Astronomy chapter 7

3 How do moons happen to be at just the right places to confine the rings? The ring particles get caught in the most ________ orbits among Saturn's ________ moons. The rings push against the inner moons, but those moons are locked in place by resonances with larger, _____ moons. Without the moons, the rings would spread and dissipate. Saturn's rings are a very thin layer of particles and nearly vanish when the rings turn edge-on to Earth. Although ripples in the rings may extend for hundreds of meters above and below the midplane, the sheet of particles may be only about 10 meters thick.

stable, innermost, outer,

Under very high pressure, liquid hydrogen becomes __________ ___________ ______________- material is good conductor of electricity. Most of Jupiter's interior is composed of this material. That large mass of conducting liquid, stirred by convection currents and spun by the planet's rapid rotation, drives the ____________ effect and generates a powerful ____________ _______. (Jupiter's field= more than 10 times stronger than Earth's.) A planet's magnetic field deflects the solar wind and dominates a volume of space around the planet called the __________________. The magnetic field around Jupiter traps charged particles from the solar wind in radiation belts a billion times more intense than the Van Allen belts that surround Earth. (radiation in these regions is more than 4000 times the radiation than would have been lethal for a human.) Jupiter's center, a so-called _______ core is hypothesized to contain heavier elements (iron, nickel, silicon, and etc). With a temperature 4x hotter than the surface of the Sun and a pressure 50 million times Earth's air pressure at sea level, this material is unlike any rock on Earth. The term rocky core refers to the ______________ composition, not to the properties of the material.

liquid metallic hydrogen, dynamo, magnetic field, magnetosphere, rocky, chemical

WHAT ARE WE? TRAPPED No one has ever been farther from Earth than the Moon. We humans have sent robotic spacecraft to visit most of the larger worlds in our Solar System, and we have found them strange and wonderful places, but no human has ever set foot on any of them. We are trapped on Earth. Getting a human crew away from Earth's gravitational field is difficult and calls for very large rockets. The U.S. built rockets in the 1960s and early 1970s that could send astronauts to the Moon, but they stopped producing them. At the time of this writing (August 2016) the largest available rockets can only take astronauts just a few hundred kilometers above Earth's surface to the International Space Station. The United States and other nations are considering sending humans back to the Moon and eventually to Mars, but budget limitations have delayed specific plans. Does Earth's civilization have the resources to build spacecraft capable of carrying human explorers to other worlds? We'll have to wait and see. Furthermore, we Earthlings have evolved to fit the environment on Earth. None of the planets or moons you explored in this chapter would welcome you. Lack of ____, and extreme _____ or _____ are obvious problems, but, also, Earthlings have evolved to live with Earth's gravity. Astronauts in space for just a few weeks suffer ___________ problems because they are no longer in Earth's gravity. Living in a colony on Mars or the Moon might raise similar problems. Just getting to the outer planets would take decades of space travel; living for years in a colony on one of the Jovian moons under low gravity and exposed to the planet's radiation belts may be beyond the capability of the human body. We may be trapped on Earth not because we lack large enough rockets but because we need Earth's protection. It seems likely that we need Earth more than it needs us. The human race is changing the world we live on at a startling pace, and some of those changes could make Earth less hospitable to human life. All of your exploring of un-Earthly worlds serves to remind you of the nurturing beauty of our home planet.

air, heat, cold, biomedical

7-2d Jupiter's Family of Moons Jupiter has 4 large moons and at least 60 smaller moons. Larger telescopes and modern techniques are finding more small moons orbiting each of the Jovian planets. Most of the small moons are probably captured ________. In contrast, the four largest moons, called the __________ moons after their discoverer and are clearly related to each other and probably ______ with Jupiter. The outermost Galilean moons, Ganymede and Callisto, are about the size of Mercury, (1.5x the size of Earth's Moon). _________ is the largest Moon in the Solar System. Ganymede and Callisto have ___ densities, 1.9 and 1.8‍g/cm3, meaning they must consist roughly of half _____ and half ___. Observations of their gravitational fields by spacecraft reveal both moons have rocky, metallic cores and lower-density icy exteriors, meaning both moons have ____________. Both moons interact with Jupiter's magnetic field in a way that shows they probably have mineral-rich layers of liquid water 100 km or more below their icy crusts. Callisto's surface, and most of Ganymede's surface, appear old because they are heavily _______ and very ____. The continuous blast of micrometeorites ________ surface ice, leaving behind embedded minerals to form a dark skin like the grimy crust on an old snowbank, so surfaces get _______ with age. More recent impacts dig up cleaner ice and leave _____ craters, as seen on Callisto. Ganymede has some younger, brighter grooved terrain believed to be systems of ____ in the brittle crust. Some sets of grooves overlap other sets of grooves, suggesting extended episodes of geological activity.

asteroids, Galilean, formed, Ganymede, low, rock, ice, differentiated, cratered, dark, evaporates, darker, bright, faults

