Astronomy 8.1: A Different Kind of Planet

Clouds of different compositions and colors form at ___________ in each jovian planet's atmosphere.

different altitudes

Figure 8.10 Selected views of weather patterns on the four jovian planets.

The rapid rotation of the jovian planets helps drive strong winds, creating their banded appearances and sometimes giving rise to huge storms.

Definition of Tidal Force:

- A tidal force arises from a difference in the strength of a gravitational attraction across an object, causing the object to stretch. - For example, the Moon exerts a gravitational attraction on Earth, - but this attraction is stronger on the side of Earth that is facing the Moon than on Earth's opposite side. - Note that in the video, the tidal force is represented by the difference in the lengths of the two arrows. (Which represent the gravitational force between Jupiter and the two sides of Io).

Definition of tidal force:

- A tidal force is a force arising from a difference in the strength of a gravitational attraction across an object, causing the object to stretch. - For example, the Moon exerts a gravitational attraction on Earth, but this attraction is stronger on the side of Earth that is facing the Moon than on Earth's opposite side. - Note that in the video, the tidal force is represented by the difference in the lengths of the two arrows (which represent the gravitational force between Jupiter and the two sides of Io).

Definition of orbital resonance:

- An orbital resonance means that one object's orbital period is a simple fraction of another's, such as 1/2 or 1/3 or 1/4. - In such cases, the objects periodically line up in a way that allows their mutual gravity to affect their orbits.

The other jovian planets also have dramatic weather patterns (Figure 8.10b-d). As on Jupiter, Saturn's rapid rotation creates?

- As on Jupiter, Saturn's rapid rotation creates alternating bands of rising and falling air, along with rapid east-west winds. - In fact, Saturn's winds are even faster than Jupiter's —a surprise that scientists have yet to explain. - Neptune's atmosphere is also banded, and we have seen a high-pressure storm, called the Great Dark Spot, -> similar to Jupiter's Great Red Spot. - However, the Great Dark Spot did not last as long; - it disappeared from view just 6 years after its discovery. - Uranus had a more subdued appearance when Voyager 2 flew past it in 1986, - But now seems to have more frequent storms. - Probably due to the slow but dramatic change of seasons caused by its extreme axis tilt and 84-year orbit around the Sun.

Jovian Planets' Clouds:

- Clouds form when a gas condenses to make tiny liquid droplets or solid flakes. - Water vapor is the only gas that can condense to form clouds in Earth's atmosphere, but Jupiter's atmosphere has three major types of clouds, each of which forms at different altitudes. - Looking from the bottom up in Figure 8.6, Jupiter's lowest cloud layer occurs about 100 kilometers below the highest cloud tops. - At this depth, temperatures are nearly Earth-like and water can condense to form clouds. - The temperature drops as you go higher, and about 50 kilometers above the water clouds it is cold enough for a gas called ammonium hydrosulfide (NH4SH) to condense into clouds. - These ammonium hydrosulfide clouds reflect brown and red light, producing many of the dark colors of Jupiter. - Higher still, the temperature is so cold that ammonia (NH3) condenses to make an upper layer of white clouds.

Computer models tell us that Jupiter has?

- Computer models tell us that Jupiter has fairly distinct interior layers. - The layers do not differ much in composition—all except the core are mostly hydrogen and helium. - Instead they differ in the phase (such as liquid or gas) of their hydrogen. - The outer layer is the only region in which conditions are moderate enough for hydrogen to remain in its familiar, gaseous form. - This layer makes up about the outer 10% of Jupiter and represents what we usually think of as Jupiter's atmosphere. - As we look deeper, the high pressures compress the hydrogen into liquid form in the next 10% of Jupiter's depth, and below that the temperatures and pressures become so extreme that hydrogen is forced into a compact, liquid metallic (electrically conducting) form. - Finally, the models tell us that Jupiter's core is a mix of hydrogen compounds, rock, and metal, but compressed to such extremes of temperature and density that this mix bears little resemblance to familiar solids or liquids.

Figure 8.3 - Jupiter's interior structure, labeled with the pressure, temperature, and density at various depths. - Earth's interior structure is shown to scale for comparison. (The thicknesses of Earth's crust and atmosphere are exaggerated.) - Note that Jupiter's core is only slightly larger than Earth but is about 10 times as massive.

- If you plunged below Jupiter's clouds, you'd never encounter a solid surface—just ever denser and hotter hydrogen/helium compressed into bizarre liquid and metallic phases.

What is the Weather Like on Jovian Planets?

- Jovian atmospheres have dynamic winds and weather, with colorful clouds and enormous storms. - Weather on these planets is driven not only by energy from the Sun (as on the terrestrial planets), - but also by heat generated within the planets themselves. - All but Uranus generate a great deal of internal heat. - No one knows the precise source of the internal heat on jovian planets, - but it probably comes from the conversion of gravitational potential energy to thermal energy inside them. - The best guesses are that this conversion comes from a slow but imperceptible contraction in overall size, - or from ongoing differentiation as heavier materials continue to sink toward the core.

