature is so high that the gas glows with red visible light
8) What atmospheric constituent is responsible for the blue color of Uranus and Neptune?
A) methane
B) hydrogen
C) water
D) ammonia
9) How does the strength of Jupiter’s magnetic field compare to that of Earth’s magnetic field?
A) Jupiter’s magnetic field is about 20,000 times as strong as Earth’s.
B) Jupiter’s magnetic field strength is about the same as Earth’s.
C) Jupiter’s magnetic field is about twice as strong as Earth’s.
D) Jupiter’s magnetic field is much weaker than Earth’s.
10) Which of the following statements about the moons of the jovian planets is not true?
A) Most of the moons are large enough to be spherical in shape, but a few have the more potato-
like shapes of asteroids.
B) Some of the moons are big enough that we’d call them planets (or dwarf planets) if they
orbited the Sun.
C) One of the moons has a thick atmosphere.
D) Many of the moons are made largely of ices.
11) Which statement about Io is true?
A) It is the most volcanically active body in our solar system.
B) It is thought to have a deep, subsurface ocean of liquid water.
C) It is the largest moon in the solar system.
D) It is the only moon in the solar system with a thick atmosphere.
12) Which moon has a thick atmosphere made mostly of nitrogen?
A) Titan
B) Triton
C) Ganymede
D) Europa
13) The Huygens probe took numerous pictures as it descended to Titan’s surface in 2005. What
did the pictures show?
A) features of erosion, including what appeared to be dry river valleys and lakebeds
B) primitive life forms
C) a densely cratered surface
D) lava flows of molten basalt
14) Which moon of Jupiter is thought to contain liquid water somewhere in its interior?
A) Europa
B) Ganymede
C) Callisto
D) all of the above
15) Which large jovian moon is thought to have been captured into its present orbit?
A) Triton
B) Callisto
C) Titan
D) Io
16) Suppose you could float in space just a few meters above Saturn’s rings. What would you see
as you looked down on the rings?
A) countless icy particles, ranging in size from dust grains to large boulders
B) a solid, shiny surface, looking much like a piece of a DVD but a lot bigger
C) dozens of large “moonlets” made of metal and rock, each a few kilometers across
D) Nothing-up close; the rings would be so completely invisible that you’d have no way to know
they are there. They can be seen only from a distance.
17) Which statement about planetary rings is not true?
A) Saturn’s rings formed along with its moons 4.6 billion years ago.
B) All four jovian planets have rings.
C) Individual ring particles orbit their planet in accord with Kepler’s laws, so that particles closer
in orbit faster than particles farther out.
D) Rings are always located closer to a planet’s surface than any large moons.
8.6 Mastering Astronomy Concept Quiz
1) Which of the following gases is not a significant ingredient of the jovian planet atmospheres?
A) carbon dioxide
B) hydrogen
C) helium
D) water
2) Jupiter and the other jovian planets are sometimes called “gas giants.” In what sense is this
term misleading?
A) They actually contain relatively little material in a gaseous state.
B) The materials they are made of are more solid than gaseous.
C) They are not in any sense “giants.”
D) Actually, it’s a great description, because these worlds are big and gaseous throughout.
3) What would happen to Jupiter if we could somehow double its mass?
A) Its density would increase, but its diameter would barely change.
B) Its density would decrease, and its diameter would double.
C) Its density would stay about the same, and its volume would double.
D) It would become a star, with nuclear fusion in its core.
4) According to our theory of solar system formation, why did Uranus and Neptune end up to be
much less massive than Jupiter and Saturn?
A) Particles in the solar nebula were more spread out at greater distances, so that accretion took
longer and there was less time to pull in gas before the solar wind cleared the nebula.
B) Ices were able to condense at the distance of Jupiter and Saturn, but only rock and metal
could condense at the distances of Uranus and Neptune.
C) The colder gas in the outer regions of the solar nebula had less gravity and therefore could not
gather up into such large balls as it could closer in.
D) The size differences are thought to be a random coincidence.
5) What causes the vivid bands seen in Jupiter’s upper atmosphere?
A) Rising and falling gas is stretched by Jupiter’s rapid rotation into bands of weather that
encircle the planet.
B) Different materials are separated into bands by the centripetal force of Jupiter’s rapid rotation.
C) The lighter bands are clouds seen above the darker solid surface below.