If a dust speck gets knocked loose from a larger rock inside the Roche limit, the rock's gravity ______ hold the dust speck. For that reason, the billions of dust specks in the rings can't pull themselves together to make a moon because of ______ _______ inside the Roche limit. Jupiter's ring particles are not old. The pressure of sunlight and the planet's powerful magnetic field alter the _______ of the particles. Images show faint ring material extending down toward the cloud tops; this is dust grains spiraling _______ the planet. Dust is also destroyed by the intense _________ around Jupiter that grinds the dust specks down to nothing. The rings you see today, can't be material left over from the formation of Jupiter—the rings of Jupiter must be continuously ________ with new dust. Observations made by spacecraft provide evidence that the source of ring material comes from micrometeorites eroding small _______ orbiting near or within the rings. The rings around Sat, Uran, and Nep are also known to be short lived, and they also must be resupplied by new material, probably eroded from nearby moons. Besides supplying the Jovian rings with particles, moons _________ the rings, keep them from spreading outward, and alter their _______.

cannot, tidal forces, orbits, into, radiation, resupplied, moons, confine, shapes

7-3c Saturn's Family of Moons Saturn has more than 60 known moons, many of which are small and contain mixtures of ice and rock. It is probable that many are __________ objects. The largest of Saturn's moons, called _______, is a bit larger than the planet Mercury. Its density suggests that it must contain a _____ core under a thick mantle of ___. Titan is so ____ that its gas molecules do not travel fast enough to escape, so it has an atmosphere composed mostly of ______ with traces of argon and methane. Sunlight converts some of the methane into complex carbon-rich molecules that collect into small particles filling the atmosphere with orange smog. These particles are understood to slowly settle downward to the surface in the form of a dark organic goo, meaning it is composed of carbon-rich molecules.

captured, titan, rocky, ices, cold, nitrogen,

1 The rings of Saturn are made up of billions of ice particles ranging from microscopic specks to chunks bigger than a house. Each particle orbits Saturn in its own _______ orbit. Much of what is known about the rings has been learned from Voyager 1 and 2 flybys and Cassini orbiter. From Earth, astronomers see three rings labeled A, B, and C. Images reveal over a thousand _______ within the rings. Saturn's rings can't be leftover material from the formation of Saturn. The rings are made of ice particles, and the planet would have been so hot when it formed that it would have ______ and driven away any icy material. Rather, the rings must be _______ from collisions between Saturn's icy moons and passing comets or asteroids. Large _______ can scatter ice throughout the Saturn system occur about every 100 million years or so. The ice would quickly settle into the _______ plane, and some would become trapped in rings. Although the ice will waste away because of meteorite impacts and damage from radiation in Saturn's magnetosphere, new impacts could ______ the rings with fresh ice. The bright, beautiful rings you see today may be only a temporary enhancement caused by an impact that occurred since the extinction of the dinosaurs.

circular, ringlets, vaporized, debris, impacts, equatorial, replenish

2 Because of _______ among ring particles, planetary rings should spread outward. The sharp outer edge of the A ring and the narrow F ring are confined by _______ _______ that gravitationally usher straying particles back into the rings. Some gaps in the rings, such as the Cassini Division, are caused by ___________ with moons. A particle in the Cassini Division orbits Saturn twice for each orbit of the moon Mimas. On every other orbit, the particle feels a gravitational tug from Mimas. These tugs always occur at the same ______ in the orbit and force the orbit to become slightly _________. Such an orbit crosses the orbits of other particles, which results in collisions, and that _________ the particle from the gap. (The Cassini division is caused by the pull of one of Saturn's moons called Mimas. A ring particle in the Cassini division would go around Saturn twice for every time Mimas goes around once; this is called a "2:1 resonance orbit". What happens is that if a ring particle were in the Cassini division, it would be pulled on by Mimas's gravity at the same place in its orbit every time Mimas passes by; the little gravitional "tugs" add up, just as pushing someone on a swing over and over makes the swing go higher. The gravitational tugs by Mimas eventually would pull the ring particle out of the Cassini division -- and that's why there's a gap there, with no ring particles inside.)

collisions, shepherd satellites, resonances, places, elliptical, removes

7-2a Jupiter's Interior Jupiter is only 1.3 times denser than water. Earth is more than 5.5 times denser than water. Density gives clue about the average ______________ of the planet's interior. Jupiter's __________ gives information about its interior. Jupiter and the other Jovian planets are all slightly ____________. A world with a large rocky core and mantle would not be flattened much by rotation, but an all-liquid planet would flatten significantly. Thus Jupiter's oblateness, the fraction by which its equatorial diameter exceeds its polar diameter, combined with its average density, helps astronomers model the interior. Interior of Jupiter is mostly ___________ ______________. The base of the atmosphere is so _____ and the ______________ is so high that there is no sudden boundary between liquid and gas. As you fall deeper and deeper through the atmosphere, you would find the gas density ___________ around you until you were sinking through a liquid, but you would never splash into a distinct liquid surface.

composition, shape, flattened, liquid hydrogen, hot, pressure, increased

7-4c Uranus's Rings The rings of Uranus are _____ and ______, contain little dust, are confined by _______ _______, and must be continuously resupplied with material from the moons. They are not easily visible from Earth—the first hint that Uranus had rings came from __________, the passage of the planet in front of a star. Most of what is known about these rings comes from observations by Voyager 2 spacecraft. Their composition appears to be _____ ______ mixed with ________ that has been darkened by _________ to radiation. In 2006, found two new, very faint rings orbiting far outside the previously known rings of Uranus. The newly discovered satellite _____ appears to be the source of particles for the larger ring, and the smaller of the new rings is confined between the orbits of the moons Portia and Rosalind. Note that the International Astronomical Union (IAU) has declared that the newly discovered moons of Uranus are to be named after characters in Shakespeare's plays.

