Chapter 18 Astronomy
How does a thin planetary ring retain its shape?
Small moons orbiting just inside and outside the rings shepherd the ring particles.
Examining the given table, we can see that the Galilean satellites of Jupiter which are ________ Jupiter have ________ density.
farther from; lower
What difference in the rings of Uranus and Neptune was first revealed in observations from Earth-based telescopes?
the clumpy ring arcs of Neptune
The surface age of Triton is thought to be about 100 million years. What is the evidence for such an age determination?
the density of impact craters
We could divide the Jovian planets into two subclasses: the "gas giants" and the "ice giants." Into which group should we place the four Jovian planets?
the gas giants are Jupiter & Saturn, and the ice giants are Uranus & Neptune
What gives Saturn's rings their beautiful structure?
the gravitational influence of Saturn's moons on the ring particles
What is our current best hypothesis as to how the whole Uranian system came to have such a large inclination?
A large impact during the latter stages of planet building tipped Uranus on its side.
With respect to the moons of Saturn, select all of the correct statements from the following list.
All of Saturn's moons are a mixture of rock and ice. Titan is the only solar system moon with a substantial atmosphere. Some of Saturn's moons may have been captured asteroids or Kuiper belt objects. Smaller moons of Saturn have cracks and smooth areas that suggest past geologic activity.
The discoveries of Uranus, Neptune, and Pluto all came long after the death of Isaac Newton. How was Newton involved in the discovery of a new planet?
All of these choices are correct.
What evidence do we have that Jupiter is primarily composed of hydrogen and helium rather than rock?
All of these choices are correct.
The surface of which of Jupiter's moons is seen in the figure?
Callisto
A Sense of Proportion: Arrange the following planets in order of increasing diameter:
Earth , Neptune , Uranus , Saturn , Jupiter
What evidence do we have that the surface of Europa is young and active?
Europa has very few impact craters and the icy crust of Europa is highly reflective.
How can small worlds like Triton have atmospheres, when larger objects like Ganymede have none?
Farther from the sun, it is colder and easier to retain gases and most of the atmospheric gases sublimate from ice on the surfaces of the objects.
How does Ganymede differ from Callisto?
Ganymede is differentiated and Callisto is not.
Using the table above, which list below ranks the Galilean satellites of Jupiter in order of decreasing size, from left to right?
Ganymede, Callisto, Io, Europa
How can worlds like Triton and Pluto have atmospheres when a larger world such as Ganymede has none?
Gas molecules move more slowly at low temperatures.
Why does Europa have few impact craters?
Geological activity has erased them.
Why does Io have no impact craters?
Geological activity has erased them.
Examining the table above, we see that ______ is the most abundant substance in both Jupiter and Saturn.
H2
Examining the table above, we see that ______ is the second most abundant substance in both Jupiter and Saturn.
He
The shape of larger satellites should be spherical, while the smaller ones shouldn't be. Which is a pair of moons that are not spherical?
Hyperion and Phoebe
The leading sides of some satellites tend to be darker with brighter trailing sides. Which moon of Saturn is an example of this?
Iapetus
Why would you expect Io to have more impact craters than Callisto?
Io is closer to Jupiter, so it's subject to more potentially impacting objects.
What evidence do we have that Jupiter has a very hot interior?
It emits 70% more energy at infrared wavelengths than it receives from the sun.
If Jupiter had a moon the size of Earth's moon orbiting beyond Callisto, what would you predict for its surface features?
It should be dominated by impact craters with little sign of geological activity.
If Jupiter had a moon the size of Earth's moon orbiting beyond Callisto, what would you predict for its density?
It should have a low density, less than 2 g/cm3.
What does it mean when a planet is "oblate?"
Its equatorial diameter is larger than its polar axis and it bulges around the equator.
With respect to the evolution of Jupiter's moon and ring systems, and how Jupiter is different than Earth, select all of the correct statements from the following list.