Jovian planets also show numerous storms, the most famous being?

- Jovian planets also show numerous storms, the most famous being Jupiter's Great Red Spot, which is more than twice as wide as Earth. - The Great Red Spot is somewhat like a hurricane on Earth, except that its winds circulate around a high- rather than low-pressure region (Figure 8.9). - It is also extremely long-lived compared to storms on Earth: - Astronomers have seen it throughout the three centuries during which telescopes have been powerful enough to detect it. - No one knows why the Great Red Spot has lasted so long. - However, storms on Earth tend to lose their strength when they pass over land. - Perhaps Jupiter's biggest storms last for centuries simply because there's no solid surface effect to sap their energy. - Two other long-lived storms have recently been observed to undergo a mysterious change, turning from white to red. - The more recent one was torn apart by the Great Red Spot as it passed nearby (Figure 8.10a).

Jupiter's magnetic field:

- Jupiter's magnetic field is by far the strongest—some 20,000 times as strong as Earth's. - This strong field, generated in Jupiter's thick layer of metallic hydrogen, creates an enormous magnetosphere that begins to deflect the solar wind some 3 million kilometers in front of Jupiter (Figure 8.5). - If we could see Jupiter's magnetosphere, it would be larger than the full moon in our sky. - Gases escaping from volcanoes on Jupiter's moon Io feed vast numbers of particles into the magnetosphere, where they become ionized and form a donut-shaped charged particle belt (called the Io torus) that approximately traces Io's orbit. - The particles also create belts of intense radiation and contribute to auroras on Jupiter.

Jovian Planets' Colors:

- Many mysteries remain about the colors of the jovian planets, but clouds play a major role. - Earth's clouds look white from space because they are made of water that reflects the white light of the Sun. - The jovian planets have clouds of several different types, and some of these reflect light of other colors.

Which of the following shows the four jovian planets correctly scaled in size?

- Notice that Jupiter and Saturn (aside from the rings) are similar in size, even though Jupiter is more than three times as massive. - Uranus and Neptune are much smaller, but similar to each other in both size and mass.

Jovian Planets: Global Winds and Storms

- One of the most striking visual features of the jovian planets is the striped appearance of Jupiter. - The stripes represent alternating bands of rising and falling air, and their colors arise from the clouds that we see. - Bands of rising air are white because the rising air condenses and forms white ammonia clouds at high altitudes (see Figure 8.6). - Bands of falling air do not contain ammonia clouds, allowing us to see the reddish-brown ammonium hydrosulfide clouds that lie at lower altitudes. - The fact that these bands wrap around Jupiter is a consequence of the same effect (called the Coriolis effect) that makes storms around low-pressure regions on Earth circulate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere (Figure 8.8a). - Jupiter's faster rotation and larger size make this effect much stronger, in essence stretching the circulation east-west to the point that it wraps all the way around the planet (Figure 8.8b). - Jupiter therefore has very high east-west wind speeds—sometimes more than 400 kilometers per hour (250 miles per hour).

Densities of major ingredients in planetary composition:

- Recall that planets are made from four major categories of ingredients, shown in the table below. - In general, the densities of the ingredients in the table increase from top to bottom; metals are the most dense, and hydrogen and helium gas are the least dense. - Consider how this trend in the densities of the different materials would be expected to affect the densities of the jovian planets.

Saturn has the same basic layering as Jupiter, but its lower mass makes the weight of the overlying layers ______ than on Jupiter.

- Saturn has the same basic layering as Jupiter, but its lower mass makes the weight of the overlying layers less than on Jupiter. - As a result, we must look deeper into Saturn to find each level where pressure changes hydrogen from one phase to another. - Uranus and Neptune have somewhat different layering because their internal pressures never become high enough to form liquid or metallic hydrogen, so they have only a thick layer of gaseous hydrogen surrounding their cores. - Models suggest that their core mix of hydrogen compounds, rock, and metal may be liquid, making for very odd "oceans" buried deep inside Uranus and Neptune; - The cores may also be differentiated so that hydrogen compounds reside in an outer core above an inner core of rock and metal.

Saturn has the same set of three cloud layers as Jupiter, but?

- Saturn has the same set of three cloud layers as Jupiter, but Saturn's lower temperatures (due to both its greater distance from the Sun and its weaker gravity) mean these layers occur deeper in Saturn's atmosphere. - This fact probably explains Saturn's more subdued colors: - Less light penetrates to the depths at which Saturn's clouds are found, and the light they reflect is more obscured by the atmosphere above them.

What is the name of the feature indicated by the arrow in this photo?

- The Great Red Spot is a very large storm, wide enough to swallow two or three Earths.