dark, faint, shepherd satellites, occultations, water ice, methane, exposure, Mab

7-2c Jupiter's Rings Jupiter's rings were not discovered until 1979. Less than 1 percent as bright as Saturn's icy rings, Jupiter's rings are very _____ and ________, indicating that the rings are _______ material rather than icy. The ring particles are mostly ___________. Photos of the rings show that they are very bright when illuminated from ______—in other words, they are scattering light forward. Large particles do not scatter light forward—a ring filled with basketball-size particles would look dark when illuminated from behind. Forward scattering of visible light tells you the rings are mostly made of tiny grains with diameters approximately equal to the wavelengths of visible light, about the size of particles in cigarette smoke. The rings orbit inside the Roche limit, the distance from a planet within which a moon cannot hold itself together by its own gravity. If a moon comes inside the Roche limit, tidal forces overcome the moon's gravity and pull the moon ______. Raw material for a moon cannot coalesce (unit) inside the Roche limit. The Roche limit is about 2.4x the planet's radius, depending somewhat on the relative densities of the planet and the moon material. Jupiter's ______, (and Saturn, Uranus, and Neptune) lie inside the respective Roche limits for each planet.

dark, reddish, rocky, microscopic, behind, apart, rings

1a An astronaut could swim through the rings. Although the particles orbit Saturn at high velocity, all particles at the same _______ from the planet orbit at about the same speed, so they collide gently at ___ velocities. If you could visit the rings, you could push your way from one icy particle to the next. This artwork is based on a model of particle sizes in the A ring. The C ring contains ______-size chunks of ice, whereas most particles in the A and B rings are more like _____ ______, down to _____-size ice crystals. Further, C ring particles are less than half as bright as particles in the A and B rings. Cassini observations show that the C ring particles contain less ice and more __________. Inner to outer: D ring, Ring C, Ring B, Cassini Division, Ring A, Encke Division, F ring, A) rings illuminated by sunlight from below, Saturn's sunlight falls across the rings B) The F ring is clumpy and sometimes appears braided because of 2 shepherd satellites C) Encke Gap is not empty, (ripples at inner edge) A small Moon orbits inside the gap D)Saturn does not hav enough moons to produce all of its ringlets by resonances. Many are the result of tightly wound density waves, something like spiral arms found in disk galaxies E) Waves in Ring A

distance, low, boulder, golf balls, dust, minerals

Titan's surface is mainly composed of ices of water and methane at -180°C‍(-290°F). Cassini spacecraft dropped the Huygens probe into the atmosphere of Titan, and it photographed dark _______ _______ suggesting that liquid methane falls as rain, washes the dark goo off the higher terrain, and drains into the ______. Methane downpours may be rare. No direct evidence of liquid methane was detected as the probe descended, but later radar and spectroscopic observations made by the Cassini orbiter detected _____ of methane and ethane. Infrared images suggest the presence of methane _________ that replenish the methane in the atmosphere, so Titan must have some internal heat source to power the activity. Most of the remaining moons of Saturn are small and icy, have ___ atmospheres, are heavily cratered, and have dark, ancient surfaces. The moon _________, however, shows signs of recent geological activity. Some parts of its surface contain 1000x fewer craters than other regions, and infrared observations show that its south polar region is unusually _____ and venting water and ice geysers. Evidently, a reservoir of ______ water lies below the surface. At some point this moon must have been caught in a resonance with another moon and was warmed by ______ _______. Enceladus appears to maintain the faint E ring that extends far beyond the visible rings. Astronomers detected infrared radiation from a dark ring 13 million km in radius, beyond the orbits of most of Saturn's moons.

drainage channels, lowlands, lakes, volcanoes, no, Enceladus, warm, liquid, tidal heating

2 Jupiter's cloud layers lie at certain temperatures within the atmosphere where ammonia, ammonium hydrosulfide, and water can condense into _________. If you could put thermometers into the different levels of the atmosphere, you would discover that the temperatures rise as you _______ beneath the uppermost clouds, represented for Jupiter by the solid orange line. Because Saturn is farther from the Sun, its temperature is _______, shown by the green line. The cloud layers on Saturn form at the same ________ as the cloud layers on Jupiter, but they are ________ in Saturn's hazy atmosphere.

droplets, descend, colder, temperature, deeper

_______ ___________- A body that independently orbits the Sun or another star, is massive enough to pull itself into a spherical shape but not massive enough to clear out other bodies in and near its orbit; for example, Pluto, Eris, and Ceres. 1) orbits the Sun 2) have sufficient mass for its self-gravity to overcome rigid body forces, so that it assumes a hydrostatic equilibrium (nearly round) shape 3) Has not cleared the neighborhood around its orbit 4) is not a satellite

dwarf planet

Infrared measurements of the heat flowing out of Jupiter reveals the planet _______ about twice as much energy as it absorbs from the Sun. This energy is the heat left over from the _____________ of the planet. Jupiter should have grown very hot when it formed, and some of that heat remains in its interior. The Juno spacecraft orbited Jupiter to make detailed measurements of Jupiter's gravitational field, magnetic field, and heat flow, aiming to better determine the planet's internal structure.