D) Jupiter’s powerful magnetic field causes charged particles in its atmosphere to line up into
bands.
6) What is a likely reason why a large storm like the Great Red Spot on Jupiter can last so long?
A) There is no solid surface underneath the storm to sap its energy.
B) Jupiter is unique from the other jovians since it spins much faster, allowing storms to last
longer.
C) Chemical reactions within the atmosphere release energy, which prolongs the storm.
D) Low pressure systems form easily and last a long time on the jovian planets since their
atmospheres are so cold.
7) Uranus and Neptune have methane clouds but Jupiter and Saturn do not. Which of the
following explains why?
A) Temperatures on Jupiter and Saturn are too high for methane to condense.
B) Jupiter and Saturn do not contain any methane gas.
C) The rapid rotation of Jupiter and Saturn prevents methane clouds from forming.
D) The stronger gravity on Jupiter and Saturn pulls methane downward so that it can’t form
clouds.
8) Which jovian planet should have the most extreme seasonal changes?
A) Uranus
B) Jupiter
C) Saturn
D) Neptune
9) Why is the radiation so intense in the region that traces Io’s orbit around Jupiter (the Io torus)?
A) The region is full of gases that become ionized by Jupiter’s magnetic field after they are
released from volcanoes on Io.
B) Io’s gravity allows this region to capture huge numbers of charged particles from the solar
wind.
C) An orbital resonance between Io, Europa, and Ganymede makes the radiation intense.
D) Jupiter’s strong magnetic field makes the radiation intense everywhere, and the region around
Io is no different than any other region.
10) Which of the following best explains why many jovian moons have been more geologically
active than the Moon or Mercury?
A) Jovian moons are made mostly of ice that can melt or deform at lower temperatures than can
the rock and metal that make up the Moon and Mercury.
B) The jovian moons are considerably larger than the Moon and Mercury and therefore have
retained much more internal heat.
C) The jovian moons probably have far more internal heat generated by radioactive decay than
do the Moon or Mercury.
D) Because of their greater distances from the Sun, the jovian moons receive much less heat
from the Sun.
11) All the following statements are true. Which one is most important in explaining the
tremendous tidal heating that occurs on Io?
A) Io orbits Jupiter on an elliptical orbit, due to orbital resonances with other satellites.
B) Io is made of different material than the other Galilean moons.
C) Io exhibits synchronous rotation, meaning that its rotation period and orbital period are the
same.
D) Io orbits Jupiter in the Io torus, and therefore has a surface that is bombarded by many
charged particles.
12) Which of the following is not a piece of evidence supporting the idea that Europa may have a
subsurface ocean?
A) Astronomers have detected small lakes of liquid water on Europa’s surface.
B) Europa has a magnetic field that appears to respond to Jupiter’s magnetic field.
C) Photos of Europa’s surface show regions that appear to consist of jumbled icebergs frozen in
place.
D) Europa’s surface shows very few impact craters.
13) Which of the following is most unlikely to be found on Titan?
A) lakes of liquid water in the warmer equatorial regions
B) lakes of liquid methane
C) rain or snow consisting of methane or ethane droplets or ice crystals
D) volcanic outgassing of methane and other gases
14) Why do astronomers believe that Triton is a captured moon?
A) Triton orbits Neptune in a direction opposite that of Neptune’s rotation.
B) Triton is very small and potato-shaped, which is common of captured moons.
C) Triton is too large to have been formed in the “miniature solar nebula” thought to have
surrounded Neptune in its very early history.
D) Triton appears to be made mostly of ice.
15) Which statement about Saturn’s rings is not true?
A) The rings must look much the same today as they did shortly after Saturn formed.
B) The large gap known as the Cassini Division is shaped by an orbital resonance with the moon
Mimas, which orbits well outside the rings.
C) Some features of the rings are shaped by small moons that actually orbit within the ring
system.
D) The rings are so thin that they essentially disappear from view when seen edge-on.
16) According to current understanding, which of the following is required for a planet to have
rings that last for a very long time?
A) The planet must have many small moons that orbit relatively close to the planet in its
equatorial plane.
B) The planet must be at least as massive as Saturn.
C) The planet must orbit its star at a distance greater than Mars orbits the Sun.
D) The planet must once have had a large moon that came too close to it, shattering the moon
and creating the ring particles.