Major categories of ingredients in planetary composition:

- The following table shows the four major categories of ingredient that were present in the solar nebula and from which planets are made. - Note: that these categories are abbreviated in the figure as "H, He" for hydrogen and helium gas, and "H compounds" for hydrogen compounds.

Sort each of the planetary properties below based on whether they apply to some, all, or none of the four jovian planets in our solar system.

- The jovian planets share many characteristics in common such as approximate core size, severe weather, rings and numerous moons, and strong magnetic fields. - Jupiter and Saturn have similar compositions of hydrogen and helium, while Uranus and Neptune are composed primarily of hydrogen compounds. - Unlike the terrestrial planets, the jovian planets do not have solid surfaces. Return to Assignment

The other jovian planets also have magnetic fields and magnetospheres, but theirs are much _______ than Jupiter's.

- The other jovian planets also have magnetic fields and magnetospheres, but theirs are much weaker than Jupiter's (although still much stronger than Earth's). - Saturn's magnetic field is weaker than Jupiter's because it has a thinner layer of electrically conducting metallic hydrogen. - Uranus and Neptune, smaller still, have no metallic hydrogen at all. - Their relatively weak magnetic fields must be generated in their core "oceans" of hydrogen compounds, rock, and metal.

Definition of Tidal Heating:

- Tidal heating is a source of internal heat created by tidal friction. - This friction is generated as a result of a varying tidal force.

Uranus and Neptune are so cold that any cloud layers similar to those of Jupiter or Saturn would be?

- Uranus and Neptune are so cold that any cloud layers similar to those of Jupiter or Saturn would be buried too deep in their atmospheres for us to see. - However, the cold temperatures allow some of their abundant methane gas to condense into clouds. - Methane gas also absorbs red light, allowing only blue light to penetrate to the level at which the methane clouds form. - The methane clouds reflect this blue light upward, giving these two planets their blue colors

Figure 8.4 - These diagrams compare the interior structures of the jovian planets, shown approximately to scale. - All four planets have cores of rock, metal, and hydrogen compounds, with masses about 10 times the mass of Earth. - They differ primarily in the depth of the hydrogen/helium layers that surround their cores. - The cores of Uranus and Neptune are differentiated into separate layers of rock/metal and hydrogen compounds.

- We can extend the ideas from Jupiter to the other jovian planets. - Because all four jovian planets have cores of about the same mass, their interiors differ mainly in the hydrogen/helium layers that surround their cores (Figure 8.4). - Remember that while the outer layers are named for the phase of their hydrogen, they also contain helium and hydrogen compounds.

Jupiter and Saturn Composition:

-Jupiter and Saturn are made mostly of hydrogen and helium, giving them compositions much more similar to that of the Sun than to that of the terrestrial planets. -Some people even call Jupiter a "failed star" because it has a starlike composition but lacks the nuclear fusion needed to make it shine. -This is a consequence of its size: Although Jupiter is large for a planet, it is only about 1/80 as massive as the lowest-mass stars. -As a result, its gravity is too weak to compress its interior to the extreme temperatures and densities needed for nuclear fusion.

Jupiter and Saturn captured so much _______________ gas that?

-Jupiter and Saturn captured so much hydrogen and helium gas that these gases now make up the vast majority of their masses. -The ice-rich planetesimals from which they grew now represent only about 3% of Jupiter's mass and about 10% of Saturn's mass. -Uranus and Neptune pulled in much less gas from the solar nebula, so hydrogen and helium make up less than half of their total masses.

Is Jupiter is smaller or larger than Saturn in its radius?

-Jupiter is only slightly larger than Saturn in radius even though it is more than three times as massive. -The extra mass of Jupiter compresses its interior to a much higher density. -More precise calculations show that Jupiter's radius is almost the maximum possible radius for a jovian planet. -If much more gas were added to Jupiter, its weight would actually compress the interior enough to make the planet smaller rather than larger (Figure 8.2b). -Some extrasolar planets that are larger in mass than Jupiter are therefore smaller in size.

Jupiter's lack of a solid surface makes it tempting to think of the planet as "all atmosphere," but?

-Jupiter's lack of a solid surface makes it tempting to think of the planet as "all atmosphere," but you could not fly through Jupiter's interior in the way airplanes fly through air. -A spacecraft plunging into Jupiter would find increasingly higher temperatures and pressures as it descended. -The Galileo spacecraft dropped a scientific probe into Jupiter in 1995 that collected measurements for about an hour before the ever increasing pressures and temperatures destroyed it. -The probe provided valuable data about Jupiter's atmosphere but didn't last long enough to sample the interior: -It survived to a depth of only about 200 kilometers, or about 0.3% of Jupiter's radius.

Saturn is considerably ______ dense than Uranus or Neptune. Why?

-Saturn is considerably less dense than Uranus or Neptune. -This should make sense, because the hydrogen compounds, rock, and metal that make up Uranus and Neptune are normally much more dense than hydrogen or helium gas. -However, by the same logic we'd expect Jupiter to be even less dense than Saturn—but it's not.