emits, formation

7-5c Neptune's Rings Neptune's rings are _____ and very hard to detect from Earth, but they illustrate some interesting processes of comparative planetology . Neptune's rings are similar to those of Uranus but contain more _____ dust particles. The gravitational influence of one of Neptune's moons causes the ______ ring to be concentrated into _____ ____. Neptune's ring system, like the others, is apparently resupplied by impacts on moons scattering debris that fall into the most stable places among the orbits of the moons. ((a) The rings of Uranus were discovered in 1977, when Uranus crossed in front of a star. During this occultation, astronomers saw the star dim a number of times before and again after the planet crossed over the star. The dips in brightness were caused by rings circling Uranus. (b) The bright disk of Neptune is hidden behind the black bar in this Voyager 2 image. Two narrow rings are visible, and a wider, fainter ring lies closer to the planet. More ring material is visible between the two narrow rings. The rings are bright in forward-scattered light, indicating that the rings contain significant amounts of very small dust particles with short lifetimes. Like the rings of Uranus, the rings of Neptune reflect very little light and probably contain methane-rich ice darkened by radiation.)

faint, small, outermost, short arcs,

7-3a Planet Saturn Figure 7-1, Saturn has only ______ belt-zone circulation, but Voyager, Hubble Space Telescope, and Cassini images show that belts and zones are present, and that the associated _______ _______ up to 3x faster than on Jupiter. Belts and zones on Saturn are less visible than on Jupiter because they occur _______ in the cold atmosphere, below a layer of methane haze. Saturn is less dense than water, suggesting that it is, like Jupiter, rich in __________ and _____. Saturn is the most _____ (flat) of the planets, telling you that its interior is mostly _______ with possibly a small core of heavy elements. Because its internal pressure is lower, Saturn has less liquid metallic hydrogen than Jupiter. Perhaps that is why Saturn's magnetic field is 20x _______ than Jupiter's. Like Jupiter, Saturn _______ more energy than it receives from the Sun, and models predict that it has a very hot interior.

faint, winds blow, deeper, hydrogen, helium, oblate, liquid, weaker, radiates

____________ ______________- The optical property of finely divided particles to preferentially direct light in the original direction of the light's travel.

forward scattering

Pluto is very difficult to observe from Earth; its diameter is 2370 km, smaller than Australia and only 2/3 the diameter of Earth's Moon. In Earth-based telescopes, Pluto never looks like more than a faint point of light, and the Hubble Space Telescope images shows little detail. Orbiting so far from the Sun, Pluto is cold enough to ________ most compounds you think of as ______, and spectroscopic observations have found evidence of nitrogen and methane ices on its surface. Pluto has a ______ atmosphere of nitrogen, carbon monoxide, and small amounts of methane. Pluto has 5 known moons. ____ are quite small, but _______ is relatively large (half of Pluto's diameter). Charon orbits Pluto in an orbit inclined 118 degrees to the plane of Pluto's orbit around the Sun, meaning it has _________. Pluto and Charon are tidally locked ________ each other, so Pluto's axis of rotation is inclined at the same large angle to its orbit and its _________ is also retrograde. Knowing Charon's orbital period- 6.4 days and orbit semimajor axis- 19,600 km allows you to use Kepler's third law to calculate that the total mass of the system is only about 0.0024 Earth mass. Most of that mass is ______, which has about 9x the mass of Charon. Knowing the diameters and masses of Pluto and Charon allows determination that their densities are respectively about 1.9 and 1.7‍ g/cm³ . This indicates that both Pluto and Charon must contain about 30 to 40% _____ and 60 to 70% ______.

freeze, gases, thin, 4, charon, retrograde, facing, rotation, Pluto, ice, rock

The atmospheric activity on Neptune is apparently driven by _____ flowing from the ________ plus some contribution by dim light from the Sun 30 AU away. Neptune may have more atmospheric activity than Uranus because it has ______ heat flowing out of its interior, for reasons that are unclear. Like Uranus, Neptune has a highly _______ magnetic field that must be linked to circulation in the _______. In both cases, astronomers suspect that ______ dissolved in the liquid water mantle makes the mantle a good electrical ______ and that convection in the water, coupled with the _______ of the planet, drives the dynamo effect and generates the magnetic field.

heat, interior, more, inclined, interior, ammonia, conductor, rotation

7-2e A History of Jupiter Jupiter formed far enough from the Sun to incorporate large amounts of ices containing ___________, so it must have grown rapidly. Once it became about 10 to 15x more massive than Earth, it could begin to grow further by gravitational _______, capturing gas directly from the solar nebula. Thus, grew rich in hydrogen and helium. Its present composition resembles the composition of the ______ ______ and is quite sunlike. Jupiter's gravity is strong enough to hold on to all of its gases. Most of the moons may be captured asteroids, and Jupiter may still encounter a wandering asteroid or comet now and then. Some of these are deflected, some captured into orbit, and some, like comet Shoemaker-Levy 9 and unidentified fragments, actually ______ with the planet. Dust blasted off of the inner moons by micrometeorites settles into the equatorial plane to form Jupiter's ______. The four Galilean moons are large and seem to have formed like a mini Solar System in a disk of gas and dust around the forming planet. The innermost, Io, is _______, and the densities of the others ________ as you move away from Jupiter, like densities of the planets decrease with distance from the Sun. Perhaps the inner moons incorporated less ice because they formed closer to the _____ of the growing planet. The tidal heating has been important and the intense warming of the inner moons could have driven off much of their ices. Thus, two processes together are probably responsible for the differences in compositions of the Galilean moons.