Jupiter has a small solid core, a deep liquid mantle, and a gaseous atmosphere. There is water in Jupiter's atmosphere. Jupiter has over 10 times the diameter and over 300 times the mass of Earth.
In the 1950s radio telescopes first detected synchrotron radiation from Jupiter. What did this discovery tell us about Jupiter?
Jupiter has a strong magnetic field.
This diagram illustrates a model of Saturn's interior. Why is the metallic hydrogen zone for Saturn smaller than Jupiter's metallic hydrogen zone?
Jupiter has more mass and thus greater gravitational compression at a depth.
How do the differences in the interiors of Saturn and Jupiter affect the planets' magnetic fields?
Jupiter's is stronger than Saturn's.
The shape of small satellites differ from large satellites. What is the reason for this?
Larger moons have enough mass to gravitationally pull themselves into a spherical shape, and smaller ones do not.
How do the appearance of the leading and trailing sides of some satellites differ?
Leading sides tend to be darker, and trailing sides brighter.
What is the evidence for the origin of the rings of Neptune?
Neptune's rings are trapped among the orbits of small moons and Neptune's moons show evidence of having been impacted.
If Neptune had no satellites, would you expect it to have rings?
No; ring material comes from the moons.
How do Saturn's three layers of clouds differ from Jupiter's three layers of clouds?
None of these choices are correct.
With respect to the outer planets, select all of the correct statements from the following list. Note that Pluto is now defined as a dwarf planet.
Pluto's characteristics do not fit in with the other outer planets'. Being rich in hydrogen, the large outer planets are low in density. The outer planets (except Pluto) are larger than Earth. All Jovian planets have rings and moon systems.
In which way does Saturn differ from Jupiter?
Saturn has a smaller zone of liquid metallic hydrogen.
This figure shows the orientation of the rotational axis of Uranus relative to its orbital plane throughout its 84-year-long trip around the sun. How do the seasons on Uranus differ from the seasons on Earth?
Seasons on Uranus are 84 times longer and more extreme than on Earth.
With respect to Saturn and its differences with Jupiter, select all of the correct statements from the following list.
Smaller moons "shepherd" particles in the ring system, or keep them in their rings. Some ring particles are small moons that were pulled apart by tidal forces. Although it has the most extensive one, Saturn is not the only planet with a ring system. Being twice as far from the sun, Saturn is much colder than Jupiter, making its atmosphere much less active. Saturn's rings are made mostly of ice particles.
What evidence do we have that Io's crust and lava is mostly silicate rock rather than sulfur compounds?
Some mountains on Io are much higher than any mountains on Earth and much of the lava flowing from Io's volcanoes is hotter than Earth lava.
With respect to Jupiter's family of moons, select all of the correct statements from the following list.
Some of Jupiter's smaller moons are probably captured asteroids. Callisto's old, cratered surface tells us that it has never been geologically active. Ganymede probably was geologically active in the past. Volcanic activity has been observed on lo.
What evidence do we have that Pluto and Charon are made of mixtures of rock and ice?
Spectra show that both bodies have some surface ices and both bodies have a density of 2 grams per cubic centimeter.
What evidence supports the model of Jupiter's Galilean satellites forming in a mini accretion disk around Jupiter?
The density trend of these four moons is highest close to Jupiter and decreases with distance and the two inner moons are much smaller than the two outer moons of this group.
The figure is an image of the Encke division in Saturn's rings recorded by the Cassini spacecraft. The picture above has a prominent clue as to the nature of the processes that confine and shape ring systems. What do these clues suggest?
The division and ripples indicate a small moon orbits in the division.
How would you expect the shape of small satellites to differ from large satellites?
The larger ones should be spherical, and the smaller ones shouldn't be.
What causes the leading side of Saturn's small moon Iapetus to differ from its trailing side?
The leading side is darker as it collides with and captures dark dust.
What keeps small shepherd moons from breaking apart within the Roche limit of a planet?