Why did the different planets capture different amounts of gas?

-The answer probably lies in their distances from the Sun as they formed. -The solid particles that condensed farther from the Sun should have been more widely spread out than those that condensed nearer to the Sun, which means it would have taken longer for them to accrete into large, icy planetesimals. -As the nearest jovian planet to the Sun, Jupiter would have been the first to get a planetesimal large enough for its gravity to start drawing in gas, followed by Saturn, Uranus, and Neptune. -Because all the planets stopped accreting gas at the same time—when the solar wind blew all the remaining gas into interstellar space—the more distant planets had less time to capture gas and ended up smaller in size. -Similar processes, played out to different extents in different planetary systems, may explain much of the wider variety of planetary types that scientists have discovered among planets around other stars

The differences in composition among the jovian planets can probably be traced to?

-The differences in composition among the jovian planets can probably be traced to their origins. (Recall that the jovian planets formed in the outer solar system, where it was cold enough for hydrogen compounds to condense into ices.) -Because hydrogen compounds were so much more abundant than metal and rock, some of the ice-rich planetesimals of the outer solar system grew to great size. -Once these planetesimals became sufficiently massive, their gravity allowed them to draw in the hydrogen and helium gas that surrounded them. -Models suggest that all four jovian planets grew from ice-rich planetesimals of about the same mass — roughly 10 times the mass of Earth —But they captured different amounts of hydrogen and helium gas from the surrounding solar nebula.

What are Jovian Planets Made Of?

-The jovian planets are made mostly of hydrogen, helium, and hydrogen compounds, making them very different from the rocky terrestrial worlds. -However, the jovian planets do not all have exactly the same composition, and they also differ in their interior structures.

Uranus and Neptune differ from Jupiter and Saturn because?

-Uranus and Neptune differ from Jupiter and Saturn both in being much smaller and in having much smaller proportions of hydrogen and helium, leaving them with compositions consisting primarily of hydrogen compounds—especially water (H2O), methane (CH4), and ammonia (NH3)—along with smaller amounts of metal and rock.

We can understand Jupiter's surprisingly high density by?

-We can understand Jupiter's surprisingly high density by thinking about how massive planets are affected by their own gravity. -Building a planet of hydrogen and helium is a bit like making one out of fluffy pillows. -Imagine assembling a planet pillow by pillow. -As each new pillow is added, those on the bottom are compressed more by those above. -As the lower pillows are forced closer together, their mutual gravitational attraction increases, compressing them even further. -At first the stack grows substantially with each pillow, but eventually the growth slows until adding pillows barely increases the height of the stack (Figure 8.2a).

Spacecraft images show fountains of ice spraying into space from Saturn's moon _____________.

Enceladus

Jupiter has three moons for which there is evidence of a global, subsurface ocean of liquid water, with the strongest evidence favoring an ocean on ___________.

Europa

Which of the following photos shows the planet Neptune?

3rd down bright blue - Notice the deep blue color and the storm called the Great Dark Spot.

The two moons that are larger than the planet Mercury are Titan and _________, which is also the largest of Jupiter's moons (and largest moon in the solar system).

Ganymede

____________ is the most volcanically active world in the solar system.

Lo

Recall that Earth has a global magnetic field generated by the movements of charged particles in our planet's outer core of molten metal. What about Jovian planets?

The jovian planets also have global magnetic fields generated by motions of charged particles deep in their interiors.

Definition of tidal heating:

Tidal heating is a source of internal heat created by tidal friction, which is friction generated as a result of a varying tidal force.

Scientists have detected lakes of liquid methane and ethane on the surface of __________.

Titan

True or False? In our solar system, the jovian planets are all farther from the Sun than are the terrestrial planets.

True - As your response indicates, all of the terrestrial planets are closer to the Sun than are the jovian planets. Consider how that will affect your ranking.

Saturn's rings look bright because __________. a) light from the Sun reflects off the material in the rings b) the material in the rings is hot and creates its own light c) light from Saturn reflects off the material in the rings

a) light from the Sun reflects off the material in the rings - Saturn's rings look bright because icy particles in the rings reflect (scatter) sunlight.

The two jovian planets that contain the highest proportions of hydrogen compounds are ___________.

Uranus and Neptune

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) Liquid core of hydrogen compounds; liquid hydrogen layer; metallic hydrogen layer; gaseous hydrogen layer; cloud layer. c) Solid rock core; layer of solid metallic hydrogen; layer of pure liquid hydrogen; cloud layer. d) Core of rock and metal; mantle of lower density rock; upper layer of gaseous hydrogen; cloud layer

a) Core of rock, metal, and hydrogen compounds; thick layer of metallic hydrogen; layer of liquid hydrogen; layer of gaseous hydrogen; cloud layer - You can see the relative depths of these layers in the figure of Jupiter's interior in Section 8.1 of The Essential Cosmic Perspective.