hydrogen, collapse, solar nebula, collide, rings, densest, decrease, heat

7-1b Atmospheres and Interiors The four Jovian worlds have __________-rich atmospheres filled with clouds. The atmospheres are _____ very deep; Jupiter's atmosphere makes up only about 1 percent of its radius. On Jupiter and Saturn, you can see that the clouds form _______ that circle each planet. You will find traces of these features on Uranus and Neptune, but they are not very distinct. Models indicate that below their atmospheres Jupiter and Saturn are mostly __________, so the old term for these planets, the gas giants, should probably be changed to the liquid giants. Uranus and Neptune are sometimes called the ice giants because they are rich in _______ in both solid and liquid forms. Near their centers the Jovian planets probably have cores of _________ material with the composition of rock and metal. None of them has a definite ________ surface. Jovian planets have ______ density because they are formed in the outer solar __________ where water vapor could ___________ to form ice particles. The ice accumulated into protoplanets with density lower than the rocky Terrestrial planets and asteroids. Once the Jovian planets grew _________ enough, they could draw in even lower-density hydrogen and helium gas directly from the nebula by gravitational collapse.

hydrogen, not, stripes, liquid, water, dense, solid, low, nebula, freeze, massive

7-2b Jupiter's Complex Atmosphere (Art 7A) Jupiter's Atmosphere, Magnetosphere, and Rings and, notice the following three important ideas: 1) The atmosphere is ___________ rich, and the clouds are confined to a __________ layer. 2) The cloud layers are located at certain ____________ within the atmosphere where ammonia (NH₃), ammonium hydrosulfide (NH₄SH), and water (H₂O), respectively, can condense. 3) The belt-zone circulation pattern of colored cloud bands circling the planet like stripes on a child's ball is related to the high- and low-_______ areas found in Earth's atmosphere. The large circular or oval spots seen in Jupiter's clouds are circulating ______ that can remain stable for decades or even centuries.

hydrogen, shallow, temperatures, pressure, storms

7-3b Saturn's Rings Study Concept Art 7B , The Ice Rings of Saturn, and notice the following three ideas: 1) The rings are made up of billions of _____ particles, each in its own _____ around the planet. The ring particles you observe now can't be as old as Saturn. The rings must be _______ now and then by impacts on Saturn's moons or other processes. The same is true of the rings around the other Jovian planets. 2) The gravitational effects of small _______ can confine some rings in narrow strands or keep the edges of rings sharp. Moons can also produce ______ in the rings that are visible as tightly wound ringlets. 3) The ring particles are confined in a ____ layer in Saturn's equatorial plane, spread among small moons and confined by gravitational interactions with larger moons. The rings of Saturn, and other Jovian worlds, are created and controlled by the planet's _____. Without the moons, there would be no rings.

ice, orbit, replenished, moons, waves, thin, moons

HOW DO WE KNOW? FUNDING FOR BASIC RESEARCH Who pays for science? Searching out scientific knowledge can be expensive, and that raises the question of funding. Some science has direct applications, and _______ supports such research. For example, pharmaceutical companies have large budgets for scientific research leading to the creation of new drugs. But some basic science is of no immediate practical value, with no obvious commercial applications. A paleontologist is a scientist who studies ancient life-forms by examining fossils of plant and animal remains. Except for the rare Hollywood producer about to release a dinosaur movie, corporations can't make a profit from the discovery of a new dinosaur. The practical-minded stockholders of a company will not approve major investments in such research. Consequently, digging up dinosaurs, like astronomy, is not well funded by industry. It falls to ________ institutions and private foundations to pay the bill for this kind of research. The Keck Foundation built two giant telescopes on Mauna Kea in Hawai'i with no expectation of financial return, and the National Science Foundation has funded thousands of astronomy research projects for the benefit of society. The discovery of a new dinosaur or a new Galaxy is of no great financial value, but such scientific knowledge is not worthless. Its value lies in what it tells us about the world we live in. Such scientific research enriches our lives by helping us understand what we are. Ultimately, funding basic scientific research is a public responsibility that society must balance against other needs. There isn't anyone else to pick up the tab.

industry, government

7-6a What Defines a Planet? To understand why Pluto is no longer considered a planet, you will need to consider the _______ ______ of small bodies orbiting on the ______ edge of the Solar System. Since 1992, astronomers have discovered about a thousand icy bodies orbiting beyond Neptune. There may be as many as 100 million objects in the Kuiper Belt larger than 1 km in diameter. They are understood to be _____ bodies left over from the _________ of the outer Solar System. Some of the Kuiper Belt Objects are quite large, and one, named Eris, has about the _____ diameter as Pluto, but is 27% more massive. Three other Kuiper Belt Objects found so far, Sedna, Orcus, and Quaoar, are half the size of Pluto or larger. Some of these objects have ______ of their own. In that way, they resemble Pluto and its moons. Comparative planetology shows that Pluto is not related to the Jovian or Terrestrial planets; it is a member of a newfound family of icy worlds that orbit beyond Neptune. These bodies must have formed at about the _____ time as the 8 classical planets of the Solar System, but they did not grow ______ enough to clear their orbital zones of remnant objects and remain embedded among a swarm of other objects in the Kuiper Belt. One of the IAU's criteria for planet status is that an object must be large enough to dominate and gravitationally clear its ______ region of most, or all, other objects. Eris and Pluto, the largest objects found so far in the Kuiper Belt, and Ceres, the largest object in the asteroid belt, do not meet that standard. On the other hand, all three are large enough for their ______ to have pulled them into __________ shapes, so they are the prototypes of a new class of objects defined by the IAU as _______ _______.