The moons must be structurally strong (which means that they are kept from breaking apart by the electrostatic bonds of the moon's material).
Jupiter's ring appears dark in back-scattered light, yet appears bright in forward-scattered light. What does this tell us about the particles that make up Jupiter's ring?
The particles' average diameter is a few micrometers and are most likely dust.
Why is there no liquid metallic hydrogen zone in the interiors of Uranus or Neptune?
The pressure is too low for hydrogen to be metallic.
In this image you can see Jupiter's main ring appear bright in forward-scattered light. What does this indicate about the ring particles in Jupiter's main ring?
The ring particles are about the size of the wavelength of visible light.
What evidence indicates that the rings of Uranus have little dust and the rings of Neptune contain a lot of dust?
The rings of Uranus appear dark in forward-scattered light and the rings of Neptune appear bright in forward-scattered light.
What are the leading and trailing sides of a satellite?
The sides that always face forward and backward to the direction of its orbit around the planet.
Both Uranus and Neptune have a blue-green tint when observed through a telescope. What does this tell you about their composition?
Their atmospheres contain some methane.
How can the cores of Uranus and Neptune have magnetic fields?
Their magnetic fields are believed to be generated by convection in the liquid mantle
What evidence is there that Neptune's moon Triton is geologically active?
There are few craters and there are cracks in the ice.
What does the color of Uranus and Neptune tell you about their composition?
There is an abundance of methane in their atmospheres.
If Saturn had no moons, what do you suppose its rings would look like? Why is this?
There would be no rings since without moons, there would be no material available to be part of the ring system.
If Saturn had no moons, what do you suppose its rings would look like?
There would be no rings.
Why are Europa, Ganymede, and Callisto necessary for the continued heating of Io?
These moons periodically tug on Io and keep its orbit elliptical.
In the atmospheres of Jupiter and Saturn, we see ammonia, ammonia hydrosulfide, and water clouds in three distinct layers. Why don't we see these same three cloud layers in the atmospheres of Uranus and Neptune?
These three layers are likely hidden beneath a higher layer of methane clouds.
Why are the belts and zones on Saturn less distinct than those on Jupiter?
They are deeper inside Saturn's atmosphere.
The mantles of Uranus and Neptune are believed to be which of the following?
They are liquid.
What is the origin of the rings of Neptune?
They are made of debris from impacts on Neptune's moons.
What is the origin of the rings of Uranus?
They are made of debris from impacts on Uranus's moons.
What are the seasons like on Uranus?
They are much more extreme than Earth's, and longer.
The cores of Uranus and Neptune are believed to be which of the following?
They are solid.
Where do astronomers think the particles being added today to Saturn's rings come from?
They are the remains of moons that got too close to Saturn and were crushed by tidal forces.
The shape of larger satellites should be spherical, while the smaller ones shouldn't be. Which is a pair of moons that is an example of this?
Titan and Hyperion
How can Titan have a nitrogen-methane atmosphere with a surface pressure 1.5 times that of Earth's atmosphere, whereas the larger and more massive Ganymede has no atmosphere at all?
Titan is farther from the sun and thus colder than Ganymede.
With respect to how Neptune is different from Uranus, and how its rings and moons formed and evolved, select all of the correct statements from the following list.
Triton has a thin atmosphere and may be geologically active. Neptune's largest moon, Triton, has a retrograde orbit, which suggests that it was captured. Neptune's position was predicted before it was discovered. Neptune is similar to Uranus as far as size, mass, composition, and interior structure.
What is peculiar about the orbits of Neptune's moons Triton and Nereid?
Triton's orbit is in the retrograde direction, and Nereid's orbit is large and very elliptical.
In what way is Uranus different than the other Jovian planets?
Uranus has little remaining heat of formation.
With respect to how Uranus is different from Jupiter, and how its rings and moons formed and evolved, select all of the correct statements from the following list.