Based on the leading scientific theory of solar system formation, which of the following statements best explains why Uranus and Neptune have a significantly different composition than Jupiter and Saturn? a) Jupiter and Saturn captured more gas from the solar nebula than Uranus and Neptune. b) Jupiter and Saturn formed closer to the Sun, where there was more hydrogen and helium gas and less hydrogen compounds and rock. c) The lower masses of Uranus and Neptune allowed more of their hydrogen and helium gas to escape into space. d) The lower temperatures at the locations of Uranus and Neptune allowed more material to condense into solid form.

a) Jupiter and Saturn captured more gas from the solar nebula than Uranus and Neptune. - Accretion is thought to have occurred more rapidly in the denser regions of the solar nebula that were closer to the Sun. - Therefore, although all four jovian planets captured hydrogen and helium gas from the solar nebula around similar-mass planetesimals (made of hydrogen compounds and rock), Jupiter and Saturn had more time to capture this gas. - As a result, Jupiter and Saturn accreted so much hydrogen and helium gas that these ingredients ended up dominating their composition. - In contrast, Uranus and Neptune were left with compositions dominated by hydrogen compounds and rock.

Which of the following best explains why Jupiter's density is higher than Saturn's? a) Jupiter is more massive than Saturn. b) Jupiter has a stronger magnetic field than Saturn. c) Jupiter has a higher proportion of hydrogen compounds and rock than Saturn. d) Jupiter is closer to the Sun than Saturn. Submit

a) Jupiter is more massive than Saturn. - Because Jupiter and Saturn have nearly identical composition, Jupiter's higher density indicates that its interior is more compressed than Saturn's. - This greater compression is due to gravity, which is stronger for Jupiter because of its greater mass.

What is this object? a) Jupiter's moon Europa b) Uranus's moon Miranda c) Neptune's moon Nereid d) Jupiter's moon Callisto e) Saturn's moon Titan

a) Jupiter's moon Europa Notice the long cracks in the icy surface.

How does mass affect density? Suppose that two planets have the exactly the same composition but very different masses. Which statement will be true? a) The more massive planet will have higher density. b) The more massive planet will have lower density. c) As long as the compositions are the same, both planets will have equal density.

a) The more massive planet will have higher density. - More mass means stronger gravity, which compresses the interior of a planet to higher density. - Moreover, for a two planets of the same mass, gravity is stronger for the denser planet (because it has a smaller radius), compressing it even further.

Which of the following statements best explains why the densities of Uranus and Neptune are higher than that of Saturn, even though Saturn is much more massive? a) They have a higher proportion of hydrogen compounds and rock. b) They are at greater distances from the Sun. c) They have stronger magnetic fields. d) Their interiors are more compressed due to stronger gravity. e) They have higher masses.

a) They have a higher proportion of hydrogen compounds and rock. - At similar temperature and pressure, hydrogen compounds and rock are much higher in density than hydrogen and helium. - The internal conditions in the jovian planets are similar enough so that composition has a major effect on average density. - Uranus and Neptune are higher in density than because they are made primarily of higher-density hydrogen compounds and rock.

We cannot see tidal forces or tidal heating; rather, we predict that they must occur based on the orbital characteristics of the moons. What observational evidence confirms that tidal heating is important on Io? a) active volcanoes on Io b) Io's surprisingly elliptical orbit c) Io's unusual, egg-like shape d) the orbital resonance between Io, Europa, and Ganymede

a) active volcanoes on Io - Io is barely larger than our Moon, and the Moon long ago cooled enough so that it no longer has volcanic activity. - Without some ongoing source of internal heating, Io would be similarly inactive. - Therefore, the fact that Io is the most volcanically active world in the solar system indicates that it must have an ongoing internal heat source, which we identify as tidal heating.

Overall, Jupiter's composition is most like that of _________. a) the Sun b) a comet c) an asteroid d) Earth

a) the Sun - Both are made mostly of hydrogen and helium.

How many orbiting objects are required for an orbital resonance? What is the minimum number of moons that must be orbiting a planet for the moons to have an orbital resonance? a) 1 b) 2 c) 3

b) 2 - An orbital resonance occurs when one moon's orbital period is a simple fraction of the other's, such as 1/2 or 1/3 or 1/4. - This means that at least two moons are required.

If Saturn's rings consisted only of chunks of coal, they would appear _____. a) brighter b) darker c) red hot

b) darker - Rings made of coal would be darker because they would not be as reflective as icy particles.

Which of the following statements correctly describes the motion of the particles in Saturn's rings? a) Particles in all the rings hover motionlessly high above Saturn. b) Particles in the inner rings orbit Saturn at a faster speed than particles in the outer rings. c) Particles in the inner rings orbit Saturn at a slower speed than particles in the outer rings. d) All the particles in the rings orbit Saturn with the same orbital period. Submit

b) Particles in the inner rings orbit Saturn at a faster speed than particles in the outer rings. - In accord with Kepler's third law, particles closer to Saturn orbit at a faster speed than more distant particles.