kuiper belt, outer, icy, formation, same, moons, same, massive, orbital, gravities, spherical, dwarf planets

7-5b Neptune's Moons Neptune has 2 moons that were discovered from Earth. The passing spacecraft discovered 6 more, very small moons. A few more small moons have been found by astronomers using large Earth-based telescopes. The two largest moons have peculiar orbits. Nereid, about 1/10 the size of Earth's Moon, follows a ______, ________ orbit, taking about an Earth-year to circle Neptune once. Triton, about 80 percent the size of Earth's Moon, orbits Neptune backward—________ as seen from the north. These odd orbits suggest that the system was disturbed long ago in an interaction with some other body, such as a massive object. _____ has an atmosphere of nitrogen and methane about 105 times less dense than Earth's, and temperature= 36 K (- 395 ° F) . A significant part of Triton is ____, and deposits of ________ ______ are visible at the southern pole. Many features on Triton suggest it has had an active past. It has few craters on its surface, but it does have long ______ that appear to have formed when the icy crust broke, plus large _______ that seem to have been flooded repeatedly by liquids from the interior. Even more interesting are the dark smudges visible in the southern polar cap that are interpreted as sunlight-darkened deposits of __________ erupted out of liquid nitrogen geysers.

large, elliptical, clockwise, triton, ice, nitrogen frost, faults, basins, methane

______________ _______________ ________________- A form of liquid hydrogen that is a good electrical conductor, inferred to exist in the interiors of Jupiter and Saturn.

liquid metallic hydrogen

_________________________- The volume of space around a planet within which the motion of charged particles is dominated by the planetary magnetic field rather than the solar wind.

magnetosphere

7-2 JUPITER Jupiter is named for the Roman king of the gods. It can be very bright in the night sky, and its cloud belts and four largest moons can be seen through even a small telescope. Jupiter is the largest and most massive of the Jovian planets, containing 71 percent of all the planetary _______ in the entire Solar System. You can use Jupiter as basis for comparison with the other Jovian planets.

matter

7-1c Satellite Systems All of the outer Solar System planets have extensive ________ systems. In many cases the moons interact gravitationally, mutually adjusting their orbits and also affecting the planetary ______ systems. Some of the moons are geologically _______, while others show signs of past activity. (geological activity requires heat flow from the interior)

moon, ring, active

The migration of the outer planets would have upset the _____ of some of these Kuiper Belt Objects, and some could have been thrown _______ where they could interact with the Jovian planets. Some of those objects may have been captured as _____, and astronomers wonder if moons, such as Neptune's Triton, could have started life as Kuiper Belt Objects. Other objects may have impacted bodies in the inner Solar System and caused the _____ ________ __________ episode especially evident on the surface of Earth's Moon. The small frozen worlds on the fringes of the Solar System hold clues to the formation of Earth and the other planets 4.6 billion years ago.

motion, inward, moons, late heavy bombardment

(New Horizons captured a near-sunset view of the rugged, icy __________ and flat ice _____ extending to Pluto's horizon. The backlighting reveals more than a dozen layers of haze in Pluto's tenuous but extended atmosphere.) The New Horizons spacecraft flew past Pluto, radioing back impressive images and other measurements. Close-up pictures show mountains up to 3.5 km (11,000 ft) high (Figure 7-12b). Methane and nitrogen ice would not be strong enough to stand that tall, so planetary scientists conclude that the mountains must be made of ______ ____ that would be rock-hard at Pluto's temperature The lack of ______ on and near those mountains indicates that this particular landscape is very young—no older than 100 million years, one of the youngest surfaces observed in the Solar System. Pluto has been active geologically _______, which means that heat must be flowing outward, although scientists wonder what the internal heat source could be. Charon's orbit is perfectly _______, so tidal heating is not the explanation. ___________ ________ would seem to be the only plausible alternative, although that heat source should also have faded long ago.

mountains, plains, water ice, craters, recently, circular, radioactive decay,

Topic 7-CI CHAPTER INTRODUCTION In this chapter, the Jovian (Jupiter-like) planets will be a challenge to your imagination. They are such alien worlds, they would be unbelievable if you didn't have direct observational evidence to tell you what they are like. In contrast, Pluto and the other bodies in the Kuiper Belt are _____ planets but small objects bearing intriguing clues about the planet construction process.