Uranus is much smaller and less massive than Jupiter. Uranus's appearance is nearly featureless; very bland. Uranus has some large moons and rings. Uranus rotates on its side, giving it extreme seasons. This may have been caused by an impact.
What is the evidence for the origin of the rings of Uranus?
Uranus's rings are trapped among the orbits of small moons and Uranus's moons show evidence of having been impacted.
How do we get an accurate measurement of the rotational period of Uranus?
We measure the period of the cyclic fluctuation in the synchrotron radiation emitted by Uranus.
Jupiter's mass is approximately 0.001 solar masses. How is the mass of Jupiter determined?
We use Newton's form of Kepler's third law and the period and semimajor axis of Callisto's orbit around Jupiter.
Assume the values in the table below. Make a plot with the orbital velocities on the vertical axis and distance from Saturn along the horizontal axis. Repeat the graph using only the orbital velocity of the planets and distances from the Sun. From analysis of your data, do the rings of Saturn have Keplerian motion?
Yes
Jupiter is more oblate than Earth. Would you expect the other Jovian planets to be more oblate than Earth as well?
Yes. None of them are solid and they all rotate quickly.
What is a zone?
a bright band of clouds in a Jovian planet's atmosphere
What is a belt?
a dark band of clouds in a Jovian planet's atmosphere
Why is Jupiter more oblate than Earth?
because its outer layers are not solid and it rotates quickly
What color do Uranus and Neptune appear to be?
blue-green
If you piloted a spacecraft to Saturn's moons and wanted to look for a geologically active surface, what factors would you look for?
both smooth and grooved areas and volcanic features
The figure is an image of the Encke division in Saturn's rings recorded by the Cassini spacecraft. The picture above has prominent clues as to the nature of the processes that confine and shape ring systems. What is(are) the clue(s)?
both the division itself and the edges of the ring in the division appear "rippled"
This diagram shows the orbit of Charon around Pluto to scale with Earth. The closeness of the two bodies creates strong tidal forces that have set up synchronous orbit and rotations for Pluto and its moon. If you visited one location on the surface of Pluto and found Charon at full phase directly overhead, where would Charon be in the sky when it reaches third-quarter phase 38.3 hours later?
directly overhead
What causes ring particles to darken?
exposure to radiation
The two requirements for a strong planetary magnetic field are rapid rotation and a convective interior zone composed of an electrically conductive material. Jupiter's rotational period is slightly less than 10 hours. What type of matter fulfills the second requirement?
liquid metallic hydrogen
Why is the surface in the above figure so dark?
meteorite dust dirtying the ice
Why are some areas lighter?
more-recent impacts have dug craters deeper into the ice
If you piloted a spacecraft to Saturn's moons and wanted to look for a geologically active surface, what factors would you avoid?
old, cratered areas
If Triton is geologically active, what is its energy source?
radioactive decay in its interior and sunlight
Most of the composition of Pluto and Charon is which of the following?
rock
The outer edge of Saturn's B ring has a radius of 117,500 km, and the inner edge has a radius of 92,000 km. Which edge will have the faster orbital velocity? This difference is possible because Saturn's rings are __________.
the inner edge; a sheet of individual chunks of material each orbiting separately
What is the Roche limit?
the maximum distance from a planet at which planetary rings can exist
If you were to record the spectrum of Saturn and its rings, you should find light from one edge of the rings on the west (right) side of the image red-shifted and light from the other east (left) edge blue-shifted relative to light from the planet itself. This is interpreted as due to ___________.
the orbital motion of the ring particles around Saturn itself
Which interior zone of Uranus and Neptune do we suspect contains the electrically conducting fluid that is responsible for planetary magnetic fields?
the zone of liquid water with dissolved ammonia and methane
What evidence is there that Pluto and Charon are made of rock and ice
their densities
What energy source drives the weather that we see on Jupiter?
thermal energy escaping from Jupiter's interior that is still hot from formation