What is this object? a) Uranus's moon Miranda b) Saturn's moon Titan c) Jupiter's moon Europa d) Neptune's moon Triton e) Jupiter's moon Callisto

b) Saturn's moon Titan - Notice the fuzzy atmosphere that is clearly visible.

Look at the average densities of the jovian planets given in the figure. Can you identify a trend in jovian planet densities with mass or distance from the Sun? a) The more massive the planet, the lower the density. b) There is no clear trend in the densities with mass or distance. c) The densities increase in order of distance from the Sun. d) The more massive the planet, the higher the density. e) The densities decrease in order of distance from the Sun.

b) There is no clear trend in the densities with mass or distance. - There is no obvious trend in the average densities of the jovian planets. - For example, Jupiter is the nearest and most massive of the four planets, but it is the second-highest in average density. - The lack of a clear trend tells us that we need to look deeper at the nature of these planets in order to understand their densities.

Which of the following is not a general characteristic of the four jovian planets in our solar system? a) They lack solid surfaces. b) They are higher in average density than are the terrestrial planets. c) They are much more massive then any of the terrestrial planets. d) They are composed mainly of hydrogen, helium, and hydrogen compounds. Submit

b) They are higher in average density than are the terrestrial planets. - The jovian planets are lower in density than the terrestrial planets, largely because they have much lower proportions of metal and rock.

What are all the black spots on this object? a) Methane lakes on Saturn's moon Titan b) Volcanoes on Jupiter's moon Io c) Impact craters on Uranus's moon Miranda d) Giant cliffs on the planet Mercury e) Wind streaks on Neptune's moon Triton

b) Volcanoes on Jupiter's moon Io - Tidal heating makes Io the most volcanically active place in the solar system.

According to this graph, a planet with 10 times the mass of Jupiter would be ___________. a) about 100 times as large as Jupiter in size (radius) b) about the same size (radius) as Jupiter c) about ten times as large as Jupiter in size (radius) d) about 60% as large as Jupiter in size (radius)

b) about the same size (radius) as Jupiter - Notice that the curve turns back downward at masses just a couple times that of Jupiter, and the radius of a 10 Jupiter-mass object is about the same as the radius of Jupiter.

What does tidal heating do? If a world is subject to tidal heating, we'd expect it to have a __________. a) high surface temperature b) high internal temperature c) shape that is nonspherical

b) high internal temperature - Tidal heating affects the interior of a world, making the interior much hotter than it would be otherwise.

Kepler's third law tells us that __________. a) all planets orbit the Sun at the same speed b) planets nearer to the Sun orbit at higher speed than planets farther from the Sun c) planets nearer to the Sun orbit at slower speed than planets farther from the Sun

b) planets nearer to the Sun orbit at higher speed than planets farther from the Sun - Kepler's laws apply to all orbiting objects; that is, particles in the rings of Saturn must obey the same laws as planets orbiting the Sun.

This painting shows an artist's conception of what it would look like to be within Saturn's system of rings. Notice the many whitish "balls" visible in this painting. Based on what you have learned about rings, about how large are each of these "balls," on average? a) They are microscopic clusters of about 10 to 20 atoms each. b) About the size of Earth's Moon c) About a size that you could hold in your arms d) About the size of a large asteroid

c) About a size that you could hold in your arms - Most of the ring particles are about this size, though there is lots of variation.

Which of the following best describes the leading model for the formation of the jovian planets? a) Each planet formed with a composition that reflected the general composition of the solar nebula at its particular distance from the Sun. b) Huge balls of gas formed from the solar nebula, which then differentiated so that heavier ingredients sunk to the center while lighter gases escaped into space. c) Accretion built solid planetesimals of rock and ice with about 10 times the mass of Earth, and the gravity of these planetesimals then pulled in hydrogen and helium gas from the surrounding nebula.

c) Accretion built solid planetesimals of rock and ice with about 10 times the mass of Earth, and the gravity of these planetesimals then pulled in hydrogen and helium gas from the surrounding nebula. - This process explains why all four jovian planets are thought to have similar cores of about 10 Earth masses, and differ primarily in the amount of other material that surrounds those cores.

What is the orbital resonance among Io, Europa, and Ganymede? a) Io, Europa, and Ganymede all orbit Jupiter in the same direction and in nearly the same plane. b) Ganymede's orbit is exactly twice as far from Jupiter as Europa, and exactly four times as far from Jupiter as Io. c) Io completes exactly 4 orbits for every 2 orbits of Europa and every 1 orbit of Ganymede.

c) Io completes exactly 4 orbits for every 2 orbits of Europa and every 1 orbit of Ganymede. - As shown in the video, this means that these moons periodically line up in ways that contribute the same gravitational tugs as they move in their orbits.