not

CONCEPT ART 7A JUPITER'S ATMOSPHERE, MAGNETOSPHERE, AND RINGS 1 The visible clouds are _____ at the top of the atmosphere; an upper atmosphere of clear hydrogen and helium extends far above the cloud tops. Jupiter's atmosphere makes up only _____ percent of its radius. Major spots on Jupiter, like the Great Red Spot, are embedded circulating _______. They can remain stable for decades or even centuries. 1a Cloud belts and zones circle Jupiter like ______ on a ball. This form of atmospheric circulation is belt-zone circulation. The poles and equator on Jupiter are about the same ________, perhaps because of heat rising from the interior. Because of that, and because of Jupiter's rapid rotation, instead of wave-shaped winds as on Earth, Jupiter's high- and low-pressure areas are stretched into ______ and ______ parallel to the equator. Zones are _______ than belts because rising gas forms clouds high in the atmosphere where sunlight is stronger and reflected back to outside viewers. (belt- low, North and zone-high, equator)

not, one, storms, stripes, temperature, belts, zones, brighter

_____________________- The flattening of a spherical body, usually caused by rotation.

oblateness

_____________- The passage of a larger body in front of a smaller body.

occultations

7-1a Planets and Dwarf Planets The ______________ planets in our Solar System are Jupiter, Saturn, Uranus, and Neptune. They are often called the "Jovian planets," meaning they resemble Jupiter. Each have own separate personalities. Jupiter is the ______________ of the Jovian planets, more than 11 times the diameter of Earth. Saturn is slightly smaller. (Cloud belt and zones on Saturn are less distinct than those on Jupiter) Uranus and Neptune are quite a bit smaller than Jupiter. (4 times Earth's size, green and blue colored because of methane in their hydrogen-rich atmosphere) Pluto, is smaller than Earth's Moon but was considered a planet from the time of its discovery in 1930 until a decision by the International Astronomical Union (IAU) that reclassified Pluto as a __________ planet. Saturn's rings composed of billions of ice particles. Jupiter, Uranus, and Neptune also have rings, but they are not easily detected from Earth. (will be able to compare four different sets of planetary rings)

outermost, largest, dwarf

The activity on the Galilean moons must be driven by energy flowing ______, yet these objects are too small to have remained hot from the time of their formation. Io's volcanism seems to be driven by ______ ________. Io follows a slightly eccentric orbit caused by its interactions with the other moons. Jupiter's gravitational field flexes Io with tides, and the resulting ________ heats its interior. That heat flowing outward causes the volcanism. Europa is not as active as Io, but it too must have a heat source, presumably tidal heating. Ganymede is ___ longer active, but when it was younger it must have had internal heat to break the crust and produce the grooved terrain.

outward, tidal heating, friction, no

________- The large oval grooves found on Uranus's moon Miranda that indicate past geologic activity.

ovoids

___________- One of the icy Kuiper Belt Objects that, like Pluto, is caught in a 3:2 orbital resonance with Neptune. (For every 3 orbits of the Sun completed by Neptune, Pluto completes 2 orbits.)

plutinos

7-6b Pluto and the Plutinos The history of the dwarf planets will take you back 4.6 billion years to watch the outer planets form. More than a hundred known Kuiper Belt Objects are caught with Pluto in a 3:2 ________ with Neptune. They orbit the Sun ______ while Neptune orbits three times. These Kuiper Belt Objects have been named __________. The plutinos formed in the outer solar nebula, but how did they get caught in resonances with Neptune? The models of the formation of the planets suggest that Uranus and Neptune may have formed _____ to the Sun and that sometime later, gravitational interactions among the Jovian planets could have gradually shifted Uranus and Neptune _______. As Neptune migrated outward, its orbital resonances could have swept up small objects like a strange kind of snowplow. The Plutinos are caught in the 3:2 resonance, and other Kuiper Belt Objects are caught in other resonances. This appears to support the models that predict that Uranus and Neptune migrated outward.

resonance, twice, plutinos, closer, outward

______ _________- The minimum distance between a planet and a satellite that can hold itself together by its own gravity.

roche limit

The density of the next moon inward, Europa, (3‍g/cm³), high enough to mean that it is mostly _____ with a thin icy crust. The visible surface is very clean ice, contains very few craters, has long cracks in the icy crust, and has complicated terrain that resembles blocks of ice in Arctic Ocean. The lack of craters tells you that Europa is an ______ world where craters are quickly erased. The pattern of folds on its surface suggests that the icy crust breaks as the moon is flexed by _____. Europa's gravitational influence on the spacecraft indicates that a liquid-water _______ lies below the 10- to 100-km-thick crust. Images from spacecraft reveal that Io, innermost Galilean moons, has more than 150 _________ vents on its surface. The active volcanoes throw sulfur-rich gas and ash high above the surface; the ash falls back to bury the surface at a rate of a few millimeters a year. This explains why you see no impact craters on Io— they are covered up as fast as they form. Io's density is 3.6‍g/cm³, showing that it is (not ice) _____ and ______. Its gravitational influence on the passing spacecraft revealed that it is ________ into a large metallic core, a rocky mantle, and a low-density crust.

rock, active, tides, ocean, volcanic, rock, metal, differentiated

7-5a Planet Neptune Almost exactly the ______ size as Uranus, Neptune is calculated to have a similar interior: a small core of ______ elements lies within a slushy mantle of ______, ices, and minerals (rock) below a __________-rich atmosphere. Yet Neptune looks quite different; it is dramatically blue and has active ______ formations. Neptune has a dark blue tint because its atmosphere contains 1.5 times more _________ than Uranus. Methane absorbs ____ photons better than blue and scatters ____ photons better than red, giving Neptune a blue color and Uranus a green-blue color. Atmospheric circulation on Neptune is much more dramatic than on Uranus. When Voyager 2 flew by Neptune, the largest feature was the ______ ______ ______. Roughly the size of Earth, spot seemed to be an ________ ______ similar to J's Great Red Spot. Smaller spots were visible in Neptune's atmosphere and they were circulating like hurricanes. More recently, the Hubble Space Telescope has photographed Neptune and found that the Great Dark Spot is gone, and new cloud formations have appeared. Evidently, the ______ on Neptune is surprisingly changeable.

same, heavy, water, hydrogen, cloud, methane, red, blue, great dark spot, atmospheric circulation, weather

____________ ___________- A satellite that, by its gravitational field, confines particles to a planetary ring.

shepherd satellite

Uranus rotates on its ______, equator inclined about 98 degrees to its orbit. With an orbital period of 84 years, each of the four seasons lasts _______, and the winter-summer contrast is extreme. During a season when one of its poles is nearly ________ at the Sun (a solstice), inhabitants of Uranus would never see the Sun ____/____. Uranus's odd rotation may have been produced when it was ______ by a very large object late in its formation, or by _____ interactions with the other giant planets as it migrated outward early in the history of the Solar System. Voyager 2 photos show a nearly _______ ball. The atmosphere is mostly hydrogen and helium, but traces of ______ absorb red light and thus make the atmosphere look blue or teal. There is no belt-zone circulation visible in Voyager 2 photographs, although computer enhancement revealed a ____ clouds and bands around the ____ ____. Decades after Voyager 2 flew past Uranus, ______ has come to the ________ Hemisphere of Uranus and ________ to the _________ Hemisphere. Hubble Space Telescope images reveal _________ clouds and cloud bands. Infrared measurements show that Uranus is radiating about the _____ amount of energy that it receives from the Sun, meaning it has much less heat flowing out of its interior than Jupiter, Saturn, or Neptune). This may account for its limited _________ activity. Astronomers are not sure why Uranus differs in this respect from the other Jovian worlds.

side, 21 years, pointed, rise/set, struck, tidal, featureless, methane, few, south pole, spring, northern, autumn, southern, changing, same, atmospheric

7-6 PLUTO: PLANET NO MORE On the edge of the Solar System orbits a family of small, icy worlds. Pluto was discovered in 1930 but modern telescopes have found more. You may have learned there are 9 planets in our Solar System, but (2006) the IAU voted to remove Pluto from the list of planets. Pluto is a very ______, ____ world—NOT Jovian, and NOT Terrestrial. Its orbit is highly _______ and so elliptical that Pluto actually comes _____ to the Sun than Neptune at times. To understand Pluto's status, so use comparative planetology to analyze Pluto and compare it with its neighbors.

small, icy, inclined, closer

7-4b Uranus's Moons Until recently, astronomers could see only 5 moons orbiting Uranus. Voyager 2 discovered 10 more small moons and yet more have been found in images recorded by Earth-based telescopes. The five major moons of Uranus are ______ than Earth's Moon and have old, ____, ________ surfaces. A few have deep cracks, produced, perhaps, when the interior ______ and ______. In some cases, liquid ______ "lava" appears to have erupted and smoothed over some regions. _______, the innermost moon, is only 14 percent the diameter of Earth's moon, but its surface is marked by grooves called _____. These may have been caused by internal heat driving ________ in the icy mantle. By counting craters on the ovoids, astronomers conclude that the entire surface is old, and the Moon is ___ longer active.

smaller, dark, cratered, froze, expanded, water, Miranda, ovoids, convection, no

_________ ____________- The heating of a planet or satellite because of friction caused by flexing due to the gravitational influence of a nearby body.

tidal heating

3 A planet's magnetic field deflects the solar wind and dominates a _______ of space around the planet called the magnetosphere. Jupiter's magnetosphere is 100x larger than Earth's (would be 6 times larger than the full moon.) 3a Interactions between Jupiter's magnetic field and the solar wind generate powerful _______ ______ that flow around the planet's magnetic poles. These _______ on Jupiter are larger in diameter than Earth, and are confined to the north and south magnetic poles.

volume, electric currents, aurorae

7-4a Planet Uranus Uranus is only ____ the diameter of Jupiter and only _____ as massive, and, being 4x farther from the Sun, its atmosphere is almost 100 ° C colder than Jupiter's. Uranus never grew _______ enough to capture large amounts of gas from the nebula as Jupiter and Saturn did, so it has ____ hydrogen and helium. Its internal pressure is enough lower than Jupiter's that it should ____ contain any liquid metallic hydrogen. Models of Uranus, based on its density and oblateness, suggest that it has a small core of _____ elements and a deep mantle of ______ solid water. Although referred to as ice, this material is not anything like ice on Earth, given the temperatures and pressures inside Uranus. The mantle contains ______-composition material and dissolved ammonia and methane. Circulation in this _________ conducting mantle may generate the planet's peculiar magnetic field, which is highly inclined to its _____ of rotation. Above this mantle lies a deep hydrogen and helium ________.

1/3, 1/20, massive, less, not, heavy, partly, rocky, electrically, axis, atmosphere