Io experiences tidal heating primarily because __________. a) It has an elongated shape that makes it look more like an egg than a sphere. b) It is made of relatively soft materials that deform quite easily. c) Its elliptical orbit causes the tidal force to vary as Io orbits Jupiter. d) It is located very close to Jupiter.

c) Its elliptical orbit causes the tidal force to vary as Io orbits Jupiter. - The strength of the tidal force depends on Io's distance from Jupiter, so the tidal force varies as Io moves around its elliptical orbit. - The tidal bulge even changes direction slightly because the orbital speed varies. - These tidal effects essentially stretch and compress Io's interior, and this tidal friction causes the tidal heating.

What is the source of the tidal force acting on Io? The tidal force that acts on Io is due primarily to the gravity of __________. a) both Europa and Ganymede b) Europa c) Jupiter

c) Jupiter - As indicated by the force arrows in the video, the tidal force on Io is caused by the gravity of Jupiter. - Keep in mind that, because gravity weakens with distance, tidal forces must also weaken with distance. - In fact, the tidal force weakens more rapidly with distance than the gravitational force.

What are all the blue lines around Jupiter supposed to represent in this picture? a) Blue light reflected from methane clouds b) The solar wind c) Jupiter's magnetic field d) The orbits of some of Jupiter's many moons.

c) Jupiter's magnetic field - The magnetic field is stronger where the lines are closer together and weaker where they are farther apart.

What explains the cores and compositions of jovian planets? According to the leading model, which of the following best summarizes how the jovian planets formed? a) The process was different for each jovian planet, with the smaller jovian planets forming from smaller planetesimals. b) Accretion gradually pulled a mixture of hydrogen and helium gas into large balls that became the jovian planets. c) Large planetesimals of ice and rock accreted; the gravity of these planetesimals then drew in surrounding gas from the solar nebula.

c) Large planetesimals of ice and rock accreted; the gravity of these planetesimals then drew in surrounding gas from the solar nebula. - All four jovian planets are thought to have formed around planetesimals of about 10 Earth masses, composed of a mixture of hydrogen compounds (ices) and rock. - These planetesimals became the cores of the jovian planets. - The planets have different atmospheric compositions today because each one captured different amounts of hydrogen and helium gas from the solar nebula.

What is the strength of the tidal force acting on Io? a) The tidal force varies. It is strongest when Io is farthest from Jupiter and weakest when Io is closest to Jupiter. b) The tidal force is the constant throughout Io's orbit. c) The tidal force varies. It is strongest when Io is closest to Jupiter and weakest when Io is farthest from Jupiter.

c) The tidal force varies. It is strongest when Io is closest to Jupiter and weakest when Io is farthest from Jupiter. - This varying tidal force essentially stretches and compresses Io's interior as it orbits Jupiter, generating friction and heat.

Which of the following statements best describes the general pattern of composition among the four jovian planets? a) Jupiter is made mostly of hydrogen and helium, while the other three jovian planets are made mostly of hydrogen compounds. b) All four planets have essentially the same composition. c) Uranus and Neptune contain relatively more rock and hydrogen compounds than Jupiter and Saturn. d) Jupiter is made mostly of hydrogen, Saturn is made mostly of helium, Uranus is made mostly of hydrogen compounds, and Neptune is made mostly of rock.

c) Uranus and Neptune contain relatively more rock and hydrogen compounds than Jupiter and Saturn. - As the figure shows, Jupiter and Saturn are made mostly of hydrogen and helium, while Uranus and Neptune are primarily made of hydrogen compounds — such as water (H2O), methane (CH4), and ammonia (NH3) — along with a substantial relative amount of rock.

We now know of many Jupiter-size planets around other stars. Suppose that future observations show that one of these planets has two orbiting moons. What additional information, if any, would we need to decide whether these moons experience tidal heating? a) We need to know whether either moon is volcanically active. b) We need to know whether the planet also has a third moon. c) We need to know their orbital periods. d) No other information is needed: With two moons, there is sure to be tidal heating. e) No other information is needed: With two moons, there is no chance of any tidal heating.

c) We need to know their orbital periods. - We expect tidal heating to be possible only if there is an orbital resonance that helps maintain an elliptical orbit. - An orbital resonance occurs when one moon's orbital period is a simple fraction of the other's, such as 1/2 or 1/3 or 1/4. - Therefore, by measuring their orbital periods, we can determine if there is a resonance. - Having an orbital resonance doesn't automatically mean that there is tidal heating, but it makes it a good possibility.

Which of the following best describes the internal layering of Jupiter, from the center outward? a) liquid core of hydrogen compounds; liquid hydrogen layer; metallic hydrogen layer; gaseous hydrogen layer; cloud layer b) core of rock and metal; mantle of lower density rock; upper layer of gaseous hydrogen; cloud layer c) core of rock, metal, and hydrogen compounds; thick layer of metallic hydrogen; layer of liquid hydrogen; layer of gaseous hydrogen; cloud layer d) solid rock core; layer of solid metallic hydrogen; layer of pure liquid hydrogen; cloud layer

c) core of rock, metal, and hydrogen compounds; thick layer of metallic hydrogen; layer of liquid hydrogen; layer of gaseous hydrogen; cloud layer

Saturn's rings are composed of __________. a) gas from the early solar system b) a series of solid concentric circles c) lots of individual particles of ice and rock d) parts of Saturn's upper atmosphere being vented into space Submit

c) lots of individual particles of ice and rock - Although Saturn's rings appear solid when viewed from Earth, they are actually made of countless icy particles ranging in size from dust grains to small boulders.

Overall, Jupiter's composition is most like that of _________. a) an asteroid b) Earth c) the Sun d) a comet

c) the Sun

The jovian planets are often called "gas giants," making it sound as if they were entirely gaseous like air on Earth. However, while it is true that they are made mostly of materials that would be gases on Earth, the high pressures in jovian interiors?

compress these materials to different forms.

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 ammonium hydrosulfide b) Clouds of water c) Clouds of ammonia d) Clouds of sulfuric acid

d) Clouds of sulfuric acid - Jupiter does not have sulfuric acid clouds. (Sulfuric acid clouds are found on Venus.)

Lo's elliptical orbit is necessary to its tidal heating. This elliptical orbit, in turn, is a result of the orbital resonance among Io, Europa, and Ganymede. This orbital resonance causes Io to have a more elliptical orbit than it would otherwise, because __________. a) all three moons orbit with the same period, staying aligned at all times b) Europa and Ganymede are unusually large moons c) Europa and Ganymede always pull on Io from the same direction as Jupiter pulls on Io d) Io, Europa and Ganymede periodically return to the same orbital positions, creating the same gravitational tugs

d) Io, Europa and Ganymede periodically return to the same orbital positions, creating the same gravitational tugs - The repeated passes at the same orbital position mean that Io experiences repeated gravitational tugs at the same place in each orbit, and these tugs make its orbit more elliptical than it would be otherwise.

This photo shows one of Saturn's moons. Based on its shape, what can you conclude? a) It is a captured asteroid. b) It is made entirely of water ice. c) It is a gap moon within Saturn's rings. d) It is quite small in size compared to moons that are spherical.

d) It is quite small in size compared to moons that are spherical. - If it were larger, it would be spherical.

Which of the following statements comparing the jovian interiors is not thought to be true? a) Deep inside them, they all have pressures far higher than that found on the bottom of the ocean on Earth. b) They all have cores that contain at least some rock and metal. c) They all have cores of roughly the same mass. d) They all have the same exact set of internal layers, though these layers differ in size.

d) They all have the same exact set of internal layers, though these layers differ in size. - The layers on Uranus and Neptune are significantly different from those on Jupiter and Saturn.

Which of the following best describes the nature of planetary rings? a) The are solid, concentric rings around a planet. b) They are composed of reflective molecules of gas. c) They are a solid sheet of material around a planet, looking much like a DVD or blu-ray disk. d) They are composed of countless individual particles.

d) They are composed of countless individual particles. - The particles range in size from dust grains to large boulders, and each particle orbits its planet independently in accord with Kepler's laws.

Which of the following is a general characteristic of the four jovian planets in our solar system? a) They have solid surfaces. b) They are less massive than any of the terrestrial planets. c) They have very little hydrogen, helium, and hydrogen compounds. d) They are lower in average density than are the terrestrial planets.

d) They are lower in average density than are the terrestrial planets.

How do typical wind speeds in Jupiter's atmosphere compare to typical wind speeds on Earth? a) They are slightly faster than average winds on Earth. b) They are slightly slower than average winds on Earth. c) They are about the same as average winds on Earth. d) They are much faster than hurricane winds on Earth.

d) They are much faster than hurricane winds on Earth.

Orbital resonance also gives Europa an elliptical orbit, so it experiences tidal heating, too. However, Europa experiences less tidal heating than Io, because Europa __________ than Io. a) is much smaller b) contains much more ice c) is more perfectly spherical in shape d) is farther from Jupiter

d) is farther from Jupiter - It is Jupiter's gravity that exerts the primary tidal force on the Galilean moons, and both this force and the difference in this force across a moon (the source of tidal heating) weaken with distance from Jupiter. - Io is closest to Jupiter and therefore experiences the most tidal heating; - Europa experiences less tidal heating, and Ganymede experiences the least tidal heating. (Callisto is not expected to have any tidal heating since it does not participate in the orbital resonance that makes the other moons' orbits more elliptical.)

What atmospheric constituent is responsible for the blue color of Uranus and Neptune? a) ammonia b) water c) hydrogen d) methane

d) methane

The jovian planets farther from the Sun took ________ to form and captured ____ hydrogen and helium gas, explaining why Uranus and Neptune have larger proportions of hydrogen compounds, rock, and metal.

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